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Plastering & Rendering

Top coat of new render blown

Anonymous user 28/02/2024 - 2.59 PM

I rendered my new concrete block porch two weeks ago. 1 in 4 cement sand and added sbr waterproofer then scratched the whole lot. Last weekend I soaked the scratch and then applied the top coat 1 in 5 added plastersizer ruled of then poly floated then a quick rub with sponge. It was perfect. Today I went out and all the top coat was cracked and blown. It literally fell off the wall when I got a scraper underneath it. I would appreciate some advice. Hi Jamie. Thanks for this, New to this site so don't know how to reply, lol I used plastering sand and scratch coat was pretty well scratched. I think you're right, by adding the sbr to the scratch I've killed the suction and by allowing it to dry out I'm knackered. Reckon I may have to hack it all off and start again, this time scratch and top coat within 24-48hrs, don't want too but looked on all the Web and called a few bodies and all of them say the same, they don't know if there's anything that will solve the problem. Cheers

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1 Answer

Hitchman - Plastering & Rendering

Rating: 5 out of 5

Hastings

Hi, Sounds like you might have not keyed the scratch coat enough, and possibly used building sand in the top coat?? If so, and there was direct sunlight on it for a while, that would cause it to crack. Also, if you use SBR in the scratch it becomes like a barrier...not helpful when wanting the top coat to cure. The idea is to control the suction not kill it...ie you want moisture to be taken in by the scratch coat. I never use waterproofer, just soak the scratch coat with water. Thing is, everyone does it differently, some swear by waterproofer, so be prepared for mixed answers. Hope this helps!

Answered24 September 2013