View Full Version : Plaster repair

03-25-2004, 09:15 AM
I am prepping 100 year old plaster walls for paint. At first I assumed that they were plaster and lathe, but they are actually some type of cement board with a lime (I think) plaster veneer. There is some light surface cracking at the joints and peeling paint throughout. Does the following sound right: Scrape the peeling areas and open the cracks a bit. (Should I tape these seems, if so what is recommended) Apply a bonding agent to these areas and follow with setting compound and then all purpose and prime everything with USG First Coat to even it all out. I appreciate your help.

03-25-2004, 10:50 AM
Plaster looks different than drywall. So to preserve that look, imbed a fiberglass mesh across the wall set in plaster, trowel finish. Then paint as normal.


03-25-2004, 11:10 AM
So what specifically do you suggest I use rather than setting compound followed by all purpose compound? Thanks.

03-25-2004, 11:58 AM

Try this link



03-25-2004, 12:43 PM
I appreciate the advise, but I think I will have to come up with a more traditional plaster finish. I am just not certain of the best products for this application.

John McElwee
03-25-2004, 06:14 PM
How well bonded is the plaster to the cement board?
If you can scrape it off the joints can you also scrape it off in the field? If it is well bonded I think your idea is fine. I know nothing about First Coat and drywall but setting compounds work pretty well for shallow repairs in plaster.

03-25-2004, 10:17 PM
While I have not gotten too far into it yet, the paint is flaking off pretty well in spots right down to the plaster, but the plaster seems pretty good. None of the cracks are very deep. Do you think I need to tape the cracks at the seems or just scrape them out and fill with setting compound and finish with all purpose?

03-26-2004, 02:43 AM
The first question should be:

They didn't have CBU's 100 years ago (Cementacious Backer Board)

03-26-2004, 08:07 AM
Don't know why the paint is peeling. I have read that different types of paints over the years have had different moisture absorption rates and that this can cause uneven swelling and separation. I expect the last coat of paint is around 30 years old which seems to be a fair life span for a coat of paint so I have not gotten too hung up on the issue. As for what is underneath, I don't know that either. As I said, I thought it would be wood lathe, but it is not. It is some sort of cement based product and it is original to the 100 year old home.

03-26-2004, 09:56 AM
I think when he says cenment based product, he may be looking at a repaired site, or a prior exterior stucco wall that is now interior or just a coase plaster job. A picture would help.


03-26-2004, 10:16 AM
Once a wall is opened I will provide a picture, but when I look up from the basement or through existing holes, the back sides of the interior walls throughout the house look like smooth cement board without the fiberglass backing. There is no lathe. The texture of the material under the plaster is cement. Those are the facts.

03-26-2004, 10:27 AM

I don't know if I am picking this up right, but it seems as if I have offended you from the tone of your response. If I have, I apologize, it was not my intent.

Looking forward to the picture. Any paper behind the back of the smooth board? Sounds more and more like a plaster over stucco. Any wire through any of the holes you have found?


03-26-2004, 11:11 AM
I may be offended by some things, but not by anything relating to these walls. I appreciate the reply though. Anyway, I have no idea what the wall board is made of, I am just trying to figure out what to do with what is on the surface. I will be removing some wall paper in a couple of areas prior to getting to the plaster. I am thinking of using the steamer on some areas of the walls with loose paint and see if that makes it easier to scrape. I appreciate the advise.

John McElwee
03-26-2004, 11:38 AM
Something else that would be useful information is the thickness of the plaster substrate, whatever it is.
Also, do you know from what you have seen from the back side that the substrate is in panels or are you assuming that from the pattern of the cracks on the surface? You could indeed have Portland cement plaster but it has to be on something--expanded metal lath or woven wire netting. Gypsum plaster could also have been done the same way; maybe a progressive builder was experimenting. From the back side you could tell if it's expanded metal. Perhaps you are seeing the back side of building paper and beyond that (as seen from the back) is woven wire mesh. This would be unusual construction but not unheard of. Concrete is usually a darker grey than is gypsum plaster.
If you are seing cracks at the joints in something how large are the panels?

You really have my curiousity up on this one keep us informed.

Since you ask only about paint can we assume you are not doing any cutting or patching in the house/ If that is the case then does it really matter what is behind the paint? It does for our curiousity but not for your painting. I think your original plan is still good. Here is a thought, years ago I scraped the paint off of some plaster walls that were over Portland cement plaster (stucco) but on the interior. The finish was smooth. The finish was so hard that I could not damage it with any kind of scraper. Looking back I think is was a very rich or neat Portland cement finish troweled into the wet and still green concrete basecoat. What a durable finish. This was on a basement wall and there was a crack at about the grade line where the foundation changed from poured concrete to concrete block. I have since had success making very smooth walls with the method I described. If the timing is right the walls are as smooth as if they were done over gypsum plaster with whitecoat but much, much harder. If one struck it with a nail it would leave a black mark but no scratch.
Maybe you are very fortunate.

03-26-2004, 12:13 PM
I'll be in the house tomorrow. I'll see what I find once I get to do a little more inspecting. Though, as you said, I am really more concerned about the surface than the substrate. Thanks.

03-29-2004, 07:23 PM
I run into this all the time in old homes...... I am in the painting and renovation business and have some techniques that I usually use in these situations. Once you thoroughly scrape the loose paint down to the plaster I always stabilize the areas(or the whole room if needed) with an OIL based primer(Kilz or Cover Stain or the like). The oil primer seals the surface from moisture absorption from the spackle you will use to fill the areas,and prevents blistering of the old paint. Latex primers tend to worsen the peeling paint situation. Once the oil primer is dry , go ahead and fill the areas or skim coat the entire wall if needed. I like to use 20 min. setting compound, followed by ready mixed joint compound, because you can finish the spackling in one day. Once the spackle has dried I like to seal the entire surface with a latex sealer(Kilz premium or the like)then paint with acrylic flat.If you need to fill cracks I would tape with fiberglass mesh followed by setting compound and ready mix joint compound. This is a slow job and takes some patience but is worth going through all the steps to prevent problems from occurring. Good luck......