Plaster is hard.
It cracks as houses settle and time passes. To really understand why plaster cracks you need to understand what makes up a plaster wall. You often hear of these walls being referred to as "Plaster and Lath" or "Plaster on Lath" with the latter being a more correct description. The lath is a series of wood strips nailed to the wall joists. The plaster is made up of two different materials, the first (which can actually be a couple of layers) being called the scratch coat which is a darker and more coarse material and the second being the finish coat which is white, very smooth and usually fairly thin in comparison to the scratch coat. The scratch coat's purpose is to lock into the lath. This occurs when the dead men who built these homes would put a healthy layer of the scratch coat onto the lath, pressing it in deeply to create "Keys." These Keys were the portion of the plaster which curled around the back side of the lath and held the wall onto the lath. The finish coat was then laid on and tooled to create the wonderfully smooth surfaces we know and love.
As time progresses these keys can break off from the surrounding plaster due to settling, vibrations and sometimes abuse. When this happens the symptoms manifest in a couple different ways such as cracking and bulging of the walls. There are many ways to "fix" these problems. The uninitiated or just plain lazy will slap some spackle on there and sand and repaint those cracked sections, some people may just ignore the bulging walls and some extra horrible people (the same folks who buy Vinyl replacement windows) will tear the plaster out completely and replace it with drywall. That said, there are times where it just doesn't make sense to repair plaster... For example when dealing with ceilings that have been repaired over and over, walls that were repaired poorly, repairing previous botched repairs (are we seeing a trend here) or when its just too cost prohibitive. I'll get into how to laminate ceilings and do patch repairs with Drywall in another post but I am not a hardcore restorationist and I identify the need to sometimes just strip a wall and start fresh (gutting a historic house to studs and redrywalling though is just heartbreaking).
Now, I'm sure you've heard it time and time again, "Plaster walls always crack and no matter what will keep cracking." This is bunk... slap the next person who says this to you (you may have to wait a while). Plaster walls can be repaired and there are two great and fairly easy ways to do it. The first is with what are called "plaster buttons." These buttons are little steel washers that you screw into the wall which stabilize any sections that may have come loose due to broken keys. Then you just apply a surfacing material (joint compound or if you have the cash a plaster veneer material like Master of Plaster) to level the surface and prepare it for paint. The second option is to use an adhesive system like Big Wally's Plaster Magic to bond the plaster back to the lath. This involves drilling holes near the cracks, conditioning the lath and plaster, squirting adhesive between the lath and plaster, clamping it with washers, removing said washers after the adhesive has cured and then refinishing as above.
So now that I've gone off on a bit of a tangent I'll update everyone on some progress we never blogged about and circle back to the most important part of plaster repair (any repair really) which is the prep.
We initially tossed the idea of using a wallpaper stripper out the window because the dry stripping method worked very well for us and most of the walls had been recently painted by the previous owner which made stripping with a stripping solution fairly difficult if not impossible (even with a paper tiger!) as the paper couldn't really absorb the stripping agent. What we found with the dry stripping though was that we were often left with bits of the backing paper stuck to the wall which wasn't OK as we were planning on painting those walls. So when we found ourselves unable to get under the wallpaper backer in the master bedroom we gave the DIF wallpaper stripper a go. To our surprise the backing paper was lifting right off since it was totally exposed to the stripping agent. So that was our method going forward, we would strip the top painted layer off then douse the backer paper with the DIF solution (buy the concentrate.. a bottle is enough for an entire house!) using a garden sprayer. Using this method we were able to strip the master bedroom, the small guest bedroom/office and clean up all the remaining scraps from the living room and entry/stairwell pretty much all in one weekend.
During this process Becky discovered a "soft spot" which became apparent when we wet down the walls with the stripper. You see, plaster cures which is a permanent chemical process but joint compound dries which means if you wet it, it becomes soft again. While scraping Becky found a spot that had become very soft. Being a strong believer in the mentality that ignorance is not bliss, especially when it comes to homes, I started digging away at the joint compound which revealed a crack in the plaster and by the time I was done we were left with this:
A gaping hole in the wall with lath exposed.
Becky was a bit horrified at how much joy I took in chipping away all the loose plaster bits. The thing is though that you can't repair plaster in situations like this until you get to either solid plaster or the lath as you need to ensure your repair will take hold properly. We'll fix this by using the patching plaster we bought from the Plaster Magic site and then skim coat over it. I'm a bit torn as to what I want to use to skim coat the walls as joint compound is easy to work with and inexpensive but soft while a veneer plaster product is much more appropriate it is traditionally more difficult to work and is not meant to be sanded so if you goof up you can end up in a bit of a bind... oh and at roughly $150 per 4.5gal bucket it is quite expensive since that generally covers 600sqft of wall. There is the option of a setting type compound such as easysand 90 which is not as hard as plaster but sands well and is not going to get soft if it gets wet. A final option I've been keyed into is that of mixing plaster of paris into premix joint compound. I've read many arguments about this solution and honestly still don't know if its the best or worst idea ever.
Thoughts? Advice? Think I'm crazy? Let us know!
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