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  1. #1
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    Question What's the appropriate primer/sealer for new plaster walls?

    Hi. I have brand spanking new plaster walls in my kitchen/dining room.

    I am doing the painting, and my contractor said I need to use an oil based primer on the freshly dried plaster.

    However, a dude at Home Depot said to use some sort of plaster first coat...

    and a guy at my neighborhood paint store said to use a PVA drywall sealer followed by a 100% acrylic water based primer. I don't know if he understood that plaster walls are a whole different ballgame than drywall.

    Any input is appreciated to clear this matter up for me!

    Thanks.

  2. #2
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    Default Re: What's the appropriate primer/sealer for new plaster walls?

    On plaster walls and ceilings to be painted, I prefer to use two coats of oil based Kilz. You can then use oil based or latex paint. The oil based Kilz primes and is a stain killer.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  3. #3
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    Default Re: What's the appropriate primer/sealer for new plaster walls?

    i was told you have to wait at least 30 days after the new plaster has dried before you prime the walls and if more lime to wait longer because the plaster isnt finished getting hard. I have lots of very old hair and earth based scratch plaster with new lime plaster work and paris plaster on the top.

  4. #4
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    Default Re: What's the appropriate primer/sealer for new plaster walls?

    Just out of curiosity, what was the price difference between drywall and the new plaster you had installed? Tough finding a plasterer to do the work? Thanks!

  5. #5
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    Default Re: What's the appropriate primer/sealer for new plaster walls?

    Don't overthink this guys, it's just new drywall, 2 billion square feet a year.

    PVA is great, it's cheap, Killz is better it's expensive and pointless if it's new drywall. Seal it and paint it, enough said.

  6. #6
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    Central Indiana
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    Default Re: What's the appropriate primer/sealer for new plaster walls?

    Plastering for 19 years here, having joining local 692 Indianapolis, learning from the old guys right before most of them passed. Oil based KILZ is best, and has worked better for me/my clients for years. Some oil based primers do not have stain blocking abilities. If the walls are in-fact historic/older, there are so many stain factors at play. The last project I just completed was an 1830's Greek revival in Thorntown Indiana, where the greenville treaty was signed between the miami Indians and the US army. Despite the many contributing stain factors I have encountered over the years, this one was a first. Honey bees had infested the chimney for over a century and their wax proved difficult to subdue. Even here, KILZ is the answer. central indiana stucco repair dot com



    The poster asking about cost drywall vrs Plaster. Original 3 coat plaster with lath install = 6 to 10 sqft
    Two coat plaster finish over existing = 3 to 4 sqft
    Drywall = 1 to 1.50 sqft

  7. #7
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    Default Re: What's the appropriate primer/sealer for new plaster walls?

    There has never been a "30 day cure" on anything "plaster" plaster means "gypsum" However the old spec's called for "21 day cure" on anything "stucco" stucco being "cement" or "cement based plaster" The 21 days were 7 days of spraying water over the walls between all three coats. With the older Tiger limes you had to hydrate your plaster the night before by soaking it in water before mixing. However the new Autoclaved materials "pre hydrated" are ready to mix right out of the bag, are cured and ready once dry when installed correctly. If you trowel these materials on to thin, or you have excessive air circulation, you will will get "dryout" whereby the plaster is exponentially white in spots and dry with a chalk-like state that is easily dusted off the wall. So it is possible to incorrectly apply plaster and not gain a full curing, but generally, if installed correctly, plaster is ready to paint the next day. Thicker areas remaining darker "green" may retain water and need longer time frames before painting. To much water, moisture or humidity will result in "sweat-out" and cause green areas, whereby the biodegrading properties start to actually rot on the wall. Gypsum is biodegradable and is subject to mold.

  8. #8
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    Default Re: What's the appropriate primer/sealer for new plaster walls?

    A lime plaster finish should be checked for the proper pH reading as recommended by the manufacturer of the primer.
    A pH of 7 would be exceptable by most paint manufacturers.
    Your paint store should have a pH test kit or pH pencel both of which would be matched to the test kit chart.
    Most new plaster will have a pH reading of about 12 to 13.
    Painting a lime finish early could stop the RECARBONATION of the lime plaster.This will result in a weak finish coat.
    Keep in mind that lime does not cure or hydrate.
    So take your time for the very best results.

