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Posted: Mon Nov 26, 2007 6:43 pm
by hondacrm
The town where I live is having some extensive paving works being carried out. Walking past an area of pavement where block paving was being laid, I noticed one of the lads dipping the bottom part of the block into a bucket of what looked like a diluted PVA mix and then placing it onto the screeded bed.
Just curious if anyone has heard of this before and what benefit it would be?
Cheers
Posted: Mon Nov 26, 2007 6:48 pm
by James.Q
its a new one on me the only pva looking mix id use is a joint stabalising solution used after blocks have been laid
Posted: Mon Nov 26, 2007 8:14 pm
by lutonlagerlout
new one on me too
sounds very time consuming
???
LLL
Posted: Mon Nov 26, 2007 8:44 pm
by Pablo
Completely useless too unless they were laying onto a sand/ cement base still wouldn't be any guarantee it would stick either. Maybe for efflorence but clutching at straws there.
Posted: Mon Nov 26, 2007 9:09 pm
by simeonronacrete
PVA with cement will help increase the bond strength. But as PVA is mositure sensitive its efffectiveness will eventually be lost.
Better to use 1:1 Ronafix with cement, more durable.
Posted: Mon Nov 26, 2007 9:37 pm
by James.Q
unless block are being re layed and washed before laying now look whos clutching at staws lol
Posted: Sat Dec 01, 2007 1:57 pm
by Tony McC
There's a spec doing the rounds at the moment, largely derived from BS7533, whereby the underside of a paving unit is painted with PVA or similar to ...
1 - increase bond strength between paving and laying course
2 - prevent groundwater wicking to the surface of the paving unit
This is seen most commonly with granite flagstones, and I am still not convinced of its long-term efficacy.
Regarding bond strength: if the laying course is an hydraulically bound material (what we used to call mortar before the bureaucrats took over the building trade), then any additives deemed necessary can be added to the mix, rather than relying on the contractor to haphazardly daub the underside of each individual unit. The concern regarding a dry (and possibly dusty) underside coming into contact with a wet mortar...ooops! a wet hydraulically bound material, can be countered by inverting the units prior to laying and hosing down the lot in one, simple 2 minute operation.
Regarding the water wicking issue: as Simeon pointed out, PVA is water sensitive so its usefulness fizzles out over time. However, it does work for the first 12-24 months, and as this is now the standard retention/defects period, the practice is being adopted to ensure that no wicking problems become evident during that period so that the contractor can reclaim the retention sum with no problems. If wicking then starts to occur, who gives a toss/ The contractor has got his few quid and the client has no lever to force remedial work.
However, just why PVA (or similar) should be applied to the underside of concrete block paving laid onto an unbound (sand) laying course is completely beyond me. Sounds like the sort of knobhead idea that a halfwit architect/designer comes up with after reading about the above and failing to grasp the fact that it only has any validity when working with hydraulically bound laying courses.
Posted: Sun Dec 02, 2007 12:03 am
by haggistini
good answer!
Posted: Sun Dec 02, 2007 11:31 am
by matt h
aren't they always:D
Posted: Sun Dec 02, 2007 11:48 am
by Dave_L
matt h wrote:aren't they always:D
Depends how much ale he's drunk!!! 