# dont know much about plaster



## Quaid? (Mar 13, 2009)

im gonna have some walls in the near future that i have to paint that are plaster. the plaster guys will be finished on friday. i havnt painted over fresh plaster before, so how long do you guys wait before painting over new plaster? also, can latex primer be applied over fresh plaster?


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## painttofish (Aug 28, 2007)

It depends on the plaster but 30 days is a general rule. Provided temp and humidity are regulated. Good info here.


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## chrisn (Jul 15, 2007)

Ask the guys that are doing the work, they should know better than anyone.


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## Capt-sheetrock (Feb 10, 2008)

chrisn said:


> Ask the guys that are doing the work, they should know better than anyone.


Go to your room !!!!

Isn't that asking a drywaller a question about drywall????

How could you,,, How could you ??????


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## DeanV (Apr 18, 2007)

Plaster guys seem to be a little behind the times when it comes to priming now. From what I have read, modern plaster have very little lime in them, so they can be primer with acrylic instead of oil, but most plaster guys are old school and insist on oil primer out of old habit. And they often want the slow dry oil Benjamin Moore Primer. I am not spraying out an entire home with the stuff. No thank you.


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## CApainter (Jun 29, 2007)

Interesting site about plaster

http://www.nps.gov/history/HPS/TPS/briefs/brief21.htm

The key to a successful paint job is proper drying of the plaster. Historically, lime plasters were allowed to cure for at least a year before the walls were painted or papered. With modern ventilation, plaster cures in a shorter time; however, fresh gypsum plaster with a lime finish coat should still be perfectly dry before paint is applied--or the paint may peel. (Plasterers traditionally used the "match test" on new plaster. If a match would light by striking it on the new plaster surface, the plaster was considered dry.) Today it is best to allow new plaster to cure two to three weeks. A good alkaline-resistant primer, specifically formulated for new plaster, should then be used. A compatible latex or oil-based paint can be used for the final coat. (referenced from the web site)


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## IHATE_HOMEDEPOT (May 27, 2008)

I would find out how long they have been on the job. They might have applied the first coat 2 weeks ago. 30 days is what I have always been told. I used ZPrime last time and it was stinky of coarse but it turned out sweet.


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## chrisn (Jul 15, 2007)

Capt-sheetrock said:


> Go to your room !!!!
> 
> Isn't that asking a drywaller a question about drywall????
> 
> How could you,,, How could you ??????


I would hope that anyone still doing real plaster work would know more than drywallers


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## astrofgen (Feb 18, 2010)

PPG SPEEDHIDE 6-2 is a beautiful thing. I don't know of any other latex primer that slides so well.


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## Marion (Mar 30, 2009)

Speaking of plaster.... The job I'm on now- a 1950ish house, original plaster & PAINT! 40-50 year old original brush finish paint. Patching plaster and re-paint with oil. Priming with Zinzzer Cover Stain (oil). Hello Pete! I haven't brushed ceilings and walls since a teenager!


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## Quaid? (Mar 13, 2009)

the plaster guys on the jobsite today (they are a reputable company who has been in business for a long time) they said that 7 days was plenty of cure time if youre using latex, and they said 7 days is just a precaution, 3 days would be fine. they also usually do the priming, so if it didnt work they would obviously know. so why are they contradicting everything on this forum? they would know if 7 days is too early.


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## DeanV (Apr 18, 2007)

I think there is a lot of misinformation about plaster because old time plaster is completely different than modern plaster, but the old advice seems to still dominate.


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## daArch (Mar 15, 2008)

Quaid,

They speak the acceptable truth.

Today's plaster is gypsum, which is neutral pH, so you don't have the high pH problem. Yes, the skim (veneer) coat usually has lime in it, but not 100%. 

Also, waterborne paint can stand a higher pH than alkyds so there is not the issue of saponification as there is with oil. HOWEVER, waterbornes can not withstand a exceptionally high pH. Off the cuff, I would limit it to 10. Although I think the Big Z states one of their products can stand a pH of 12 (I wouldn't trust any coating on something that hot).

3 days dry time for skim coat over blue board is the acceptable norm these days. Waiting 7 is good measure. Ben Moore used to say (maybe they still do) to tape all four edges of a piece of plastic (like one sq foot) onto the wall and wait 24 hours. If there is condensation on the inside of the plastic, then the plaster is not dry. 