  9. #9
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    Default Re: What's the appropriate primer/sealer for new plaster walls?

    Given the choice, I would opt for giving the plaster at least a couple weeks to cure. Better safe than sorry!

    Unless there are other considerations, I would opt for a 100% acrylic drywall/plaster primer over the PVA. PVA is not the best primer on the market, especially in a kitchen where you will probably be using a satin or semi-gloss finish coat. The finish coat will not hold its sheen evenly over PVA primer. Indeed, even a 100% acrylic primer may not seal the wall sufficiently for a single coat of semi-gloss paint to hold its sheen.

    I would not bother with an oil primer unless there are other circumstances to consider. This is virgin plaster being considered here, not a hodge podge of plaster repairs abutting existing surfaces or stains leeching through from past problems.

    More than one coat of primer is a waste of time. Spend the effort on a second finish coat, if neccessary, to get a nice even sheen.

    In fifty years of painting in the Chicago area, I can't remember ever doing a new house that had plaster. What plaster I encountered was the patching of existing plaster from years way past. I did work closely with a talented plasterer and felt happy to have him. It is generally a dying trade.
    I do know that plaster veneer jobs are not that uncommon in other areas of the country, especially the North-East. Veneering is kind of a cross between drywall and plaster, with a skim coat of plaster being applied over "blue board".

  10. #10
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    Default Re: What's the appropriate primer/sealer for new plaster walls?

    Silverlake:

    The answer to your question (and the reason you're getting conflicting answers from equally knowledgeable people) is that it depends entirely on what kind of plaster was put on your walls.

    Nowadays, there are a lot of "acrylic" plasters which I know nothing of, and I suspect that these acrylic plasters can be primed with an oil based or PVA primer immediately after they're dry (but don't quote me on that).

    HOWEVER, real slaked lime putty based plaster calls for mixing slaked lime (which is hydrated lime) with Plaster of Paris (and sand if the objective is to make a base coat plaster). in any event, you have a lot of hydrated lime in your top coat of plaster.

    NOW, hydrated lime is calcium hydroxide or Ca(OH)2, and it's those OH groups that make real plaster highly alkaline. I therefore agree 100 percent with the post that said it was necessary to check the alkalinity of the plaster before priming it.

    If in doubt, what you can do is use a CONCRETE primer. This is an acrylic primer meant for priming fresh concrete, which is also highly alkaline. If you use a concrete primer, then it won't matter what kind of plaster you have, the primer will tolerate the alkalinity of the plaster no matter how high it is.

    (Note that normally, concrete is rough enough not to need a primer before painting. So, when someone says "concrete primer", the purpose of priming isn't to make the top coat of paint stick any better; it's to establish a physical barrier between the highly alkaline concrete and any subsequent top coat of paint that might not have good alkaline resistance.)

    The problem you run into priming over new LIME PUTTY based plaster (or any plaster made with hydrated lime) is it's high alkalinity, and oil based primers are particularily susceptible to something called "saponification". Saponification is the process whereby a strong alkali converts a plant oil or animal fat into soap. So, if this was a lime putty based plaster, an oil based primer wouldn't stand up well on it because the fragments of plant oils in the alkyd resins would be converted into a crude form of soap, and the primer would deteriorate rapidly.

    When my parents built the home I grew up in during the late 1950's, they were told not to paint the walls or ceilings for the first two months they occupied the house. That's because the plaster walls were made with hydrated lime, Plaster of Paris and sand, and the only paints available at the time were made of linseed oil. Painting over that plaster with linseed oil woulda resulting in a lotta peeling deteriorated soap.

    However, concrete is so prevalent in our building industry, and the need to COMPLETE projects on time meant that there had to be some way of painting fresh concrete shortly after it was poured. As a result, acrylic primers were developed that will stand up to the high alkalinity of fresh concrete. Once primed, any paint can be used over the acrylic concrete primer. So, if you can't get a good answer from your contractor as to whether there's any lime in your plaster or not, then use a concrete primer to be on the safe side.

