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Kelly M Bray 11-01-2009 07:52 PM

Fixing plaster cracks once and for all
I went through the forum, and I did not find exactly what I was looking for. I am going to paint a friends living room. The house was built in the late 50's, plaster and button board. There are long cracks on the ceiling along the joints of the board. I see evidence that someone filled them in with just a little spackle and they came back. I want a permanent solution short of ripping down the ceiling. I was told to clean the cracks out a little and put in caulking (?). Then tape and mud the seams of the cracks, feathering it out. I am not the best taper so I was going to use the yellow self stick. Any ideas or critiques?

Nestor_Kelebay 11-01-2009 11:29 PM

Normally, cracks in plaster are caused by small amounts of movement in the building itself, and that's something you really can't prevent.

For example, clays absorb moisture and swell up. If your house is build on soil with a high clay content, then during a drought, the soil can dry out a lot, and that means the clay (and soil) will shrink. After a rain, the clay will swell. The shrinking and swelling of the soil depending on it's moisture content can cause your house to move, and the lifting by the clay won't necessarily be uniform. And, that's just one of the things that can cause the ground to move, which in turn will cause your house to move, and cause the plaster walls and ceilings in it to crack.

There is no "once and for all" way to prevent plaster cracks from opening and closing short of stopping the house from moving, and if the ground moves, the house will move.

If you live where the ground freezes in winter, then the freezing of the moisture in the ground can cause frost heave, and that can toss a house around like a cork on the ocean.

What I do to "fix" hairline cracks in plaster is to use a wide (4 inch, say) putty knife to pack joint compound into the crack, and then immediately wipe the excess joint compound off with a damp sponge. The result is joint compound in the crack, but not all over the wall.

But, that won't stop your house from moving, and won't stop the crack from opening and closing either.

Kelly M Bray 11-02-2009 12:14 AM

No high clay content, more sandy and silty. No freezing, two miles from the beach. I am aware of the movement issue.I am trying to find the best practice for this problem. I am wondering if something like painters caulk might be a better idea than joint compound. It has some flexibility to it. In the past I have used tape and 30 minute hot mud, then feathering with topping mud. I moved after three years so I don't know if this repair held.

Nestor_Kelebay 11-04-2009 09:18 AM


"Painter's caulk" is ordinary latex caulk, also called "Acrylic caulk". It dries by water evaporation, and forms a solid exactly the same way as latex paints do.
(post again if you want to know more about tha process, called "coalescence")

If I were to do what you're wanting to do, I would:

1. Dilute some white wood glue with water to make a liquid of paintable consistancy, and paint that into the crack with an artist's paint brush first. The white wood glue will get absorbed into the plaster on both sides of the crack and glue all the sand grains together as it dries. This at least ensures you have a consolidated surface to stick something to. Allow a day or two for the glue to dry.

2. Caulk the crack with any latex or Acrylic caulk, use a putty knife to force the caulk deeper into the crack, and then immediately wipe across the crack's surface with a damp sponge. This will remove the caulk from the surface of the wall and leave it only in the crack. Latex (aka: Acrylic) products will shrink as they dry, so you may need to repeat this step to fill in the shrinkage. Also, fill in only short sections of crack each time because the latex caulk will dry quickly, and will be more difficult to remove from the surface once it's dry. Keep a green Scotchbrite pad handy in case you need to remove dry latex caulk from the surface of your wall. (dip Scotchbrite pad in water and scrub caulk off, if necessary)

3. Now, paint over the crack with paint that matches the rest of the wall. Latex caulks are "paintable" (which is why they're also called "painter's caulk", so you don't need to prime the caulk before painting it.

Following those steps will give you your best chance of success in my view, but it's only going to work if the amount of movement in that crack can be accomodated by the stretching/compression of the caulk. Once you exceed the ability of the caulk to accomodate the movement, it's gonna open up again no matter what you do.

GBR 11-05-2009 10:20 PM

Plaster Cracks? Surefire Plaster Repair Tips
Be safe, Gary

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