Repair plaster behind tiles

8 years ago

I'm in the process of re-tiling my bathroom. The house was built in 1940 and all of the walls are plaster. The plaster behind the tiles is different than the rest of the house though. Most of the plaster has fine sand in it and is on wood lath. The plaster behind the tiles has a coarser sand, is on metal lath, and is 2-3 inches thick.

The tile and plaster held up very well over the past 75 years but the tile color was revolting so we decided to replace it. He tiles bound so well to the plaster I had to pulverize them with a hammer drill (with a chisel attachment) to remove it. Most of the thick plaster behind the tiles is still in great shape. However someone previously repay aced the shower diverted and the plaster in that area broke up when I removed the tiles.

What can can I use to repair the plaster before I replace the tiles? Someone suggested that plaster is called "thick set" or a "thick mortar bed". I came across Laticrete 226 thick bed mortar but I can't find a local dealer or anyone who knows anything about it. Is there an alternative product anyone can suggest?

Featured Answer

MongoCT

8 years ago

We all have different methods. Here's my recommendation:

Tuck some tar paper (or some other barrier) between the copper and the existing metal lathe if you can. Wrap the tub stub with tar paper, tape it in place. Doesn;t need to be anything purdy or fancy. You want to keep any cement-based product off the copper.

Patch in new expanded lathe over the tar paper, you can weave it in to blend the new metal with the old.

You'll want to mix two things up; a portland cement slurry, and fat mud.

Portland cement bonding slurry. This will act as a bonding agent to help the new mud stick to the existing wall mud. Simply mix portland cement with water to make a thin paste. Brush it on the existing mud to help the new mud stick to the old. Pretty simple.

Fat mud. You'll fill that gap with fat mud. "Fat" simply means it has lime in it. Lime make a bit sticky. Recipes vary, but generally, mix by volume 4 parts sand, 1 part portland cement, and 1 part lime. You can buy bags of each individual component at most any box store.

Dry mix all the ingredients. Add water carefully. You mix it wetter than deck mud (deck mud is wetted until it's barely moist, it's grainy like beach sand used to build a sand castle) but not as wet as a concrete mix that can flow out when poured on a flat surface. When shaped into a mound, fat mud will hold that shape instead of slumping flat. The goal is to get the fat mud to be wet enough to stick to itself, but dry enough to stick to vertical surfaces and not slump or fall off the wall.

If you do youtube seach for "fat mud shower wall" I'm sure there are videos out there.

When ready, clean existing surfaces, then paint them with the portland cement slurry. There's no magic here. Just get it on there.

Then fill your hole with the fat mud. You can pack it in with a trowel, build it out so the mud patch s slightly proud of the surrounding surface. Then take a stick that's wider than the patch, place it against the good wall below your patch, and use a left/right sawing motion to shave the mud flush with the existing wall.

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