building hearth pad on uneven floor

mmckeon · Jan 12, 2012

I've spent a good bit of time reading through the posts on building hearth pad and have found them to be very helpful. I haven't been able to find the answer to this question so I figured I'd take the next step and post it.

I had a contractor install my stove (Napoleon 1100) - he was supposed to come back to build and install a hearth pad but hasn't (despite promising to do so a few times). So my plan now is to build the hearth pad myself in the same room as the stove, and to have some volunteers help to lift the stove so I can slide the hearth pad under it (as the contractor was going to do).

Because the hearth pad will extend past a walkway in the house I'm hoping to make it as thin as possible. I also want to preserve the hard wood floors so the hearth pad will go on top of the existing flooring. I'm concerned about the tile cracking because the floor in the spot isn't quite even (it's an old house) - though mostly I think it's slanted rather than uneven. I'm guessing that the advice to have tiles on 1/2 inch cement board won't be enough support in this case? Would it be better then to have plywood or a second layer of cement board underneath? Someone even suggested using self leveler to me but I'm not sure how that could be worked in without damaging the floor and if it would even be necessary. I've had someone else suggest that if thinness was so important that I could use fire resistant laminate flooring right over my hard wood and that that could be my fire barrier.

Any thoughts or advice would be a help! My insurance company is looking for the installation questionnaire and photos for early next week so I'm kind running against the clock.

thanks!
Margaret

begreen · Jan 12, 2012

Have you called the dealer to find out why the delay? Perhaps he spotted something about the floor that concerns him.

It will be important to know whether the floor is uneven in this area or just slanted. The stove be on solid footing. If the floor is just slanted then a stock floor protector may work. If it is uneven, then the question is how bad? I would have a carpenter check it out with an 8ft, straight edge or long level first. He will determine if the floor is just tilting or crowned, etc. and should be able to lay down some shim stock to create a level surface on which to put the pad. The shim stock might just be some cut pieces of sheet metal if the problem is small.

If you decide to build one then I would have the surface shimmed to level, then put down a layer of plywood, cement board and tile. But do note that the manual is bad here and only specifies the stove must be installed "on an approved non-combustible hearth pad." Check with your insurance company in advance to be sure that they will accept a home-made hearth.

nate379 · Jan 12, 2012

I would pull the stove and tile the hearth pad in place. If you try to build it off site and carry it in you will probably crack tiles or grout... plus it will be HEAVY. I built mine with 2 layers of 3/4" plywood, then 1/2" concrete board on top. It's in a corner and around 5ft by 5ft. I don't know the weight, but it was a real chore getting it from the garage to the house by myself. Had I tried to do that with the tiles on it as well, no freaking way without another person or even 2.

mmckeon · Jan 12, 2012

BeGreen said:
Have you called the dealer to find out why the delay? Perhaps he spotted something about the floor that concerns him.

It will be important to know whether the floor is uneven in this area or just slanted. The stove be on solid footing. If the floor is just slanted then a stock floor protector may work. If it is uneven, then the question is how bad? I would have a carpenter check it out with an 8ft, straight edge or long level first. He will determine if the floor is just tilting or crowned, etc. and should be able to lay down some shim stock to create a level surface on which to put the pad. The shim stock might just be some cut pieces of sheet metal if the problem is small.

If you decide to build one then I would have the surface shimmed to level, then put down a layer of plywood, cement board and tile. But do note that the manual is bad here and only specifies the stove must be installed "on an approved non-combustible hearth pad." Check with your insurance company in advance to be sure that they will accept a home-made hearth.

My understanding is that the contractor is busy now with snowclearing instead. He was going to put the tiles directly on plywood so my efforts are likely to be an improvement of his effort as they'll bond better to the cement board.

Thanks for your responses!

The floor doesn't have great slope - in any one direction in the corner the bubble on the spirit level almost reaches but doesn't extend past the line marker. The stove itself is installed and has a gentle slope to it from the corner forward but is on solid footing without any movement at all.

I don't have experience with tiling. How forgiving are the tiles on a hearth pad with only 1/2 cement board as backing? Or with cement board and plywood? What would be the minimum thickness of plywood that would be adequate in this case?

I was planing to build the hearth pad in the same room as the stove and slide it under but perhaps it'll be important to remove the stove and build the pad in place to be able to assess if shims are needed.... Does the stove need to be totally level or is it mostly important that it is secure on its footings?

HollowHill · Jan 12, 2012

I'm no expert in this area, but I do have an old house and just had a hearth laid by my contractor. The floor was off by an 1/8" or so from side to side and to make matters worse, this hearth was going over a previous hearth and extending over the floor in front. The previous hearth, stone, was level, but the floor was not. What he did was apply the new hearth (durock next gen, 1/2") directly over the stone and floor, levelling with thinset underneath the durock. Once he got that level, then he applied the tiles into another layer of thinset on top of the durock.

begreen · Jan 12, 2012

mmckeon said:
BeGreen said:

Have you called the dealer to find out why the delay? Perhaps he spotted something about the floor that concerns him.

