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JerMann 09-12-2010 10:16 AM

Skim Coat on Ceiling is Bubbling
 
Hi all,

My first post here...

I am taking my ceilings back to smooth. The house is 1926. I took the texture off my living room ceiling using a drywall sander (rented the Porter Cable). It took it down to sort of a knock-down texture. The current surface texture is joint compound of some type over top of plaster, or perhaps even over old paint?

Last night I tested skim coating in a small area. I applied a paper thin skim coat--just enough to fill the low spots. And within 2 hours I saw bubbles forming, about 1-2 inches in diameter. Full disclosure, I forgot to wipe down the ceiling first. So I am going to wipe it down and do another small test area and see if that does it. But I am posting here because I wonder if I am doing this right...

This happened in the dining room, too, last week. But I was not skim coating in there--just painting. And I did wipe it down first. (The dining room was smooth already--an existing skim coat over the plaster. There were small cracks--1/8th or 1/4 inch-- I did not notice and when the paint got under that old skim coat those bubbles showed up. That was the dining room.)

Now in the living room, the knock-down texture makes it impossible to see if there are the same cracks.

I guess my question is did my skim coat technique somehow cause this because it was too thin? Should I put on a thicker coat, such as 1/6th inch or 1/32nd inch? Everywhere I read it talks about 2 or 3 coats and sanding. But why can't I just put on one super thin coat and sand and paint?

Sorry for the scattered post.

Thanks,
Jerry

JerMann 09-12-2010 11:23 AM

Update, with pix
 
2 Attachment(s)
I just finished wiping a section of ceiling, and could see that the old skim coat softens so much it just scrapes off with my fingernail. It takes it down to the old paint layer (how old? probably very old, when the house still had a smooth ceiling). I could "easily" scrape the whole ceiling in a matter of 2 hours and not have to skim coat.

EXCEPT, I checked out the bubbles from last night's skim coat test and the bubble is forming under the OLD layer of paint, at the plaster level.

I have attached 2 photos: one wider shot, and a close up.

The right side of photo is my skim coat. You can see the bubbles that I have scraped. They were just 1 or 2" wide before scraping, but quickly opened up to much larger. The yellow area is the bare plaster.

Left lower side of photo is the knock-down texture that I skimmed, after being wiped with sponge.

Left upper side of photo is after sponging knock-down and scraping. The texture came off like nothing. What you see in the section of photo is the old paint on the smooth ceiling.

Please, any suggestions are appreciated. I am tempted to sponge and scrape the old texture off, but am worried that one application of paint will cause bubbles anyway. But why worry?

Thanks,

Jerry

housepaintingny 09-12-2010 11:40 AM

If you have an original plaster ceiling, you need to seal it first with an oil based primer, other wise the water in the joint compound and water in the water based paint will act with the plaster and cause what you are describing. I'm not sure if that's the problem without really looking at your ceiling, but I've seen it happen before with original, old plaster ceilings and walls where bubbles appear and the paint and/or compound won't adhere. Sealing the plaster with a quality oil base primer will give you a good base to skim coat and paint.

JerMann 09-12-2010 12:07 PM

Thanks for the quick response.

So I should put the oil based primer right over the knocked down texture? I thought they were fazing out oil based paints.

Jerry

Windows 09-12-2010 12:51 PM

I undertook a very similar project in my house - I have plaster walls/ceilings that had been textured with drywall mud in the 70s and I wanted to return them to smooth. Here's what I did: I scraped off all the texture that could reasonably be scraped off - then I skim coated with Durabond (brown bag) which is a plaster like setting compound that adheres very well to both plaster and drywall. This is a critical step as it is my understanding that applying a drywall skim coat over plaster can be risky in the long run, because the two expand and contract at different rates, and the durabond acts as the necessary buffer between the old plaster and the new mud. Over top of the durabond I did 2 or 3 thin skim coats with drywall mud, followed by 2 coats of drywall primer, and my walls turned out very well.

One last thing -- durabond also permanently repairs any hairline cracks in the plaster - filled in only with drywall mud, those cracks will return shortly.

Matthewt1970 09-12-2010 02:39 PM

Quote:

Originally Posted by housepaintingny (Post 499851)
If you have an original plaster ceiling, you need to seal it first with an oil based primer, other wise the water in the joint compound and water in the water based paint will act with the plaster and cause what you are describing. I'm not sure if that's the problem without really looking at your ceiling, but I've seen it happen before with original, old plaster ceilings and walls where bubbles appear and the paint and/or compound won't adhere. Sealing the plaster with a quality oil base primer will give you a good base to skim coat and paint.

