aj mccormack and son

Flags & Slabs - Page 09
The Brew Cabin
flags and slabs


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Forum Question Grouting Perfecta slabs - Pete C - Jul 23rd 2003
I`ve just had my Perfecta slabs delivered and I think I know what I'm doing....Geofix grout sounds easy and quick but what colour do I use? You can't see a sample!

The slabs are 450x450 natural about 14 sq metres. I'm thinking of 5-7mm gaps and I'd like to finish the grout close to the suface 2-3mm. Any tips?

forum answer Tony McCormack - Jul 24th 2003
With the smooth ground Perfecta flags, I like to use a dry grout, but you can use Geo-Fix if you wish (and you have money to burn!!).

The standard colour, a sort of buff, will be fine, as the joints should only be 5mm wide and, in 3 or 4 months time, the surface will have discoloured and become covered in detritus, so you'd have no idea which colour (from the vast choice of 2) was used originally.

Pete C
Jul 25th 2003
Thanks for that Tony, this site is worth its weight in Geofix...5mm does look better as you say, but what dry mix would you grout them with? And is the patchy dark and light areas on these flags normal? Is this just residual wetness, will they dry out to an even colour?

Regards - Pete

Tony McCormack
Jul 28th 2003
Use a 3:1 dry mix, preferably silver sand, if you can get it at a reasonable price, but normal building sand is just as good.

Patchy dark/light areas? That doesn't sound right - do you have a photo or a fuller description?

Forum Question Efflorescence and Patio Sealants - Jerome - Jul 29th 2003
My patio has been laid for one year so far. The flags used are Marshalls Heritage - Calder Brown. I prefer the look and colour of the flags when they are wet and am considering using a patio sealant to bring out the colour of the flags, akin to when they are wet. Approximately on third of the flags have white efflorescence to varying degrees, which having browsed your site, I am not unduly worried about (apart from the look).

My question is - when the flags are wet the efflorescence is not visible, therefore is it recommended to use a patio sealant if there is still efflorescence present or best to wait until this has passed? (which could be a while, I guess)

Any advice would be very helpful.

Many thanks

forum answer Tony McCormack - Jul 30th 2003
It's best to wait until the efflorescence has abated, as it can, and does, show up beneath a sealant, sometimes. I'm surprised you're still being troubled with the bloom after 12 months, though: the worst is usually over and done with in 6 months or so, especially if it's been 'over-wintered'.

I'd leave it for this summer, then look at it again next spring, when, hopefully, all the eff. will be long gone.   smile

Forum Question Stone & Style Rockstone - Dave Parry - Jul 31st 2003
I am about to lay a path/patio in my back garden and am having trouble finding slabs I like. I really like the Stone & Style Rockstone silver/grey pavers, but need 450x450x50 slabs. These are only available in 200x200x50 max.  

The path will form a step edge so the slab sides need to look good too.

Does anyone know of similar products in larger sizes? I have a charcon sample on order (moorgate grey) but haven't found any other.

forum answer Tony McCormack - Jul 31st 2003
Stone & Style Rockstone in Silver Grey is available as a 300x200x60 unit, for the UK market. There are larger sizes available on the continent, but they are only available on special order in the UK (ie, 180m² or more). This is because, in the UK, they are marketed as block pavers rather than flags/slabs and the generally accepted opinion is that owt smaller than 300x300 is a block, and owt bigger is a flag.   smile

There are no readily available "similar products" on the British market. Marshalls have their Stein & Design imports from Germany, but these are really aimed at commercial works rather than patios, which is reflected in the cost. No British manufacturer has a washed aggregate block paver, currently.

There are other textured pavers, such as bush-hammered or shot-blasted, but these textures should not be compared directly with a washed aggregate, as they still rely on the artificial dyes in the concrete matrix for their colouring, unlike the Washed Aggs. which derive the vast majority, if not all, of their colouring from the aggregate which is exposed by the washing process.

The Charcon Moordale is, if I recall correctly, a shot-blasted product, and so the surface exposes both the concrete matrix and a small proportion of natural aggregate. As far as I know, the texturing is only carried out to the top face, so the sides/edges of the flags would not be similarly textured, which may not be what you're looking for.

Forum Question Re-laying existing Patio - PNE - Aug 6th 2003
I have at present I have a patio that I laid myself last April and am now keen to take it up along with the pathway and re-design it all and then re-lay it. There are a few things I would like advice on though please :-

  1. Can you suggest the easiest way to lift the old slabs up so they do not break as I am looking to use them again?
  2. Will there be any issues in my doing the above that you can see?
  3. Once they are all up , do you suggest flattening the whole lot with a wacker plate?
  4. Will it be suffice to then lay the slabs on the previous mix by just putting a fresh mix on top?
  5. What mix should I use...last time I believe I did 5:1. Is that OK?
  6. I will also be digging up some more of the grass to put down more slabs. Now should I put down a sub-base this time as I felt last I should have done especially as the ground consist of a fair bit of clay ?

The current patio hasn`t suffered too much at all but I am wondering whether some of the imperfections I have experienced are due to no sub-base?

