Forum: Flags and Slabs
Topic: Sandstone staining
started by: andymoz
Posted by andymoz on 10 June 2019,17:42Guys, I have a question.
Firstly, credit to this website, which became the core source of information from substrates and mixes to the choice of sealer.
I completed a large self-build project, towards the end of last year, however staining or pigment has formed along the front row of the paving, (pictured).
My own conclusion is due to sub-surface water, given the direction of gradient, as other paving stones around the garden have not suffered similar effects.
The paving was laid over 150mm of MOT, using a full 6:1 mortar bed, finished using HD sealer.
All thoughts are welcome, anyone agree that this is due to water, can it be removed, will it get worse?
Wish I could post some photos, but just cant work out how to do it?
Image tab asks for a URL?
Posted by geordieboy on 11 June 2019,12:08Andy, go to the noticeboard and you will find How to upload photies
Posted by Tony McC on 20 June 2019,17:10Or send them to me and I can upload on your behalf.....
Posted by Tony McC on 26 June 2019,11:12The images....
Posted by xssc32x on 01 July 2019,14:16Hi, have exactly the same issue on my Digby stone forest green slabs. Have you found out how to remove staining?
Posted by andymoz on 01 July 2019,16:03Still scratching my head over this one Si,
Clarification would be great, but subsurface water is my best guess?
Hoping someone has experience of the cause and how to remove?
Obvs wanting to stay away from chemicals, and with the paving down nearly year, intended to carefully run a wire brush across the worst of it, prior to pressure washing and resealing.
Posted by Tony McC on 09 July 2019,10:14I think some of the staining is moisture contaminating the sealant. Impossible to be certain without feeling it and seeing it for myself, but those white streaks are archetypical of moisture contamination.
I also suspect there is a dash of efflorescence, which has been more of a problem this spring/summer than usual. That probably arises from the bedding mortar.
If you use an appropriate sealant stripper that would verify whether it really is an issue with moisture. < FAQ - When Sealants Go Wreong >
Posted by andymoz on 17 July 2019,18:33Cheers for the reply, the surface feels smooth, I’ve mechanically scraped into the stone, and it seems to be pigmented within the stone rather than staining sitting under the sealer.
Interestingly, staining is not present in areas; back butted using SBR slurry mix!
Unfortunately the Mira strip / clean products recommended at the ‘’When sealants go wrong page’ are no longer available. Therefore intend to use one of the following products to give it a really good clean, and prior to resealing.
< https://www.ebay.co.uk/itm....45cfWbC >
< https://www.pureadhesion.co.uk/ecoprot....re.html >
Posted by Tony McC on 17 July 2019,19:13I'll wait for our own resident cleaning expert to comment on those products, but I'm surprised the Mira stuff is no longer on sale.
Due to the almost imminent launch of the new website, I can't update anything at all on the current site, but I'll make a note to look into this and update the new site as soon as I possible can with current information.
Posted by andymoz on 17 July 2019,19:39Tony that's great, would rather wait and use a product that comes recommended.
For info, it looks like the Mira stuff has re-branded to 'Miracle Sealants Tile and Stone Cleaner', also unavailable in the UK.
Posted by R&A Pressure Washing on 19 July 2019,15:06I don't know either of those 2 products mentioned above, so can't really comment, as for Mira Strip, yes the Americans (Miracle) have stopped shipping it abroad and was told they have stopped making it full stop, as everything is going over to water based strippers?, which is a shame as it was a really good solvent stripper, the nearest thing to Mira-Strip is Lithofins Wax-Off, a solvent and will remove some coatings, but as always won't get all of them. There are other strippers I use, mainly from Tensid, but I'd really need to know what it is that needs to be removed?, before advising, some of them have very long dwell times & you also need heat/steam to assist the removal.
Posted by andymoz on 30 July 2019,18:30Taking good advice from this website, I applied 2 coats of ADSEAL Heavy Duty Sealer last summer, using a roller, it applied very well leaving a linear finish.
Ill take advise, but to be honest, if it wasn't for the strange staining (Pictured above), I'd be happy to pressure wash and reseal.
