aj mccormack and son

Flags & Slabs - Page 04
The Brew Cabin
flags and slabs


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Forum Question Sealing Stone Flags - Anneli - 29 Jul 2002
We have just finished laying about 90m² of beautiful Indian sandstone in large flags in our garden - I would like them to stay beautiful - how can I protect them ? - Can I prime or seal them with anything? Does this alter the looks of the stone? Please advise pros and cons... thank you very much for a great website.....
forum answer Tony McCormack - 29 Jul 2002
You can protect your sandstone flags with a sealant, Anneli. There's some basic info on the Sealants page, but you must ensure the sealant you choose is suitable for stone pavings, not just for concrete.

Pros and cons - the paving is well protected from stains, it's less likely to be affected by moss/lichen and other vegetation, and the colouring is enhanced, but the treatment may need to be repeated every so often and some people are none too keen on the glossy 'wet look'. Some sealants offer a semi-matt finish which is more acceptable to some, but this tends to offer less protection that the 2-coat 'wet look'.

It all boils down to what look you like. Personally, I wouldn't use a sealant on stone flags outdoors, as I like the way they weather and the way the mosses and other vegetation take over, but I know that's not to everyone's taste.

29 Jul 2002
Thank you very much for your fast response -
Forum Question Sub base - Olddog - 29 Jul 2002
I've just taken up my old patio which was bedded down on 50mm sand/cement screed with 50mm of fairly loose sandy gravel by the looks of it.  This was all on top of Chiltern orange clay with large flint nodules in. A bugger to dig but it seems pretty stable.

I need to remove about 6" of this clay so that the new patio has a good clearance from the dpc but can I get away with just 50mm of compacted type 1 followed by 50mm of 10:1 sand/cement screed then the slabs? The old patio had been down for about 5 years an seemed fine, no cracks or bulges.

One last thing, and I know it's not really to do with slabs but, on the same clay, do you think the same 50mm type 1 sub base followed by 125mm of concrete, 50mm of insulation and 65mm screed is OK for a conservatory floor? Or should I give the floor a thicker sub base?

Thanks very much for any comments or suggestions you might have.


forum answer Tony McCormack - 29 Jul 2002
For the patio, you could lay the flags on just a 50mm bed of 10:1 sand/cement and omit the sub-base altogether, given that the sub-grade is so hard, but, if you must use a sub-base, then 50mm would be adequate for this type of construction, as it is basically a fill layer, rather than a structural layer (which would need to be at least 75mm thick).

However, for the conservatory floor, I'd go for a 100mm sub-base and then 100-125mm of concrete over a damp proof membrane, as any movement beneath the conservatory floor is much more of a problem than movement/settlement beneath a patio.

Have you thought of asking your local Building Control Office what they normally recommend for a conservatory floor? That's what they're there for! smiley

29 Jul 2002
Thanks for that. I will ask the Building Control Officer, I never thought of that.

With regards the sub base for the patio, I don't actually need to add the 50mm as a filler as I am going to have to dig the clay and flint away in the first place. I just wasn't sure if it was OK to screed straight over the clay & flint. Should I go over the clay with something to tamp it down flat first? It wont be very level otherwise what with the tops of flint nodules sticking up etc.

Tony McCormack
30 Jul 2002
Eliminate any high spots (flint nodules and the like) from the sub-grade, and then use perhaps 25mm of sub-base material to 'regulate' the sub-grade - that is, to get it all reasonably level so that the same depth of bedding will be used everywhere. You should compact the regulating sub-base material; a wacker is ideal, but, if you don't have one, a punnel or even just stamping with the boots should be ok.

What you need to avoid is the tops of any flint nodules poking through, as these may develop into 'rocking points' once the rest of the paving is laid.

30 Jul 2002
Thanks for the advice and for putting together such a brilliant site. I owe you a Guiness!
Tony McCormack
My mouth is a-watering in anticipation. smiley
Forum Question New Patio - BW - 31 Jul 2002
Firstly - thank you for putting together such a great site - a big relief to find Im not alone in my paving troubles! I've read the other posts and really I just want to seek confirmation that what I am about to do is the correct thing!

Before I describe this, can I just say this is the very first time I have attempted a patio (Im more at home with PC's or wooden flooring than concrete) and Im probably being (stupid?!) by attempting to do the whole thing myself (usual budget reasons!).

Current situation:
Planned area is roughly about 2.5m by 4.5m, half of which has a set of dreadful looking flags of about 60x60 in size. I removed the top-soil in the remainder area each side to reveal concrete/compacted rubble falling away from the existing patio (ie. I will be able to use this for the new stuff, but add to it with some of my own rubble).

Problem is: Im not fit enough (slight bad back) to lift the existing flags (60x60 weigh a ton for me). Can I simply build up the surrounding area with sand/rubble, then lay the new flags (400x400x25mm!) on top of the old ones?

I assume as the new ones are so thin (typical Homebase 25mm) I cant go for the 5 cement dabs as you have mentioned in previous postings, but the sand/cement mix spread evenly is a better bet? If so, to what depth? and do i still need it spread over the area already covered by old flags, or just the rubble either side?

My assumption is that I should even-out the surrounding rubble to the level just below the existing flags, then lay the sand/cement mix (came in pre-mixed bags from homebase) over the whole area (both rubble and old-flags) with a slight gradient of 1:40, then just drop the flags straight on and hammer a little? If I can avoid cement up until pointing, I would be happier...

