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Tuesday, July 15, 2008

Flexible Grout and New Plaster in a Stairwell

This wall of a stairwell had cracks covered with fiberglass mesh tape and mud. The cracks had fully broken through the tape in just a few years, and gaps were large in areas of extensive weakness. Here, the mud and tape have been sliced off, and plaster has been liberally removed where weak. An island of new plaster solidly bonded to lath does much to stabilize the entire wall.

I do most prep work with a 3" flexible-blade putty knife, with the grip and force that can be comfortably maintained with one hand. I cut mud with slicing action. The blade is self-sharpening, and develops beneficial rounded corners. To do crack repairs with flexible grout, slice all the way to the lath, veeing one or both sides to an opening of about 1/8"

I bond plaster along the veed-out cracks, with my flexible grout. Working from bottom up, I progressively flood the gap using a spray bottle, and trowel in flexible grout at paste consistency. The water in the
crack dissolves the paste, and under pressure of the trowel, the gap is completely filled. At this wet consistency, the grout measurably shrinks upon drying, and repeat application is needed to fill flush. Further application of grout is best done after plaster fill at the exposed lath.

Cured flexible grout along the groove of a plastic container lid tolerates severe bending. I have not found any other simple-to-use patch material that passes this test of adhesion and flexibility.

My plastering kit consists of this plastic utility tub, basecoat plaster in two-pound peanut butter jars, an 8-inch magnesium plastering hawk, a 5 1/2" pointing trowel, a 48" magnesium featheredge, water in a bucket and in a spray bottle, and a sturdy mixing stick.

This quantity of plaster is just sufficient for a first base coat over all open lath on this wall. I tilt the tub, and add water by pouring, to start.

I squeeze water from the sponge to get desired peanut butter consistency.

A first coat deliberately under-fills, leaving good bonding opportunities for a second coat. While still wet, excess is sliced off (not scraped) using multiple strokes of the featheredge. Keep the featheredge clean and wet

I rarely use Finish Plaster. A second Basecoat application worked here. The surface is still very slightly under-filled, and may be completed with flexible grout or setting mud.


JLP said...

These pics are of our stairwell. We originally thought we just had to have repairs to some cracks, but as you can see, when Phil opened up the cracks there was a fair amount of loose plaster. For a homeowner that is not a particularly comforting feeling. Some of the cracks were repaired in the conventional method about 10 years ago and as you can see, the original repair didn't hold up. Phil did a great job and we are extremely pleased.

BTW, Phil's grout does not require a large amount of sanding. This is a huge benefit especially when the area being repaired cannot be closed off to the rest of the house. If you have ever had any sanding of plaster in your home you will instantly understand this benefit .

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