Posts Tagged ‘mastic’

Removing Mirror Rips Drywall

September 19, 2017

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This powder room in the Medical Center area of Houston had a mirror glued to the wall.  The homeowners want a different mirror, so had the original one removed.  The mirror was attached to the wall with a tar-like substance called mastic.  The glass guys use suction cups to clamp onto the mirror, then they pull it away from the wall.  Some globs of mastic will be left on the wall, and this is a problem, because these tar-like substance will bleed through the new wallpaper.

So, to prevent any mastic / tar residue from bleeding through the wallpaper, the handyman took a Stanley knife / box cutter and cut out the top paper layer of drywall that had any mastic on it.

To smooth over the uneven edges, the handyman skim-floated the area with joint compound.  The moisture in the joint compound caused the exposed paper inside the drywall to swell.

So what you are seeing in the top photo is a wrinkled section of drywall caused by moisture.  This will show under wallpaper.

So I took a Stanley knife and cut out the handyman’s patch, to remove the wrinkled drywall paper layer.  I sealed it with a penetrating primer called Gardz, which soaks in, binds surfaces together, and dries hard.

Once that was dry, I skim-floated over it (and the entire area), to get a smooth finish.  Once my skim-float layer was dry, I sanded it smooth, and then primed again with Gardz.

The Gardz did its job, and did not allow moisture to penetrate into the exposed drywall, so no more wrinkles developed.  See the second photo.  Now the wall is nicely prepared and ready for wallpaper.

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Mirror “Tar” Will Bleed Through Wallpaper – Prevention

May 17, 2017

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Originally, this powder room in a newish townhome in the Rice Military neighborhood of Houston had a mirror that was glued to the wall. Removing it left globs of mastic (tar-like adhesive) stuck to the wall. See Photo 1.

Mastic is petroleum-based, and it, like other similar substances such as grease, oil, and crayon, as well as other compounds like blood, rust, water, tobacco tar, and others, will work their way from behind the wallpaper up through it and then onto the surface, causing an unsightly stain.

KILZ Original oil-based primer and stain blocker is a superb product for sealing these substances. However, I feel more confident if the suspect material is removed entirely.

The best way to do this is to take a Stanley knife (utility knife / box cutter) and cut around the stain and into the wall. Then you can use a stiff 3″ putty knife to peel up the top layer of drywall, taking the staining material with it.

This leaves a patch of Sheetrock without its protective top layer. See Photo 3. These layers of torn Sheetrock will absorb moisture from anything you put on top (paint, primer, joint compound, etc.), and will swell, creating ugly bubbles that will mar the finished job.

So I brushed on Gardz, a penetrating sealer / primer by Zinsser. This is cool stuff, because it soaks into the surface and then dries hard, binding everything together.

In Photo 4, I have skim-floated over the areas where I have cut out the mastic. To skim-float, I trowel on a smoothing material called joint compound. Once that is dry, I will go back and sand it smooth, creating a perfectly smooth surface ready to accept the new wallpaper.