The existing flags which I am to lay over are 2 bricks down from the DPC, so I intend to leave a 10mm gap between the brick and new flags, and fill with.. (shingle?) like this?:

     H  |
     O  |
     U  |  |XXXXXXXXX|XXXXXXXXX|new flags
     E  |$$$$$$$$$ rubble $$$$$$$$$$$$$$ SOIL SOIL SOIL

Oh, and this is for the back-garden - which slopes *towards* the house :(  so it regularly collects puddles of water - so I will slant the flags towards the lawn (away from the house) and where the slanting lawn meets slanting paving, try to dig in a length of half-drain-pipe or similar in a feeble attempt to take the water out of the garden into the adjacent road...   am I doing the right thing here as well?

Any advice/hints/tips/corrections on my assumptions or advice to stick to my day-job, extremely welcome! smiley

Many thanks!

forum answer Tony McCormack - 31 Jul 2002
I really don't like laying new flags over owld shi....err...rubbish, but, given your plea of mitigating circumstances (Welcome to the Bad Back Club), I'll make an exception.

The existing concrete should be firm. Any rubble you add must be thoroughly compacted, hammered down so there is no chance of any settlement. Use a hammer if you've no wacker plate, or stir in sand and cement and turn it into a weak concrete.

So, assuming you get all the base prepared, you can set about laying those wafers you've bought. I'm sure there's a law about minimum thicknesses before you can call them 'flags' and 25mm is well below it. These will be painfully fragile, so you're going to have to be very, very gentle with them.

I'd opt for a full mortar bed, as there's little or no chance of you being able to tap down the flags sufficiently on a semi-dry mix without the damn things falling apart. Mix the mortar at about 6:1 but keep it reasonably stiff - not sloppy so that is drips off the trowel, but stiff enough to stand in peaks, and for no water to drip out when you squeeze a handful.

Spread out a layer of the mortar over the base and ripple the surface with the edge of the trowel. Press the flag down into the mortar bed and then tap it very, very gently with a rubber hammer (a clonker, as we call them) until the flag is settled to the correct level. If you haven't got a clonker, put a piece of 3x2 over the flag and tap that with a lump hammer.

If the flag won't settle to the correct level with a few taps, take it up, scrape out some of the bedding and start again - don't be tempted to pummel it into submission: at 25mm, there's no chance of them bloody things being able to take any rough treatment.

Check your levels as you proceed, making sure you're sloping away from the house. Use a taut string line and/or a straight-edged timber to guide you.

TAKE YOUR TIME - a rushed job is a botched job.

Don't walk on the wafers...err...flags for 48 hours, so try to point-up as you proceed.

I'm not sure what this 10mm gap idea is - a typical joint is 10-15mm - did you mean 100mm (10cm)? Even if you did, I can't understand what the 'shingle' is supposed to achieve? Can you enlighten me?

1 Aug 2002
Thank you for your long and detailed reply - it was an educational read for sure! Nice to know there are still helpful souls on the planet!

Glad to be part of the bad-back club. smiley

I will compact the new rubble as you describe, yes. And your right - I should really call them wafers!!

Just to clarify though - should I place sand over the existing slabs, then a layer of mortar over that? or just mortar on the existing slabs direct, then the wafers?  In a diagram:

<new wafer>
<thin mortar bed>
<sharp sand>
<existing flag>
<existing hardcore>

Either way, I will still put sand down on the areas where its just rubble, and use a mortar bed.

I take it therefore, I have no use for the dry-mix stuff I have bought? (fortunately only 2 small bags!).

I have a clonker, so no problems there (see, Im learning the lingo! I appreciate this!).

A bout the 10mm gap - sorry I did mean 10cm between the house and the new wafers. Anyone reading this may need to correct me, but I assumed a 10cm gap filled with decorative stones/shingle would solve the issue of running too close to the DPC. I'll try again with an ASCII diagram:

------------------         <---  Damp Proof Course
brick 1 |                                  
brick 2 |<10cm><new wafer><new wafer>  
               <old-flag to keep><old flag etc.>

In words: the existing patio is 2 bricks below the DPC, but by laying the new wafers on top, would effectively cover half of brick 2 in the diagram. Therefore, with only 1.5 brick height between the wafer and the DPC, I though it best to bring the new wafers forward a little, and fill the gap with stones to help prevent damp problems. Hope this explains what I was trying to describe (I can see it clearly in my head, but putting it into words... )

I guess this gap may not actually be useful after-all?

Again - thank you so much for this advice - if one could send a virtual beer, I would! smiley


Tony McCormack
1 Aug 2002
You could put a thin scattering of sand over the existing flags, as it would prevent the mortar bedding bonding to them, which would make it a right sodding nightmare to take up at some future date. I've included this on the drawing below, but it isn't essential.

If you have any voids in the rubble/hardcore sections, though, these are best blinded with sand before placing the mortar bedding. Ideally, when you come to start laying the wafers, the whole base should be a graded flat plane, sloping away from the walls, with no holes, voids or gaps.

So, if you use a 6mm blinding of sand, and a 10mm bed of mortar, you can keep the paving to 109mm below dpc, which is just about tolerable. If you omit the sand blinding, and keep the bedding thin (10-12mm) you can save a few more millimetres, but it's not worth fretting over.


