mickg wrote:I used PVA from 1975 onwards and it was never an issue, plasterers used it prior to applying the first coat of render to a wall. tilers used it on bare plaster without any issues and now your a cowboy if you utter these words from your mouth
PVA is still used by a lot of the guys laying Indian stone and its applied as a watered down wash to the back side of the paving days before its laid, if SPR was used and it was splashed on the the face of the paving and left to dry it can't be removed
I'm perfectly happy with the idea of sealing walls, old plaster with diluted (2or3:1) pva, before tiling or plastering, I have even mixed pva in with plaster and seen this done by pros.
I was clearly under the misapprehension that it wasn't any good outside.
the PVA or SBR is to seal the rear of the paving to stop any salts or cement staining from leeching up into the surface of the paving from the cement bed what they have been laid on and is definitely an issue what needs to be addressed especially with the calibrated high end price paving products
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PVA *was* a popular choice for bonding, but it could be unreliable, especially on sites that had a high water table or were almost permanently damp.
SBR is a different type of product altogether and isn't susceptible to damp. It's main purpose is to create an incredibly strong bond between paving and bed and thereby reduce or eliminate the number of 'rockers' and the risk of rotation, especially with smaller units such as setts. It also forms a reasonably effective barrier to some salts and groundwater. It can be a real boon when working with a porous stone such as the G603 silver-grey granite as it minimises the appearance of damp patches.
Comparing the two isn't easy. If it's bond strength, then SBR is a far better product, but if it's as an underside sealant, I'm really not sure which is better, but given SBR's proven bonding abilities, I always err on the side of caution and plump for that.
since we started to use our new sealant we have had very few instances with effo coming through our paving. The only times it has come through is when the sealant has been badly installed.
What is the cost per m2 approx if you want to SBR or PVA the backs of slabs?
I was watching/filming some Chinese York Stone (I know!) being laid last Autumn, and they were getting a lot more than 25m² from a 5 litre container of SBR. I'd have to check with the project manager, but I must have watched them lay 50m² with no change to the dip bath.
I know they were using SBR with cement powder, but maybe they diluted it
It's always struck me that some brands of SBR are more viscous than others, which suggests some suppliers are diluting it to be able to sell it that bit cheaper. Not knowing enough about the chemsitry, I wonder if there is some recommended viscosity or ppm content for a good quality SBR, or whether it's just a matter of what the manufacturer thinks they can get away with?
I have finished the two way sloping sections, i took the gafers advice and put a row of blocks in the middle of the wood section, although this did involve adjusting the layout to give me a straight edge, I'm pleased with the side furthest side of the picture, closest to the down pipe but not so much with the other side, I think I was rushing it and the type 1 levels weren't as good.
