Salvage My Plaster Repair

8 Jan 2011
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United Kingdom
Im looking for some advice (hopefully which saves me a lot of effort) i repaired a piece of blown plaster on a wall im decorating at the moment.

The plaster was blown all the way back to the brickwork (about 2" deep)on a patch about 8" square. I pulled it all off and repaired with polycell plaster repair and then skimmed the area. All seemed fine but doing this on a short timeline in hindsight i dont think the original plaster repair hardened properly (although i left 24 hrs as recomended).

I applied some size to the walls and then put up lining paper. As the paper has been driying (one of the seams crosses the patch) the seam and plaster has started to expand and bulge out by a couple of mm.

So is there anything i can do to salvage the efforts or is the only solution to strip it all back and plaster again?

Any advice welcome, thanks.
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I would do exactly what you said at the end of you post,,,,, take it all off back to brick and start again. This time though, use a "proper" plaster. Some of this mickey mouse stuff that's on the market might look good on the tub, but if you want to patch plaster properly, use the proper plaster. For a patch that deep, 2" (is very deep), i'd use British Gypsum bonding undercoat plaster. Prep the patch first,, wet/clean it down, then use pva onto the brickwork and around the existing plaster edges. While it's still all tacky, start filling in the patch. "Don't" fill it out all in one coat,, bring the thickness out by a half to two thirds at first,, let it firm up a bit, say half an hour or so, then scratch it and "let it set". After it's set, mix up enough bonding coat to bring it out to more or less flush. Let is set again, than put on a skim of multi finish or similar. Let the patch dry out completely, (a few days), then prep and paper.
Another option would be to fill the hole out with one coat plaster, when that goes off you can rub it back a little and skim the top with easy fill and sand until happy.
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If the plaster was two inches deep, then I would have thought it more likely that it is lime plaster, in which case adding anything modern is a bodge job which will not last. The only solution is to build up layers of lime mortar, starting with a haired coat, and allowing it to cure properly between coats (like weeks not hours).

In my 1830s house there are numerous modern patches on the lime plaster and without exception they are all loose, so they are coming out! (The modern stuff used is cement, gypsum, plaster of Paris, Polyfilla, you name it.)

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