As you can see from the drawing, the 100mm gravel strip doesn't achieve very much. In this scenario, I'd be tempted to omit it completely and pave right up to the wall, making sure there was ample fall (1:40) on that first flag. Yes, you will get some splashback, but not much.
1 Aug 2002
Superb! smiley

Thanks for the diagram! Will keep this with me when Im digging this weekend.

The question now is - when will us Brits get some decent weather??

Thanks again,

P.S will keep you posted on developments!

Forum Question How much sub-base? - Paul Olivier - 1 Aug 2002
Just measured out my patio area, not sure how much quarry waste to order. The area is roughly 44 square metres and i am putting about four inches of sub-base down. If i use two inches depth of sand on top i assume i need halve the sub-base weight.
forum answer Tony McCormack - 1 Aug 2002
Are you using this iffy quarry waste as a bedding material? 5 Tonnes will be plenty - you might get away with 4 if you keep it down to 35mm of bedding, but, if you're going for the full 50mm, and you have a bit of concreting work to do, then get 5 Tonnes.

Quarry waste varies from quarry to quarry. The stuff classed as waste from some of the northern limestone and gritstone quarries is usually ok for bedding, but some of the hardstone wastes, or slate waste, can be nothing more than a nuisance.

Forum Question What pointing? - Tony Poole - 6 Aug 2002
I had a small patio area (stonemarkets weathered york random slabs) laid by a contractor about 5 years ago and he used a dry-mix mortar to point. After a couple of years it crumbled in parts and a year later the odd weed would come through. Worse still when I used a pressure washer to clean the patio the pointing was blasted out entirely in many places.

I have just laid the same slabs down the side of my house (and it certainly looks better than what the contractor did - and a lot cheaper!) but am unsure which pointing method to use. Is it unreasonable to expect the previous pointing method to withstand a pressure washer or is it just the way it was done that caused it to fail? I'm going to rake out all the old pointing and do the whole lot in one go - but which method should/would withstand the use of a PW? GeoFix was recommended to me but apart from the expense it doesn't appear to be that popular throughout this site - and a great site it is too.

forum answer Tony McCormack - 6 Aug 2002
I'd go for a standard Class II mortar, Tony. If the flags are well-bedded and there's no movement to engender cracks, it will be fine and will be able to withstand the blast from a typical domestic pressure washer. You could add a measure of SBR, a hardening agent, to get a better bond with the paving and an even harder finish, if you were concerned.

Dry jointing isn't suitable for riven paving that will be pressure washed - it's just a way of filling the gaps rather than creating a sound joint.

GeoFix, as you say, isn't the cheapest jollop on the market, and I have reservations about its use in wider joints because it does not bond to the paving itself. Even on relatively tight joints (6mm or less) I've managed to blast out GeoFix with a small Kew power washer.

I know mortar can be messy and is slow work if you're not used to it, but it's still the best option on these small domestic patios.

7 Aug 2002
I was afraid you might recommend the usual mortar route which, by my experience, is a real pain the butt!! No matter how careful I seem to be I always end up with a certain amount of staining on the slabs. I will try your suggested two trowel method and hope that makes a better job of it.

Thanks for the quick response.

Tony McCormack
7 Aug 2002
If you're really, really crap at mortar pointing, you can get a roll of 50-75mm wide masking tape or packing box tape and use that to protect the edges of the flags.

As we always said to the apprentices - TAKE YOUR TIME! And hurry up! wink

7 Aug 2002
Nice idea but the time it takes to mask up I could really, really take my time to absolutely ensure all the muck goes in the gaps and not over the flags! I wouldn't necessarily call myself a complete novice but I'm very picky when it comes to getting a good job done, which invariably means taking twice as long as maybe it should do - much to the annoyance of my wife although she always loves the results. Never bloody satisfied are they!!

Thanks again.

Forum Question Laying my own - abs - 7 Aug 2002
I have the grand task of laying 300 marshalls timber decking flags (i.e. wood effect) over an area of 68 sq m. i have had a couple of guys come and give me quotes for the job and a price was agreed. all the materials were ordered and they were meant to start last weekend. they arrived on time and dropped off their tools etc, i even hired a compactor for the job. they told me that they had another job and would return on sunday. sunday came and went. i rang them to be told that one of them had injured his back on the other job. so not only did i order all the materials for the job and hire a compactor i have now been let down. i am trying to find someone else to quote me but failing that i will attempt the job myself.

as i was saying before i got carried away.. the area is 68sqm which is a soil base. this area is at the end of my lawn and is elevated 2 ft above the lawn. at either side of this area is fence panelling and at the back of the area is a brick wall. the flags are 450mmx450mm.

questions :

A / i have order 5 tonnes of sand grit for the base, is this all i will need to apply to the surface before i compact ?

B / when laying the flags what mixture will i need for the mortar and how do you measure the correct amount. i have read 5:1 sand/cement mixture but how do you measure the amount to be used.

C/ will i need to build some sort of retention wall around the perimeter area  to support the flags? instead of a wall can i use railway sleepers?

i hope my questions make sense and any help is appreciated.


forum answer Tony McCormack - 7 Aug 2002
A - the bedding: This depends on what the existing sub-grade is like. If it's reasonably form and dry, then you could spread the grit sand over the area. However, it's best to stir in a bit of cement with the bedding sand, and this can only be done as you progress with the laying, otherwise it will have set by the time you get to covering the last of the 68m².

So, spread the sand, if you must, and compact it with the plate, but you;ll need to disturb the top 25mm or so to mix in a trowelful of cement as you prepare the bed.