    In these DIY Q&A forums there's lots of people talking about using KILZ sealer, but I find there's very very few people that actually understand the stuff. If they did, they probably wouldn't be so keen to recommend it for all the things they do.

    Take a look at the MSDS sheet for KILZ sealer:

    http://www.conncoll.edu/offices/envh...rades/kilz.htm

    1. The 15 to 25 percent alkyd resin content tells you it's an ordinary alkyd coating.

    2. Magnesium silicate is nothing more than talcum powder. In fact, this magnesium silicate isn't even good quality talcum powder because it's not ground finely enough to be sold as talcum powder. It's very coarsely ground talcum powder, and it's job is to make the KILZ dry to a flat gloss so the top coat of paint has a rough surface to stick better to.

    3. Titanium dioxide is simply a white pigment. It's what makes the KILZ white in colour.

    The solids content of KILZ is typical of a normal alkyd primer.

    But, note that the liquids in it consist of 60% naptha and 40% mineral spirits. A normal alkyd primer would use 100% mineral spirits as it's thinner. So, KILZ is in every respect an ordinary alkyd primer except that most of the mineral spirits thinner in it has been replaced with naptha.

    Naptha is camping fuel, and in order to keep a good cooking flame going on a windy day, the naptha has to evaporate very rapidly. It's the high evaporation rate of the naptha that makes KILZ sealer dry faster than other alkyd primers. That is, the only difference between KILZ and other alkyd primers is in what evaporates from the primer film as it dries. What remains behind on the wall is pretty much the same as with any other alkyd primer.

    So, if someone tells you to use KILZ sealer instead of an ordinary alkyd primer, please please please ASK THEM WHY!!! If their reasoning doesn't make good sense to you based on what you've read here, they probably don't have a good reason for recommending it over an ordinary alkyd primer. Most likely it's a case of them having been told by someone else to use KILZ, and them never having questioned that advice. So, they pass that advice on as knowledge acquired through decades of experience, but really, it's knowledge passed on from someone else who probably didn't know any more about it than you do.

    KILZ stops stains by denying the stain sufficient time to diffuse through the wet primer film to discolour the surface of the wet primer, thereby preventing stains from "bleeding through" the primer. KILZ does that by drying very rapidly, and thereby impeding the diffusion process. But, in your case, there's no staining to be prevented, and so there's no benefit in using KILZ. In fact, you're just making life more difficult by using a primer that's more prone to leave brush strokes because it dries too fast to allow for the proper self leveling of the wet primer film.

    FIND OUT whether or not your plaster is highly alkaline, even if you have to go to buy a pH testing kit and test it yourself. As long as it's highly alkaline, your only two options are:

    A) use an acrylic primer meant for painting over highly alkaline fresh concrete, or

    B) wait several weeks to several months for the alkalinity of your plaster to subside. (The hydrated lime (Ca(OH)2) in your plaster will react with CO2 in the air to gradually transform into calcium carbonate (CaCO3) and the release of an H2O molecule (that turns into a butterfly and flies away). As that process (called the "Lime Cycle") gradually turns the lime in your plaster into limestone, the OH groups are eliminated and the alkalinity of the plaster subsides. Once the pH of the plaster is within the manufacturer's limits, then any primer can be used over your plaster, even an oil based primer.)

    http://www.graymont.com/what_is_lime.shtml

    If the plaster is highly alkaline, the worst primer you can put on it is an oil based primer because of that saponification thing that'll turn your primer into soap. Using KILZ instead of an ordinary alkyd primer is just plain dumb because you get that same saponification process, but the primer being turned into soap has more brush strokes in it and was more aggrivating to apply with a paint brush because of the brush strokes.

    If it's an "acrylic plaster", then I don't know if it's alkaline or not (prolly not) and so none of this business about a highly alkaline plaster turning your oil based primer into soap necessarily applies. But, if it's real plaster made with real slaked lime putty, or even hydrated lime, then all of it applies. That's why you're getting different answers from knowledgeable people. If you knew whether your plaster was alkaline or not, we'd all be in agreement and this would be a short thread.

    Hope you followed that. Post again with any questions.
    Last edited by Nestor; 07-30-2011 at 11:04 PM.

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