Repairing Plaster Walls
Restoring Plaster Walls - Setting Type Joint Compounds
If you have ever owned an older home, you must surely be aware of the pluses and minuses of plaster walls. Their durability, smoothness, sound deadening qualities and sheer mass make them very attractive. Plasters only negative, as I see it, is that it tends to react like glass when subjected to stress. In other words, plaster cracks.
Random or Systematic?
Cracks in plaster happen for a variety of reasons. Lumber shrinkage, seasonal moisture changes, wind forces, foundation movement, expansive clay soil movement, excessive loading, etc. all can cause cracks in plaster. Some cracks can be traced directly to a certain cause while some are tougher to diagnose.
It is important to try to determine the cause of cracking prior to repair. The reason being that if your house, wall or ceiling is mobile or in a state of motion, the crack will undoubtedly reappear. Certain cracks are very interesting. These are the ones that plague many houses in climates that experience wide humidity changes from summer to winter.
Wood - Like a Sponge...
Wood expands and contracts in response to changes in the humidity of the air that surrounds it. In other words, wood is a hygroscopic material. Plaster, on the other hand, is very stable. It is very strong if you try to squeeze it, however it is very weak if you try to bend or stretch it.
Thus, if the wood framing members of your house begin to stretch or expand, the plaster can and will pop. There is very little you can do to prevent this, other than trying to maintain a constant indoor humidity level.
Plaster and Old Age
Remember your body and skin when you were 10 years old? I'll bet it was smooth and virtually blemish free. What do you think your skin will look like when you are 70 or 80 years old? Well, a house is not much different.
Houses develop joints just like your elbows and knees where they bend to relieve stresses. Walls and ceilings also react to the force of gravity over time, just as our skin. Thus, it is not unreasonable for an older house to exhibit wrinkles, cracks, and other blemishes.
Fixing the Cracks
OK, so now that the plaster is cracked it is time to fix it. Time after time I have seen homeowners struggle to fix a crack using spackling compound. They are told to chisel the crack into a V shape and fill away! Well the patch looks fine until the house or wall moves the next time. The crack reappears.
The most long lasting repairs are made when you bridge the crack with a material that can absorb the periodic movement that most cracks experience. This is achieved by using either a standard drywall paper tape or a fiberglass mesh tape. The crack is coated with a compound that adheres to the plaster and coats the tape at the same time.
In all but the worst cases, cracks repaired with tape remain smooth for a long period of time.
One of the first jobs I did after I got married was the rehabilitation of an old farm house. I was helping some friends. Marcy was helping me apply some premixed drywall joint compounds onto new drywall. She used to call the material Gop. I feel it is a very fitting name as it sounds much like the product appears and reacts when dropped. Premixed joint compounds are wonderful products. For all intents and purposes, they are simply water soluble glues mixed with fillers. These premixed compounds work fine for drywall. However, for serious plaster repair you need to use either real plaster or a product that has the properties of both plaster and premixed joint compounds.
You can purchase some wonderful plaster patching compounds that come in 25 pound bags. They are powdered setting type joint compounds. These products actually grow tiny crystals as they dry. These crystals lock into the coarse texture of the plaster base and/or the smooth white or top coat plaster. You can even add sand to these mixtures if you wish to create a textured look.
These compounds come dry because when they are mixed with water they begin to harden. Some of these products contain higher amounts of gypsum. These tend to set up or get hard within 30 minutes of mixing. You can buy mixes that take up to two hours to harden.
An additional advantage of using these products is that in one day repairs are possible. Premixed joint compounds can take a day or more to dry. Repairs can stretch out. I have used the setting type joint compounds and repaired a plaster hole from start to finish in as little as two hours!
Where Do You Get Them?
That is one of the most frequently asked questions. Homeowners miss out on tons of great products. These special dry setting joint compounds are found at drywall supply houses or building supply houses that sell plaster supplies. Only on one occasion have I seen them in a giant home center store.
If you want to get some of these great compounds, you will have to find out where your local builder or remodeler buys drywall.
This column was shared with my readers in the April 4, 2013 AsktheBuilder Newsletter.