B - Mortar: I assume you mean mortar for pointing and not that stupid, silly, nasty, amateurish 5-spot method of laying flags that is the universal indicator of a true eejit?

You measure in 'units', whether the units are spadefuls, half-buckets, kilograms, pint pots or whatever. You mix, for example, 4 spadefuls of sand with 1 spadeful of cement.

C- Retainer: If your flags are going to be higher than the immediately adjacent area, then you will need some form of retainer, and it should be a brick or concrete retainer, rather than wood, which can (and will) swell and shrink over the season. A flag -on-edge is a simple and cheap retainer, if one is needed.

7 Aug 2002
thanks for the reply tony.

re point C flag on edge i take it means as it reads using the edge of the flag as a retainer.

Tony McCormack
7 Aug 2002
No - it's a flag set vertically on its edge - see the Edgings and Kerbs section of the site for a fuller explanation.
Forum Question Indoor Flags - Danny Lee - Jan 11th 2001
I wish to lay your stone flags inside my barn conversion. The screed contains under floor heating pipes. Are there any special consideration for the inside nature or the UFH. Laid on mortar, or special adhesive? Lean mix or strong, etc?
forum answer Tony McCormack - 9 Aug 2002
Lay on a 12-25mm thick bed of 6:1 mortar, and allow for movement joints on any span of more than 6m
Forum Question Flagstone porch repair - Caron - 11 Aug 2002
I sure hope you all can help me here in Colorado.
We have a small (20' x 10') covered flagstone porch that is in need of minor repair.
It looks like the previous owners tried to fill in some of the mortar with some kind of premixed (grey) cement. Not only does it look horrible but in the two years we have been here the cement is coming out leaving the original 50 yr old coarse pink mortar at a lower depth than the stone in most places. The flagstone is irrregularly shaped and is in good condition except for the sloppy job with the cement on some of the stone.
I would like to make the necessary repairs and also have the mortar a darker color to contrast with the lovely dark pink stone (I'm thinking a dark green to match the moss covered mortar of the same type flagstone path in front of the house and thru the garden.
Can you give me any direction on this type of repair, what to use and how to do the job so it will last?
forum answer Tony McCormack - 11 Aug 2002
Hi Caron,

I think the best way of tackling this job would be to cut out all the existing mortar to a depth of at least 25mm (1 inch for you non-metric N.Americans!) and then re-point with a new mortar that has been coloured and strengthened to meet your needs. It would be even better if you could cut out all of the 'grey' mortar and get down to the 'pink' pre-existing mortar, so that you're laying the fresh stuff onto a reasonably sound substrate, rather than overlaying the known-to-be-iffy grey patch pointing.

I'm not familiar with what's available in N.America, but a good mix would be 4 parts building sand, 1 part cement, plus your chosen colour dye, and then a strengthener, such as SBR (Styrene Butadiene Resin ) which makes a normal mortar much harder and creates a stronger bond between the paving and the mortar itself.

There's a product I know is sold in the US that might be suitable - Dynabond (or is it Dynobond? ) Anyway, it's an epoxy-based mortar, so it will be incredibly hard-wearing and strong.

Once you've got the mortar, follow the guide given on the Pointing page to fill in the empty joints. Feed it into the joints and then smooth it off so it's 1-3mm (one-eighth inch ) lower than the surface of the flagstone.

H ope that helps

11 Aug 2002
Thanks Tony for your speedy reply!!

I can remove all the patch job, but some of the original mortar is level with the flagstone (out of the high traffic areas such as nearer the house). How would I remove this (it's very hard) without damaging the flagstone?

Or, can I give it a light coating on top so that all the mortar will match??

Tony McCormack
11 Aug 2002
Are you familiar with an Angle Grinder? You can use one of these, with a stone-cutting disc fitted, to cut out any old mortar.

Score the old, stubborn mortar pointing with the angle grinder to a reasonable depth (25-40mm ) then use a hammer and bolster/chisel to break out anything lect behind. You'll need mask and goggle, of course, but it's not that hard a job.

11 Aug 2002
Got it!! Thanks for the info on this.
Btw, great site you have here!
Forum Question New Flagging - Troy Tempest - 14 Aug 2002
Hi there,
I am flagging an area of about 8 sq meters around the dog kennel for the dog to use as a run. I have been told that I can lay 3 x 2 flags directly onto 50mm crusher run as it will also assist with drainage. Not sure about this, can you offer your advise please?
forum answer Tony McCormack - 14 Aug 2002
It is possible to lay the flags directly onto a 50mm crusher run, but it's bloody hard work! That's why we prefer to use a grit sand - it makes the bed preparation 100 times easier!

The bit about crusher run inmproving drainage is rubbish. It's no different to using sand bedding.

With dog runs, you really need a gully present so that you can swill down the area with a hosepipe from time to time. If you leave open joints in the paving, the urine finds its way into the bedding, and the sub-base or sub-grade, and begins to stink after a few weeks. sulk

Troy Tempest
14 Aug 2002
Thanks for your advice smiley

I will use 2' x 2' x 2" flags on a gritsand base (minimum 50mm) and butt joint the flags. I was planning on having a gentle slope towards a boundary wall where I was going to put some limestone down, about 8" wide x 12" deep. We used a similar set up before we moved house (already built) and kept smell to a minimum by bleaching/hosing down regularly.

Do you think this is ok or have you any more advise?