Thanks very much in advance


forum answer Tony McCormack - Aug 7th 2003
1 - lifting the existing paving: easiest is to use a pick, driving the point in under the flags and then levering them up. 2 - the only 'issues' of any importance are dealing with any old mortar adhering to the flags. You mention that the flags were laid on a 5:1 mix, previously. If this was a wet mortar, the flags may well have bonded to the mortar and it will need chiselling off, if the flags are to be re-used. This is best done with a bolster and lump hammer.
Any joint mortar that remaind attached to the flag edges can similarly be removed.

3 - compaction with a vibrating plate can't do any harm, but I'm not sure it would do any good if it's simply a matter of running the vib plate over old mortar.

4 - You could re-lay on fresh bedding over the old mortar bed, as long as there is no problem with DPC and levels, but see (6)

5 - There's no need for a bedding mix to have such a high cement content. 10:1 is fine - see the Laying Flags page for info on my preferred bedding mix.

6 - A sub-base is not essential beneath a residential patio, but can be used if there is a problem with bad ground or with levels that required lifting.

If this were my job, I'd actually rip out the old mortar bedding and either bin it or break it up to pieces of 50mm or less and sprread it out over the whole site as what we call a 'blinding' layer. Then, if there is a need for a sub-base, lay that, compact it with the vib plate, and then re-lay the new patio, on my 10:1 semi-dry bedding mix. I would not be 100% happy laying parts of the new patio on top of old mortar (a rigid base) and part of it on a flexible sub-base, as the two parts would behave differently over time and you could end up with the dreaded differential settlement.

How's that?

Aug 7th 2003
Thanks for a quick reply and looking at your comments it has started to give me faith in my own abilty again and I might just pull this off.

Anyway just a couple more questions for you...

  1. If I decide to break up the old mortar and use it for a "binding layer", will I need to use a vib plate on that or not?
  2. Will I need in your opinion to hire a "breaker" of some desciption to do it the breaking with?
  3. And if I feel I do need a sub-base after all that, what do you recommend? and this I guess will need compacting?

I think that is it for the moment but I have a feeling that once I start this job in earnest, I will be picking your brain again.

Well done for a gem of a site.

Cheers - Chas

Tony McCormack
Aug 7th 2003
1 - yes - use a plate compactor to rattle over the blinding layer. It's not essential, but, if you're going to have a plate on hire anyway (for the sub-base) you might as well make best use of it.

2 - probably not. Old mortar, even a 5:1 mix isn't terribly hard stuff and breaks up with a few thwacks from a pick and/or a sledgehammer.

3 - For a patio, you can use whatever is easiest to get hold of. That might be DTp1 from a local BM or "Crusher Run" from one of the DIY sheds, or cruushed concrete, 'ballast', 'scalpings' or whatever else is on offer. As long as its a good mix of fines and lumps, and compacts well with the vib plate, it'll do for a patio.

For driveways, I don't believe in spoiling the ship for a ha'p'orth of tar, and always recommend genuine DTp1, but for patios, almost any crushed aggregate will do.

Let us know how you get on, and take photies as you go. The feedback I get tells me that folk love gawping at other folks' DIY efforts!   smile

Aug 7th 2003
Thanks again Tony

and I sure will sent some photos as it progresses.

Watch this space

Cheers - Chas

Aug 8th 2003
Hi Tony

Sorry to bother you again sooner than I thought but there are just a couple more things I need to ask :-

  1. I forgot to say that under part of the path that I am taking up and then breaking up the old mortar , there is an electricity cable that runs from the house and into the garage. Now will this be a problem if I start breaking up the old mortar i.e I could go through the cable?
  2. Also where part of the original path/patio was laid ( which was done by the builders and not me ) they have taken part of the patio right up to the house and in the other part there is a 4 inch gap filled with gravel between the house and the slabs which coincidentally is around the same place as the electricity cable comes out from the house. Again would this have been done for a reason or will it still be OK to put the new patio right up to the house at this point like the other bit of the patio?

Hopefully that will be it for a while

Thanks in advance

Tony McCormack
Aug 12th 2003
1 - not if you're careful. It should be an armoured cable, and, if you can verify that it is, indeed, an armoured cable, and you know, more or less, just where it is, you can work carefully in that area. Consider re-laying the cable in a duct - it makes life much simpler, and safer!

2 - the mystery gap between the house and the paving sounds like a bit of laziness. Maybe they couldn't be bothered cutting flags to fit, or maybe they couldn't be bothered knocking up a bit of grano to infill the gap, but you can safely pave right up to the house when you come to do the work.

Good luck!

Forum Question Expanding foam sub-strate repair system - David Moore - Aug 11th 2003
Tameside Metropolitan Borough Council are using expanding foam as a repair medium for loose flags/paviours and setts. We in Northern Ireland are looking to trial this as a possible way forward for similar repairs here. We are currently looking for feedback from anyone who has carried out this repair method successfully as this information may prove valuable in our report.
forum answer Tony McCormack - Aug 12th 2003
We have used it as a temporary, "emergency" repair medium on pavings at a chain of nursing homes we used to maintain, but the foam was always replaced within a month with a 'permanent' repair.

We found it worked best with wider joints, especially on setts/cubes, but that is was less successful when it came to curing 'rocking' flags as it didn't sem to penetrate beneath the flags and fill the gap/void in the bedding. Also, on some paths laid on spot bedding (not laid by us, I hasten to add!!) the ability of the paving to swallow huge volumes of the foam was frightening.

