Cement board hearth pad question (previously was "Foolish question")

Once again back to the topic at hand, the goal is to build a particular hearth pad that specifically meets the code requirements of the particular stove the OP has purchased and about to install.

The use of thinset as a bonding agent has been long established and provided the thinset (or any suitable adhesive) will bond to both the plywood and the cement board will determine if it gets used in preference to or in addition to any other method of securing the cement board to the plywood.

Please note the use of the weasel word suitable in the above statement.

The OP is in the process of obtaining the information required to meet code, the pad will get built to meet code.

Every different pellet stove can have different requirements, several Harman folks have found that out (along with a few dealers) after the installation.

Over building sometimes has huge benefits.

SmokeyTheBear said:

The use of thinset as a bonding agent has been long established and provided the thinset (or any suitable adhesive) will bond to both the plywood and the cement board will determine if it gets used in preference to or in addition to any other method of securing the cement board to the plywood.

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The manufacturers of Durock, Hardiebacker and Wonderboard all recommend fastening their product with specific screws or nails. As a commercial construction professional I'm used to dealing with specific installations that require the endorsement of the manufacturer as a back up. Certain things fail in commercial buildings so they need to be installed per manufacturer's recommendation otherwise it is solely the installer's fault. Lots of commercial flooring installers would be out of work if they simply laid down a backer board on thinset mortar and did not use specified screws or nails. There are even nail guns that will fasten cemment board to metal with specific nails. This step is not often overlooked in the construction business.

EDIT:

I looked up the hardieboard web site nand they do recommend the use of thinset mortar under their backerboard so I'm learning something here too. So if you want to be 100% correct with the instal use both thinset under the backerboard and specific fastener's recommended by the manufacturer.

This one's from the manufacturer of hardiebacker:

Attach HardieBacker® cement board to subfloor


Apply a supporting bed of mortar or modified thinset to subfloor using a 1/4" square-notched trowel.

Embed HardieBacker cement board firmly and evenly in the wet mortar.

Use the fastener pattern as a guide. Fasten HardieBacker cement board with specified nails or screws (as listed in "Materials Required") every 8" over the entire surface. Keep fasteners 3/8" from board edges and 2" in from board corners.

Set fastener heads flush with the surface without overdriving.

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From this link:
http://www.jameshardie.com/homeowner/products_backerboard_halfInch.shtml

Manufacturers of Durock and Wonderboard do not say this step is necessary. But they do say make sure the underlayment is level.

nancyp said:

Thanks so much guys. I'll be using mortar under the cement board and hardiebacker screws around the footprint.
This was a very informative thread.

AND I'LL UPLOAD THE PICTURES!!

Nancy

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If you find non-specific information then your stove probably only requires that the surface it's placed on be non-combustible.

In my case all I used was a 26 gauge piece of tin.

I used the special screws made for the hardiboard. They had special heads that were self counter sinking.

nancyp said:

The wood pellet stove is a John Deere Wood Pellet Stove (HR-WPS02) and for all intents and purposes it's REALLY a St. Croix Prescott EXP. It came with the same manual and looks just like it. It also requires the same distances from combustibles. For floor protection it says:

"The stove must be installed on a non-combustible protective pad. May be placed directly on a non-combustible hearth. (68-0486 square) (68-0487 corner). Floor protection is required for the area directly under the stove and extending six (6) inches beyond the front of the stove."

My corner hearth is about 4.5ft x 4.5ft so it certainly extends beyond the front of the stove and it sits about 6inches high, made as I indicated above. I'm feeling pretty confident that it is non-combustible but was kind of curious about the cement board as I have NO experience with it.

Thanks again.

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All you need is a non-combustible surface with integrity suitable for a stove to sit on. A piece of sheet-metal would be adequate in your application. What you are doing is waaaaayyyyyyyy overkill so no need to worry.