troweling plaster on brick
I have an exterior brick wall with old horsehair plaster--nearly 1" thick. I had to tear some of it the plaster down due to old water damage (bad roof thanks to former owner). Now comes the repair work.
I've heard that USG's Structolite is a good product for this. Has anyone used it in this manner? Also, I'm trying to figure it out if I can apply it directly to the brick surface or if I first need to apply a coat of something else to the brick. Finally, will I need to use some sort of finishing coat (over both areas with new structolite and old horsehair/paint) or can I just spread structolite over the old stuff? I think I've seen "Durabond 90" spoken of as a finishing coat. Is this necessary?
Thanks in advance for any advice!
Use structo-lite followed by durabond
Yes you can apply stucto-lite over brick. Stucto-lite is the modern version of brown coat plaster and like brown coat it is intended to have a white or putty coat applied over it. This would be plaster of paris for original plaster. Use durabond for a more user friendly white coat plaster.
To repair your brick/plaster wall: Make sure to brush off any loose brick mortar, sand and other debris with a stiff brush first. Seal the brick, especially if as you say it was water damaged. Use a shellac-based primer/sealer over the brick and surrounding plaster brown coat and white coat. Any other part of the wall surface that has suffered water damage should be primed with the sealer to block water stains and ensure the repair compound and paint bond well with the wall. Let the sealer dry for an hour or more.
Apply the structo-lite leaving an eigth inch or more wall surface to be leveled out with the durabond. Let the structo-lite set for at least a day (over night is usually enough). It will crack as it sets. This is pretty hard to avoid but it has never created any problems for me (25 year of plaster repair). You can spray the structo-lite with a mist of water as it sets to try and prevent the cracks.
Apply the durabond using a straight edge to float the surface smooth and level as possible. Don't let it bulge above the surface of the wall. If anything make sure it's a little below the surface of the surrouding wall. Let durabond 90 set for an hour. Mix and apply a couple skim coats of durabond. Let each coat set for 30 to 60 minutes. Sand the final coat after it has set and dried for at least 2 or 3 hours. It can be painted the next day.
thanks for that excellent advice. what do you recommend for the straight edge? i've seen trowels with square corners and with rounded corners--which is preferable?
I use a board like a 1x3 or 1x4 to level the structo-lite and the first coat of durabond. If you fill the area to over flowing with durabond and then knock off the excess, resting the ends of the board on the surrounding wall as a guide, it will give you a good starting point for applying the finish skim coats. The first coat of durabond will be rough when it sets. You can scrape off any bubbles or ridges in the surface after it sets if you do it within the first hour or two. After that it gets much harder to remove. Use a drywall joint knife to scrape or you can sand the set mud with 50 or 80 grit sandpaper. Smooth the edges of the mud at the same time.
To finish I use a 6" drywall joint knife to apply several thin skim coats of durabond. You can even use ready-mixed joint compound for the last couple of skim coats to make final sanding easier. We have a website with illustrated instructions for repairing all types of wall damage. I can't post it here but I'll email the url to you if you want. My email firstname.lastname@example.org.
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