Best way to render a painted brick wall?
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Answers:
yeah, do as above or cover wall with sheets of expanding mesh. nail it on with washer headed oboes. plaster away at it.
no messing about with scutch hammers or unibond and its gaurenteed to stick. try it..
After scraping any loose paint off, make the masonry surface rough, by chipping at it with a scutch hammer, which will make the render 'key' to the wall.
You must also use unibond pva (PVA), paint this on and use a milton plastering sand mixture with some plasticiser added at a ratio of 5-10% to the water. You can also add a liquid/jelly waterproofer admixture in the render coat itself.
Add cement to the mixture at 1:5 parts ratio and trowel it on to a thickness of 5-10mm. Spend some time trowelling up the surface after the application, in order to create a smooth surface. Usually the second coat is much easier to trowel up, best applied the same day as the first or 'scratchcoat'. Or apply PVA again between coats.
You must do this type of work preferably when there is no sign of impending rain or ice/frost or extreme temperatures.
2 options
to get a key for the render you can use a scutching hammer and hack the paint all over this would create a key hold for the scratch coat render.
or paint on pva, use liberally and apply the first scratch coat cement render and key this coat for the final render.
the final coat of render/cement should have a waterproofer mixed in with the cement to protect from the elements
render should be trowelled off a made good to cure
pva (unibond) it acouple of times first to make it adhesive, then you're up & running
if you want it to stay on permanently the only way to do it is either sand blast the wall until all paint has gone or fix steel mesh over all of wall and then render
DO NOT use any sort of sealer at all, because no matter what you put on the paint it is only as strong as the adhesion of the paint to the wall.
EXPERMET mesh fixed with obo/hilti nails is best option.
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