I have low garden wall which has been painted over the years. I used a wire brush and PVA on the surface prior to adding a mortar . The end product was that it was very bumpy. The next day I brushed down the wall and hosed it down before adding the render which was 4 parts sharp sand and 1 part cement and 1 part lime.
The result was that it did not stick and fell off.
Can someone advise where I went wrong .
First of all using sharp sand is not good for the cement to bond as it does not spread as good as building sand. And the walls require r.s.b blue gritt as it has a stronger pva mix to stop moisture and loose mortar from coming through.
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Mix should be gauged 3parts building sand 1part sharp 1part cement and surface should be dust free and pva applied before scratch coat
either garden wall to dirty for second coat or to much water in in retaining wall or possible to much feb/waterproofer in first mix.hope that helps a little.
I think it was still wet and Maybe another coat of pva on top of your first coat
Did you use some sbr in your mix it helps the mix to go fluffy. If I was you I would put a thin coat on first and then scratch it then put your second coat on after.
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Also need to see it before.
dont use pva use a morter adhesive and you should be fine
The render will not stick to painted brick work try getting all the paint off rake all the joints back to get a good key then 3/1/1 mix and top with a 5/1/1 mix.
First off you went wrong with using sharp sand for rending also using sand and cement over paint work it doesnt stick and just becomes blown render the best way to tackle something like is give it a key if its solid or if blown take the blown render off if not use a splits mix which is 1 soft wash sand and 1 cement paste it on and gives it a good solid key to render over the top
Try a sbr stabiliser this will seal any dust damp etc and will act like a pva adhesives.
I would paint on a soverign SBR slurry mix first after wetting the walls down (instructions to mix ratio easily explained on the tub, that gives it the adhesiveness to stick to the original wall. Then lay up your scratch coat as the SBR residue becomes justt slightly tacky. Scratch in your lines once staffed. Then couple days laters wet the wall down again and proceed to lay on your top coat as normal. Both coats we mix at a 4:1 ratio of sand and cement with febmix added into the water before.
You need to get a bondit called blue grit it will come in a tub that paint usually conea in
I would suggest you get a plasterer to look at it as may be the type of brick you are trying to hardwall onto
Painted surfaces are always a risk with render or plaster,best product to use is sbr quick coat of that and itll sort it,the mix was also an issue firstly you need a scratch coat on of 4t1 4 part plastering sand 1 part opc,then a top coat