If you think the plaster might be too hot, I would test the pH. One paper hanger I know insists that use of a pH pencil is critical for anyone who applies anything to plaster. You can do a google for pH pencils and find many listings. And if the plaster is too hot, you must douche it thoroughly with an acid wash. Vinegar is the standard, but there are many acids that will suffice.

What you do NOT want to happen is this:


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## Quaid? (Mar 13, 2009)

i may invest in the ph pencil, cuz if that failure happened i think i would probably put a bullet in my head and call it a day


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## plainpainter (Nov 6, 2007)

Uni-Kal, the most popular plaster around here for blueboard veneer work is a ph of 12, says so right on their online msds sheet.

You can't prime that stuff for a period of at least 2 months - I have dozens of jobs where the primer didn't hold. You have to wait for four months before you can use an oil based primer.

Uni-Kal is 30% Calcium Hydroxide - that will turn any oil base into soap, unless it's allowed to cure a minimum of 90-120 days.

You can take all the advice out there about how you can paint this stuff in as little as 7 days - and shove it where the sun don't shine.

Most homeowners are too much in a rush to wait, I had one idiot who added so much retardent to his mix, the plaster was 'soft' - and just putting your hands on the wall was like putting it on a dusty chalkboard. I even followed the advice from P&L about spraying on a diluted mix of white vinegar and rinsing - got rid of the dust, but the primer still failed {Ben Moore Fresh Start 100% acrylic} the only thing that survived was the walls the homeowner waited 3 months before painting - then I used an oil primer.


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## Roadog (Apr 18, 2007)

What daArch says. Zinsser 123 is high PH primer that works well also. Done it. And it is mostly gypsum.


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## Capt-sheetrock (Feb 10, 2008)

chrisn said:


> I would hope that anyone still doing real plaster work would know more than drywallers


Of course,,, anyone with one eye and 1/2 sense knows more than drywallers,,,,,, they are the dumbest people on earth


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## daArch (Mar 15, 2008)

plainpainter said:


> I even followed the advice from P&L about spraying on a diluted mix of white vinegar and rinsing - got rid of the dust, but the primer still failed {Ben Moore Fresh Start 100% acrylic} the only thing that survived was the walls the homeowner waited 3 months before painting - then I used an oil primer.


Well that's just wrong advice you got to bring down high pH. First, it needs be UNDILUTED, and second you need to really soak the plaster . . . and obviously let it dry. 

Dan, why do you prime with an oil? Latexes are much more suitable for plaster.

I got burned once with an oil on a new ceiling. It had cured for 30 days and it was a gypsum based veneer. Never again did I apply oil over new plaster.


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## DeanV (Apr 18, 2007)

From what I have heard, with old, lime based plaster the water from latex primers would spike the pH even higher when it reacted with the lime, causing failure, so oil was used to avoid spiking the pH. Now, waterbased does not spike the pH in modern plaster since there is no to very little lime.


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## NEPS.US (Feb 6, 2008)

I have painted 100's of houses with plaster that has only cured for 7-21 days and have NEVER had a problem. Some of you guys look for reasons to make the painting industry harder or just need a excuse to stay home. Ridiculous.


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## DeanV (Apr 18, 2007)

So far on new homes, we have done plaster 3 times and never let wait and have not seen any issues.


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## Wallpaper Gypsy (Feb 22, 2010)

I would just like to add that Emulsi bond is a good product to add to an acrylic primer (in my opinion). Muralo, if you can find it or Aqua lock I think are good ones for plaster. But these days, since Sherwin Williams bought everything up and changed the formulas, it's hard to know what is what anymore.


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## daArch (Mar 15, 2008)

DeanV said:


> From what I have heard, with old, lime based plaster the water from latex primers would spike the pH even higher when it reacted with the lime, causing failure, so oil was used to avoid spiking the pH. Now, waterbased does not spike the pH in modern plaster since there is no to very little lime.


Dean, that's the first I've heard that. 

I wonder if it was the ammonia content in the old latexes that spiked the pH, and not the water. 

And then if one used oil on "hot" lime plaster, the risk of saponification was high. 

One of the books I read about plastering said that some houses with full three coat lime plaster were not painted for a full year !!!

No wonder calcimine was used :whistling2:


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## Quaid? (Mar 13, 2009)

thanks for all the good advice guys. and double thanks for not going on for 15 pages with inside jokes..


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