cracked hearth extension

[walkingbaboon]

We have an older (1917) masonry fireplace that had a ceramic tile hearth extension that was flush with our hardwood floors. The hearth extension had a few large cracks, some of the tiles were missing, and we want to install a wood-burning insert.

So now we're in the process of removing the tiles (slowly) an have found that the cement pad underlying the hearth extension has many more cracks in it. I'm assuming that our house is not going to settle much so we shouldn't see any new crack formation, but I'm wondering whether I need to fix this concrete base before we put down new tile and install the insert? If we do need to fix it I'm hoping for some advice about how. I would prefer not to rip out the entire concrete pad (because it's too much work), but I'd also like for our new tiles to be flush with the hardwood again (so any repair, and mortar to put the tiles in place would have to be quite thin).

I'm grateful for any advice.
With thanks,

John

 

[KaptJaq]

Pictures always help around here...

Do you know which insert you plan to install? Was the Vermont Castings 2461 located in this fireplace?

What is under the cement pad? Wood support beams? Earth?

To know how to repair the hearth first you need to know the hearth requirements of the insert. Some just need ember protection, others need thermal resistance ("R" factor). My insert needed an R factor of 1.49. Even though the existing hearth was intact it was not thick enough to provide the protection required by the insert. I ended up taking out the layer of tiles, building up the hearth with mineral fiber board and cement board and then putting new tiles down.

Provide a little more information and I am sure the people around here will come up with some suggestions...

KaptJaq

 

[begreen]

Sounds like at some point someone might have been splitting wood or dropping logs on the hearth. To fix, I think I would first make sure that the concrete hearth is well supported underneath. Then I would clean out the cracks, spray dampen the areas needing repair, then force mortar down into the cracks. Let cure for at least a week, then proceed with latex modified thinset and new tile. If you can post a picture of the current state of the hearth we may be able to spot other issues.

 

[walkingbaboon]

I'm so grateful to get your advice! We're not yet through removing the old brown tile. It does look like the hearth extension has had a few impacts of some sort. Some of the cracks extend onto the floor of the hearth as well. In answer to the KaptJaq: The cement pad is more than 2"thick. I suspect it's much more than that, The one piece of the pad that I could pull up to check went down that far, and there was more cement below. The hearth is on the main floor of our house, and there is a finished part of the basement below. We have standard (for 1917) wooden floor joists that run parallel to the front of the hearth opening. I imagine there's some sort of wood base below the concrete but haven't wanted to open my drywalled basement ceiling to find out for sure.

The Vermont Castings stove is located in our cabin. We're looking for some nice toasty warm wood-heat here at home.

As for the inserts that we're considering, we're a bit limited by the depth of the existing fireplace (15" deep at 24" above the ground). We'd been thinking about the Lopi Republic 1750, as well as the Drolet 1400 or 1800. We're open to other recommendations too (but we've been looking at other threads for this info). For all of the inserts we're going to have to extend the extension a few more inches away from the hearth opening. We're not going to be pouring concrete for that, but will put down some cement board.

How thick does this base need to be at the end of the hearth that is furthest from the fire? Presumably it wouldn't need the same R value as the part that is directly in contact with the stove?

Are there any issues with stone or marble rather than tile for a replacement surface for the hearth extension?

Any suggestions for removing the last bits of tile without causing more damage?

With thanks,

Walkingbaboon

 

[fishingpol]

I had a similar situation here too, but not as much cracking. You may want to try to stand on the area of tile/concrete and see if there is much deflection in the floor. Looking at the number of cracks, there does not seem to be a lot of integrity there and I would think that any repair may crack again. With the weight of the insert getting moved in and an installer or two standing on the pad, it may cause cracking again.

To get the reset of the tiles off I would probably rent a smaller Hilti demolition hammer with a wide scaler tip to remove the tile. They work very well for this, but a few small pieces of concrete may get popped up. Those can be filled in later.

I did remove the all the concrete and tiles and glad I did. It is rock solid now and finished with vermont slate tiles. By carefully measuring, the tiles are flush with the floor.

I can't offer any advice on the insert, but ripping stuff out, I can.

 

[KaptJaq]

How thick does this base need to be at the end of the hearth that is furthest from the fire? Presumably it wouldn't need the same R value as the part that is directly in contact with the stove?

Most manuals for in-production inserts can be found online. Take a look at them to see what the hearth requirements are.

When the secondaries are going in my insert the tiles 10" in front of the stove are hotter than the tiles right near the stove. I have measured those tiles at over 160 degrees F. The radiant heat from the secondary burn tubes at the top of the stove passes through the viewing window and heats the tiles.

My poured concrete hearth was 11" thick right near the stove but only 6" thick 18" out from the stove. As mentioned above I had to remove the tiles and build up with micor and cement board to attain the proper R value.

Since your concrete is so badly cracked you may be able to remove the entire piece and rebuild with layers, starting from the bottom,of 3/4" plywood, sheet metal, cement board, mineral fiber board, cement board, then tiles. Picking the materials to match the R requirement of your insert.

KaptJaq