We were obliged by the property owner to effect 'permanent' repairs as soon as practically possible, although some of the smaller repairs could have been left as they were. However, with some sett work that had been patch-repaired with foam, visitors to the nursing home in question were complaining that ladies' heels were penetrating the foam and getting stuck, hence the requirement to replace the foam with a solid joint medium asap.

I also seem to recall that it was less successful on pavements that were subject to vehicular traffic, even though it was only low speed "car park" traffic. Several of the sett rumble strips we repaired in this way worked themselves loose again in just a matter of days.

I'll dig out the job records later and see if I made any other notes regarding the efficacy or otherwise of the foam repairs.


Forum Question Bedding for sandstone flags - Max - Aug 11th 2003
Proposed site is a 3 * 10 m rectangle. At the moment it is lawned, but well drained. The lawn surface is approaching the 150mm limit to the house dpc, but the flags would end 500mm before house.

I have read ( with great interest) much of the information displayed on this excellent site relating to the laying of these varying thickness flags (your warning about excessive work in adjusting height of individual flags was noted).  I notice that individual flags can vary from 20mmm to 35mm, depending on the stone or the pack. However, to get to the main point of my enquiry. I would like to keep the final surface stone as dry as is practical, to discourage it from developing surface growth which may be slippery in periods of damp Autumn and Winter weather. The area is very shaded, to the north side of trees. The shade is desirable in our current hot spell, so removing it is not an option. The prepartion is going to be a large part of the work, so I want to make sure that I get this aspect of it done properly.

What depth of base would be best or adequate since I will be moving topsoil. I can arrange for an adequate fall and good surface drainage, so the ground is unlikely ever to be waterlogged.

I inspected the stone (not bought yet) and the pack sizes seem to vary from 12sqm to 15sqm . The sizes being 60cm sq or 60 x 90cm. I noticed that some split packs were available with different shades/stone in, and even 120 x 60 flags. Some of the shades look good, but is this size too awkward to handle?

The prices are £14/sqm ex VAT, so quite an attractive price, but I have to arrange all of my own transportation.

I could send digital images of the project if you are interested...before during and after. I assume that these would be attached to an email directly to you?

forum answer Tony McCormack - Aug 12th 2003
Hi Max,

taking your queries one at a time....

"What depth of base would be best?"

The bedding should not be more than 50mm deep, but, if you want to lay a sub-base (not essential beneath a patio, but useful on suspect ground or when levels have to be elevated) then a minimum of 75mm is the usual recommendation. 100mm is ideal.

"120 x 60 flags - is this size too awkward to handle?"

It can be if you're not used to flagging, but, by including a few of them, you increase the random appearance of the stone. I'd also consider splitting a few of the 600x600 squares into two 600x300 rectangles for the same reason. If you rely on just two sizes (600x600 and 600x900) the paving becomes very repetitive and doesn't show off the natiural variation of the stone as well as it could.

And I'm definitely interested in photos - send them as email attachments or post them directly to this forum.

Forum Question Choosing patio flags / drainage problem - Grahame Watts - Aug 12th 2003
I am a DIY gardener who is attempting to do some major changes to our uneven and neglected garden. I have built three linked ponds -two raised for fish with a waterfall between them and a small wildlife pond adjacent to these and have planned a patio around them. I have got a lot of advice from this web site that has given me confidence to do more than I would have attempted previously- pinning the railway sleepers that I have used for the raised pool sides was a great help.

I am now in the process of needing to order the flags and set out for drainage etc now that the ponds are complete. The patio will surround the ponds and in total has an area of about 45 sqm. Marshalls riven flags seem too expensive - would Builder Centre brand - Salisbury be a safe choice? (450X450 £2.34) How could I work out a random pattern- they come in 4 sizes?

Another problem I have is the path from the back door of the house has two sewer manhole covers - old and ugly made of large concrete slabs with a cast iron lid. I would like to replace these with something that flags would sit into but don't know what would span the present manhole. Please can you advise?


forum answer Tony McCormack - Aug 13th 2003
Hi Grahame,

when it comes to flags, you gets what you pays for. The Salisbury range are a "Budget" version of Marshalls' Heritage or Bradstone Old Riven and you have to ask where the cost savings are made - by using poorer dyes, less of them, and a lower cement content. You might save a fiver per square metre, but, in 2 or 3 years time, they start to look like what they are - concrete copies. Many folk are now switching to the imported sandstone flags - they cost a few quid more, admittedly, but they are genuine stone and can't end up looking like poor concrete copies a few years down the line.

However, as I always say, it's you that has to live with these flags, not me, so you must choose what you like, not what I like!

For a random pattern, you might find that the manufacturer offers a basic random layout that you can adapt, or you might be able to use the misleadingly named Random Patio Generator from Bradstone, or you can work out a pattern for yourself, as described on the Random Layouts page. If you have an irregularly shaped area, a custom-designed layout is your best option.

And finally, for your ugly MH covers - replace them, with Recess Tray covers, as described in the block paving section of the website. Regardless of what size are the existing covers, there is a tray available to replace them and make them damn near 'invisible'.   smile

Grahame Watts
Aug 14th 2003
Thanks for your reply Tony. I'm going to go for the Marshalls flags.

I have asked around builders suppliers and am having difficulty in getting a recessed tray that will bridge the brick manholes I spoke of. The internal measurement of the MH is 38"x28 1/2". Can you advise me on a supplier in the Merseyside area that could supply a suitable tray?