It will be important to know whether the floor is uneven in this area or just slanted. The stove be on solid footing. If the floor is just slanted then a stock floor protector may work. If it is uneven, then the question is how bad? I would have a carpenter check it out with an 8ft, straight edge or long level first. He will determine if the floor is just tilting or crowned, etc. and should be able to lay down some shim stock to create a level surface on which to put the pad. The shim stock might just be some cut pieces of sheet metal if the problem is small.

If you decide to build one then I would have the surface shimmed to level, then put down a layer of plywood, cement board and tile. But do note that the manual is bad here and only specifies the stove must be installed "on an approved non-combustible hearth pad." Check with your insurance company in advance to be sure that they will accept a home-made hearth.

Click to expand...

My understanding is that the contractor is busy now with snowclearing instead. He was going to put the tiles directly on plywood so my efforts are likely to be an improvement of his effort as they'll bond better to the cement board.

Thanks for your responses!

The floor doesn't have great slope - in any one direction in the corner the bubble on the spirit level almost reaches but doesn't extend past the line marker. The stove itself is installed and has a gentle slope to it from the corner forward but is on solid footing without any movement at all.

I don't have experience with tiling. How forgiving are the tiles on a hearth pad with only 1/2 cement board as backing? Or with cement board and plywood? What would be the minimum thickness of plywood that would be adequate in this case?

I was planing to build the hearth pad in the same room as the stove and slide it under but perhaps it'll be important to remove the stove and build the pad in place to be able to assess if shims are needed.... Does the stove need to be totally level or is it mostly important that it is secure on its footings?

Let me be sure I understand the current scenario. Are you saying that the stove is installed, sitting on a wood floor? Is there any kind of hearth protection right now?

You are definitely correct about the durock being a much better substrate for the tile. I appreciate your not wanting to damage the underlying floor. If it is a slight continuous slope of say less than 1/8" per foot, then your plan should work. You might even be able to put down the 3/4" plywood, then a layer of thinset that is leveled, then the durock?

begreen · Jan 12, 2012

mmckeon said:
BeGreen said:

Have you called the dealer to find out why the delay? Perhaps he spotted something about the floor that concerns him.

It will be important to know whether the floor is uneven in this area or just slanted. The stove be on solid footing. If the floor is just slanted then a stock floor protector may work. If it is uneven, then the question is how bad? I would have a carpenter check it out with an 8ft, straight edge or long level first. He will determine if the floor is just tilting or crowned, etc. and should be able to lay down some shim stock to create a level surface on which to put the pad. The shim stock might just be some cut pieces of sheet metal if the problem is small.

If you decide to build one then I would have the surface shimmed to level, then put down a layer of plywood, cement board and tile. But do note that the manual is bad here and only specifies the stove must be installed "on an approved non-combustible hearth pad." Check with your insurance company in advance to be sure that they will accept a home-made hearth.

Click to expand...

My understanding is that the contractor is busy now with snowclearing instead. He was going to put the tiles directly on plywood so my efforts are likely to be an improvement of his effort as they'll bond better to the cement board.

Thanks for your responses!

The floor doesn't have great slope - in any one direction in the corner the bubble on the spirit level almost reaches but doesn't extend past the line marker. The stove itself is installed and has a gentle slope to it from the corner forward but is on solid footing without any movement at all.

I don't have experience with tiling. How forgiving are the tiles on a hearth pad with only 1/2 cement board as backing? Or with cement board and plywood? What would be the minimum thickness of plywood that would be adequate in this case?

I was planing to build the hearth pad in the same room as the stove and slide it under but perhaps it'll be important to remove the stove and build the pad in place to be able to assess if shims are needed.... Does the stove need to be totally level or is it mostly important that it is secure on its footings?

Let me be sure I understand the current scenario. Is the stove installed sitting directly on a wood floor with no protection?

You are definitely correct about the durock being a much better substrate for the tile. I appreciate your not wanting to damage the underlying floor. If it is a slight continuous slope of say less than 1/8" per foot, then your plan should work. You might even be able to put down the 3/4" plywood, then a layer of thinset that is leveled, then the durock?

pyper · Jan 12, 2012

Tape a piece of string down somewhere on your floor and pull it tight. Now you can easily see how flat the floor is. Level really doesn't matter. If your floor is flat, then remove the stove, put down your tile, and put the stove back. I think trying to move tiled backerboard is probably a bad idea, especially since backerboard comes in 2x4 foot sections. You'll have several to get to the size you want, and there's no way it will hold together on it's own, which is probably why your man was going to use plywood -- so he could put it all on a single piece. I don't think that would be a very good solution.

