Newbie hearth pad questions

[a_saccharum]

Hi everyone,

We're getting our first woodstove and would like to try making the hearth pad. I have some info from the installers, and have been doing some research, but thought I would ask here to see if I could get a better idea of what we need to do. Stove is a Lopi Liberty (on legs, corner installation). It is being installed in a finished basement area, carpeting over cement slab. We have flagstone (well, basically flat rocks that we packed in from the back 40) that we'd like to use.

The installer told me to attach Duroc on top of a sheet of plywood (1/2 or 3/4 inch) and add 2x4s or other lumber to make sides. Then fill with type S mortar and lay stones inside. He said that it does not need to be attached to the floor and the carpet shouldn't need to be removed (pending final approval from the code officer, of course).

My questions:

What is the purpose of the plywood? It seems that it would be safer not to add a combustible material there. Is it needed to secure the sides, or can I screw them right into the Duroc? I don't know the R-value needed offhand (will be asking the installers, or maybe one of you helpful folks knows?) but if I removed the carpet and just had the Duroc, mortar and stone on the concrete slab then there would be no combustibles under the stove at all.

How do I go about laying the stones? I'm assuming that I level the mortar and just set them in as desired, smoothing out the mortar in between stones as needed. Do I need to "shim" under stones that are thinner, or not level on the bottom, or is the wet mortar viscous enough to support them? How much time will I have to manipulate them before the mortar dries?

Thanks,
Sarah

 

[begreen]

Welcome Sarah. If this is on a concrete slab, you don't need anything as long as the carpet and pad are removed. If you want to build a nice stone hearth, I'd mortar it directly on the slab. The mortar will act like a bedding, it is mixed thick, like peanut butter and will help level things out.

There are several web sites that have tips for this. It is similar to laying stone tile on a patio. Here's an example:
http://www.ehow.com/how_7417616_lay-natural-stone-concrete-patio.html

A great forum for tile and stone advice is john bridge:
http://www.johnbridge.com/messages/topic/4053-1.html

 

[Creature]

Hi Sarah,

I am also carpet on slab and wanted to lay flagstone. I just pulled the carpet up and cemented the flagstone in place. The only problem I had was leveling, since it is a natural stone you can never get it exactly level, but a little work with the leveling feet on my stove and I'm good to go. I do have to say: check with the stove manufacurer and local building codes, but for my area and stove this was fine.

If I can get at my home server I'll post a picture ....

 

[Creature]

Took a little work getting it off the server, but here is how mine turned out ...

 

[ansehnlich1]

If your carpet is not glued down that would be a good thing. I'd loosen the carpet from the region of the intended hearth, if possible, and pull the carpet back. Otherwise I'd cut out the area needed to lay the stone. I'd be certain to cut the minimum beyond the needed hearth size so as to be able to re-install the carpet against the stonework when finished. In fact, the carpet could be cut so as it could be 'rolled' back on three sides, leaving plenty to re-install upon completion of the hearth, only area of concern being the corners of the hearth extension, make certain not to cut beyond each of those two corners.

Indeed, I'd start with a cleaned concrete slab, no glue or carpet backing residue, being certain the concrete slab is indeed just that, and no combustibles are present underneath the proposed location of the hearth.

I'd dry lay the stone pattern first, then move that pattern off to the side, then work in small sections, laying the stone on a bed of thinset thick enough to accomodate most of the height variations in the stone itself. Use a level to make certain the stone is seated in the mortar bed relatively level across the hearth as you proceed. Push the stone downward firmly into the mortar bed, moving it slightly back and forth, to ensure it is seated in the mortar bed.

Allow the thing to set up and then re-install the carpet up agains the stone.

Be aware of hearth size recommendations. You could even run a 2 or 3 inch oak or some other such trim around the stonework to finish it off.

Also, be aware of chimney considerations, where the stove pipe is going to go, in particular if it is to go straight up you want to consider ceiling joists/roof trusses. If you are going through a wall/thimble pass through then center on that.

Take pics and others will post and help you out

 

[a_saccharum]

Thanks, everyone, for your helpful responses! I'm a little uncomfortable mortaring directly on the slab because I've never done anything like this before and don't want to end up with something ugly/not precisely to spec that is difficult to get rid of. I assume I can do the same thing on a sheet of Duroc that's cut to shape and put trim around the edge, as was mentioned? The pic that Creature posted is pretty close to what we have in mind.

 

[tsc003]

If you build a platform you could always move, change it later. I built a 2x4 corner platform with 3/4" plywood, layer of steel sheeting, and two layers of duroc. I used slate tile. Just be sure to measure the stove legs so they don't end up on a seem and make sure that the tile/stone that each leg sits on are level with each other. Some adjustment may be possible on legs themselves but not sure with that stove.

 

[ansehnlich1]

Thanks, everyone, for your helpful responses! I'm a little uncomfortable mortaring directly on the slab because I've never done anything like this before and don't want to end up with something ugly/not precisely to spec that is difficult to get rid of. I assume I can do the same thing on a sheet of Duroc that's cut to shape and put trim around the edge, as was mentioned? The pic that Creature posted is pretty close to what we have in mind.

Well, in that case, back to one of your original questions, the purpose of the plywood would likely be to establish increased strength and rigidity.....strength to hold the weight of a 400+ pound stove and rigidity to ensure the stonework is solid and does not crack as a result of flexing.

And yes, you an build a framework of 2x4's, either metal or wood, then plywood atop for strength, then the durock for the stone installation.

Make sure you KNOW the hearth requirements before building it....meaning specifically, does your stove have an "r" value requirement for the hearth pad.

 

[Creature]

Thanks, everyone, for your helpful responses! I'm a little uncomfortable mortaring directly on the slab because I've never done anything like this before and don't want to end up with something ugly/not precisely to spec that is difficult to get rid of. I assume I can do the same thing on a sheet of Duroc that's cut to shape and put trim around the edge, as was mentioned? The pic that Creature posted is pretty close to what we have in mind.

Sarah.

I highly recommend going to a garden supply yard for the flagstone, it's way cheaper. The slate flagstone I'm using is local to this province. It was a bit of work with a hammer and cold chisel to even the pieces out so they weren't so difficult to mortar and level. Probably a few hours. Then I laid them dry to find a pattern I could live with. I did pay someone to mortar them in (modified thinset if your going to adhere it to the slab), and grout (sanded, of course) the voids, since I've never done it before and didn't want to leave that to a noob (me). He did shim them in places underneath while the mortar set so the tops stayed as level a possible. I must have put down 7 or 8 layers of sealant on them too.

Good luck with your hearth pad!