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How To: Diagnose Common Plaster Problems

How To: Diagnose Common Plaster Problems

After a century or so, plaster walls and ceilings can develop a variety of problems from neglect or abuse. Your plaster can tell you a ton about issues that may be developing around your house if you know how to listen to what it is saying.

In this post, I’ll show you how to diagnose the most common plaster problems and what they mean. Plaster is often like the canary in the coal mine. If there is a problem brewing, it will likely show up first in the plaster. So, knowing how to diagnose plaster problems will help you solve little problems before they become big ones.

Cracked Plaster

This is probably the most common problem people notice with their old plaster walls. The good news is that cracks in your plaster don’t necessarily mean trouble. Sometimes they are a warning sign, but other times they’re just like wrinkles on our faces that appear with age. How do you know the difference?

hairine cracks
Hairline Cracks

Hairline Cracks – These cracks are small enough that you can barely fit a fingernail in them. It doesn’t matter which way they are running either, vertical, horizontal, or diagonal, these are the most benign of all the cracks, and unless they are growing or you really can’t stand the sight of them, there is no reason to mess with them.

delaminating cracks
Delaminating Cracks

Delaminating Cracks – These cracks are a sign of plaster pulling away from the lath behind it. These show up on both ceilings and walls, but can be the most dangerous on ceilings. When plaster begins to pull away from the lath, there is a chance it may fall away from the wall or ceiling and come crashing down. The cracks often run parallel to the lath (horizontally on walls and lengthwise on ceilings). You may see multiple cracks or bulges running parallel on the ceiling like in the picture, which is a sure sign of plaster pulling away from the lath. You can use the video tutorial to learn how to reattach the plaster and prevent further damage.

  • settlement cracks
    Settlement Cracks
    Photo Credit: //www.warreninspect.com

    Settlement Cracks – If a part of the house is sagging, you may find converging cracks running across your plaster walls. Yes, you’ll want to patch and fill these cracks, but address the bigger issue of foundation problems first. A group of cracks converging in one direction are often signs of settling. If you see this kind of crack, call a professional, especially if they are new and growing.

    Discolored Plaster

    water stained plaster
    Discolored Water Stained Plaster

    This is the early signs of water damage to plaster. Brown water stains will begin to show up soon after a leak begins. The easy way to solve them is with a stain blocking primer, but that won’t do anything to resolve the water issue. You need to find the leak and seal it up before things get worse. Don’t delay.

    Bubbling Plaster

    bubbling plaster
    Bubbling Plaster

    Once the water damage becomes severe, then the plaster will begin bubbling and bulging. You may reach this stage without any noticeable water stains, but when this happens, a portion of the plaster will have to be removed and patched. Use the steps in my post How To: Patch Plaster to repair the damaged sections.

    If not repaired soon, the damage will just continue and you run the risk of developing mold in the affected area. Water and plaster are not a good combination, so find the source of the leak first and do everything you can to stop the water.

    Bulging Plaster

    Plaster is a pretty incredible material. I have seen a plaster wall come completely loose of the lath and bulge out about 4 inches from the wall without falling or even cracking! It’s not just cracks that mean plaster has come loose of its lath. Just like delaminating cracks, bulging plaster looks exactly the same, except this time there aren’t cracks in the surface.

    If you see bulges in your wall or ceiling and the plaster can be pushed back up against the wall, then it’s time to reattach that section of plaster. Use the steps in my post How To: Repair Plaster Walls to get things stabilized again.

    Remember, plaster is the canary in the coal mine and these are just some of the most common plaster problems. It will start showing you leaks and settling before anything else, so look for the signs and fix the issues before they demand your attention in a more expensive way.

    If you have any plaster issues not mentioned here, leave a comment below and I’ll try to answer as many as I can about how to resolve the issue. Good luck and watch that plaster!

