Replies

1. 
   ahneedhelp | Jun 22, 2004 05:59am | #1

   First, try doing a search at Breaktime for skim coat plaster or plaster.

   Many previous threads on this topic.

   Yes, it is plaster but not in the traditional sense.

   (Visit US Gypsum's web site - tons of information.)

   It's a thin layer applied over a modern susbstrate for such an application.

   Typically on blueboard.

   Properly applied and finished by an experienced expert, should not require any sanding.

   I have a friend who skim coated some walls - with a bit of practice it isn't beyond the ability of an accomplished novice.

   It definitely helps if you are fortunate enough to observe a pro in action.

1. 
   razorsharp | Jun 23, 2004 03:25am | #6

   Thanks for your reply. Glad to hear that you think a novice can get an acceptable result with some practice because I like doing work around the house myself. The main thing that was confusing me about the prior Breaktime threads on the subject was that there seemed to be no consistency in what people were using to skimcoat. Drywall mud, plaster, special plaster with other stuff mixed in to help it adhere, etc. I naively thought that I would just go to Home Depot and get a tub or bag of 'skimcoating compound' and use that... Then some people say don't try it because it's a lot harder than it looks and calling a pro is smarter, and others like you who think a novice with practice can do it. I guess I'll try one room and if it's a disaster I'll get a pro for the other rooms..

2. 
   Dryrot | Jun 22, 2004 09:55am | #2

   90 year old plaster huh? First off, why not just ask a neighbor or two what they did and how?

   I imagine they most likely used drywall joint compound. I have "skim coated" quite a few old plaster walls this way. Just use a broad drywall blade like 16 inch to apply the mud. Some people also use a damp sponge to smooth the surface. I usually don't bother. This method doesn't usually need much sanding. After I get it pretty smooth I usually paint on a thin coat of primer. This lets you see any flaws that you can smooth with more compound.

   Cracks can be scratched out and taped with fiberglass drywall tape and wiped with compound. It also helps to coat the old walls with an acrylic primer of bonding agent first (ask at your paint store).

   All this is assuming the plaster is sound and not coming loose from the wood lathe. If some areas are, you can repair those areas with drywall & joint compound.

   I've renovated over 50 houses built around the turn of the century and used this rather low-tech method quite a bit. It is kinda slow and labor intensive compared to just ripping out the plaster and hanging new drywall. But, it is ideal for a DYI job. You can't really do it wrong, because you can sand out your mistakes... :-)

    --- BRICK

    

   "They say that there is a fine line between genius and insanity. I like to color outside the lines...and then eat the crayons." ~ Me
1. 
   razorsharp | Jun 23, 2004 03:04am | #4

   Thank you very much for your reply. The plaster is mostly sound- the problem is when I scraped the peeling paint some of it scraped off, some stuck and didn't come off at all, and in some places I gouged the plaster with the scraper. So a thin coating should make a big difference. I've heard that skim coating is harder than it looks and takes skill to get it right, but if I can sand out mistakes then I'll give it a try. The bonding agent suggestion also sounds like something I'll be glad I did a year or two down the road.

1. 
   Dryrot | Jun 23, 2004 03:35am | #7

   Joint compound usually takes multiple coats because it shrinks somewhat.

   I have never had any problem using the acrylic bonding agent type of primer. Oil base will work too... but the acrylic stuff works fine for me. It has always been dry enough to start skim coating the next day, in my experience. So, I don't know why the other poster had a problem? It has held up for over 20 years in my own house... --- BRICK

    

   "They say that there is a fine line between genius and insanity. I like to color outside the lines...and then eat the crayons." ~ Me

1. 
   razorsharp | Jun 24, 2004 07:04am | #13

   Brick- sounds like you are talking about a primer before skimcoating, whereas Frankie was talking about what primer he uses after skimcoating, but before painting. Or am I confused?

1. 
   Dryrot | Jun 24, 2004 08:10am | #14

   "Brick- sounds like you are talking about a primer before skimcoating, whereas Frankie was talking about what primer he uses after skimcoating, but before painting. Or am I confused?"

   Yep... I think you are right... I am talkin about primer/bonding agent BEFORE skimming the wall. Helps to seal any loose or soft plaster too. Has always worked fine for me.

   I think he must have been talking about a final primer before painting? I don't use oil for that either... I've just had better luck with acrylic primers from Ben-Moore and SW... But, heck... that's just my experience. I think we all tend to find something that works for us and stick with it. It may be a Ford vs Chevy debate... :-)

    --- BRICK

    

   "They say that there is a fine line between genius and insanity. I like to color outside the lines...and then eat the crayons." ~ Me

3. 
   Frankie | Jun 22, 2004 03:49pm | #3

   Skim coat is the application of a thin veneer (1/16" - 1/8") to a wall or ceiling. The material is customarily plaster or joint compound.

   Plaster

   Pro: No sanding, very little dust, can acheive a perfectly smooth wall. Can be tinted. Start to finish 2-6 hrs per room depending on size and number of surfaces to be coated.

