plastering over crumbling brickwork

[Ken Hurcomb]

I am attempting to replaster a wall in a 350 year old house. The house is not listed.

Some of the previous plaster bubbled up and has now been removed. I have not removed any of the plaster that appears sound. It would appear that some of the old bricks are disintegrating i.e. they are dry and crumbly on the outer surface.

Is there any way to fix the bricks before plastering and do I need to strip off the whole wall?

I have noted a suggestion as to how to fix the bricks e.g fiberglass resin but wonder if a PVA product such as Unibond would also be suitable.

Thanks in advance for any suggestions.

[stuart noble]

Fibreglass resin would be OTT and expensive. Pva diluted 1:4 with water is a well tried (by me) solution to most crumbly problems. Seal the bricks with it, then use it to mix a general purpose mortar to render them before plastering. If you have serious damp, I'd use SBR instead of pva. Expensive, but it goes a long way.

[Dave Baker]

Rake out any crumbling mortar first and repoint with a sand cement mix. Leave the pointing a little under the surface of the bricks to give something for the plaster to key onto. Wire brush the bricks to remove the worst of the flaky surface and then paint the area with unibond, maybe a couple of coats, leave to dry and then plaster over that. The plaster will key into the pointing even if some of the bricks are crumbly.

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