Dealing with plaster that is crumbling at the touch

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Topic by stefang posted 06-07-2012 04:40 PM 3674 views 0 times favorited 6 replies Add to Favorites Watch
View stefang's profile


13 posts in 1789 days

06-07-2012 04:40 PM

Problem with a Basement room
My son bought and old, but well made house built in 1953 in Sweden. It looks like the full height basement is made from cement blocks, then plastered with mortar. We are setting up a woodworking shop in one room and the plaster is just crumbling at the touch. I think perhaps a poor mix or too much water is causing the problem. It’s not wet or even damp in the basement and there are working radiators down there, so it is warm year around. I doubt the original owner did the plastering as he was a house builder and would have known how to do it right. it was probably the last owner who botched the job.

Possible Fixes
I have some experience with plastering from building my own basements/foundations, but not on a professional level. I think probably the only way to remedy the problem is to remove the plaster and either re-plaster or better yet put up a proper wall anchored into the blocks by using some kind of building glue to hold the studs in place and then platters nailed to the studs/joists.

What advice needed
My son doesn’t have a lot to spend on the basement right now as he has to build a garage, so I am looking for an inexpensive solution or a good temporary fix so we can at least use the wall space until he can afford a permanent renewal. If this is not possible, do you have any suggestions about the easiest/best way to remove the old plaster?
Here is a photo of one of the walls. The yellow color is just paint. Any suggestions are welcome and appreciated.

-- Mike an American living in Norway

View Enoelf's profile


9 posts in 1084 days

06-13-2012 02:11 PM

Do you think that water-proofing paint would work? It is supposed to penetrate the voids in cement blocks to seal them against water penetration. It might work to bind what’s on the wall so it stops crumbling away. I am not sure what it might be called in Sweden, but here in the U.S. it goes by the name “Drylock”. Here’s a link to the manufacturer….

In my humble opinion, you would want to stabilize what’s up there, or perhaps remove it before you frame the walls in.

Good luck!
Please post your solution!

-- No, finishing touches are what you do at the END of the project!

View vulpes's profile


5 posts in 897 days

10-16-2012 02:20 PM

I know the original post is a bit old, but I would like to say I had the same problem in my old European house.

It is likely water damage caused by moisture moving through the concrete by capillary action and being pulled into the warm room through the plaster. But it also appears the plaster quality is sub-standard as well (but this is difficult to gauge from a photo), and this could also affect the degree of damage.

If the wall was made properly, it should not contain enough moisture to cause much damage over the short term, but if the wall is against the soil for example, either behind it or below, then over time (some times it takes decades) interior plaster can indeed look like your photos. A lot of building methods have changed in the past 50 years, so it is likely the wall does and will contain more water content than a modern wall.

I suggest removing the old plaster, as it will only continue to deteriorate. If it is in very bad shape, just knock it away with gentle taps of a hammer. When the plaster is all off, seal the concrete wall with a liquid sealant as Enoelf suggested. Then re-plaster with a modern plaster mix designed to deal with moisture movement. Water vapor will always move through the plaster, but the modern plaster mixes should resist damage far better.

Bags of plaster are not expensive, and if you do not care how it looks, one can do the re-plastering yourself. In that case of DIY plastering, I recommend making the surface very uneven and rough on purpose by just troweling it on and leaving the trowel marks ”as is” as the ”style”. It takes a lot of skill to make plaster smooth.

Or, if there you think there is no reason to have plaster at all, and the concrete wall behind is in good shape, maybe just paint the wall with concrete paint.

-- Great minds discuss ideas, mediocre minds discuss events, and small minds discuss people.

View Puff's profile


11 posts in 1290 days

11-17-2012 11:47 PM

I had a house with similar issues in the basement. I did a lot of homework and cleaned off the wall, but I ended up selling the house to a developer who wanted to build a shopping center before I put anything over the wall.

I agree about removing all the plaster. I ended up knocking most of my plaster loose with just a broom, then a wire brush for some stubborn bits, then a hammer for the last few bits.

I have been told that it’s a flat out impossibility to “seal” the walls against moisture seeping in. Sealants help, but you can’t really stop it – the key is to keep the water away from the basement walls to begin with.

- Wait for a big rain storm and then go around outside, looking at how the water flows.
- Figure out how to keep the water flowing away from the walls instead of seeping into the ground at the walls.
- Fill in any low spots so the rain doesn’t have a tendency to puddle next to the wall.
- Make sure your downspouts are getting the water away from the soil around the basement.
- Make sure your downspouts aren’t broken underground and leaking water into the soil near the basement.

For the most part this sort of stuff should do the job. In some rare cases the house may be situated so it’s just impossible, i.e. there’s nowhere for the water to flow away to, or it would have to flow uphill. French drains around the foundation walls are one possibility, basically a performated PVC buried in a trench full of gravel, close by the foundation wall. Any water that seeps against the foundation goes into the gravel, into the PVC and drains out to wherever you send it.

I know one guy who had to put french drains inside his basement, i.e. in his basement floor around the edge of the basement, wiht a sump pump to pump it out. I’m still not sure how this helps protect the walls, maybe it simply keeps his basement from filling up with water.

If you plaster (I have no idea if that’s a good idea or not…) contractors I’ve talked to tell me that the big deal with plastering is making sure you do multiple, thin coats and wait at least a day between coats to allow the plaster to dry. Drywall mud dries fast but shrinks a lot. Plaster dries slowly and doesn’t shrink as much.

Of course the real difference between a pro and a DIYer is that their plaster looks as smooth after they trowel it on as mine does after I sand it :-).

-- "Always cut *towards* a major artery... that way you'll be careful."

View Puff's profile


11 posts in 1290 days

11-17-2012 11:51 PM

Oh, and one big gotcha to watch out for is, if you end up remortaring the walls, be very careful to figure out what the right mortar is.

My house’s foundation walls were fieldstone walls and I was warned that a classic DIY mistake is to use portland cement instead of the right mortar. The portland cement is stronger than the stones/bricks, and has a different thermal expansion coefficient, so as the walls freeze and thaw, the cement gradually crushes the bricks…

-- "Always cut *towards* a major artery... that way you'll be careful."

View DeepCreek's profile


7 posts in 861 days

12-11-2012 08:51 AM

I agree with the previous posts. Remove the old plaster, seal the concrete wall, then re-plaster it. No heavy machinery or specific professional help required, unless you are cautious about the severity of the wall condition. If you need help with another brand of waterproofing paint, try BEHR Premium. My uncle used it for his home and it fixes the problem you are having. It works for porous concrete and masonry surfaces. Is it just this one wall or are there others as well? Hope this unnecessary problem is solved for you soon.

-- Christopher Creek - http://www.deepcreekconstructionschool.com

View stefang's profile


13 posts in 1789 days

12-11-2012 10:02 AM

Thanks much for all the above suggestions. I was visiting my son for 2 months and we had rain and very warm weather during that time. The basement seemed exceptionally dry during that time, so I doubt that moisture is the problem. I tend to agree with Vulpes that the problem is likely the plaster quality. They probably used too much water in the mix, something that inexperienced DIY folks often do.

I know this reply is late in coming, but a replastering won’t be done until next summer, so the help is still very relevant. I appreciate your help with this. We will follow your advice and remove the old plaster first. Thanks again!

-- Mike an American living in Norway

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