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    79 thoughts on “How To: Diagnose Common Plaster Problems

    1. I live in an apartment and last year had my bathroom completely redone. A leak has appeared on the bathroom roof from the apartment upstairs. This is in hand to be repaired tomorrow. What has happened is where the water is coming through – a crack in the plaster has appeared which looks like a shrinkage crack, its travelled in the last two days the entire length of the room. I think the water damage has caused this, is this likely?

    2. After painting main floor level and having the basement walls in my 1899 home sprayed with foam (including all vents covered with foam also) within w year or so the plaster next to the baseboard in the main floor are now bubbling and cracking with some signs of mold. I believe the moisture has “wicked up.” I have made attempts at removing the foam around perimeter next to floor and wonder if this is the solution. Could it be the new paint holding in moisture? Or what?

    3. I have a brick cape cod built in 1950 with plaster walls and ceilings. In the corner of the living room between the chimney and the outside perpendicular wall, there are many cracks in the ceiling that run along the laths. A structural engineer told me that possibly the house was sinking in that corner and the only way to prevent the cracking is to replace the lath and plaster with drywall. I don’t want to replace the plaster but I don’t want to repair the cracks and have them reappear. I would appreciate your opinion. Thank you!

    4. Our church sanctuary, built in 1903, has plaster walls. The plaster walls had a brown stain that ran just above the wooden wainscoting. It was only on the walls that are exterior walls. I was able to clean it off easily but am wondering what caused it – especially if it’s a mold problem. The sanctuary was painted just a few years ago and is starting to flake off about 30 feet up the wall. Any insights would be appreciated! Thank you

    5. I have a house that was built in the early teens. It has been remuddled many times by Uncle John construction techniques. The major problem that I have is how to remove many layers of paint and wallpaper and not remove the plaster as it is good shape. Suggestions?????

    6. Hi! My house is roughly 120 years old and I’m not sure if anything has ever been redone (though I doubt it has). My living room ceiling has what appears to be a mix of hairline cracks and delaminating cracks. They run mostly lengthwise, but some do join up together to make an obscure shape. My bedroom is above it, but I don’t have a ton of heavy furniture or anything- queen bed frame, nightstands and a dresser. I’ve had the house almost 2 years, and they were there when I bought it but more have shown up with time. I’m just wondering if I need to be concerned about house issues, or if it’s probably just needing to be redone. There aren’t any cracks in other main floor rooms, but my adjacent kitchen does have noticeable very straight lines in somewhat the same form- just not cracked. Thoughts? Suggestions? I’m on a single income and can’t really afford an inspection right now as I care for and support my sick mother.
      Greatly appreciate anything!

    7. Ok so a sixties house and I found some small cracks and separation within the plaster walls only about an 1/8 of an inch thick? I’ve never seen or heard of this. I’m going to be remolding home anyway just need to know if fixable or needs replaced.
      Thank you

      1. Hello, I took a photo of some plaster walls in a house we are purchasing. The wall is in the stairwell and they look like a checkerboard. Shot from the side with a flashlight, the walls look like they were put up in squares if that makes sense. Is this a potential issue?

    8. When I opened our patching plaster yesterday it was like a moist play dough texture so my husband added some water and stirred it up and said it was okay. I also saw a little bit of white furry mold around the top ring he still said it was okay it smelled okay. So I applied it to some areas in our bathroom and had a really hard time with it but I guess I kind of figured it out so today I decided to paint over it with white flat ceiling and wall paint before I applied are latex paint and when it dried it is now cracking. Is the paint cracking due to the old plaster that I used or could it be something else like maybe I applied too much paint. Some websites said that if you put paint over plaster and it cracked it is because of a moisture issues, says plaster is sucking out all the moisture from the paint which kind of makes sense because it’s old plaster and we(he) had to add water to an anyways

      1. Hello. I pulled off a patch on the wall in my living room. I thought it was just loose paint. Well, it wasnt. It is a piece ofplaster about 3×5″. Should i just fill in with compound or try and glue the piece back in. It is not all the way down to the laff. Thank you

    9. My ceiling has small 2 creases (not exactly parallel) in 1 bedroom and 1 slightly bigger one in living room. They look like delaminating cracks but not quite. They look like the creases on clothes when you iron them wrong. Are they dangerous? What could be the cause?