Been having a good look round this site and I must say it is one of the best around. Not just for flagging but in ease of use and the flow it has between topics. Don't know how you get the time to keep it up to date ... nevertheless, I and lots of others are grateful that you do.



Will the 50mm grit sand be adequate. I estimate about 1/2 ton for 24 2x2 flags ... is this about right?

Tony McCormack
14 Aug 2002
You'd know better than I about looking after dogs and their toilet habits (I'm not a dog lover; they tend to chew my ankles) so, if it's worked before, it should be ok. I know from the times we've installed paving at kennels that they've used a gully or a sump to collect the wash-off, but then, that's for several dogs, not just one or two.

As for your bedding sand -

24 2x2s = 24 × 0.6m × 0.6m = 8.6m²
@ 50mm bedding = 0.43m³ @ 1.8 T/m³ = 0.8T

...I'd order a tonne (or one of those big agg bags) as it can always be used to knock up a bit of concrete or for extra flagging. Make sure you order grit (or coarse or sharp) sand and NOT building sand.

And the reason I have so much time to create and maintain the site is that I've been forced into very premature retirement due to an accident and I'd do anything to avoid having to watch daytime TV all day, every day! wink

Let us know how you get on.

Troy Tempest
19 Sep 2002
Hi there,
sorry about delay getting back.
Completed this job in August over long weekend.
Your estimates were spot on and at the end of the job there was 1 flag left over.
Using the ratio of 10:1 was brilliant. Didn't think it would work but it did. Digging out seemed to take forever! Now its been down for a few weeks it looks great and my partner was surprised by how good it is.
The aching limbs went away within days but the nail I damaged when I trapped it between flags is a good few weeks off being fully repaired.
As i didn't have the time to do another area of 10 2x3's last week I got a flagger in. Yes he was a lot quicker than me but we don't think the job is as good as mine.

Brilliant site Tony, keep it up, sure I'll be back, probably next spring. smiley

Tony McCormack
19 Sep 2002
Great to hear it all went well for you - send us a pic of your work. smile
Forum Question Flags and patterns for a small garden - Peter Behrend - 14 Aug 2002
Owing to subsidence, our front garden wall is being rebuilt, and the existing concrete covering is to be dug up and replaced. This seems like a good opportunity to replace the solid concrete with something a little more aesthetic, and have been looking at a range of paving options.

The garden is about 5m wide and 4m deep, with a small bay window intruding along one side and a crab apple tree in a raised sqaure bed about 133cms x 133cms, in the centre of the garden but oriented at 45 degrees.

The house brick is mainly yellow, and we like the look of Devonshire Stone Products' Kingsbridge Random Paving in Cotswold Stone or Harrogate. We saw these at Pinks Hill, Guildford, having seen them discussed in the forum.

A whole host of questions....

Is the garden too small and the shape too complicated to support the use of this type of paving?
Could you suggest a suitable pattern for this size and shape of garden?
How much skill will the contractors need in laying these type of flags? They have been appointed by the loss adjusters, and primarily advertise themselves as interior decorators!

Any better ideas/advice would be gratefully received - unfortunately we don't have a lot of time to get this right.

Even if you can't help, congratulations on a top site - this is what the internet should be like!

forum answer Tony McCormack - 14 Aug 2002
Hi Peter,

taking your Q's one at a time...

The size/shape is fine for using that particular flag, but I'd suggest adding a brick edging or something to give a contrast. One type of paving all on it's Jack Jones looks a bit bland. Even something like a rope top edging around the diamond bed in the centre would help 'enliven' it.

Pattern and Design - well, that's a BIG question, as I can come up with hundreds of designs, but it's finding one that suits you without being OTT or overly fussy, which would look daft in such a relatively small area. If you do go for the random stone, then a random pattern would seem to be the order of the day. Pinks Hill do a Layout service, or you can email me.

Finally, I would not let bloody interior decorators anywhere near a paving job!! Interior decorators are scared of the rain and the mud, and those nasty rough paving materials might scratch their baby-soft little hands - leave them inside sewing hems on curtains or ballsing-up the colour scheme, and insist on a professional paving contractor. wink

I'm really surprised that the Loss Adjusters have suggested you use IntDecs - if you had a gas leak, would they recommend a glazier? Each man to his trade: insist on a paving specialist. There's dozens of 'em around that part of the world.

Forum Question Cutting Circular Holes in Paving Slabs - David - 16 Aug 2002
Hi, excellent site.

I have just laid a 10m² patio using Bradstone Peak Rivan 600x600 slabs on sharp sand.

My other half wants me to cut 200mm diameter holes in some of the slabs for planting purposes.

Can you suggest a tool or technique for this. Or is it just not a good idea?

forum answer Tony McCormack - 16 Aug 2002
Not a good idea! Those wet cast flags aren't the strongest pavings to begin with, and removing the centre would make them extremely fragile, so much so that they would have to be laid on a full mortar or concrete bed to keep them intact.

If your beloved is really keen on planter pockets within the paving, replace the 600x600 unit with a 600x300 and a 300x300 in a 'L' shaped arrangement, leaving a 300x300 space for the plants.

However, if a circular hole is what is required, then the simplest DIY method is to stitch drill all around - do you know what is meant by stitch drilling or should I explain? The 'professional' way would be to use a core drill, but then, the professional wouldn't want a 200mm hole in the centre of a wet-cast flag!

If these were hydraulically pressed flags, it's possible to cut a hole of almost any shape in the centre using just hand tools, as we had to do as part of our training back in the 1970s, before power saws were common. A dying art, I'm afraid.

