Preparing an old fireplace for tile [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-06-2019, 12:41 PM
Mrs. JerseyDIY desperately wants to change the look of our fireplace. She suggested painting it, but my brother owns an Arts & Crafts/Restoration/Custom tile manufacturing company, so it's a no-brainer for me to tile over it. The fireplace was built in the 1920s and is all original as far as I can tell. We use the fireplace about 10 times per year and only burn duraflame type logs. Here's the fireplace along with some close ups of the brick corbels and stair-stepping at the top:




The condition of the bricks on the outside of the fireplace is excellent with almost no cracking or separation of the mortar.

Here are some close ups of the hearth bricks and firebox:




The grout in the hearth bricks is cracked and separated in places (no cracks in the bricks fortunately). I'm not certain if it's actually grout, or just brick mortar set nearly flush with the surface of the bricks and coated/sealed somehow. The hearth grout appears to have coarser sand than typical grout, but it's also nearing 100 years old, so who knows what it could be? I suspect that most of the cracking is due to the fact that the hearth is supported by a cantilevered half-arch of bricks set into the joists in the basement ceiling below. There has been some settling of the joists over the last century and this probably caused the cracks. However, the firebox and surrounding fireplace structure is supported by a massive stone and block solid column structure that goes all the way to the floor in the basement and it has not moved and is completely intact.

I will be tiling over all of the vertical brick surfaces outside of the firebox. No tile will be added to the inside of the firebox or to the hearth - I'm leaving those alone. I have a design that takes advantage of the corbels and stair-stepping of the bricks at the top so I'm good to go for that part of the project. I'll be using mostly 4.25" and 2.75" square tiles for the field.

I have some questions and concerns with the job that I'm hoping the JB crew can chime in on:

1. There's a bit of lippage among the existing bricks that will make tiling over the surface a bit challenging. Plus I assume the existing mortar lines will need to be filled. I'm thinking of skimming/screeding the surface of the bricks before tiling to even out the surface. Suggestions on a material to use? I'd like to keep the thickness of the skimming material thin so that the overall size of the fireplace doesn't "grow" much. What should I use to clean the bricks before skimming?

2. I'm not certain what sort of "grout" is between the hearth bricks, but I'd like to repair it. I don't really want to tile over the hearth as I like the character and design of the existing bricks. Suggestions on the best approach to repair and on what sort of material to use? I'm hoping not to have to remove all of the existing grout if possible.

3. There's a bit of spalling of some of the hearth bricks in the bottom of the firebox, and some of the vertical bricks at the back of the firebox. The hearth bricks are a different composition from the vertical bricks - smoother and more uniform. What could I do to repair these? Is it really worth the effort?

4. I'd like to clean the hearth bricks. There are a number of stains which I think are wax/soot/oil of some kind. Suggestions on what to use to clean them? Chemical? Abrasive?


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07-06-2019, 02:43 PM
1. I'd put a 1/2 inch mud bed over the face bricks except for the top row. That way the surface would be very flat. But, sounds like you want to just fill in the mortar joints and lippage. There are several products that will work similar to this.

A wire brush might clean the bricks well enough. I would try that first.

2.You might look into cleaning the bricks and filling the cracks. You will likely need to cut the cracks a little deeper for new grout to bond. A grout stain would work and possibly even help the looks of the bricks. I would experiment with that.

3. Removing bricks may turn into more of a job than you want. But, that's up to you.

4. I would start with household cleaners and go stronger if you need to.

07-07-2019, 01:14 PM
Thanks for the tips Davy.

For the skimming/screeding material I definitely want to keep it as thin as possible. Any recommendation for something that will set up a bit slower than Custom's Skim Coat? Their instructions say "Mix amounts that can be applied in 10 minutes" which isn't long for someone who likes to work slowly.

For cleaning the hearth bricks we've already tried most common household cleaners. We've also tried heating and blotting the stains, which worked to some extent, but still left the bricks stained. Any suggestions for something stronger? Muriatic Acid maybe?

07-07-2019, 01:25 PM
You can use modified thinset to fill those low areas even though it's not designed for doing this. It is slow setting.

Muratic acid isn't recommended even though it might help. The fumes are dangerous and can harm metal surfaces inside your house. It's possible the acid may harm the bricks too, depending how strong you mix it. If you plan to use it, I'd mix it about 15 parts of water to 1 acid and rinse well with water.

I'd try vinegar first.

07-07-2019, 08:29 PM
On those bricks that protrud you could put some relief cuts deep enough to make it flush with the rest of the bricks and then knock the pieces off with a chisel. Then skim everything with thinset.

02-29-2020, 11:04 AM
I removed the wooden mantle from the top of the fireplace the other day and (surprise!) there's an additional 2-3/4" high course of bricks that was hidden inside the mantle on top of the exposed bricks. The problem is that the faces of these (formerly) hidden top bricks are flush with the faces of the course of bricks directly below (those are the bricks you can see in the third photo in post #1). The newly exposed bricks don't continue the "stairstep" pattern that projects outward.

There's no way I can remove the top course of bricks (they're partly embedded into the wall), so the wife would like to continue the stairstep pattern and add an additional course of tile to the faces of the top bricks. That leaves me with the problem of how to add an additional ~1/2" of horizontal depth to the faces of all of these top bricks. In total there's about 8 linear feet of bricks in that top course.

My initial thought would be to cut 2-3/4" strips of 1/2" thick Hardiebacker. Then I'd adhere the strips to the face of the bricks with mortar and let it set. That would create the additional stairstep at the top course and then I'd just tile directly to the Hardiebacker.

Any issues with adhering a strip of hardiebacker to a brick face?

02-29-2020, 11:32 AM
To answer your question, no. Thinset will bond the Hardiboard or cement board to the brick. The problem usually is with the bricks you're sticking to. If they are crooked and not flat then your Hardi will follow it. The Hardiboard must also be cut straight.

02-29-2020, 05:04 PM
The good news is that the newly exposed bricks are very straight. So if I used long strips of Hardibacker (2-3/4" x 5') and I could get it to sit flat and straight against the bricks would that work?

02-29-2020, 07:37 PM
I don't know, might work fine, that's your call. Hardi isn't designed to be used that way and I've never tried it. I would mud it myself (see post 2).