Posts Tagged ‘stanley knife’

Mirror “Tar” Will Bleed Through Wallpaper – Prevention

May 17, 2017

Digital Image

Digital Image

Digital Image

Digital Image


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.