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Posted: Wed Apr 19, 2017 9:10 pm
by Left handed
Would applying SBR primer mix to backs of slabs do anything to limit or reduce the appearance of efflorescence on sandstone paving?
Thanks
Posted: Fri Apr 21, 2017 9:50 am
by Tony McC
Yes.
Done properly, it forms a virtually impermeable barrier and thereby prevents upwards migration of salts from the bedding material.
It's not infallible, though. I have seen some very prous (and garish) sandstone that, despite being primed with SBR/OPC paste, still suffered from eff. I initially suspected a cement haze had been left on the pavement surface, but the client, the contractor, and the contractor's semi-tame labourer all swore that no cement-containing materials were ever used anywhere near the surface, so maybe it was salt migration/eff.
Posted: Fri Jul 21, 2017 5:27 pm
by Left handed
An update to this post. Finished my project a little while ago but have still been viewing forum and regularly occurring problem seems to be paving not sticking down.
By my estimation it cost me maybe £1/m2 to use SBR primer, a small price compared with the the cost of everything else.
Patio is rock solid with not a hint of loose flagstones or hollow sounds and it really didn't cost much extra.
When you read of people being told "sorry its a rip up job" it all makes sense.
Just a thought.......
Posted: Sun Jul 23, 2017 12:07 pm
by Tony McC
....and it's vitally important that it is SBR (or a proprietary paving primer) that is used and NOT the far inferior PVA, which is water soluble and disappears after a couple of weeks. Sadly, because it's cheaper than SBR, and because some contractors are little more than eejits, it gets used, and then the problems start again.
As you say, when faced with a bill of several thousand quid to fund a rip-up and redo job, and extra quid per square metre doesn't seem all that much!