On Old Plaster, can I save it ?

Here is a really exciting topic! Old buildings and old plaster. Everyone wants to save the plaster because it is so damn much work to remove it. Is this a wise choice? Well, there are number of things to be taken into account about old plaster. For one, old buildings (when I say old I am talking 100 plus years) didn’t have insulation for many many years, this is a problem to the plaster.
The plaster in a building in New England with no insulation is doomed. Over years and years moisture builds up in the wall cavities due to the extreme temperature difference between the indoors and outdoors. This causes the condensation point to occur inside the cavity… what this means is the lath nails rust away over time.
A lath nail is a very small diameter cut nail with no corrosion resistance, it is the weak point. Once the nail rusts through the lath is essentially detached from the wall studs. What happens next is that the movement of the building (these old building do move, foundation issues, and improper loading cause deflection and uplift) flexes the plaster wall. Over time cracks begin to show, from this point on the plaster is doomed. After years of movement the lath nails are rusted through and the lath is essentially detached from the studs. The only thing holding it there is the hooking action of the plaster. When the Plaster is troweled onto the gaped lath it smears through the gaps and blobs to the inside of the wall cavity creating a hook which once hardened holds the plaster in place, kind of like Velcro.
The lath itself is rough sawn so it assists in grabbing the plaster too. Once the lathe is detached and the heaving and settling of the building work on it the ‘hooks’ of plaster shear off (partly due to the moisture inside the wall cavity causing the plaster to become soft and punky); once this occurs the plaster begins to fall off the walls.
Well I know some Mr fix it will say that you can use a washer headed screw to hold this ailing plaster on, its a short term fix.
Especially when it comes to ceilings, gravity works on the plaster and literally the ceiling falls in, and I mean large chunks of heavy plaster, a real headache. So what most Mr fix it types do next is to patch the bad spots with drywall, or they drywall over the plaster to cover it and to hold it on. All of this type of remedying the ailing plaster is even more of a blight to the ‘old building’….it is adding more dead weight to the structure, and most of these structures were under built in load bearing design. The floors were often over spanned or the distance the joists run from wall to wall or beam was too far for the depth of the joist. Most old buildings used square joists because the economy of milling beams is such that you can get more squares out of a round log than taller boards.
Taller is better in joists and beams when you talk floor deflection as long as there is blocking to hold the joists upright. Getting a bit off the subject here, back to the plaster, so more dead weight is added and now the building is groaning under the weight. This is very bad for the structures beams and joists.
Because the old builders didn’t have metal joist hangers like we use today, they notched the beams and joists together as a form of joinery, sometimes a mortise and tenon connection, they thought this was superior workmanship but as we can see in old buildings it was a mistake to notch. The notches reduce the total effective height of the joist or beam and under years of loading splits will occur in the timber beam at the notches. So the modern re-modeler that is too lazy to make a mess and clean it up that plaster removal causes adds more layers of remodel weight to a structure already ailing in load carrying capacity.
This is so chronic in old homes that it is not unusual to peal 6 or 7 layers of wood paneling, drywall, more paneling, wall paper, then plaster and lathe. In the end no builder is willing to take down the layers to the start because its just hell. It is time consuming, it is dirty, it is dangerous, and it is expensive. And after days of work the wood frame is revealed…only to show sagging beams, cracked joists at notched ends, settled and sagged floors, etc… Also once you peal all this off and clean up the mess you will usually have to bring everything up to modern code. And if not mandated to do this by municipal building codes the builder will usually suggest a complete modernization because it is so much work to do this plaster removal you should bite the bullet and really fix the building .
This will include a full redo of the wiring, insulating meaning furring the walls out to accommodate reasonable priced insulation, and creating a consistent stud layout that will accommodate drywall (16″ or
24″ on center stud spacing).

So in a nutshell if you want to buy a building with old plaster that shows cracking, you might want to reconsider …this is a very expensive proposition.

And if you do buy such a building and think a quick cover up with a skim coat of plaster is going to do the trick, well it wont last, the building will most likely be energy inefficient in that it still misses proper insulation, and worse a chunk of ceiling plaster might fall on your head as you freeze to death in your bed on a cold blustery winter night.

How about new construction? Why not spend your money where it can go towards building what you really want rather than demolition and reconstruction of what most likely is at the end of it’s life cycle anyway.

One Comment

  • Frank Bishop on Jul 20, 2009 Reply

    Brilliant post, Greeno. Thorough, clear, comprehensive.

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