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Old 12-14-2008, 08:26 PM   #1
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Default Lets talk repairing plaster fellas

Repaired (cut open, retapted and mainly skimcoated) plaster ceilings and walls this weekend. I have a fair amount of experience with it (you guys know my gig- again, my partner and I are teacher and do 25-35 hours w/k)

History- We ran into some trouble a long time ago rapairing and painting over plaster where the areas that we compounded cracked and bubbled tje next day. The BM dealer told me that I need to neutralize plaster prior to compounding or painting in latex. The reason why you need to neutralize it is b/c plaster consists of lime, calcium and gypsum. If there is any of the white powder in calcium exposed that is not neutralized, the water in the (compound or latex paint) won't ahere paint simply wouldn't adhere and/or will react to the plaster. Is this true??????? I've gotten away without neatralizing it about 15-20 times since we had that problem?????

Well we did a job and started Friday night. We scraped the peal, cut open and taped the cracks and sure enough, while I was compounding it just didn't agree. It was like mixing oil and water. The next day the compound areas had little hairline cracks. When we rolled over it some of the plaster was coming off on the roller.


You guys have any suggestions?????
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Old 12-14-2008, 08:30 PM   #2
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Are you skimming with plaster or joint compound? Plaster needs cure time before coating.



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Old 12-14-2008, 08:34 PM   #3
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I've done this numerous times in older homes and never had a issue. I think the key is to skin coat with joint compound (blue top) , sand, top coat with tinted mud to level, sand again, prime in oil and then apply 2 coats of paint.
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Old 12-14-2008, 08:49 PM   #4
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when we do old plaser repairs i have a few things that i learned and it helps a lot.
if it is really big area sometimes i use product that is called structo lite for a base coat to fill deeper spots and then topcoat whit easy sand
if you have bonding problem i suggest you try a product by USG - plaster bonder it really does help.you can roll it or brush it.
and we allways use cover stain to prime just so there's no surprises later.
hope this helps
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Old 12-14-2008, 08:52 PM   #5
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Anytime I need to repair plaster, or any deep, big cracks, I use Rapid-5 fast dry spackling compound. I don't use real plaster. If its crumbly sandy plaster, I coat it with Gardz to solidify the area first, then patch it. Rapid-5 dries super fast, and very hard. I use that to do 90% of the patch, then top coat it with regular joint compound. Don't forget to prime the patch!
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Old 12-14-2008, 08:52 PM   #6
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Quote:
Originally Posted by Jeff.Chicago View Post
I've done this numerous times in older homes and never had a issue. I think the key is to skin coat with joint compound (blue top) , sand, top coat with tinted mud to level, sand again, prime in oil and then apply 2 coats of paint.

Tinted mud??? I'm not fimiliar with it????? What is that??? We used used 45 minute compound for 2 coats and then normal joint compound (green top) for the 3rd and then let it sit for the night.

We DID NOT OIL PRIME!!! is that a problem?????????? if so why?????

A couple the areas we were compunding really didn't like it. It sort of bubbled out right away like a bad a bad reation.

Then when we were rolling the walls a couple areas of the existing (non compounded areas) came up. It pulled right off the wall. (and we scraped it pretty good prior to that)

It was was like we were trying to roll over wet compound and it just pulled out. Except it was existing plaster that we never touched???????
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Old 12-14-2008, 08:53 PM   #7
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Originally Posted by vermontpainter View Post
Are you skimming with plaster or joint compound? Plaster needs cure time before coating.
We skimmed it 2 coats in 45 minute and then the 3rd was in regular joint compound.

I would think it cured b/c we let it sit overnight.
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Old 12-14-2008, 09:06 PM   #8
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we use oil primer to prime over repaired old plaster walls, repared water damage or after we strip wallpaper and wash the glue off the walls
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Old 12-14-2008, 09:10 PM   #9
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is there a chance you left some deteriorated plaster??

who knows what everyone has done before you???

probably some completely out of control drunken plasterers,,

i have never seen this condition you are mentioning,,,is there a chance you didnt remove every bit of failing plaster???
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Old 12-14-2008, 09:18 PM   #10
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Quote:
Originally Posted by mjkpainting View Post
Tinted mud??? I'm not fimiliar with it????? What is that??? We used used 45 minute compound for 2 coats and then normal joint compound (green top) for the 3rd and then let it sit for the night.

We DID NOT OIL PRIME!!! is that a problem?????????? if so why?????

A couple the areas we were compunding really didn't like it. It sort of bubbled out right away like a bad a bad reation.

Then when we were rolling the walls a couple areas of the existing (non compounded areas) came up. It pulled right off the wall. (and we scraped it pretty good prior to that)

It was was like we were trying to roll over wet compound and it just pulled out. Except it was existing plaster that we never touched???????

Green top should be for your bottom coat since it's a pain in the ass to sand and then do how ever many coats you need over that with the blue top compound or 45 depending on your time frame. I usually tint my top coats so that I can see where my high and low spots are so that I sand off even amounts and that process makes your walls totally smooth.

U really should oil prime so that all your work is sealed and keeps the compound from cracking and falling apart. After that, apply the paint and you should be golden!
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Old 12-14-2008, 10:10 PM   #11
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U really should oil prime so that all your work is sealed and keeps the compound from cracking and falling apart.
No need for that anymore. Gardz is phenomenal in that aspect.
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Old 12-15-2008, 01:06 AM   #12
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Ah, so many questions, so many procedures, so many materials.

Plasters are made with lime or gypsum or a combo of both. To say calcium is also part of the mix is redundant as calcium is part of the compound that makes limes plaster or gypsum plaster. (Study wikipedia for more info)

Lime is naturally very alkaline (high pH). Gypsum is actually neutral. Oil paints do not tolerate high pH. You will get saponification (turns to soap, to put it simple english). Many latexs tolerate and do OK with a pH up to 9 and maybe higher.

Some folks will mix premix JC (evaporative drying) with hot mud (dries by chemical reaction) and for some reason this spikes the pH up past 12, which will raise hell with any coating.

Now, I have in the past had problems with applying JC over new hot mud - perhaps the hot mud was not cured, I don't know.

If you are in doubt, test the pH. (they make pH pencils). Douching it thoroughly with an acid should bring the pH down. Acids include vinegar, Muriatic acid, and even ammonia.

Now, if you are having bonding problems with the hot mud to the existing wall, try a bonding agent. I have not found the USG bonder in this part of the country (Mass) but Silpro's Weld-O-Bond works great. (It's made in western Mass so you should be able to find it in CT.

I agree that Structo-lite is a wonderful base coat, but remember it is a lime plaster and takes a LOOOOONG time to cure (30 days) and still may have a high pH.

If I were you, I would take the time to research on the Internet about all the plasters and be better informed about them. It ain't rocket surgery, but the chemistry is important for a painter to understand.



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Old 12-15-2008, 01:27 AM   #13
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No need for that anymore. Gardz is phenomenal in that aspect.
I have heard about that and want to use it because it's latex and it goes on easy.
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Old 12-15-2008, 09:50 AM   #14
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Quote:
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I have heard about that and want to use it because it's latex and it goes on easy.

Interesting. I will this product a shot next time. Here is a link:

GARDZ® Problem Surface Sealer Use ZINSSER FIRST to Start EVERY Job RIGHT! Quality saves time and money! - local Retail Store Locator Find Paint Primer Wall Ceiling interior exterior prevent mold mildew proof product price sell sold for sale city stat
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Old 12-15-2008, 10:07 AM   #15
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How about some pics as I'm primarily a tactile learner
I'm not sure Idaho was even a state when they quit using plaster back East
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