Patching and Plastering - Repairing plaster wall with previous moisture damage

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biederboat
03-28-07, 01:16 PM
Hi, I'm trying to repair/repaint a plaster wall. The construction method is thin plaster (< 1/8"), then a layer of what is almost like mortar (about 3/8"), over a drywall lathe (about 3/8" thick with a hole grid to hold the mortar. This is from 1947 and appears to be rather unique, haven't seen or heard of another house like it but, hey, I'm a DIY'er. Overall makes for a darn solid wall. Here's the rub: On the wall above the fireplace, there's an area spanning the mantle and going up about 12" that repeatedly lifts the paint and then "chalks" pretty bad. In the past we had some water leaking at the roofline where it meets the chimmney but I'm reasonably certain we have fixed that. If water were running down the house-side of the chimmney (on the outside surface of bricks), it would have likely puddled up behind this area. I've tried scraping/sanding/painting this area serveral times but the "disease" keeps returning. Presently, I've been scraping the area and the growth (which almost appears crystalline) returns after a few days but it's been relatively dry. Is there some treatment I can do to leach out whatever keep causing this or do I pretty much need to cut out the entire area and put in a section of sheetrock?

Thanks,
Biederboat

DaVeBoy
03-29-07, 07:37 AM
First I'd make sure there really is no more leak.

Then I'd get rid of as much chalk as freely comes off.

Then you can buy paint that is okay for chalky surfaces. There also is a paint additive for this, I think called something like Emulsibond, or something like that.

Then skim coat back to flush with something like Durobond.

Then repaint.
marksr
03-29-07, 05:10 PM
I don't repair plaster walls very often but any chalky or dusty surfaces must be taken care of prior to painting [or patching]. Emulsa bond is the name of a latex paint/primer additive to combat exterior chalk problems but I've never used it on plaster - but it might work.

I'd wash off what I could of the "chalk" and use a good bonding type primer - oil base or pigmented shellac would be best providing the plaster is good and dry.