Not sure whether anything can be done about the staining, but re-sealing may go some way to help blend it in? I'm also seeing green growth, visible across the resin jointing, probably another indication that its time to re-seal. I'm sticking with the HD stuff as I have 1/2 a tin remaining from last year.
Question: Is it best practice to strip and re-seal or pressure wash using a cleaner ahead of resealing?
Posted by R&A Pressure Washing on 30 July 2019,20:44Okay I'll give you my view on this, seeing as it is what I do for a living, the Adseal, totally the wrong sealer for your paving, more of a commercial usage, I'd do a full strip of the sealer to remove everything and you' most probably find the white staining will go, as it looks like moisture trapped under that sealer, then once completely dry apply a good quality colour enhancing impregnating sealer.
Posted by gavinruane on 01 Aug. 2019,09:53I have just completed a 100m2 kandla grey sandstone patio....in the morning the stains are prominent...on a warm day they go away...it is not sealed...i did not put a slurry on the back...anybody know how i can solve this problem please ??
Posted by gavinruane on 01 Aug. 2019,09:57Sorry i forgot to say...these slabs are very very thin..i was thinking of taking them up ..sealing the underside and then relaying them ??
Posted by gavinruane on 01 Aug. 2019,10:11But was hoping for them to dry out then seal them...but would moiture stains come back after sealing ?
Posted by Tony McC on 01 Aug. 2019,11:56What are these "stains" Gavin? Is it just moisture or something more sinister? Could it be < Reflective Staining? >
Post a photie or send one to me and I'll upload on your behalf.
Posted by R&A Pressure Washing on 02 Aug. 2019,21:33Had a good chat with Gavin on the phone on Thursday, he'll either email some photos over to you Tony or me. Think we know what the problem is, but will wait until the photos before confirming.
Posted by Tony McC on 03 Aug. 2019,12:22Furry nuff!
Posted by andymoz on 06 Aug. 2019,19:38
Roger, your advise is most appreciated, and what you have to say regards the trapped moisture make perfect sense.
I applied the HD Sealer, following a good review from this web page, and happy there seams a solution to rectify the issue.
Please can I ask your advise regards recommendations for best stripper / sealer to use going forward?
Many thanks Andy
Posted by R&A Pressure Washing on 07 Aug. 2019,16:11
To remove the sealer you'll need Tensid's Tavec 201 which is a coatings remover, but you also need to use steam, so either a Doff or Torik machine.
Posted by andymoz on 03 Sep. 2019,21:37
Sorry to flag up an older post, I've been working away, and now back in the UK I'm hoping to get this issue sorted before the weather changes.
The paving was sealed using HD Adseal, however the stinging developed some months later. I would like to remove the existing sealer, covering the effected areas, but I don't really want to go down the steam removal route due to the hassle involved.
Not sure if the Adseal caused the issue in the first place? However plan leave the unaffected areas, and simply reseal over the existing finish.
Therefore can anyone recommend a readily available the shelf sandstone stripper and sealer?
All advice welcome.
Posted by Tony McC on 04 Sep. 2019,18:12"Readily available" and "off-the-shelf" are not terms that can easily be applied to *quality* sealant strippers, mainly because they are impressively nasty chemicals - and need to be if they are to be effective.
The seriously good strippers, such as that mentioned by Roger and the Paramose range, are either sold by specialist suppliers or available to order direct from the manufacturer. You'd be very unlikely to find either at Homebase or B&Q.
As for a replacement sealant, look again at < Sandstone Sealant Trials >
Posted by andymoz on 04 Sep. 2019,18:28Okay, many thanks for the reply, I will start looking for a sandstone cleaning company this the steam machine.
Following the cleaning - will gladly take advice on what to reseal with?
I have 5L of HD ADseal remaining, but cautious of reusing this due the the problem reoccurring, if indeed the sealer was the problem in the first place?
Any recommend welcome?
Posted by andymoz on 04 Sep. 2019,21:51Tony,
Apologies, I think we had a slight time difference in above reply, as advised I will revisit the test page to scope a suitable alternative.
Whilst a quick fix was wishful thinking, as always your advice is appreciated.
Posted by Tony McC on 05 Sep. 2019,09:08You're more than welcome