I've read your pages on manholes and it looks as though I'd have to reduce the size of the hole to fit a tray- I'm a bit apprehensive about this and if I can get a ready made tray I'd feel happier.

Tony McCormack
Aug 14th 2003
What used to be Parr's at Bootle (I think it's a Builder Centre, now) should have a reducing slab for your MH and then you can use a 'standard' 600x600 or 600x450 recess tray.

To buy a tray to fit your MH exactly would cost around 600 quid and would have to be specially manufactured, whereas you can get a reducing slab for 20 quid or thereabouts, and a standard tray for under 40 quid. The reducing slab is simply bedded onto the existing brickwork and the tray sits on top of it - it's an absolute doddle! That is how a 'professional' would do the job, Grahame.

If you have no luck at Parrs/Builder Centre, there's Burdens here in Sunny Warrington, or Cooper Clarke in Bolton, both of whom definitely have the cover slabs available ex-stock.

Tony McCormack
Aug 14th 2003
I've just been having a think about your MH, Grahame. Those Imperial measurements threw me, but, when I converted them into nice, sensible, logical metric units, the scale of the problem became more apparent.

I thought you might have been able to get away with a 1200x750 rectangular cover slab, which are easily handled by a couple of fit lads (or lasses!), but the internal dimension of the chamber width is 727mm, which means there's only be 23mm (less than an inch in old money) of spead onto the side walls.

This leaves you two options - you either corbel in the top course of brickwork so that the 1200x750 reducing slab is properly supported, or you use a 1350mm dia circular 'biscuit', which is considerably heavier than a 1200x750 reducing slab - 400kg against 80kg - and would have to be craned into position....


...I think, if this is a DIY effort, the corbelling option is the simpler for you, but, if you're bringing in a contractor, then the circular biscuit might be their preferred option.

Grahame Watts
Aug 17th 2003
Sorry to bother you Tony, but please can you help me with a question about laying flags - I'm now ready to start laying the Marshalls Heritage Flags for which I've designed a random 5 size laying diagram based on your designs but added to to fit the irregular size of my patio area. I've marked out the right angle from the house wall and got the levels marked for fall and base levels (90mm below the top of final flag level). My question is do you lay the first flags to the line of the house wall or should you cut in to this like you would with floor tiles?

Thanks for your great advice in previous replies.

Tony McCormack
Aug 18th 2003
The first 'course' of flags can be laid so that the edges of the flags are tight up against the house itself (allowing for any jointing), but the opposite edge of that 'course' is staggered. If you look at any of the sample designs I provide on the Random Layouts page, you can see that two edges in any rectangular area can be laid using full flags, and the 'cuts to fit' will only be required on the other two edges.

Does that make any sense?

Forum Question Why not lay onto soil - WJC - Aug 13th 2003
What are the disadvanges of laying straight on to soil with a morter bed underneath? Or do you have to have a sharp sand bed first.
forum answer Tony McCormack - Aug 13th 2003
Soil is not inert, therefore it "moves", which means the flags laid on top of it will move, settle and become uneven. It's also difficult to achieve even compaction of a soil, which is why we always use a bedding material, usually sharp sand.

Have a read of the main site, where all this is explained in great detail.

Forum Question Building a raised patio - WJC - Aug 13th 2003
How would I create a patio 30 cm higher then ground level? Not near any dpc.
forum answer Tony McCormack - Aug 13th 2003
By building up the levels using sub-base material, with a low retainer to keep everything in place.
Aug 13th 2003
Would that be class 1 stone or could I fill with half soil?

Size 3.6 x 3.6.Retainer would thay be single brick or double and could I use concrete blocks instead single or double? How deep to make foundation?

Tony McCormack
Aug 14th 2003
I really can't tell you exactly how to build your own patio. I can give you the basics, and I can explain why things are done in a particular way with particular materials, but I can't tell you what type of retainer to use or how deep to dig the footings as I have never seen your plot and am not familiar with the exact layout.

The retainer can be brick, or an edging kerb, a flag-on-edge, a timber edging or old setts or anything you want - you only have 300mm of lift so you're spoiled for choice. If you want to use bricks, I would use 225mm engineering brickwork on a 450x100 concrete foundation at a depth of not less than 150mm, but, fo only 300mm of lift, that seems like a lot of work to me.

For the fill, you should only use inert material, so no soil. DTp1 is the best material, but you could use gravel, all-in ballast, crusher run or lean mix concrete if you preferred.

You need to come up with a plan for this patio before you start work. All the questions you might have are answered on the main site, but it involves you making decisions on what you want it all to look like once it's finished, how confident you are with your own skills, and how much you're prepared to spend. I can't take these decisions on your behalf.

Aug 14th 2003
Cheers - not planning to do it yet. Just getting some insight into what will be required. One last question would I get away with single brick to keep it all in?
Tony McCormack
Aug 14th 2003
. Yes, but it's less than ideal. If you're going to use brickwork, you might as well use a double skin as there's sod-all strength in a single skin.
Forum Question Looking for used concrete flags - Jonathan - Aug 14th 2003
I'm increasing the size of my patio and want to reuse the concrete slabs that I have and add to them rather than buy a completely new set - money is tight!!

