Paint the surface with a coat of PVA before application of the mortar. The mortar or render is best applied when the PVA is slightly tacky. Yep just like any other backing plaster and certainly no need to PVA unless its been on a good while and then you can just wet it.
Scratch coats are particularly important in the world of vertical decorative concrete. With an aggressive scratch coat, not only do you have a chemical bond but you also have a mechanical bond and this is key for thick applications of vertical decorative concrete mixes.
Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Skip to content Bonding about hours, but some do leave it to following day before skimming depends on size of area. How long does PVA need to dry before plastering? When should you PVA a wall?
Should you PVA walls before painting? Do you PVA render before plastering? Or should I stick pieces of plasterboard into the large areas and then patch it to the rest? Fill in with plaster layers or plasterboard then patch? Above was half way stage. Below was after all loose plaster removed. PVA is used for many things build related. In the instance of plastering over it, regardless of it being cement render or gypsum plaster, the PVA must be tacky.
Not wet, and most definitely not dry as that is like trying to get something to stick to plastic. If you wish to plaster then typically you need to ascertain the background type of surface upon which you wish to apply it and work out if it's high or low suction. For eg, painted walls it would be low suction near zero porosity but for old black mortar it would be high suction.
The difference is which will 'suck' the moisture out of the plaster faster or slower. And I have been watching youtube clips to see what people do. Watched one where they just sprayed the area with water before filling holes with plaster. Don't for a minute think that you'll get away with just patching in and painting as that's not going to be a practical option IMO.
After a couple of applications go over the bricks with neat PVA and then start building the gap up with bonding coat. You'll prob need to do that over two applications as its quite deep. Get that flush with the surrounding plaster and allow to dry. Prior to plastering the whole wall, I'd neat PVA the lot and allow to go tacky before skimming.
If you PVA bits of the wall the skim will start drying out at different times and make skimming a pita. All sounds like good advice. I have Thistle hardwall plaster - is that the same as bonding? So forget sticking plasterboard into the cleared area - just build up the layers with the bonding plaster?? Browning may actually be better if you are unsure about the suction, it holds its water better than bonding, but, can be a bit harder to work with. Bonding about hours, but some do leave it to following day before skimming depends on size of area.
The paint will just sit on top of the PVA and in time could peel off. Let it dry out thoroughly before applying your topcoats. How thick should a bonding coat be? Floating coats should be applied at a thickness of 8mm, up to a total plaster thickness of 25mm, and wire- scratched between each coat.
The final floating coat should be ruled to an even surface and lightly scratched to form a key for Thistle Multi-Finish.
One benefit of polyurethane glues is that because they are not water-based, they are not drawn into wood pores as drastically as PVA glue. Suction into the walls if the blocks are absorbent and they have not been dampened which might cause drying shrinkage cracks.
Hi David. Good question. If the bonding cost has been gone over with a scarifier before it dried like a hand held rake to put little troughs in it for the finishing coat to adhere to then PVA is not required. Hope this helps! Timothy David Interiors.
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