I agree. Scape down everything you can and oil prime. Most states still have oil primer. If oil is not available the use BIN shellac based primer. Like you said, after you scrape off everything you may be left with a nice smooth ceiling.

chrisn 09-12-2010 06:01 PM

I did away with oil primers a couple years ago( for the most part) and use these products. Not cheap after shipping but they sure to all the things that oil primers do.

http://www.scotchpaint.com/index.html

jackofmany 09-13-2010 08:35 AM

You want to make sure to take care of the cracks you referred to. It will only be a source of aggrevation later on if you don't. The durabond is good. Acrylic bonding agents work well too.

Another option - and this answers your other question about coating. Mark the cracks with crows feet, sand lightly and wipe clean - then tape with fiberglass mesh as though you were taping wallboard. Then knock off any edges of compound and apply a good 1\4 inch skim coat. Again scrape down any beads - then hit with another coat to fill and smoothe. When it's dead dry you can use the damp sponge (specially made for this) or sand out any imperfections.

I've done this with a few victorians and the time involved in cutting and taping (one ceiling used 225 ft of tape) still outweighed the work and mess of replacing the plaster & lathe and then white coating.

JerMann 09-13-2010 10:07 AM

Update
 
Thanks to all who posted their suggestions.

I decided to seal the old surface with the oil based primer. I went right over the old knocked-down skim coat, new mud work and old exposed plaster.

Now the skim coat.

BTW, I bought Kilz Oderless Oil-based Primer. It was soooo runny. When I put the loaded roller to ceiling it was like someone wrung out a sponge and it went all over the place. I did stir it. Home Depot shook a new can for me and it looked the same as my first one. So I went with Zinzer. As a friend said, they make it odorless, but what did the sacrifice to achieve that?

steveel 09-13-2010 01:57 PM

Quote:

Originally Posted by JerMann (Post 499810)
I am taking my ceilings back to smooth. The house is 1926. I took the texture off my living room ceiling using a drywall sander (rented the Porter Cable).


Did you test it first for asbestos? My 1954 house's popcorn ceiling came tested positive and I had to rethink.

SteveEl

JerMann 09-13-2010 02:09 PM

Well, no I did not test it. It was not popcorn, just stipled with a brush. Going on faith here. Our house is practically original--no renovations. The ceiling is the only thing really modernized, except the kitchen cabinets. So my thinking is this ceiling was untouched for a long long time. Does that eliminate asbestos as a possibility? No, but the skim coat that I just sanded down was pretty surely lightweight joint compound--it came off very easily.

Obviously I am not a pro, I don't know the diff between asbestos ceiling and other, so I may be wrong. These projects get going and are like a train--unstoppable. Especially with guests due in 2 days.

Jerry

PS: 1/3rd thru skim coat and I think it will look nice. No bubbles yet : ]

Quote:

Originally Posted by steveel (Post 500419)
Did you test it first for asbestos? My 1954 house's popcorn ceiling came tested positive and I had to rethink.

SteveEl


steveel 09-13-2010 03:19 PM

you can't tell by looking at it, and it's not like there's a layer of 100% asbestos.... it's just a component in some of the texturing stuff that was used back in the day. Mine tested at I think 4% of the material, and that material came off VERY easily. (I opted to encapsulate it in place with 1/2 panels.) TEST before doing more

Handy Vinny 09-13-2010 03:43 PM

Quote:

Originally Posted by JerMann (Post 499810)
The house is 1926. I took the texture off my living room ceiling using a drywall sander (rented the Porter Cable).

You were probably dealing with a particulate matter hazard. I sincerely hope you wore a respirator.

JerMann 09-13-2010 04:04 PM

N95. Means I will live to 95? Or does the N mean NOT?

steveel 09-13-2010 04:44 PM

Vinny, are you saying that probably none of those particles were asbestos? If so I'd be interested in your reason. Asbestos fibers were used in many ceiling texturing compounds back in the day.

I'm beating this drum for the sake of others who may pass this way before tackling their own problem textured ceilings. Get it tested first!

Sorry for harping in your thread Jerr, I hope your N95 is NeverslowedDown-At-95.

SteveEl


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