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yep & yep....
Same as with limestone etc - any porous sandstone will get Eff, Its simply a time game until all the Free Calcium carbonate in the build (mortar/base etc) has worked its way out and washed away.
Its always a massive shock to clients when the patio turns white. As David says, its just a process that needs to run its course. Going forward its worth letting clients know in advance about the possibility of effo, then its not so much of a shock to them
I onces showed a client a photo of efflorecence in the Dales near Simons seat - I wil try and get the pic - Naturally occuring, due to Gritstone (Yorkshire sandstone - the stuff walls are made from, not the flags [which are from a finer graned stone found above the grits]) natrually overlaying the limtestone, And join was very white - caused by water seeping through winter, re-occuring every year as the water moves through the rock.
Thanx for the comments. I also read that adding a frostproofer to the mortar mix increases the effects of efflorescence. I did advise my client I wont be able to seal the slabs until a later in case of this occurence but think I will add it in my terms and conditions to cover myself as the suppliers do. Never thought about sealing addin sbr to the backs of slabs but may try it out. Laid hundreds of patios and this is the first time it has occured to the extent it has which has puzzled me a bit.
I think i remember hearing that 'drytreat' the sealer can be used as it will allows efflouresence out but you'd definately need to check that. London stone do it I believe so try steve on here.
I was speaking to my contact at Drytreat about effo and he was saying that there is a lot more of it about this year due to the bad weather we have been seeing.
Using Drytreat will massively reduce efforesssence coming through. This is because the particles in Drytreat are much smaller than other impregantors and this allows drytreat to penetrate much deeper into the stone (4-8mm depending on the type of stone) You will still experienece a little bit of fine effo but it will be barely visible. Even so, with drytreat you will still need to take the usual precautions, the main one being that the stone is bone dry prior to sealing
have to say in 45 years of laying paving have never had the problem .maybe honed 20mm up does not help .i all ways lay on full bed sharp sand cement from 4/1 to 6/1 i only use bond bridge on thin and porus paving
45 years - I knew you was 10 years older than me :)
the issue is with the 22mm sawn or calibrated paving cookie
its easier for laying the calibrated or sawn paving but is causing problems on some jobs with the efflorescence bleeding through to the surface
we have now dropped down to a 8:1 or 10:1 sharp sand and cement mix and SBR the back of the flag as we are laying, the weaker mix works fine but you cant walk over the new paving for 3 - 4 days
the efflorescence is not always visible on every flag either but applying SBR to the back side of the flag when laying certainly works but is time consuming and you have to make sure there is no SBR on the face of the flag otherwise it will be there for life as it can't be removed once its dried
I have heard other contractors apply a weak coat of polybond to seal the back of the flags a few days before they start to lay the paving which I am lead to believe also works
10:1 !! Tony Mc will be proud.
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