If you just lay the backer on the floor and tile over it, then over time you'll probably find the grout cracking, especially where the joints are near the joints in the backer. If you use really big tiles you can reduce this, especially if you can span the joints.

If you screw the backer to the floor it will work a lot better, even if you just put one screw in each corner.

This is all assuming your stove only requires ember protection. If it has an R-value requirement you won't likely get it with just a layer of tile.

Wade A. · Jan 12, 2012

+1 on Pyper's assessment. I would worry primarily about the uneveness of the floor. A tile and single layer of backer board sandwhich is not as rigid as you might think. If that is merely layed on an uneven surface (i.e., not secured), deflection of the pad and cracking of the tile and/or grout lines is pretty inevitable. If you screw it down tight to the floor first, the backerboard will conform to the high/low spots on the floor and you can then level that out with thinset mortar before you lay the tiles down. Another method is to use floor leveling compound before you put the backer board down, so it will be level, and your mortar bed should be also. Leveling a floor, especially a wooden floor is a pretty exacting skill, so I'd be reluctant to take that on if I were you. (I'm not sure leveling compound is even compatible with a wooden floor either) Even if you don't level the floor first, leveling a mortar bed requires some degree of skill, so be aware of that before you take it on. Laying tile is something most anyone can do fairly well the first time, though, if they read up on it and take their time. A hearth pad is a great entry level project for the first time tile layer.

And yes, you need to verify if your stove requires just ember protection (i.e, a non-combustible pad) or some degree of thermal insulation between it and the combustible floor, measured R value. Depending, those can be very thick indeed.

mmckeon · Jan 13, 2012

I used the string trick and the floor is indeed mostly flat - only a 1/16 variation between floor boards in places if at all.

I do only need ember protection (not any R value). I visited our local flooring supply place here and their installer suggested I might be able to use plywood and then Ditra under the tiles. Because they tiles would be grouted the fire barrier would still be intact. I'm a bit concerned about having a combustible in the hearth right under the tiles.

He also suggested using smaller tiles (even mosaic tiles) as they are easier to conform to a sloped situation (as per in a shower). Does any one have any experience with using these in a hearth pad? Thoughts?

I will take out the stove and build the pad directly in place.

Thanks!

BlankBlankBlank · Jan 13, 2012

I'm a huge fan of tile jobs for hearths. They look very nice, usually. They're earthy, which I think fits well with the warm fire of most any stove. But I was looking around at a stove shop a couple months back. I saw a very nice looking metal hearth pad. It had a rustic, yet, clean look. I was very impressed. It was strong, non-combustible, and just weighty enough. I recommend looking around for one. It would save you a lot of work, especially considering you do not want to damage the floor beneath. Also, a metal pad, at least the one I saw, would deal with the unevenness you speak of. A pre-manufacture pad makes good sense.

begreen · Jan 13, 2012

Is there any protection currently on the floor? If not, the stove is not installed correctly and definitely should not be burning. I don't mean to harp on this, but no good installer would ever do this. Hopefully, this is not the case.

BobUrban · Jan 13, 2012

It would certainly help if you had photos of the stove and floor as it sits right now so that we could see what you are trying to accomplish. At least it would help me? I am better if I can see things.

I used 100+ yr old brick pavers and plan to extend the hearth L and R to complete the wall and go up the walls on both sides to have complete ends. I will also build in short walls extending out from the back wall closer to the stove on both sides to provide wood storage and extend the middle stove section another 10" forward on a curve for the new stove that loads from the front.

I cut down to the subfloor(which I recomend) and used durarock screwed to the floor. Grout on that for the bricks to sit on. If you need more height you could double up the durarock or use plywood under it. Also, grouting the durarock to the floor would be an easy way to level the hearth. Lay the grout out even and use screw tention to pull one side deeper into it than the other when screwing it down.

Here is a pic of what I have so far. Note, it is temporary in regards to a finished product so that I could legally and safely burn this winter with my old school stove. I have more bricks to finish the complete hearth in the spring and a new stove coming(most likely a E-30)

pyper · Jan 13, 2012

mmckeon said:
He also suggested using smaller tiles (even mosaic tiles) as they are easier to conform to a sloped situation (as per in a shower). Does any one have any experience with using these in a hearth pad?

That's not a slope -- that's a compound curve. Slope isn't ever an issue for tile -- you can put them on a wall or ceiling if you want. If you like the look of mosaic it's OK, but with a sub-optimal substate you are more likely to have more problems with smaller tiles -- especially if you have concentrated weight, like a wood stove. With big tiles the weight gets spread out more.

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