16 Aug 2002
Thanks for the speedy reply. Think I'll go for the 'it's not a good idea' option.
Forum Question Patio woes ... a year on !!! - Rash - 19 Aug 2002
Hi Tony et al,

It's been several months (alright a year) since I bothered this board with my garden patio woes ... but I'm back ... hopefully for a brief while only!

Heres the state of play:

- drainage sorted (a relief to all concerned)
- sub base layed, levelled and compacted
- weed control fabric layed
- bedding layer of sharp sand layed and levelled (ish)

My problem now is that I want to lay my slabs (Bradstone Wetherdales) with a gap of approx 5-10cm all round for some decorative chippings.

But, I feel that I may have been too hasty in laying the bedding layer as I did not consider mixing in 10:1 ratio of concrete.

Please advise on these follwing options:

1. take up all the sand again (boo hiss) and mix in with concrete and relay. Time consuming and will not go down well with the wife (patio was promised to her for last summer!)

2. pick up approx 15 bags of B&Q Slab fix and spread that over the sand and dry lay on top. Is this stuff any good?

3. work on a bit of the patio at a time - take up a bit of sand and mix in with concrete, relay and drop the slab on that - i.e. as per option 1 but done with the laying of the slab in the same process.

4. some other genius idea from you experts

As always, all advice is greatly appreciated.

Kind regards,

forum answer Tony McCormack - 19 Aug 2002
Hi Rash,

good to see you back - your patio endeavours have entered the annals of paving history! wink

Option 3 is the best solution. Buy a bag or three of cement (not Slabfix or Postmix or any of those other over-priced products) and sprinkle it onto the area to be paved in the following hour or two. Stir it in with a rake or the back of the spade, and that will do.

If your existing sand bed is around 50mm thick, then a 5mm covering of cement will be plenty - or approximately a spadeful per square metre.

I'd work on a couple of metres at a time, and see how you get on. If you spread and stir an area larger than you can actually complete, don't fret. As long as you don't compact it solid, it should break up pretty easily the next day and can be mixed in with some fresh sand and cement.

Let us know how you get on.

Forum Question Laying Indian Sandstone - I Hussein - 20 Aug 2002
First of all congratulations for an excellent web site full of very useful information.

Over the last two weeks I have landscaped my garden with Indian Sandstone (from StoneFlair) called Desert Sand covering almost 125 square meters. The contractor layed the stones on a 200mm bed of scalpings and a 300mm bed of 6:1 sand/cement mix of mortar. The stone was layed directly on the mortar and left overnight to set and the pointing (1:1:2 mix of white cement, Sharp Sand, Soft Sand) was done after a few days.

My concern is that some of the stones are moving (rocking) and cracks are seen between the edge of the stone and the mortar. Also when you tap some of the stones there is hallow sound to indicate there is air between the stone and the mortar. Is this common? If not I need to know immediatly as I have not paid him yet.

How should it be fixed?

forum answer Tony McCormack - 20 Aug 2002
Is that figure correct? 300mm of mortar - or did you mean 30mm? 300mm is bloody ridiculous!

Also, the mortar pointing mix is very brittle, at 1:1:2; isn't it dazzlingly bright?

If flags are rocking, then, as they've been laid on a mortar bed, they will have to be taken up, the mortar broken out and fresh mortar placed in the bed before re-laying the flag.

If some of the flags sound 'hollow', it may indicate the dreaded 'spot bedding' rather than a full mortar bed or the preferred full dry-mix bed. Spot bedding is a discredited bedding method, but is still being promoted by some manufacturers who want to make it seem easy to lay flags, and by eejit tv presenters who really ought to stick to grinning inanely in front of the camera and leave paving and groundworks to those who actually know what they're doing.

Your contractor should tell you whether they have used a full bed or spot bedding. If they've used spot bedding, ask for their reasoning and why they have not used a full bed.

The loose and/or rocking flags will have to be relaid. One of the problems with mortar or spot bedding is that any movement or rocking only gets worse with time - it never corrects itself. You should keep your wallet closed until the loose flags are fixed. smiley

I Hussein
20 Aug 2002
Sorry, I did meam 30mm for base layer and 20mm for the mortar. Thank you for the reply. Will spot bedding cause the flags to crack when a heavy load is dropped on it? I fear that they will.

The mortar is not very bright as it was mixed with red Fobtone cement colour to get the desired light pink to match the sandstone. I am happy with the colour but will the 'brittle' mix cause it to come loose with time?

Tony McCormack
20 Aug 2002
The spot-bedding may well result in cracked flags, but it's the thickness (or lack of thickness) of the Indian Sandstone flags that's the main problem if you're going to be dropping weights on them. Most are only 30-35mm thick, and that's just enough for them to take average loads, but nothing exceptional, and not vehicular traffic.

Laying on a full bed, either of mortar or semi-dry, helps spread any load applied to the paving, whereas spot bedding means the flag is only properly supported in certain parts and is left to 'bridge' the gaps in those parts where there is no bedding. With a relatively thin flag such as these, a full bed does impart some extra strength, but spot bedding exacerbates their inherent weaknesses.

The brittleness of the mortar is not a major issue, but it will crack and come loose if there is any movement in the flags. It's overly strong for pavement pointing, but it's really not a big problem - I'm more concerned about the spot bedding than the pointing.

