Dear Tim: We’re in the home stretch of a delightful bathroom remodel job. One of the final steps is to install subway ceramic tile as the backsplash above the dual-bowl sink. The plaster wall above the new granite top needs to be repaired. After we removed the old ceramic tile, there were giant holes. My husband is in a hurry and wants to do the patch fast with a pre-mixed product that comes in a tub from the local big box store. I want your expert opinion as to the best way to repair the massive depressions in the wall from where old trim tile pieces were removed. Do we need to remove the old hardened glue from the walls, too? — Pam L., Columbus, Ohio
Pam: I’ve been in this exact situation countless times while working in paying customers’ homes. The tile style changes from year to year, but the method of getting the wall ready for the tile has not changed.
Let’s talk about high-gloss-finish ceramic tile first. We need to do this to slow down your husband.
Have you ever noticed how a small dent in the door of a new car stands out like a sore thumb? The paint may not be chipped or scratched, but you can clearly see the inward depression. This happens on high-gloss surfaces such as car paint because the reflected light off the metal is bent by the dent. In other words, high-gloss finishes are unforgiving if the surface beneath the gloss is not in the same plane.
If you want every aspect of your bathroom remodeling to be gorgeous, you need to be sure the wall surface under the tile is not only perfectly smooth but also in the same plane. If the subway tile pieces are not in the same plane on a flat surface, they’ll reflect light differently, and it will look like a drunk tile setter installed them.
I see by the photos you sent that the new granite top and faucets are installed. This is going to make the job of repairing the wall much harder as you work around these finished items. The wall repair should have been done long before the cabinet, top and faucets were installed.
You also need to be concerned with what I call the chain of adhesion. What’s that old saying? “A chain is only as strong as its weakest link.” I can clearly see in your photo that you’ve got traditional plaster applied to gypsum lath panels nailed to the wall studs.
For the tile to stay affixed to the wall for decades, the bond between all the wall elements needs to be as strong as possible. The pre-mixed compounds I see in the big box stores contain very weak glues in almost all cases. What’s worse is some of the glues in these products are water soluble. Premixed drywall joint compound and common spackling are great examples of products with these weak glues.
Once these two products are dry, you can dissolve them by rubbing them with a wet sponge. Rub your plaster walls for days with a wet sponge and nothing happens except for you getting blisters and sore muscles. Plaster is waterproof and it bonds tenaciously to just about anything.
Here’s how I’d proceed to make your walls ready for the stunning subway tile I’m sure you’ve selected. First, you need to purchase some liquid adhesive remover. This product brushes on much like liquid paint remover. It’s imperative you protect the granite top and faucets and any other finished item like the front of the vanity cabinets from this harsh chemical.
Follow the directions and get all of the old yellowed tile glue off the plaster exposing the original white lime finish plaster. Once it’s off, now it’s time to start to repair the deep depressions. Buy a bag of Structo-Lite base plaster. You can get this online or from a local building supply store. Be sure the holes in the wall have all loose material removed; brush away any dust.
Mix up the Structo-Lite plaster per directions on the bag. You want it to be the consistency of somewhat stiff applesauce. Take a wet sponge and lightly pat the old base plaster in the hole to get it slightly damp just before you’re ready to apply the Structo-Lite. Pack in the new plaster, being sure to keep the new plaster an eighth of an inch lower than the existing white lime plaster finish you exposed once you removed the old glue.
Use a straightedge to ensure the Structo-Lite is lower than the old white lime plaster. Allow the Structo-Lite to cure for one day. The next day fill in the slight depression and all other tiny holes in the plaster wall with Durabond 90. This is a dry-setting joint compound that’s much like the white lime finish plaster on the wall. Mix it with water to the consistency of warm cake icing so it’s silky smooth. You only have 90 minutes to work with it before it gets hard. You can use cold water to slow the hardening process.
Take your time and be sure the wall surface is as smooth as glass and in the same plane. Use a long straightedge or metal level to help you locate small depressions that may exist in the old white plaster finish. Fill those with the Durabond 90 product so the final surface under the new subway tile is as flat as possible.