Quick floor protection idea

[Badfish740]

Boring meetings at work are a great time to do sketches! So how about this idea for a base/floor protection for my future stove?

- 3/4" OSB subfloor
- Cover 5' x 5' with 1/2" Hardi-Board
- Frame 5' x 5' platform with steel 2x4 studs on 12" centers
- Fill voids between studs with masonry sand to a depth of 2 1/2" (maintain 1" air gap)
- Epoxy (no metal fasteners) 1/2" Hardi-Board to studs
- Face platform with 1/2 bricks

For the wall immediately behind the stove I would install 1/2" Hardi-Board in place of sheetrock for the width of the platform and face with 1/2 brick. Feel free to let me know if this is a rediculous amount of overkill, but if I'm doing new construction myself, I'll only have myself to blame if something goes wrong. Also, none of the materials are terribly expensive, and I'll be doing all but the brickwork myself. Comments?

 

[Highbeam]

The single layer of hardi board above the studs will be flexy. Be sure that the legs of the stove will rest on some structural member and not in a span. I did a similar platform and used durock. The first layer was still flexy and possibly not suitable for tile. The second layer of durock with thinset between and of course screws really made the whole thing stiffer. I'd also rather see you fasten the whole thing together with the proper screws instead of depending on an adhesive.

The air gap in the platform provides lots of R-value, the sand may be actually worse than air.

You are building a very capable hearth pad.

 

[Gunner]

Well I guess it all depends on the stove you are wanting to install....get a Pacific Energy and all you have to do is tile directly on your subfloor :coolsmile: job done.

 

[begreen]

Floor protection varies a great deal between stoves. Some need only a fireproof barrier and some need significant insulation between the stove bottom and the combustible floor. What stove are we talking about here?

So far the plan described sounds like a bit of overkill. No need for the bottom layer of durock and sand, though in some cases an insulation layer of micore may be required. A double layer of durock on the top layer will have more rigidity and support if there is a heavy stove on top. And I would screw it, skip the epoxy.

 

[elkimmeg]

Forget the sand why not fiberglass insulation (Fiberglass insulation gets its insulation value from the air space it creates) I agree plan to add something where the legs would be resting and 2. 1/2 pieces of hardi backer boards

Also the adhesive might tend to get soft if exposed to heat

 

[Badfish740]

The single layer of hardi board above the studs will be flexy. Be sure that the legs of the stove will rest on some structural member and not in a span. I did a similar platform and used durock. The first layer was still flexy and possibly not suitable for tile. The second layer of durock with thinset between and of course screws really made the whole thing stiffer. I'd also rather see you fasten the whole thing together with the proper screws instead of depending on an adhesive.

The air gap in the platform provides lots of R-value, the sand may be actually worse than air.

You are building a very capable hearth pad.

Good point-how about a revision?

- 3/4” OSB subfloor
- Cover 5’ x 5’ with 1/2” Hardi-Board
- Frame 5’ x 5’ platform with steel 2x4 studs on 12” centers
- Leave voids empty for 3 1/2" air gap
- Screw layer of 1/2" Hardi-Board to steel studs
- Apply 3/8" layer of thinset
- Screw second layer of 1/2" Hardi-Board between studs
- Face platform with 1/2 bricks

*EDIT*

So I realize that after seeing a few more posts after composing this one that it is overkill, but Elkimmeg's signature sums it up perfectly for me:

"Better Safe than Sorry"

 

[begreen]

Better, but no need for the bottom layer of HB. What stove are you getting?

 

[Gunner]

Begreen said what I said but beat me to it. Stove model Please

 

[Badfish740]

I think the Dutchwest DW2000 makes the most sense for me. It is a nice looking unit, it should provide a decent amount of supplemental heat for a 1200-1600 SF home, etc... The stove is 27" x 26 1/2" and has a 10" rear wall clearance and of course an 18" front, which I've increased to 12" and 20" respectively for a hearth depth of 60" total. The side clearances are 15", so the 60" width of the hearth is certainly more than enough. Again, the materials are cheap enough and if there's one thing I don't mind overdoing, it's fire protection. Besides, I like the look of the raised hearth as it will be the centerpiece of the living room. Now to see how I can over-engineer the chimney chase!

 

[begreen]

You'll be fine with the amended plan then. While looking at stoves in this range you might want to look at the Quadrafire 3100 or the Englander 13NCL. Both are much cleaner burning stoves and the Englander will cost less.

 

[Dunadan]

I'm no expert, but I just replaced my hearth, and a few thoughts/questions?

1. Why are you laying Hardiboard over the sub-floor and then building over it? The HB offers no structural support (so I've been told) and is mainly used for insulation/good base for laying tile.

2. Again, the HB doesn't offer any structural support, but that's all you're laying down as a base prior to tiling with brick. My hearth only used 1/4" HB, but the stuff is not very strong. Between the 2 layers of HB you have 1" of total cement board - but I'd still guess if you were to stand on, you'd break right through it. Others may have more experience than I do on this, I just know the stuff doesn't have very much surface strength. Just standing on it seemed to me would cave it in.

3. I'm not sure you can go 3/8" with thinset. The Flexbond I used was good for up to 1/4". Anything more and they suggested using medium bed mortar.

4. Depending how much insulation you need below your stove, I'd think you'd be better to skip the HB over the plywood (adding another sheet of 1/2" plywood if you need the height), use the air gap as your lowest layer of insulation, and if you still need additional layers of insulation to hit your R-value, add something like Micore, sheet metal, or just add another layer of HB in place of an extra layer of plywood over your OSB.

Sean

 

[webbie]

You can definitely screw the HB to the studs - that amount of surface are could never transfer enough heat to do anything!

So keep it simple - maybe just the steel studs, 2 sheets of HB screwed down, and then the brick......PLENTY for the vast majority of stoves.

 

[Gooserider]

I feel a bit more comfortable w/ Durock than I do w/ Hardiebacker, especially on the hearth surface. I know that Elk likes HB, but Hardie gets real indecisive when you call and ask them about using the product on a hearth. (They do say it's OK for NFPA protection walls) They say that they consider HB to be to good at heat transfer as opposed to insulation, so they don't reccomend it for hearths.

Durock very specifically says they are accepted for use as hearth protection material, and has a release document detailing their reccomended procedures for using it in the application.

The difference is not big, but Durock also has a higher R-value per 1/2" layer - Durock is R-0.26, (per their spec sheets) and HB is R-0.19 (per Hardie tech support - they don't give a spec for 1/2" on their website)

I would also reduce the thickness of the thinset layer - Durock says to use a 1/4" square NOTCHED trowel for bonding layers to the subfloor or between layers. They reccomended a LATEX FORTIFIED thinset - such as Flexbond. Over on the John Bridge tile forum, I've been told that the layer thickness for thinset will typically be about 1/2 the trowel notch dimension, though it's a little bit variable. As a side note, they also said the purpose of the thinset between the layers is not so much to glue them together as it is to ensure a uniformly supportive surface. The way it was put is that the screws hold the board down, the thinset holds it UP!

Gooserider