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January 15, 2008
Help for Cracking Plaster Walls
My husband and I recently purchased our first apartment in a prewar building. There were minor cracks in the plaster walls when we purchased the apartment, but the inspector didn’t seem to think they were an indication of any structural problems. Prior to painting we fixed the existing cracks in the walls. Now, just a few months after painting, we've discovered new cracks in several of our walls. Is this normal? Is there any way to prevent future cracks or are we just destined to live in an apartment with cracked walls?
Comments
Plaster does crack, mostly on or around ceilings. It's from going from humidity of summer to dryness of winter and back again. Totally common to have to repatch cracks periodically with these old, thick plaster walls. Good news is they're more sound-absorbing. So it's worth it to patch cracks once in a while!
A big prewar building isn't going to have problems like foundation settling; that's more like what you'll have in a house.
Posted by: guest at January 15, 2008 11:49 AM
How did you fix the cracks? If you just filled it in with plaster you did a cheap/quick fix. Cracked plaster requires a mesh or tape to be applied over the crack and a plaster of paris mix to be applied over it.
Posted by: MrHancock at January 15, 2008 11:56 AM
I don't think it is normal to have to patch them every few months - however they patched them - and I've lived in a lot of prewars. Usually, patching every few years, or more (whenever you feel like you need new paint) is sufficient.
I'd explore whether there is some sorce of water leakage behind that wall - I've had it from a chimney (is there one on that wall?) that needed repair, and have seen others with water pipes or a toilet leaking, or a roof leak (if you are on the top floor.) Also, check for support problems in the basement walls - especially if it is a smaller building like a brownstone-type one.
Posted by: guest at January 15, 2008 12:20 PM
Things to check:
Is the building continuing to settle. Often these are cracks that appear at the corners of door and window frames.
If the crack keeps appearing, it may also mean the repair was not adequate.
Has the plaster come away from the wall i.e., have the keys broken. In that case you need to secure the plaster to the wall with plaster washers (easy DIY job) and then patch.
With plaster the patch needs to be widened before it is patched, and undercut, so that the patching compound has something to hold on to.
Also try caulk. Since it is flexible with temperature and humidity changes, it will hold together.
You don't have to use plaster of Paris, any of the patching compounds or even (and I will get flack for this) all purpose joint compound can work, if it's a small crack. But the mesh tape is a great idea.
Best of luck!
Posted by: ohiise at January 15, 2008 12:48 PM
It is important to open up the cracks before patching them so that the new plaster can completely fill the crack from front to back. I use a grout remover tool for this.
It's also best to use a 2/3 plaster of paris mix with 1/3 joint compound, rather than just joint compound, when filling the opened up crack. Plaster of paris expands as it sets while joint compound shrinks when it dries. So joint compound fix will cause a tension in the joint which makes it more likely to open up again. You can fix with only plaster of paris, but you only have a few minutes to work with it after it is mixed.
To mix joint compound with plaster of paris I've found it easiest to first mix the water for the plaster of paris with the joint compound (you can take as long as you like for this step). Then over about a minute, while mixing furiously, add the plaster of paris powder to the mix. Then wait a minute or two, until it is solid enough to work with. Now plaster quickly. After plastering wash out the bucket before the plaster in there sets so that the bucket can be reused the same day. If the plaster sets in the bucket, wait until it turns white then hammer the bucket to knock it out in big chunks. (Adding water will do nothing, plaster of paris hardens via a chemical reaction with water, unlike regular joint compound it is not water soluble once set.)
PS The original plaster is probably a lime plaster + plaster of paris mix. But even though lime plaster is easier to work with, you have to wait months before you can paint lime plaster so I wouldn't recommend using it for patching cracks. A professional plasterer has many tricks for extending and shortening this curing time, but it is pretty much a lost art and the few professional plasterers out there are both very expensive and are also not going to take on a small job (<$50k).
PS2 If you use 2/3 or more plaster of paris in the mix you should not need the fiberglass tape (unless these are some monster cracks). With joint compound alone, fiberglass mesh tape would probably help. But what you are really doing in this case is covering up the crack, which will reopen underneath the fiberglass tape "wall" in a few months time.