From the pics and descriptions that Tony gives, it looks like I need to find exposed aggregate slabs 3'x2's or 2'x2's. The ones I have are probably 1950s but I couldn't say for certain.

Does anyone know of a secondhand slab specialist or do I need to go round my local reclamation yards. Or at a pinch I'll buy new, but, I've not found any manufacturer making these any more - it's either riven or textured or pimpled. Ideally in the South Cheshire locality.

Thanks - Jonathan

forum answer Tony McCormack - Aug 14th 2003
They won't be 'exposed aggregate flags' from the 1950s - they're standard flags that have worn so much over the intervening years that the aggregate has become exposed.

There's no specialist supplier of reclaimed concrete flags as they are generally considered to be worthless. Your best bet is a local reclamation yard that might just have a few, or look around at your neigbours, especially if anyone is having a new driveway or patio, as their flags are probably the same and would be dumped if not salvaged. The lads laying the new paving will often let you have the old flags for a quid a piece, delivered, as they cost a small fortune to get rid of in a skip.

You have to bear in mind that, in the 1950s, there were literally hundreds of small, local manufacturers for flags, because no-one wanted to haul the damned thing a hundred miles or so, as they do nowadays. When you get to be as obsessed with paving as I've become, you start to notice the different aggregates that were used in certain towns. St. Helens, for instance, had a flag making factory at Sutton Junction, just half a mile from the old Bold Colliery/Power station complex, and their flags incorporated a lot of cinder and ash, giving them a distinctive look that can still be seen on the older flagged paths in St. Helens, Warrington, Wigan and parts of Liverpool.

It's highly likely that your flags came from Crewe or Stafford and the aggregate may well be unique to your area, so you have to hunt around locally. Do you have any photos? If you do, I might be able to identify the type you have and let you know where I've seen similar.

Forum Question Using Slab-fix - Flora - Aug 15th 2003
I am laying an Indian slate terrace at the moment and I have put down a 100mm scalping base and was going to lay the slate on a full bed of mortar. However by accident I bought bags of Slab-fix thinking it was premixed mortar. It is actually a lime and sharp sand mix and you don't add water to it. I rang the manufacturers Supamix Ltd who said the mix draws its moisture from the air over time (which could be eternity!) and will never really set hard. The information was annoyingly vague.

I'm worried as I laid part of the terrace a week ago and the slabs still move and the mix is still dry. Because it's been so hot, I did spray the slabs to give the mix some moisture, but I am not confident about continuing using it.

Help! Has anyone ever used this mix?! Also what would I point the 20mm joints with, as I think using a mortar would crack if the slabs are so mobile at the moment?

forum answer Tony McCormack - Aug 15th 2003
I had a discussion with the folk from Supamix regarding this product and the poor sod they put up to answer my questions (at a Trade Show in Birmingham) had absolutely no conception of how a pavement works or why a lime-based product was preferred to cement-based. He also suggested that the Slab-fix would be ideal for jointing, which is wrong, and that it would set as hard as "normal" concrete, which is total obllocks. I pointed out these errors and his excuse was that he was a salesman, not a paving specialist nor a builder, which left me completely unimpressed and determined not to recommend this particular product.

In theory, the Slab-fix would 'set' (I think 'stiffen' would be a more accurate term) by drawing moisture from the air and the ground, but you've been unfortunate in that we have just been through a very dry and warm spell, and, because you used a sub-base, there is little, if any, moisture in direct contact with the bedding product.

However, as you sprayed the area with water, it really should have 'stiffened' by now, which leads me to wonder whether this is a perished product, ie, one that's been left on a shelf for too long so that the lime content has hydrated before you opened the pack.

I think this stuff is an expensive bedding and a way of extracting yet more money from non-trade folk who don't realise just how simple and cheap it is to knock-up bedding mix for themselves. I would not buy any more Slab-fix, but would switch to a tried and tested bedding material, namely sharp sand and a dash of cement, such as the 10:1 mix I advocate.

As for the pointing, use a Class II mortar, as described on the main site, or take a look at the pages that deal with the art of pointing for a fully detailed guide to what works and what doesn't.

Aug 15th 2003
Thanks very much for the reply and so promptly too!  I'll feel much happier using the tried and tested method. smile
Forum Question Laying on concrete? - D Stalley - Aug 15th 2003
I have recently decided to extend the one row of paving in my garden to become a full patio. Upon lifting and excavating the area to be paved it appears that those nice builders laid the original paving slabs directly on concrete. I am presuming the best approach now would be to use a base of concrete for the entire area. Would anyone agree (or disagree and have a better idea)?

There is a lot of concrete in place at the moment, far too much to excavate without hiring some heavy machinery, and it is about 200mm below the dpc so with 35mm slabs it doesn't give much room to play with.

Thoughts and suggestions very gratefully received.


forum answer Tony McCormack - Aug 15th 2003
Will the paving of the new patio match the existing paving, or will it all be new paving?

Assuming it's all going to be new, I'd lay the extended area on my usual patio bedding mix (semi-dry, 10:1, sharp sand with cement, no added water) and lay over the old concrete base (assuming the old flags can be separated from the concrete) using a thin full bed of a Class IV mortar.

There's no need to cast a concrete slab beneath the patio just to match the one course of paving that's already present, unless you have really bad ground.