Have you got anuy pictures of this Desert Sand? I saw some at Shrewsbury Flower Show on Saturday and it looked very nice, but I'd like to see pictures of it laid in larger areas.

I Hussein
22 Aug 2002
I raised the spot bedding issue with the builder and his reply was that not all the flags are flat at the botton Some are concave causing an air vacuum under the stone. This is what causes the 'hollow' sound and is common with this stone. Out of about 600 flags, about 40 are making the 'hollow' sound. What are your views

He will remove and repoint the flags that are rocking, since the rocking is not much and only about 1 to 2 mm the re-pointing will sort that out.

I have not taken any pictures yet. When I do I will send them to you.

Tony McCormack
22 Aug 2002
Flags with a less-than-perfect bottom face are not uncommon, particularly with wet-cast products, but there is no way on God's Earth that such an imperfection could possibly cause a vacuum under the flag!! It's what we in the trade refer to as 'talking bollox"  wink

There's a hollow under the flags and there shouldn't be. If the flags are concave, then it is the responsibility of the flagger to adjust the bedding to ensure the concavity is catered for and does not result in a hollow, empty void beneath the flag.

Vacuum! I can't wait to tell my dad that one!! smiley

Looking forward to seeing the piccies - if you want to post them to this thread, see the HELP file, or you can send them to me via

Forum Question Grano for joints - A Bond - 20 Aug 2002
Just wondered how to adequately specify jointing mix for pointing slate slabs for a grey finish - would this be grano joints?
forum answer Tony McCormack - 20 Aug 2002
You could use grano (granolithic mortar), but it's not the easiest material to get to a smooth finish, especially on narrow joints. If you are dead set on having a grey-ish joint, then you could use a silver sand mortar and add black cement dye to obtain the required shade. This would give better adhesion in the joints, and a smoother finish.

What colour is the slate? A dark mortar often looks really good with slate paving.

A Bond
21 Aug 2002
Many thanks for that - I think this is going to be a very useful site!! The slate is Cornish Delabole (light blue/grey) but looks more dark blue on the brochure!
Tony McCormack
21 Aug 2002
I'm familiar with the Delabole slate, and it's one of the nicest in Britain, even though one of the images they use in their publicity material shows it laid with blindingly white joints!

Using a grey or a dark brown/black mortar will help emphasise the slate and not the pointing. Grano tends to dry a very bright colour, like a greyey-bluey-white, so go with the darkened mortar.

If you have any piccies, we'd love to see them. I've just added a help file on Posting Images - see the HELP link at the top of the page.

A Bond
21 Aug 2002
Wow - you are a helpful bunch!!

Work is due to start shortly, so I will post pics when possible.
Thanks again.

Forum Question Slabs laid in gravel - Michelle Anderson - 23 Aug 2002
How do I lay individual slabs in gravel, incorporating a weed proof membrane as well? Do I need to put a sub base under them or do I lay each on a full mortar bed on top of the membrane?
forum answer Tony McCormack - 23 Aug 2002
Hi Michelle,

these are best laid on a full bed or mortar on top of the membrane.

Allow the mortar bed to be slightly larger than the size of the flag/slab - so, if you're laying 450x450mm flags, let the bed be at least 500x500. Use a 4:1 mortar (Class II ) and make it just damp enough to cling together. Level it out with a trowel, place the flag and tap it down to level so that it beds into the mortar completely. Without standing on the flag, test it for rocking with your hands and pack extra mortar into any low corners. If there is any movement of the flag on the mortar, it will only get worse with time.

Keep off the flags for at least a day while the mortar cures, and then they should be fine. smiley

Forum Question Frost and snow - Anneli - 2 Sep 2002
Winter will soon be over us - and we are wondering what it will do to our flagstones if we are to use salt/mixed with sand on the paths to make sure the area is cleared from snow and ice?
forum answer Tony McCormack - 2 Sep 2002
It depends on the type of flags. Hydraulically pressed, uncoloured concrete flags and stone/slate flags are generally unaffected by salt, but the coloured wet-cast types, popular for patios, can suffer, particularly with the so-called de-icing salts, rather than common or garden Table Salt {NaCl}.

The de-icing salts can react with the pigments used to create the colour in the flags and make them go all funny. Reds turn to browns, buffs go quite dark and some of the darker greys/charcoals can turn either very, very black or actually be 'bleached'. It seems to depend on the actual 'salt' used and the type of dye used in the manufacture of the flag.

As with any 'chemical' treatment of paving, it's always best to test a small, discreet corner of the paving before trying it out on the main body of paving. If at all possible, try not to use salt in clearing the ice. Quite often, a spadefull of grit sand sprinkled over a frosty or icy surface ius enough to provide adequate traction, and there's no chance of the run-ff contaminating the adjacent garden, as happen with table salt and the de-cing salts sold at BMs and the DIY sheds.

Forum Question Skid resistance - Andy Wilson - 9 Sep 2002
I've been sent some info on paving flags, including that the wet polished slip resistance is over a certain value. Anyone know what the relevant standards are? Cheers
forum answer Tony McCormack - 9 Sep 2002
I can't find the actual reference just at the moment, but from memory, anything over 70 is "excellent" and over 50 is "satisfactory/good".

I had the bloody document in my hand yesterday, and I was thinking about adding a few words on PSVs to the site, but can I find it now! sulk

BS7263 for concrete flags or BSEN 1341 for natural stone

Forum Question Terracotta tiles - Neville Martin - 22 Sep 2002
I want to lay reclaimed, 6" square terracotta tiles on a new patio adjacent to the rear of the house. I'm not sure what the base should consist of, how deep each layer of material should be, nor what I should fill the gaps (which I want to keep to an absolute minimum) between the tiles with. Should I lay concrete on hard core, then a layer of mortar on top of that?

