Plaster or Drywall?


Old 06-17-06, 10:46 PM
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Question Plaster or Drywall?

I am working on a house that I was told that had plaster walls and ceilings. There is no question that some of the walls are plaster due to the rough looking surface but some of the walls and ceilings are questionable I think. The house was built in the early 1950's by a local doctor and the house is rather large. I had to add a circuit to one of the bathrooms that didn't have an outlet and when I cut the hole in the wall this is what I found. The material was thick (about 1 inch) and was not really all that hard like concrete or plaster. The material was almost like drywall just thick and I drilled through it with a wood spade bit very easily. So, is this drywall or plaster. Also, there was not any wood or metal lathe behind the material that I saw. Next question: Some of the walls uptairs have a blistering effect and the paint is popping off in these areas. The surface behind the paint is extremely slick almost as slick as glass. What type of surface is this and what is causing the blistering? Thanks!!
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Old 06-18-06, 06:21 AM
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There is more than one plaster method out there. The lathe (either metal or wood strips) is what most people thnk of with plaster. There is the newer version of this which is actuall a combination of plaster and drywall type building. It uses a blueboard backer (similar to standard drywall) and then plaster is applied over this. There is no lathe involved. It kind of sounds like you have this newer method of plaster in your house.

The shiny stuff; I have an idea but not sure. I'll let some of the more knowledgable plaster folks run with this.
Old 06-18-06, 08:56 PM
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Measure the width of the door jamb. You may have a double thickness of drywall on the inside of the bathroom, for sound attenuation.

The "shiny" surface could well be an oil based primer.
Old 06-19-06, 06:35 AM
Join Date: Jun 2006
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New plastering method

I had similar problems with some old plaster walls. went searching for what to use and ended up taliking to this guy in UK
He told me about this wetndrywall system they had invented with a thing called skimdec. Its a spray finishing system where you can spray the plaster on to the walls and it gives the same finish as proper depth plastering. He seemed to have loads of new inventions and ideas on plastering.
Old 06-19-06, 09:07 AM
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A plaster house built in the early 1950's is most likely gypsum plaster over gypsum lath. USG Called theirs RockLath and the name became associated with the material much like drywall panels are called by USG's tradename SheetRock. But I digress.
Gypsum lath was usually 3/8" thick and the pieces were 48" X 16". I understand that sometimes it was 12" X 24" X 48" or 96" . I've never seen it those dimensions. Sometimes it was perforated with 3/4" holes through which some of the plaster was pushed this provided some mechanical key as well as the bond of the plaster to the lath. The plaster is 3/8 to 1/2" thick.
The extremely slick plaster is probabaly whitecoat, a mixture of gauging plaster and lime. It could be a Keene's cement finish. These can be troweled as smooth as glass. Keene's is usually harder than whitecoat. Maybe they were troweled so smoothly and densly that paint can't get a good bond. As much as I hate to see a good plaster job sanded you might need to sand it to scuff it for the paint to bond.
A painter can tell you if some other treatment has happened to prevent a good bond.
Consider yourself fortunate to live in such a high class house.

What part of the country are you in?
Old 06-19-06, 09:09 AM
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Do you have a name or a contact for your friend in UK? An e-mail address, perhaps? How did you learn of him?
Old 06-23-06, 08:28 PM
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Thanks for all the info..I live in South Carolina in the low country. There are alot of old homes and plantation homes in this area as well as in the Charleston area. I am about one hour from Myrtle Beach!!

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