Posted by: guest at January 15, 2008 1:08 PM
Thanks for the responses. Sorry I wasn't clearer in my original post. The cracks that were repaired are fine (so far). The new cracks are in completely different areas of the walls.
Posted by: adenyce at January 15, 2008 1:36 PM
It sounds like maybe the general cracking in the plaster weren't repaired properly over the years, that's all. And now the quickie job they did before selling is opening up again, in the areas you yourself have not patched yet.
Sure it's a pain, but plaster walls are superior to drywall so it's worth it.
Posted by: guest at January 15, 2008 1:51 PM
Guest 1:08, you sound like you know what you are talking about.
Can you give me some tips on patching a much larger area, about 8 sq ft. The horsehair plaster there was removed to open the chimney, and now there is just bare brick that needs to be covered. I was planning to use Structolite Base Coat for scratch and brown coat and then Master of Plaster for the finish coat.
Posted by: ohiise at January 15, 2008 2:48 PM
2:48 you are on the right track.
To reiterate above. If it is a small crack which can be filled with painter's caulk, do that. The caulk will be flexible and allow for future movement. (Paint with a latex paint, too)
If the plater is separated from the lath (the keys are broken) use plaster washers: see http://www.modernwaylumber.com/plaster (nice graphic, but order anywhere)
As others have said, be sure to tape over the crack if you repait with mud. Mesh tape is great or flat areas, more difficult in corners.
Posted by: guest at January 15, 2008 4:27 PM
I had a similar problem with cracks in my ceiling. I came across a reference, Fitz??, on this website. He and his guys did a great job fixing the problem and educated me a bit. I don't have his number on hand, but if you search this site you may be able to find it.
More importantly, you may want to work with the co-op board to help determine the source of the problem (determine if it's foundational) and have that fixed first. It can't just be only you facing this.
Posted by: BedStuyGal at January 15, 2008 8:47 PM
Our company in southern Colorado does plaster repairs for less than $50k! Sheesh!
No one above mentioned anything about using Daraweld (concrete "glue") to prep your surfaces before patching. If you make a mixture of it, 50/50 with water, it soaks into the more fragile portions of your damage and consolidates it. Sometimes plaster becomes fragile with exposure to water, even if it's only condensation. This takes years sometimes to do the damage, but there you go. My father has used this method for thirty years, once in a large (old) auditorium ceiling and none of it has ever come down. I don't know if it's even cracked again. The stuff also acts like a microscopic cushion. When an old fogie tells you "They don't build them like they used to back in the old days!" You can tell him (or her) for me, "Thank heavens!" There have been many improvements in materials and methods. To get apprentices familiar with this material and process I have them make two small egg shapes by hand. One with a quart of Gypsum setting-mix and this mixture instead of water. The other with same and water. These get set aside until they are dry enough to sand. Handed a metal rasp I tell them to smooth the egg to a nicer shape. They usually come to me and say they can't even rasp the first one. It's too hard!
That gives them an idea of what is going on. Try it for yourself. P.S. The plaster secret is this: sugar in the water to slow it down, salt to speed it up.
Posted by: akryeguy at January 16, 2008 12:29 AM
Great tip! Is Structolite plaster really difficult to work with?
Posted by: ohiise at January 16, 2008 7:05 AM
Isn't it true that any quick fix approach to cracking plaster is bound not to last? After all, we're talking about years and years of accretion of damage over layers of repair over damage etc. Isn't the only permanent fix skim-coating all the walls?
Posted by: guest at January 16, 2008 12:55 PM
Call Mirage studios in long island city at 718 361 1071 they sell master of plaster products that completely restore old plaster walls without sanding or bonding agents.Your walls will be as smooth as glass.Check out masterofplaster.com
Posted by: guest at January 16, 2008 8:50 PM
Yeah, I just ordered from them. Their product is cool, but also not cheap.
Posted by: ohiise at January 17, 2008 11:59 AM
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