Should I use lime in any of the mixes and do I need a damp proof course? Finally, what incline would you recommend?

forum answer Tony McCormack - 23 Sep 2002
You need a concrete base, around 100mm thick, laid over a damp proof membrane, as described on the Concrete Hardstanding page, and then the tiles should be bedded on a layer of Class II mortar (see mortars page) and pointed with same. You can use lime in the mortar, if you wish, but it's not essential.

The fall will need to be around 1:60, certainly no less than 1:80.

Forum Question Indoor Sandstone and Underfloor Heat - Mark99 - 24 Sep 2002
I am completely new to all this, so apologies right away!

I am looking to lay sandstone flags (2ft x 1.5ft x 1-1.5 inch) in my kitchen. The kitchen currently has a concrete base.

I have some questions!

I am looking to put underfloor heating (electric) under the flags, but am struggling to get a straight answer as to the best type to use, how effective it will be, and the best way to lay the flags.

So, now for the questions!

1. What am I best to lay the flags on (I was planning on sand & cement). Is this OK?

2. What mixture would I use, and would it be wet or dry?

3. I have been told to paint the back of the flags in PVA bond, or SPA bond. Is this a good idea?

4. I have been advised to use a 6mm cable type system, by Cozy Heat. Any advise/experience?

5. What do I use to point the flags, can I use the same mix?

6. I am planning on using impregnator (by HG I think) to seal the flags, is this a good idea?

Sorry for the questions. I am keen to get this right, and I am keen to do it myself, rather than get someone in!!


forum answer Tony McCormack - 24 Sep 2002

the usual spec for UFH with stone flags is to lay them on a bed of semi-dry mortar, around 10:1 with just enough water to make it damp. I'm not sure what the idea is of using PVA on the backs of the flags, unless some eejit thinks it would make the flags 'stick' to the mortar, which is not even necessary!
Movement joints are not normally required, unless this is a very large project.

As for the cable system, all I can advise is to follow the manufacturers instructions to the letter and it all usually works. Usually.

Point the flags with a stronger mortar, a Class II (say 4:1), and tool it smooth. Allow the flags to stand for at least a week before applying the HG Gunk, so that the moisture level in the bedding/jointing can stabilise, and then be prepared to rub, rub, rub to achieve the desired effect.

Good luck! smile

24 Sep 2002
Thanks Tony

I think the idea behind the bonding was twofold. Firstly to make it stick better, but also to waterproof? From what you say this sounds a bit like a pointless exercise?

Another question, if my room is 19 metres square, how much sand and cement will I need to order. Is there some sort of equation to allow me to estimate?

Also, when you mention 'Movement joints' what does this mean?

Last one, is there any particular tips to motaring, as I am worried I might stain the flags? Should the impregnating be done before or after the pointing?

As before, any help welcome


Tony McCormack
There's no real need, or there should be any need, to make the floor waterproof. The concrete base is/should be waterproof, and the flags themselves, once properly laid, are as near as dammit waterproof, so forget the PVA - it's just an unnecessary expense.

So, quantities - this depends on bed thickness, which in turn depends on the flags you're planning to lay all a being a regular thickness....but, assuming you'll be using a bed that's an average of 35mm thick, then the equation you need is simply one for volume, ie, area multiplied by thickness, and then use the info on the Concretes and Mortars page to calculate your requirement in kg or 40kg bags or 1kg agg bags etc.

As a rough guide, I reckon you'll need summat like 150 kg of cement and 1200kg of grit sand, plus maybe 80kg of building sand for the jointing.

Next, movement joints. If you've only 19m², it's unlikely you'll need one, but, for completeness, there's some detail on them on the Concrete page and on the Resin Bonded Aggs page.

And finally, the jointing. If you've no confidence in your ability to point the flags without staining then you might want to use GeoFix or another polymeric sand. You can read more about these expensive products on the Alternative Jointing page.

And finally, just before I go to bed, leave the 'impregnating' until the very last, at least a week after laying, so that the mortar bedding has a chance to stabilise.

I'd be most interested to hear your experiences while laying this floor, as, I'm sure, would many readers of this forum, as UFH is becoming more and more popular and it's something I've only installed a few times myself. Your insights could be invaluable, as would any piccies you manage to take. smiley

25 Sep 2002
Thanks very much, your advice will be heeded and put into practice.

I will indeed let you know how I go on, and I am taking lots of pictures, so I will do my best to post some.

Keep up the great site, it is most valuable.


Forum Question What goes with indian sandstone? - Rich - 25 Sep 2002
I am planning on using indian sandstone for the treads on my two sets of step in my garden.

I have two seperate patio's and was wondering what would work well with indian sandstone?

I don't want to have the indian sandstone everywhere as i think this would look too much!

I was thinking of block paving with reclaimed bricks?


forum answer Tony McCormack - 25 Sep 2002
Reclaimed bricks as in reclaimed house bricks? No-no-no-no-no! They're not suitable for use as pavers.

Treat yourself to some nice clay pavers or even the small clay cobbles from Marshalls. They are also a 'natural' product and look grand with natural stone, whether it's from India or from Northern England, and they only cost about the same as reclaimed materials.


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