Posts Tagged ‘tar’

Mirror Tar Bleeds Through Wallpaper – Prevention

June 18, 2020



The owner of this newish home in the Woodland Heights (Houston) had her handyman remove the powder room mirror and its surrounding built-in wooden frame. Mirrors are often adhered to the wall with mastic, a tar-like substance. When the mirror comes off, some of the tar residue invariably remains.

In the top photo, you can see where removing the mirror took the blobs of mastic along with it, as well as round sections of the drywall. But there are small smudges of tar still remaining on the wall.

The problem is that tar (among a lot of other substances) will bleed through wallpaper (as well as paint, and a lot of other materials).

There are stain blockers like my beloved KILZ Original Oil Based, BIN shellac based, or others, that are designed to block these stains. But I don’t trust them. For water, rust, blood, wood sap, etc., yes. But for oil-based substances like tar, I want more assurance. The best way to prevent bleed-through is not to cover the stain, but to remove it.

So I take a Stanley knife and cut into the drywall and then peel up the top layer of drywall, taking along the offending tar residue.

So now the dangerous tar is gone. But you’re left with torn drywall. This is bad for several reasons. For one thing, you have an uneven surface that will look bad under the new wallpaper (or paint). And since the top, protective layer of drywall is gone, any moisture (such as from wallpaper paste or from latex paint) will penetrate into the torn paper layer – which will swell and cause bubbling.

All of which looks pretty bad under wallpaper or paint.

So I used the product Gardz to seal the torn drywall. It is formulated to soak into the paper; then it dries hard and acts as a sealer and moisture-blocker. It won’t block stains, but it will prevent moisture from penetrating the paper and causing bubbling.

Once that was dry, I skim-floated over the entire area with joint compound. It looks rough in the photo, but once it’s dry, I’ll sand it smooth. Then I’ll give it another coat of the penetrating sealer Gardz. See last photo. Once that is dry, I’ll cover it with a coat of Roman’s Ultra Prime Pro 977 wallpaper primer, when I prime the other walls in this powder room.

All of these various products do take a while to dry, especially the joint compound as thick as I applied it. So I went to this job site a few days before the install date, to do the initial prep, so it would have plenty of time to dry before I come back for the final prep and wallpaper hang.

Mirror Removed – Ready for Wallpaper? NOT!

March 20, 2018


A mirror had been glued to this wall with mastic adhesive (a tar-like substance). When the mirror was pulled off the wall, the adhesive pulled some of the drywall along with it, and in other places it left some of the tar on the wall. Then someone skimmed over the surface with joint compound.

The wet joint compound caused the torn areas of the drywall to absorb moisture and ripple, and the tar worked its way through the joint compound.

Both torn drywall and tar are problems under wallpaper. The ripples from the torn drywall will show under the new wallpaper. And moisture from the wallpaper paste is likely to make the bubbles larger. The black mastic (tar) will bleed through the wallpaper, creating black spots.

If I had been there when they removed the mirror, I would have taken a utility knife and cut the globs of mastic completely out of the wall. Removing it is preferable to trying to cover it up. Yes, this would have torn the drywall, opening it up to wrinkling when it gets wet with primer or paste.

But the penetrating sealer “Gardz” is designed to fix torn drywall. It dries hard and impermeable, so moisture cannot get through. No worries about bubbles or wrinkles! The cut areas could then be skim-floated over and then sanded smooth.

But since I didn’t get to prep from the beginning, I inherited this wall in the top photo, with torn, wrinkly areas, and with tar bleeding through the joint compound.

To prevent additional bubbling, I coated the wall with Gardz. Once that was dry, wanting to both smooth the wall and create an additional barrier to contain the mastic stains, I skim-floated the entire wall, let dry, sanded smooth, and sealed again with Gardz.

Gardz doesn’t protect against stains, though. So, to keep the mastic from bleeding through, I coated the wall with KILZ Original oil-based stain killer and blocker. This worked better having the joint compound under it, because when I’ve put KILZ directly on mastic adhesive, the two petroleum-based products simply melded into one another, and left us with the very real potential for bleeding through wallpaper (or paint, BTW).

So the KILZ should have effectively blocked any stains from the mastic. But the new problem is that wallpaper paste will not stick to modern, EPA-approved, oil-based products. Plus, I was worried that a little of the black tar might still find a way through.

So I skim-floated the wall again, creating yet another layer that would bury those tar stains. After that was sanded smooth and wiped free of dust, I applied another heavy coat of Gardz.

All this took a long time, but it’s good assurance that bubbles will not be seen under the new wallpaper, and that no black spots will grow on its surface.

Covering Rust – Rust Bleeds Through Wallpaper

April 13, 2016

Digital Image

Digital Image


The dark red stain on the edge of that outside corner is rust. It is coming from the metal bead used to define the corner when the house was built. The only problem is, in a steamy bathroom with poor ventilation, these metal beads are sometimes prone to rust.

And rust bleeds through wallpaper.

Before I started hanging the new, pastel-colored wallpaper, I had to block off the rust stains. Nothing tackles this job better than the original oil-based KILZ Original. I’ve taken a small brush and applied KILZ to a half-inch wide strip that runs the height of the wall. It dries in about an hour, so paper can be hung fairly quickly.

Other substances can stain wallpaper, so KILZ is good to have on hand. KILZ also seals off water stains, oil and tar, ink and markers, and odors, like smoke from cigarettes or fire.