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  1. #1
    Join Date
    Nov 2007
    Location
    Sacramento
    Posts
    8

    Default Can you skim coat over painted plaster?

    I just purchased a 1916 bungalow, and removed some open shelving that had been installed on a plastered wall (no back to it). The wall had been painted many times while the shelves were in place, so now that they are down there is a grid of little "channels" where there is an absence of paint buildup. I'm concerned that if I just use scraping/mud/sanding to fill in these little valleys that I will still have a visible grid, only the lines will be smooth and level to the adjacent painted surfaces. I'm thinking that to do this right, I should give it a new plaster surface, but I doubt the plaster would take to a painted surface. Is there something I can do to the painted surface that will allow it to take the plaster? Or do I need to strip all of the paint (surely it is lead based somewhere in there!). Advice greatly appreciated!
    Joanne

  2. #2
    Join Date
    Nov 2007
    Posts
    102

    Default Re: Can you skim coat over painted plaster?

    Yes you can but you have to bond the wall with bonding agent.Although I think you would be OK to s**** the paint off and use joint compound over the area to smooth it out.I hope plastermaestro agrees with me.

  3. #3
    Join Date
    Jan 2008
    Posts
    5

    Default Re: Can you skim coat over painted plaster?

    what is bonding agent? i have repairs to make to old plaster walls. some places were water damage from broken radiator pipes which bursted when home was repo. some areas damage from trying to scrap thick plaster or cement where tile was in bathroom and kitchen.

    need advise what is this agent and will it also solve peeling paint where we painted good area? used bin to prime coat first.

  4. #4
    Join Date
    Jan 2008
    Posts
    5

    Default Re: Can you skim coat over painted plaster?

    also we have hair based plaster. our old neighbor says mabe cow hair in the based plaster. also the home one time had coal fireplace and orignal coal boiler.

  5. #5
    Join Date
    Nov 2007
    Posts
    102

    Default Re: Can you skim coat over painted plaster?

    Bonding agent can be found @ home depot or probably lowes check in the paint dept.We call that up here horsehair plaster.

  6. #6
    Join Date
    Dec 2007
    Location
    Corvallis, Oregon USA
    Posts
    37

    Default Re: Can you skim coat over painted plaster?

    Bonding agent can be used in a couple of ways. If you are using hot mud, pour some into your water before you mix in the powder.

    Or, just paint it on the whole surface to be skimmed. But be sure to remove any loose/peeling paint before application.

  7. #7
    Join Date
    Nov 2007
    Posts
    102

    Default Re: Can you skim coat over painted plaster?

    Quote Originally Posted by plasterfellow View Post
    Bonding agent can be used in a couple of ways. If you are using hot mud, pour some into your water before you mix in the powder.

    Or, just paint it on the whole surface to be skimmed. But be sure to remove any loose/peeling paint before application.
    ? why add to hot mud?

  8. #8

    Default Re: Can you skim coat over painted plaster?

    I suggest not using bonding agent at all. If you need too use bonding agent you are asking your skim coat to do something that it would rather not do. That being said, ready mix joint compound has a bonding agent in it (Poly Vinyl Acetate). I'm not sure your if the durabonds of the world have an included bonding agent in them but they sure seem sticky. The point of removing the paint layer is well taken, every layer applied to the plaster surface is a link in a chain beginning with the plaster application to the lath and ending at the paint surface. If any one of those links breaks everything on top of it will come off also. Being a layer of plastic (bonding agents) they will disrupt the transpiration flow within your building. Again I would suggest that if your wall system has existed in its present form for a period of time (being historic) that changing the transpirational aspects of the wall system should be approached with caution and understanding on how this change will effect your plaster, wall, house for the extended future.

  9. #9
    Join Date
    Nov 2007
    Location
    Sacramento
    Posts
    8

    Default Re: Can you skim coat over painted plaster?

    [QUOTE=PlasterMaestro;12293]"...Being a layer of plastic (bonding agents) they will disrupt the transpiration flow within your building. Again I would suggest that if your wall system has existed in its present form for a period of time (being historic) that changing the transpirational aspects of the wall system should be approached with caution"

    Am I correct in my understanding of the above, that adding bonding agent will interfere with the ability of moisture/vapor to "transpire" through the wall, and you recommend removing the paint (down to old plaster), and then skim coating plaster over that?

    If that is the case, would chemical paint stripper be advisable, or dry scraping it off (a daunting task to be sure!) Thanks Plaster Maestro, you're expertise is appreciated!

  10. #10

    Default Re: Can you skim coat over painted plaster?

    The short story is I suggest not skim coating the original at all but if you must I would use a joint compound, either ready-mix or time setting. Conventional white coats are too brittle for long term repairs.
    PVA bonding agents (referred to in this thread as bonder)are made to grab onto an aggregate (sand) in the base coat layer of plaster. They perform this function by re-emulsifying once and conforming to the profile (or texture) of the base coat blaster then hardening. Although it is widely used as a bonding agent for white coats I suggest that it is not in the best long term interest of your home.
    Stripping the paint from your plaster with a chemical stripper can , yes, be daunting. I have used steam to strip paint in the past successfully. The combination of heat, water vapor, and NOT having to use a chemical stripper seem to make it worthwhile.
    Since you seem intent on skimming the plaster I would not strip the paint, I would stablize the wall as needed with an adhesive made for plaster repair then skim the plaster surface with the thinnest layer of joint compound to fill in the cosmetic flaws.

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