D Stalley
Aug 15th 2003
It will all be new, have already lifted the old slabs (50mm std looking pavement slabs laid directly on the concrete - they were heavy) so will crack on as suggested.

You are a legend, thanks for the time taken... might even post back when I finally get this finished, the 130 450x450x35 slabs arrive next week!!

Tony McCormack
Aug 15th 2003
Please do post back - it's always good to hear how Brew Cabin users get on with their projects, and your experiences may well help some future user.

Good luck!   smile

Forum Question Slate in a cold climate - Tom Dawson - Aug 17th 2003
We live in a very cold climate with major frost heaves and we wanted to create our slate patio (about 240 sqft) without using concrete but it seems the base of compacted crush topped with 2" of sand isn't allowing the 2" slate pieces to set - we are still experiencing some of the slates lifting/shifting when they are walked on - we have wet the sand repeatly and have swept on new sand to fill to no avail...

is it not possible to lay on sand only - does it have to have a concrete component?

thanks for your help

forum answer Tony McCormack - Aug 18th 2003
It is possible to lay on a sand bed, but you will have to accept some movement of the paving, if you live in a country that experiences frost heave in winter.

We in Britain and Ireland are lucky in that we don't get any frost heave worth mentioning, otherwise the national rail network would use it as yet another excuse for not running any trains. Consequently, I don't have much experience of pavement design in continental climates, but, from what my colleagues tell me, a flexible construction (sand only) is expected to move, but a rigid construction (cement-bound) has to be of sufficient thickness to withstand significant heave, which can be as much as 600mm, I'm told. So, the short answer is that, if you want a non-moving patio, you need to use concrete as a bed.   frown

Tom Dawson
Aug 30th 2003
Thanks - we do have to worry about frost heaves here in Northern Alberta, Canada

I'd really like to reduce the amount of "movement" and P'd like to reduce the "dusting" from the sand between the joints - is there anything you can think of that we might introduce to the sand e.g. soil, much lighter amount of dry concrete, shale dust etc. that might help "set" the stones and reduce the dust?

thanks for your help -

while I've never had the pleasure of visiting your country, I have vicariously through my wife - smile - she designs, markets and leads tour groups to gardens throughout England and Europe.... maybe someday I'll get to go as well ...


Tony McCormack
Aug 30th 2003
To reduce 'dusting' of the sand joints, you might want to consider using a stabilising compound or a polymeric sand. I can't tell you the name of products that are available in Canada, but a good place to start would be with Envirobond, based in Ontario (I think!) as they are one of the biggest manufacturers of polymeric stabilising compounds in N.America and their CEO is a damned nice bloke (He's actually over here at the moment, allegedly on business!)

These products work by 'glueing' together the sand grains, preventing them being blown or washed out.

Their website is at and I'd be glad to hear how you get on.  smile

Tom Dawson
Aug 30th 2003
Thanks - i've sent an email to the Canadien head office outlining my dilemna - if you are talking to the CEO would you mind mentioning my query - he might want to check out the results when done at

By the way, do you think I will have to replace the underlaying sand (about 2-4") or just the joint sand?

thanks again for your help

Tony McCormack
Aug 30th 2003
I'm hoping to meet up with Mr Envirobond this coming week, so I'll take him a print out of one or two of your photos and see what he suggests.

The first thing I'd say is that joints between your slate pieces are awfully wide. When constructing what we call Crazy paving, the trick is to keep the joints to a minimum width, filling in wider joints with additional stone pieces as required. I've nicked one of your images, shrunk it, compressed it and reproduce it here for the benefit of other readers....

slate patio

Where wide joints like these are unavoidable, they're normally filled with concrete/mortar, and then topped with a surface dressing or gravel or grit, so that it doesn't look like concrete but has its strength and prevent the jointing being scuffed or kicked about everywhere. If this were mine, I'd seriously consider using an Exposed Aggregate finish concrete in the joints, because I know I could make it look really good.

Here's an image of crazy paving from a derelict garden I frequent on the outskirts of Bolton, Lancashire.....

crazy paving

...notice how 'tight' are the joints, compared to your project.

The joints are the weakness in a pavement such as this, so, by keeping them to a minimum, you maximise the strength and longevity of the paving. The example above was paved around 1906 and has never been relaid!

BRW - nice garden - You can take a peek at my garden and see how it contrasts with the gardens in your part of the world.  smile

Tom Dawson
Aug 30th 2003
The widest joints shown are actually going to be covered by our stairs - we just finished cutting up an old 60' power pole for the stair "legs" - the balance of the gaps are only a few inches at best - would you suggest we make them tighter before we try and do the "bonding" - I worry about the concrete as we get a fair bit of frost heave in this part of the country ( our winters can get down to -30+C )
Tony McCormack
Aug 31st 2003
If you have to lift or re-lay the paving, then I'd definitely re-lay them with minimal joints. I'm not sure what effect severe cold/frost would have on the polymeric sands (but I can ask) but from an aesthetic point of view, it's the stone you want to see, not the jointing.

Aug 11st 2003
Thanks - as the joints in the other areas are quite a bit smaller I may not move them immediately - besides my wife Donna wants to plant between the joints with woolly thyme etc.

