On Original Plaster and Its Repair

Plaster conservator Rory Brennan touts the advantages of three-coat plaster walls and ceilings, and explains how plaster can be repaired, even by do-it-yourselfers.

From the early 19th century through the early 20th century, American residential plaster consisted of a wet plaster applied to wood lath, followed by finish coats, to form walls and ceilings. While the type of wood lath (later, metal) and the type of plaster changed over time, this system is always a substantial part of the home. Whether as a durable sanitary wall or stabilizing component to the structure, it’s a system that was meant to last for generations.

Room before patching.

Like many elements of historic homes, plaster system was designed to be maintained. Because of the inherent durability of plaster, minor cracking etc. often didn’t come to the attention of occupants in the first, second, or even third generation of owners. As a result, repair was often deferred.

Keep in mind that repairs for stability are different from cosmetic solutions. Stability repairs take in the subsurface, and usually involve reattaching loose plaster back to the lath when the plaster “keys” have failed. Plaster Magic is the only adhesive designed specifically for this purpose.  Cosmetics involved the surface only — how the plaster looks. Resurfacing, painting, and wallpapering won’t last if the plaster has not been stabilized.

Unpatched section.

The most common cause of plaster problems is structural movement in the building. This can because by any number of things: settlement, water and humidity, even “old age.” Historic homes have been subjected to rain, snow or wind, all exerting lateral force and sometimes causing the plaster to crack. Perpendicular to the lath, this happens after about 40 years, and parallel with the lath at about 75 years. This movement has an effect on the plaster keys (the wet plaster than was squeezed between laths, “keying” plaster to the substrate once the plaster cured).  Keys can break off or crack, degrading their structural integrity, and causing the plaster to drop, especially if it’s ceiling plaster. The good news is this is usually gradual. This means it can be caught and plaster re-secured before it falls. As soon as the plaster hits the floor, the cost goes up. Falling may not happen as often with walls, but nevertheless movement shows up as bulges, often though not always beside the staircase.

Unless the plaster has been subjected to long-term water infiltration or leaks from, say, backed up ice dams at the roof, repair is straight-forward. That’s because the plaster itself isn’t the problem. Rather, it’s the plaster’s attachment to the lath. I’d say that accounts for 99% of old-house plaster problems. Fix that and the wall is as good as new.

If when you purchase your new (old) house it has falling-down ceilings or big bulges in the walls, with layers of wallpaper or calcimine paint, it might get discouraging to see all this deferred maintenance. Take heart, as plaster repair is simple to understand and, for the most part, can be accomplished by the attentive DIYer.

Halfway mark.

Maintenance—inserting small amounts of money, steadily over the time of your tenure—is the least expensive path. We spent most of the 20th century figuring out that maintenance-free windows, doors, wall systems etc. don’t exist. Like it vinyl siding and lower-quality replacement windows, gypsum wallboard (GWB, or drywall) in the place of plaster will lessen the value of a historic house.

Don’t be discouraged if repairs seem costly. Unfortunately (but not uncommonly),  you are making up for all the deferred maintenance the previous owners did not do. Remember that your good repairs will last.

Home-maintenance 101 tells you to seal the building envelope first — most importantly, the roof. This is where water comes in, causing plaster problems. Wet plaster “blooms” with efflorescence, which requires attention and something replacement patches. Once plaster has soaked up enough water it will fall. So tend to the roof; it it’s old or a material including slate, do a yearly inspection. In cold regions, be sure insulation and edge treatments are dealing with ice dams, which cause water to back up on the roof and find its way into walls.

The section after patching.

Plaster is a durable system. As part of the whole package, it adds stability and solidity to the structure. A story-and-a-half Cape Cod, a relatively small house, contains approximately six or seven tons of plaster. This weight keeps the building solidly on the foundation. The density inhibits sound transmission, keeping your home quiet. Abrasion resistance is also a positive. Much old plaster was made with lime, which is fire resistant and very sanitary. It’s a rock surface vs. a paper surface.

If a contractor suggests replacement with GWB or even veneer plaster (over a board substrate), it means they are trying to save themselves (not you) money, or they don’t know how to properly repair plaster. Remove and replace is costly — and unnecessary.  The value of your building is reduced and material lost forever. Once the plaster is removed, it almost never is replaced with something as good as the original. Any real-estate agent will tell you a fully plastered house is worth move than one that is all GWB. Its like putting money in the dumpster.

The fact that the original plaster is still here attests to its durability. If it has lasted 100 years, there is no reason it can’t last another 100 years. Again, maintenance is key. If your house is built from materials that have this kind of duration, it will certainly be worth more on the resale market.

RORY BRENNAN is a preservation plasterer and conservator based in Vermont. He has worked on such significant buildings as the Massachusetts State House and Washington’s Mount Vernon. Brennan developed a repair system called Plaster Magic — the only construction-adhesive system designed specifically for the long-term repair of historic plaster.


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