Plaster repair and skim coating questions ...

etainJuly 12, 2010

I have a Michigan Greek Revival, circa 1840. I have just finished steaming several layers of wall paper from the master bedroom walls. I have uncovered nice smooth plaster in reasonably good condition, other than hairline cracks and this pink flaky stuff that I assume is adhesive from the original wall paper. The parts of the wall that are free of pink flaky stuff are a natural creamy color. I assume that either the walls were never painted or it has been discolored over the years. I can post pictures if it will help. I still have to remove the wallpaper from the ceiling :(

Should I skim coat the plaster or is there are really great primer like product out there that would fill in the hairline cracks and make for a nice painting surface? If I should skim coat the plaster, what type of material and technique should I use?

I've been reading and it seems that Durabond and Easysand are common recommendations and that premixed drywall mud is evil. I know nothing about plaster, I wouldn't mind trying it, but I have no clue where to start. I am very much a beginner. I'm going for smooth walls but imperfections aren't a big deal (a few streaks here and there isn't going to bother me). I'm leaning towards plaster or Durabond, something that you put on in one coat and don't have to sand (I'll sand if you tell me that I really have to). I do not want to use a drywall compound that shrinks and end up with tons of little cracks. I do want something that will adhere well to the existing plaster (or a bonding agent) and paint easily. I don't mind waiting for something to cure, it will allow me to procrastinate a bit longer on picking a paint color. Suggestions?

My second problem is that one very small wall that was built in an alcove to create a closet (prob mid 20th century) appears to be drywall. The steamer made it very nasty, soft when steamed and impossible to scrape. I did not get all the wallpaper off, but where I managed to get through, I exposed brown fiber stuff, I suspect that I removed the paper surface of the drywall along with the wallpaper. Now it's just a patchy mess. I'm wondering if I should skim coat that wall? Maybe I should seal it with something first to prep the surface?

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First off, it's natural for the white coat of plaster to have spiderweb cracks all over the surface. These are only in the white coat and are very closely spaced and interconnected. By closely I mean 1/4" apart. _Those_ are nothing to fix or worry about. Cracks that extend into the base coat, and have movement that you can see by pressing, and seem "broken" are something to fix. I like to spray the cracks with bonding agent (garden sprayer) and sponge the stuff in (don't leave any drips of bonding agent; hard to skim over them). It seems to stop any movement for some time. Then add fiberglass mesh tape and the durabond routine, as you have read.
The closet area, maybe sand the mess a little smoother to take off any high spots, the prime and then tape. We always use an oil primer around unknown/unforeseeable problem areas, because it really seals anything "bad" like wallpaper glue and prevents problems in the future, and durabond or regular mud sticks to the primer. Regular mud is not optimal for plaster repair in areas where is has to build up thickness; that's where you run into drying cracks (plus it takes lots of time for all the water to evaporate) and when/if it ever gets wet again it falls off lime plaster in sheets. It won't fall off if you oil prime first, and use it sparingly. Use brown coat plaster like Structolite (or Gypsolite), on top of a bonding agent like Link or Plasterweld if down to the lath, use durabond or easysand when the white coat is damaged or missing, use regular mud only for small imperfections and the final touchups, and you'll be fine.

    Bookmark   July 12, 2010 at 5:49PM
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If the cracks are tightly closed,even on each side (no real height difference across the crack), and the finish coat is solid a coat of primer and two coats of paint should cover everything.

You do need to clean off all the old wallpaper glue.

Hot water and TSP make short work of it.

Wipe with an almost dripping sponge, let the solution sit on the wall a few minutes, then wipe off.
After it dries you should rinse with clear water one more time.

Allow to dry and prime.

    Bookmark   July 12, 2010 at 9:15PM
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Thank you both. I think I'll try washing the walls with TSP and priming. Do you have a favorite primer that you'd recommend for this job?

I do have a few small spots to patch, around new outlets and heat registers and in the corners of the room. The contractor has already started using premixed drywall compound on those spots. I know that's not desirable, but since it's already started, should I finish with that and just feather it into the existing plaster finish as much as possible?

    Bookmark   July 13, 2010 at 9:17AM
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etain, as to your last question; I'd say "yes". We've used premixed drywall compound on similar spots in our house and have never had a subsequent problem with them (some have been repaired this way nearly 20 years). The feathering into existing plaster finish takes patience and practice, but you can make it work. If the spots are small, you can blend the edges in with a damp sponge instead of sanding too.

    Bookmark   July 13, 2010 at 11:36AM
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The pink stuff didn't come off, no matter how hard I scrubbed with TSP, it must not be glue. So, I think I'm back to skim coating.

The walls do already have a number of pre-mixed drywall mud repairs that appear to have adhered well (even when a steamer was held over the spot for 30+ seconds multiple times). Would it be completely crazy to do a very thin skim coat with pre-mixed mud that I know sticks to the wall?

If I use Easy Sand, is it a good idea to cover the walls in a bonding agent or an oil based primer before applying the skim coat or would it be a waste of time?

    Bookmark   July 19, 2010 at 10:53AM
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We had pink plaster patches on some areas of our walls. Maybe that is what you have. I used Weldbond on the plaster that needed to be patched or skimcoated. Used a Magic Trowel (love it) to smooth out the new plaster and only used dry wall mud for small spots later on. I also used shellac-based primer rather than oil-based because in another room the paint peeled off the oil-based primer. Don't knnow why. We are very happy with the results.

    Bookmark   July 27, 2010 at 5:50PM
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