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Posted: Sun May 08, 2005 11:54 am
by pilgrim
We recently had a dark grey sandstone paving patio laid (kadapha from pavestone). After cleaning off the mortar stains, we applied a first coat to seal it using Thompson's patio seal. After applying we had to go out for a couple of hours. It was sunny and bright all the time we were out a few miles away. However, on our return we noticed that some areas of the patio had small grey'ish white marks that hadn't been there before. The only thing I can think of is that there was a very brief shower of rain which caused spotting, but my better half thinks this unlikely as the markings are only on one part of the patio. Can anyone advise what might have caused this and how best to get rid of them? Any advice much appreciated.
Posted: Sun May 08, 2005 5:09 pm
by ABILITY
You mention cleaning off motar stains prior to sealing. How did you do this? Acid brick cleaner ?
Posted: Sun May 08, 2005 10:46 pm
by Tony McC
There are other reported problems with Thomsons Patio Seal and wet weather, damp flags, dew, mist and light showers. I've not been able to witness it for myself, but from the reports coming in by 'phone and email, it does seem to be primarily occurring with imported sandstone flags.
Thomsons are not particularly responsive. If you can get me some photies to add to my existing 'file' (pronounced as "pile of paper and photies precariously balancing on top of a unstable stack of CDroms") I can try and get an answer from Thomsons. My own belief is (and I stress that I am not a materials scientist) that the acrylic resins used in the Thomson's jollop is particularly hydrophobic (can't stand water, in other words).
Of course, it could be summat else altogether, but without photies, there's not much I can say.
Posted: Tue May 10, 2005 7:25 pm
by pilgrim
Yes, we did use a very very diluted mortar cleaner, which having read this site, I now realise may have been a big mistake. But too late now I suppose. However, I'm also interested in what Tony says about Thomson's products as since we applied the stuff we hadn't had any more rain until today, but after a heavy downpour the rain has formed into little pools almost like globules of oil on water. If this is the effect you are talking about, I can definitely try and get a photo to you.
Posted: Tue May 10, 2005 8:29 pm
by Tony McC
The problem with rain and Patio Seal is more of a 'blistering' than formation of globules on the surface. What has happened on other jobs I've seen is that blisters or pock-marks appear, and these often have a frosted, murky look to them. However, I'm always happy enough to look at any photies, especially if they feature paving! 
Posted: Thu May 12, 2005 2:32 pm
by pilgrim
Since last speaking, we haven't had any more rain, but I have noticed that the white marks have become more pronounced. Is there anything we can do to resolve this? As a last resort we do have some spare slabs. So how easy would it be to replace the ones that are really bad? Also with regard to the "pooling" of water on top of the sealant, will this diminish with wear do you think? and then would it be ok to re-seal with a differnt and better product???
Help !
Posted: Sat May 14, 2005 12:42 pm
by mouldmaker
When you seal your paving, you are making it impermeable. That's why the water forms droplets and pools - just like when you wax your car.
Resealing with a different product won't make it less waterproof.