Hearth Pad Hardieboard Thickness

[jpvonhemel]

I am building a hearth pad for the P68 harman. I plan to use 3/4 inch plywood on top of 2 x 4 frame. 3/4 inch plywood on that, then 1/2 inch hardieboard on top. Then I plan to place porcelain tile on top of the hardie board.

Considering they spec only a 20 gauge steel pad, will this layering be sufficient?

Thanks,

Jerold

 

[SmokeyTheBear]

I am building a hearth pad for the P68 harman. I plan to use 3/4 inch plywood on top of 2 x 4 frame. 3/4 inch plywood on that, then 1/2 inch hardieboard on top. Then I plan to place porcelain tile on top of the hardie board.

Considering they spec only a 20 gauge steel pad, will this layering be sufficient?

Thanks,

Jerold

Make certain that you only have to provide ember protection for that stove because that is what the 20 gauge steel pad is, a number of Harman stoves require heat protection as well these days, there were changes due to finding evidence of prolonged heat damage under some of the stoves with only ember protection.

If ember protection is still the requirement then what you describe is fine.

ETC: gauge number

 

[jpvonhemel]

Smokey,

Thank you for replying. I want to be certain that the pad I build is not going to come back and bite me on the ass down the road. I have an opportunity to do it correctly now, but the manual is not much help. The install manual for the Harmon P68 does not mention an r-value, just minimum floor protector material is 20 gauge sheet metal. That sounds like ember protection like you said. Considering placing two layers of hardiebacker on top of the 3/4 inch plywood for a total of 1 inch of non-combustable board before the tile.

Here is what the Harmon P68 manual says as of a few weeks ago.

Place the stove on a noncombustible type floor or floor
protector that extends a minimum of 6 inches (152mm) to the 9"(228mm)-
front of the load door opening, 6 inches (152mm) to the sides of the door opening, and 6 inches to the rear. Floor protection must also extend 2 inches (51mm) beyond each side of any horizontal flue pipe. The minimum floor protector material is 20 gauge sheet metal. Other floor protector materials are ceramic tile, stone, brick, etc.
13"(330mm)
Place the stove away from combustible walls at least as far
as shown in Figures 3, 4, and 5. Please note the difference in
side wall clearance with and without side shields. 13"(330mm) Without Side Shields
Note that the clearances shown are minimum for safety but do not leave much room for access when cleaning or servicing. Please take this into account when placing the stove.

Jerold

 

[SmokeyTheBear]

Looks like you are all set then.

 

[nporter1]

I am building a hearth pad for the P68 harman. I plan to use 3/4 inch plywood on top of 2 x 4 frame. 3/4 inch plywood on that, then 1/2 inch hardieboard on top. Then I plan to place porcelain tile on top of the hardie board.

Considering they spec only a 20 gauge steel pad, will this layering be sufficient?

Thanks,

Jerold

This is very similar to the hearth I built for my John Deer stove. I also used hardieboard for it. The distances from front and sides of stove were the same as yours and there was no "R" factor indicated in manual either. The code guy hardly looked at it but the install guys thought it was great.

My original thread question was here:
https://www.hearth.com/econtent/index.php/forums/viewthread/82127/

To see finished product:
https://www.hearth.com/econtent/index.php/forums/viewthread/84813/

Everyone was VERY helpful. (esp. SmokeyTheBear!)
Couldn't have done it without the input of this forum!
Nancy

 

[bcb1]

When I did mine, it was even simpler. Just 3/4" industrial grade particleboard - which won't warp like plywood, then 1/4" ceramic backer board over that, then ceramic tile on top. I finished it off with a nice solid oak edging at the sides. Cost me about $65 in materials and I've been using it since 2004.

The dealer wanted $275 for their hearth pads, and I like the look of mine much better than anything they had to offer.

 

[jpvonhemel]

Thanks for the help. I went with the 3/4 inch plywood with 1/2 inch hardie backer on top. The tile is laid out and only needed about 5 cut pieces. I'll put up some pics when I get home.

Jerold

 

[bcb1]

Good luck. My stove hearth board was my first ceramic tile project ever and it came out great. My only mistake was buying one of those cheap tile cutters at Lowes, I could never get the thing to make a perfect cut. Not wanting to spend $109 on a tile saw for one project, I just marked all the tiles that I needed cut, took them to Lowes and they cut them for .25 cents each. Well worth the couple bucks to have them cut the tiles for me.

 

[PoolGuyinCT]

i dont believe tile over wood rates as a non combustable substrate.
the thickness of the cbu / hardi is of no consequence. cbu is only used to decouple the tile install from the wood substrate. cbu adds no strength to the build, and is the weakest material in the equation. so the stiffness of the lumber work will determine a failed or successful install.


and btw, http://www.johnbridge.com/vbulletin/deflecto.pl

yes i am a trowel, mortar slingin geek.

ray