    10. Hi I have a newly plastered ceiling which had an airline crack which I filled, it’s now bulging. The ceiling was plastered on top of artex and PVA glue was used. I was told it had 3 skims to cover the artex any advice would be great thanks

      1. We don’t recommend this method of removing Artex ceilings. Its the least preferred, as the preparation can release asbestos into the environment. Also, it adds a lot of weight to a ceiling. Many Artex ceilings were installed as a cheap fix – the artex covered the cracks and bulges. If you come along 30 years later and add the weight of plaster to it, its no surprise an already weak ceiling would bulge.

    11. I have bubbling plaster & the bumps are hard. I had a aluminum siding company come & put instillation in the ceiling. We thought that this would stop any moisture that could be caused by the cool air from the outside clashing with the warm air from Inside the house. I deal with a handyman that doesn’t believe that the moisture is coming from small flat top roof. It’s driving me crazy. Do you have any ideas what could be causing the hard bumps?

    12. I have a home built in 1956 I recently purchased and am renovating. The stairwell and upstairs have thin spiderweb cracks that are showing when I started to prime the walls. Any suggestions on how to get rid of them? Sand?

      Thanks much.


    13. The plaster wall around my ac vent has began to crumble and created a pile of plaster dust on the floor. It is in the corner of the room, partially obstructed by a crib. What would be cause? Major problem?

    14. The plaster ceiling in my 1949 home sustained water damage from a roof leak — discoloration, bulging, flaking, falling, etc. I’d say the area was about 3 square feet. We put on a new roof and fixed the ceiling — scraped, mudded, painted. That was a year and half ago. I just noticed that it’s starting to bulge and flake again in the same area (though no discoloration). Does this mean we didn’t fix the original problem??

    15. After about 3 roof leaks over 2 years, my horsehair ceiling has cracking paint, but no water stains that I can see. How does horsehair react to water damage? Could the cracking paint be related to the water leak? Thanks!

      1. I would guess the the cracking paint is due to the water leaks but the plaster can stand up to the abuse a little better. Just make sure the leak has stopped and the plaster is still well adhered to the lath.

    16. Have found on my newly acquired 1923 Foursquare that when the asbestos containing Vermiculite attic insulation was removed (done properly) that *both* the plaster and lath has pulled away from the joists (spaced 24”). Seems like the small nails used to secure the lath could not hold over time. I am trying to avoid the mess and the work of dropping the ceilings. It seems the best approach may be to set up temporary walls to push the plaster lath back up and the reattach using something like narrow crown staples for each lath at each joist? Seems like a lot of work and the full dimension 2×4 joists should probably be reinforced. I suspect that the joists aren’t stiff enough and that people and things stored in the attic may have caused them to flex this allowing the nails to work loose due to time and gravity. Also, the Vermiculite particles could become wedged in the gaps.

      Looking for suggestions.

    17. I keep finding plaster pieces on my rug and table seems like it must be falling from the ceiling but I’ve never seen it happen and there doesn’t seem to be any damage on the ceiling. I can’t figure out how this is happening! It’s a high ceiling with a wooden beam across the top. The ceiling was painted a year ago.

    18. Hi
      Wallpaper has cracked open about six inches and plaster has expanded and appears to have crystallised into something which looks like shards of fibreglass. Any ideas of the cause and solution?

    19. I am getting lots of powdery dust from the plaster on my wall. As I was cleaning it up I got a taste of salt from the dust. This has happened before but It is getting worse. What can be causing this?

      1. Plaster is flat , no cracks in the area but 100 yr old wall paper is bubbling at a few seams and trying to pull away.No dampness or water around… why??

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