Fixing a Cracked Plaster Corner with Metal Edge and Flexible Grout

Defects at this corner in a high-traffic hallway were particularly daunting to the homeowner, leading to a call for help after attempted painting prep with removal of kitchen wallpaper. Enamel finish is poorly bonded. A horizontal crack is bulged out. A vertical crack 1 1/2" from the corner is unstable. Old repairs with paper tape and mud have come undone.


Here the corner is ready for grouting. No cracks are large enough to permit repair with plaster. If the only tools in the box were brittle setting mud and Fix-It-All, one would choose Fix-It-All. "Durabond" is sometimes recommended, but that is just a brand name for setting mud. A flexible and adhesive patch material will survive corner impact: my flexible grout.

All filling was done in about three troweled applications of flexible grout. The final result met the goals of prep: nothing to be seen, and confidence in durability.

The adjacent enamel paint edges are sandably stabilized by the flexible grout. The enamel adhesion is poor, but I had to stop peeling somewhere. This will hold. Where adjacent paint is latex and also not well bonded, the flexible grout is even more useful. Water in mud tends to aggravate the paint release; not so flexible grout with its acrylic base.

Grout at a Ceiling Edge

This is a common situation with plaster crack repair. A 1/4" drywall covering of ruined ceiling plaster was dressed at edges with paper tape. The walls were good enough, where several layers of wallpaper concealed cracks. Several more layers of wallpaper were applied through the years after the ceiling improvement. Now, I have the job of fixing the cracked plaster walls. The tape up onto the ceiling is simply razored into the corner, to retain texture.


Mud would NOT last here. Retaping the corner would be painful, with spread of texture damage on the ceiling from troweling and wetness. Fix-All might survive if pushed into the gap, but application would be aggravating, with short pot life, and with difficulties of cleanup.

I wet the gap by spray bottle as I progress, and push flexible grout into the gaps, by fingertips. The application will be easier yet, dispensing grout with caulking tubes. Going around again if necessary, I can spot-apply a matching texture pattern with flexible grout.

More photos of completed crack-repair prep

Simple closure of a crack using flexible grout is quickest, but general instability in a wall may be more-permanently cured with willingness to set in fresh plaster. Here is the opposing stairwell wall, ready for smoothing with setting mud.

Here is the prep of a bathroom ceiling, a first application of flexible grout, and two coats of basecoat plaster. The next step is near-leveling of all repairs using flexible grout. Finish with careful buildup of setting mud.

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.

Plaster Repair How To

This blog will detail the advocacy of plaster repairs using a crack-repair material I make and offer for manufacture, that I call "Flexible Grout." Along with detail repair at cracks, I will address the durable replacement at large fractured areas, with "real" basecoat and finish plaster.

I will develop and post case studies, with pictures. I will also post related studies offered by others, including constructive comment upon trial of Flexible Grout. I will offer free samples of Flexible Grout upon sincere query, with mutual promise of blog-posted, unedited discussion. We will agree that any differences of view will be addressed by comments to a posting.