I'd be really interested to hear Envirobond's thoughts on the poly / frost question - also, i'd like to know whether they feel we need to remove all the sand or just the sand in the joints ....

thanks again for your answers - they are appreciated

Forum Question Cracks in Mortared Joints - nlsdoe - Aug 20th 2003
Hello Everyone,

I replaced an old poorly laid patio last August using riven slabs on a 10:1 bed. For the joints I used a 3:1 mortar mix. I noticed around June this year that at one end of the patio, where it butts up against the house brickwork, that the mortar has cracked along the edge (I've a photo I can send in). This has pissed me off enormously! Any ideas as to why this may have happened? Is it most likely down to settlement? Should I have used a Class 2 Sand, Lime & Cement mortar?

forum answer Tony McCormack - Aug 24th 2003
I can't say why your pointing has cracked without seeing it for myself, but it's relatively easy to replace. It may be due to thermal expansion/contraction of the vertical masonry, in which case, whatever you use to fill that joint, cracking will occur, so perhaps a dry sand or polymeric sand joint would be a better option.
Aug 30th 2003
For any joint where movement is possible a lime mortar is much better than a cement one. For outdoor work you need to use a hydraulic or semi-hydraulic lime, as a fat lime will stay soft when damp.
Forum Question Laying slabs directly onto concrete - David Stanley - Aug 26th 2003
Can slabs be layed directly onto a fresh (wet) concrete base? The concrete would be on a firm soil base. What are the pros & cons. The slabs will form a path for light use and a mowing strip in a garden.
forum answer Tony McCormack - Aug 30th 2003
Yes, you can lay directly onto fresh concrete. best use a semi-dry mix, thougfh, as very wet concrete (greater than 25mm slump) allows flags to 'float' and shift in level when their neighbours are tapped down to level.

Pros - unlikely to move

Cons - expensive, unforgiving if you don't get it right first time, and limited working time.

Forum Question Sharp or concreting sand? - Bonzo - Aug 11th 2003
Years ago I laid a raised patio by simply bedding the flags on top of 2 inch of stone chippings and 2 inch of sand. This lasted but over time it has sunk in places a little.

I have started to relay the flags by bedding them on 1 inch of a 5 to 1 mix of what was sold to me as concreting sand and cement. The mix has no water added to it. This is of course on top of the well compacted bed that was still there.

I assume the 'concreting sand' is sharp sand but it does seem very gritty - is there a difference please?

Is this method ok to use please? The ones that have been down a few days seem very solid.

I would be grateful for any comments.

forum answer Tony McCormack - Aug 30th 2003
There is no real difference between concreting sand, grit sand and sharp sand - it's all down to local terminology. There are technical classifications for sands which you can read about on the Aggregates page, but, for your purposes, a sharp, gritty, concreting sand will be fine.   smile
Forum Question Fall on Indian Sandstone Flags - Chris May - Aug 31st 2003
We have employed a contractor to lay some 85 square meters of Indian Sandstone Flags around our house. They have just completed two small sections but still have the bulk of it to lay.

They say that the fall needs to be 50mm in 2.5m, whereas we understood the fall should be 10mm in 1metre which is only half the fall that they are recommending. The problem is that a lot of the patios are in walled areas on two or three sides so the slope is very noticeable and gives the appearance that the wall slopes downhill. At one point we have measured a fall of 65mm over 1.8m. Is this correct and if not what fall would you recommend?

Chris May

forum answer Tony McCormack - Sep 1st 2003
50mm over 2.5m is 1 in 50, which is not really excessive, but is a bit steeper than absolutely necessary for a patio. If you're prepared to accept small pools of water lodging in the low-points of the riven textured surface, then you can get away with a fall as low as 1:80, which is 12.5mm per metre, but I'd suggest somewhere between 1:60 and 1:80.

You have to find a balance between adequate fall for drainage, without it feeling/looking odd, and without the patio table inducing a feeling of sea-sickness. At the end of the day, the choice is yours - if you instruct the contractor to lay at, say, 1:70 (15mm per metre), then you can't complain if you get small, short-lived puddles after a downpour. Personally, I wouldn't be too worried about 1:70   :)

Forum Question Garage Roof Paving - Screwmydriver - Sep 2nd 2003
Only when I have no money - now - am I a DIY enthusiast. So I hope someone can advise a rank amateur.

I have a garage - floor, walls and flat roof all in concrete. The roof has been covered in 'Isoflex' a rubberoid product from Ronseal. There are small cracks in the roof so I assume this was done to keep out the rain.

Bizarre as it may seem, the layout of the house - split level - means that it is easy to walk from the kitchen straight onto this garage roof and overlook the garden. BUT the Isoflex will not stand up to regular walking on and certainly not a table and chairs. I emailed Isoflex/Ronseal and was advised there is no surface you can put onto it.

This may be true but would it be completely daft to place small discs (made of what?) say 2cm thick onto the isoflex so that these can support in each corner concrete paving slabs with say, 5mm gaps in between the slabs so that the rain can run between the slabs onto the isoflex and away? I gather that if you put slabs direct onto the isoflex they will lift.

Or has anyone any other suggestion?

Help would be much appreciated.

forum answer Tony McCormack - Sep 2nd 2003
You might think it's daft, but a company by the name of Caro make a nice living producing such 'little discs' that allow flags to be laid to flat roofs while allowing water to flow beneath!

The usual spec is to re-cover the roof with a particular membrane or tanking, then the Caro-Supports, and then the lightweight flags, which are sometimes known as Promenade Pavers (complicated, because Baggeridge Brick make a range of clay pavers sold under the name 'Promenade').

