Renovation & Design

An awkward union

Drywall and plaster finally come to terms

Photos by Marc LaBossiere / Winnipeg Free Press

Multiple ceiling lines converge near the closet which was extended by removing an impractical dividing wall from an earlier renovation.

New framing was added to accommodate the new floor plan, revealing some tricky fixes in this 115 year-old house.

The drywall is mounted atop self-adhesive shim strips along the studs to meet the thickness of the adjacent plaster.

Drywall is fashioned to mimic the curvature of the adjacent plaster by scoring the backside of the drywall and snapping each score without damaging the front.

One of the toughest challenges in the renovation industry involves the remodeling of a space within a century-old house. Because construction practices have evolved through years, a current approach will often clash with the ways of old. A current jobsite has presented me with just such an issue, revealing several obstacles to overcome in preparing the shell of a third-floor three-piece bathroom.

Beyond the obvious, it appears as though this bathroom has received a few modifications over the years, rendering it hard to decipher the true origins of this room. And unfortunately, these prior renovations had not been achieved in a manner to which the new design could be easily adapted. As such, it was best to bare the old as much as needed to increase the possibility for a satisfactory outcome.

Much like any pre-reno bathroom demolition, the old bathroom amenities were systematically removed to accommodate the new floor plan. Once the toilet and pedestal sink were removed, the existing jet-tub (obviously not original, and from a prior renovation) was carefully extracted from the back corner wall, revealing the secondary sub-floor that had been added above the old. The existing water feeds and ABS drains were cut away to make room for the new runs, that will eventually supply the new 36-inch wide sink vanity, high-efficiency toilet, and stand-alone tub which will be positioned parallel to the back wall, perpendicularly to its predecessor. As such, the rough plumb for the water feeds and ABS were carefully run to the newly assigned amenity locations, awaiting tie-in at a later time.

The open secondary sub floor was carefully filled in using two-by-fours on the flat, shimmed to level upon the old sub-floor that has several elevation idiosyncrasies throughout. With the top joisting leveled, three-quarter-inch ply was set to flush adjacent the existing secondary sub-floor. With these steps achieved, the biggest hurdles would now be addressed — how to reposition the closet wall, and close-in the extended bump-out along the vanity wall with drywall, when the rest of the room is sheathed in plaster.

The issue with plaster is its depth inconsistency — at any given area, the plaster thickness can vary as much as a quarter inch. Therefore, cutting a straight line down a plaster wall may provide a flush surface against which a sheet of drywall can rest. However, the drywall once fastened to the stub behind will exaggerate these thickness discrepancies and render the mud and taping stage near impossible. Moreover, several areas along the walls and ceiling in this little bathroom have curves and rounded features, atypical when doing standard drywalling. To accommodate where drywall meets plaster, a few extra steps are taken to influence the desired result.

Firstly, addressing the plaster thickness issue would require pre-shimming the stud behind the drywall just enough, to push the drywall out flush to the plaster beside it. Seems simple enough, if the plaster is the same thickness from floor to ceiling, which is not often the case. To overcome this challenge, I elected to use a shim layering technique along the studs, adjusting the thickness of the shims to reflect the inconsistencies of the plaster. Instead of trying to pre-cut and fasten shims along every stud, peel and stick tile flooring was used by first cutting the tiles into thin strips and adding layers of these strips to the stud face, until reaching the desired & required thickness. It worked out very well, because the strips held in place, eliminating the need to secure shims. Every stud next to a plaster area was prepped in this manner, allowing the drywall to then be fastened with long drywall screws. The use of a sticky shim truly hastened the process. The seams were then taped and mudded as usual, and quite easily.

Next came the burden of rounded plaster elements along the walls and ceiling. Because the entire ceiling would remain intact, the only areas provoking a mudding solution were found at the expanded closet entry, where two ceiling lines meet, and along the back wall behind the intended vanity location — and this area was in rough shape, having been chopped away erratically during a previous renovation, slyly hidden by a four-inch section of unsightly trim (that would not return).

After pondering my approach, it was evident that filling the deep crevasses with mud only would not suffice. As such, any area whereby the new drywall did not adequately meet the uneven and jagged plaster, small pieces of drywall were first inserted to provide a rigid surface upon which the mud could be added later. Along the bump-out extension, the upper portion must mimic the curvature of the adjacent plaster. To achieve this, a section of drywall cut to size was scored along the backside of the drywall, in one-inch increments. The drywall was then snapped carefully at every score line, without breaching the front face of the drywall, allowing it to bend. Using shims to provide a rigid surface behind the “curved” drywall, the small section was secured using drywall screws, in a manner that mimics the curvature of the plaster next to it. All seams were taped, and mudded. Subsequent coats of mud will eventually be applied as to fully create a concave surface, to be refined and smoothed out during the sanding stage prior to priming and painting. It is a laborious activity, that has provided the desired look — to match the old plaster.

The crucial aspect to remember when applying mud coats is this — it can’t be done in one coat. Patience is key, and dry times are imperative. The first coat is used to bond the seamed surfaces to the tape, and/or corner bead — in this instance, drywall adjacent plaster. The next coats fill in the areas of mud that have contracted slightly during the drying process. By the fifth coat, so little finishing mud is required that the trowel barely leaves a wet patch as the trowel is drawn over the surface. And when that final coat has dried, the mudded area should feel smooth as glass. Once the entire space is primed and painted, the areas where drywall meets plaster will have vanished, and the room will appear as though it has always been that way. And that’s the ultimate goal.


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