   Con:. Dries so hard it's unsanandable. You have a small window of time to apply the plaster (30 - 60 min) No touch-ups. Have the ladders/ scaffolds in place prior to mixing. (It's a dry mix.) Best/ easiest when done by 3 people. Must be mixed will with mixing paddle.

   Joint compound

   Pro: Comes ready mixed. Sandable (DYI friendly). Easily applied with almost no time restriction.

   Con: Requires 3 coats. Day of drying btwn coats. Must be sanded - scraped between coats and sanded after final coat. Do not expect to sand after priming. Any correction then is an additive process with a bit of sanding of the new material. Cannot be tinted well.

   Plaster types include USG"s Diamond Coat and Imperial Coat. Imperial is/ dries to a harder finish and therefore a bit more difficult to apply.

   Joint compound is avaliable in to types - reg and light weight. My men swear by the light weight. Other crews prefer the reg.

   With either material, plaster or compound, do NOT use an acrylic or latex primer. They WILL soften, peel or scratch if not cured 1 - 2 weeks. We use an alkyd/ oil base primer. 8 hr dry time. After skimming with either material, only prime with an alkyd/ oil based primer. If you use any other primer on compound it will peel off in short order - either right away or in 3-6 months with a few changes in room temp.

   F

1. 
   razorsharp | Jun 23, 2004 03:14am | #5

   Thank you Frankie. Your overview of the technique was exactly what I was looking for. I'll probably try the joint compound since it's my first attempt and I will probably be slow. Also, likely I will have to sand it to smooth it out.

   QUESTION: Why does joint compound require 3 coats? Wouldn't the number of coats would depend on how bad the surface was to start?

   Also, your tip about the primer will definitely save me some grief. As an amateur, I generally use latex primer when I paint because it cleans up easily and I would have used it here but for your warning.

   QUESTION: What about a regular drywall wall that has drywall compound in every joint? Is it the case that latex primer shouldn't be used in that case as well, or does your warning only apply to a skimcoated wall where the whole thing is covered in compound?

1. 
   Frankie | Jun 23, 2004 07:59am | #9

   First coat just skims the wall and has really no thickness dimension. You are basically puting material on and scraping it off. Only the now spots are filled. This provides the base for the subsequent coats. It does not look pretty.

   The second coat builds on the high and filled low spots equally. Prettier, but not prettiest.

   Third coat is the polish coat. Pretty nice.

   Now for some sanding. OOOOO.

   Use an oil primer if MORE than 50% of the wall is compound; acrylic/ latex primer if MORE than 50% is the paper surface of drywall.

   If you or another poster want to do things differently, cool. There's more than one way to .......... The right way, the wrong way, and my way. I am just offering my opinion and experience regarding my way.

   F.

1. 
   Piffin | Jun 23, 2004 11:47am | #10

   There's a couple things that I don't think anyone has mentioned.

   OI wash the walls first wih TSP and rinse unless I am really convinced they are fairly new and clean.

   Then I roll on a bondiong agent if IO am using setting compound or SR mud over plater.

   If I am having a plastereer do another veneer, i just get out of his way 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

2. 
   razorsharp | Jun 24, 2004 07:00am | #12

   Thanks for the follow-up Frankie- now I see why you say three coats. Do you use exactly the same mud for each, or do you thin it at the end? As for the primer, you're referring to primer after the skimcoating is done, before the painting, right?

1. 
   Frankie | Jun 24, 2004 09:55am | #15

   Oil prime the wall or ceiling before skimming AND after skimming. I went back and reread my posts and admit that I was not clear about that. Sorry.

   Some people use PlasterWeld as a bonding agent for compound, however the fine folks at PlasterWeld have told me that it is not formulated for joint compound and therefore the chemical reaction which creates the bond, does not happen. It is worthless for this use. For bonding new plaster to old plaster it's great.

   I don't know of any other bonding agent for compound other than oil base primer. It seals the surface and provides a good grip for the compound.

   Have fun!

   F.

2. 
   razorsharp | Jun 25, 2004 06:27am | #16

   Brick, Frankie-

   I actually feel confident enough to tackle this job now. Thanks for all the info. I'm beginning to see why this is a mysterious process- everyone has their own way of doing it. Ironically, I think I could build a new wall (studs and drywall) in less time than adding 3/16 inch to the current wall will take.

   As for the Ford vs Chevy debate, where's the debate? It's Ford all the way ;-)

4. 
   sungod | Jun 23, 2004 07:50am | #8

   The SECRET to skim coat is not to sand between dried coats, scrape all lumps and bumps with a clean blade, then puddy some more.

   The other secret, is to "bow the blade" so there is two sides to use.  One side lets the outer edges touch for laying mud with its center.  The other side leaves no lines.

   Get a pool plaster trowel it has no sharp corners.  When placed on a flat surface its edges dont touch, it leaves no lines.

1. 
   razorsharp | Jun 24, 2004 06:54am | #11

   Thanks for those tips. I will definitely look for the right kind of trowel- having no sharp corners to dig in makes a lot of sense.