I've only ever been involved in this type of job once, and the roof had to be demonstrably strong enough to carry the weight of the paving plus the additional imposed loads. This 'proof' is done by a structural engineer - just laying flags to your flat roof quite probably invalidates your Bricks'n'Mortar insurance!

I'm not sure how suitable a job it is for DIY. From what I recall, and I'm going back about 8 years or so, it was ridiculously expensive work. The membrane/tanking cost a small fortune, and it took us twice as long as anticipated, but, to date, there's been no comebacks (Thank God!!)

Forum Question Correct bedding mix for patio - KJ Godalming - Sep 3rd 2003
I have to rebuild my patio as the previous owner used spot bedding, the levels dropped and most of the sharp sand he used as a bedding layer washed out of a crumbling wall. It was also plagued by several ants nests.

The patio is not too big (18 m²) but it is raised. The crumbling wall has been replaced by a proper retaining wall, but I ran out of funds to pay for my builder to relay the patio.

I live on a very steep hill which has a very large amount of surface water run off when it rains (our road looks like a river !). Hence there is a large amount of surface water I have included a soakaway at the lowest point.

My questions are:-  

  1. Will your recommended 10:1 mix bedding mix be suitable for my project, given the high levels of surface water, or should I use another bedding mix.
  2. If 10:1 mix is OK will sharp sand and cement be sufficient as recommended by my local Jewsons.

I intend to lay my flags by individual bedding as quickly as I can, working at weekends and evenings when I have time.

Would screeding be more suitable given the British weather?

My sub base is scalpings, laid to 70 mm so far, but I will be adding another 50 mm more to raise the levels. I intended to use approx 75mm bedding, but after discovering your website is this too much, would 50 mm be more suitable?

Many thanks - Ken

forum answer Tony McCormack - Sep 3rd 2003
Hi Ken,

it's good to see someone else validating my crusade to rid the world of the evil that is known as "Spot Bedding" for truly it is an abomination that must be eradicated and its proponents slung into the pit of despair!

The 10:1 bedding mix should be more than capable of dealing with you patio and the heavier-than-normal surface water regime. The purpose of the cement is to bind the aggregates, rather than make it hard-wearing or incredibly strong. As long as the cement content is adequate to hold together the aggregate particles, it will be fine, and, in my experience, 10:1 is about right. You can elect to make up the "10" from 5 parts gravel and 5 parts sharp sand, if you wish, or you can 'edge-your-bets and up the cement content to a 8:1 mix, but these are minor details that I leave to your choice.

Screeding is possible if you're using regular thickness flags or block pavers, but, if you're using the riven types, other wet-cast products or natural stone paving, individual bedding is the best method to employ. Keep the bedding to a maximum of 50mm, and no more. 35-50mm is the standard specification.

Good luck and let us know how you get on. smile

Forum Question Lead Pointing - Danny Lee - Sep 3rd 2003
I have seen molten lead 'pointing' of flagstones, I wish to reproduce this on my patio. Do you have any advice on this potentially hazardous practice.
forum answer Tony McCormack - Sep 3rd 2003
Lead pointing was used very, very rarely, and usually on specific projects that, for one reason or another, couldn't accept a standard lime mortar or cement mortar joint. The biggest problem with lead jointing was that it was prone to mysteriously disappearing overnight, much like the lead from church roofs.

I've never used lead pointing in over 30 years of laying flags, and the only time I've ever seen it is on a certain ecclesiastical property in the north-east of England, which I won't name for fear of it being visited by the lead goblins when darkness falls.

Where have you seen it, Danny? Send the answer by email or use the confidential Messenger system above, if you prefer. I wonder if we're both talking about the same place?

Personally, I can't see any advantage to lead jointing of paving. It doesn't form a watertight joint, as you'd get with a mortar or with pitch; it goes dull with time, so no-one can tell it's lead unless they look very carefully, and you can achieve a similar effect using a dusting of lead, tin or solder on top of a 'proper' mortar joint.

If you must, though, then all I can advise is that you get yourself kitted up with a mask, long gloves, decent boots and use a long-handled pitch-pot over a gas ring, which you can get from any decent Hire Shop. I'm not sure what grade of lead you should use - perhaps a plumbing specialist could advise, or you might be able to get more info from British Lead Mills (BLM).

I'd be interested to hear how it goes, and, if you do lead your joints, I'd love to see pictures!  smile

Sep 3rd 2003
Bearing in mind all the problems that lead smelters and people living in their neighbourhood have suffered over the years, the last thing you would want to be doing is melting lead on your patio.

Having said that we used to get bits of lead from the printing works and melt them in a baked bean tin on the gas ring, and it doesn't seem to have affected me too much!

Sep 16th 2003
I think you will have a lot of trouble pointing with lead, when it is molten it will act like water and most of it will end up running under the flags in to any small voids. If I was you I would try a small test area first before spending a lot of money on lead.
Tony McCormack
Sep 16th 2003
Danny mentioned, in a private email, that he was planning to partially fill the joints with a semi-dry sand & cement mix before pouring in the molten lead. He's hoping that the semi-dry grout will help 'dam up' any voids or escape routes and so avoid wasting too much lead, much the same as is done when working with molten pitch.

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