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Posted: Tue Jan 08, 2013 9:04 pm
by Mikey_C
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.
Posted: Tue Jan 08, 2013 11:04 pm
by mickg
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
Posted: Wed Jan 09, 2013 10:17 am
by Tony McC
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.
Posted: Wed Jan 09, 2013 1:29 pm
by London Stone Paving
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?
Posted: Wed Jan 09, 2013 4:55 pm
by lutonlagerlout
5 litres would do 25M2
so £7 for PVA or £16 for SBR
LLL
Posted: Wed Jan 09, 2013 7:41 pm
by Tony McC
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
Posted: Wed Jan 09, 2013 8:11 pm
by lutonlagerlout
depends how thick you knock it up i suppose
on a 50 metre patio i use 10 litres in the bedding mix and that works well for me
LLL 
Posted: Wed Jan 09, 2013 10:00 pm
by Kuts
last time i used it i read the back an im sure it said something like 5l to 25kg of cement :0
http://www.everbuild.co.uk/image....ond.doc
and
http://www.google.co.uk/url?sa=....cad=rja
i've had a glass of merlot tonight so will read up 2morra
Posted: Thu Jan 10, 2013 10:22 am
by Tony McC
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?
Posted: Thu Jan 10, 2013 1:20 pm
by London Stone Paving
Its exactly the same with sealants Tony. The more expensive ones generally have less carrier in them. As always you get what you pay for
Posted: Sat Jun 22, 2013 2:52 pm
by Mikey_C
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.
photos below
Posted: Sat Jun 22, 2013 2:54 pm
by Mikey_C
Posted: Sat Jun 22, 2013 7:38 pm
by mike builder/landscaper
Spend a bit of time with a 9inch grinder and even the joints out and it will look ok.
