Planning a hearth pad, got a question

[wendell]

For my Oslo to be, I am in the planning stages for my hearth pad. I just put down Pergo flooring in the room the stove is going in just this past spring so not too interested in tearing some of it out. Plus, if we ever sell the house and the new owner doesn't want a stove they can tear it out and have a floor underneath.

So anyway, my plan is to buy some 3/4" OSB or plywood, cut it to shape and just lay it on the floor, put down some Hardibacker, thinset and tile. I only need ember protection.

Will it be OK to glue the hardibacker to the OSB? They don't make screws short enough so that I won't go down into the floor.

There will need to be seam in both the plywood and the hardibacker. Will putting them in different places be enough or am I guaranteeing myself some cracked tiles down the road? If so, how I can I secure everything without adding a lot more weight and thickness. I am going to be also building a pedestal to put the stove on to make loading and viewing better so maybe if the seam in the plywood will be mostly underneath the pedestal?

Anything else I need to take into account?

 

[firefighterjake]

A few suggestions . . . but take them for what they're worth . . . offered freely . . . and this is from a guy who believes in over-building and erring on the side of caution . . . or in this case erring on the side of over-building so I don't have to deal with cracked tiles/stone.

I would go with at least two layers of 1/2 inch or more of plywood . . . my reasoning . . . a firmer base will result in less flex which should in theory result in a reduced chance of the tile cracking. Adding a second layer of wood shouldn't add much weight or cost to the project.

I would go with Wonderboard vs. Hardiboard . . . yes, only ember-protection is needed, but why not go with a product that is listed and offers some R value anyways . . . think of it as extra protection . . . and you would be paying around the same price regardless of which product you used.

I would go with the screws . . . and find some that are smaller . . . or if you opt for two layers of plywood you should be OK with the longer screws . . . the temps don't get that high underneath the stove, but they can get pretty warm in front of the hearth . . . rather than risking the glue off-gassing or simply not holding up and allowing movement I would go with the sure thing -- screws. Then again . . . I think I screwed and mortared the Durock to the plywood base.

Seams . . . I staggered mine . . . again . . . thinking it would help with less movement.

Again . . . take the advice for what it's worth . . . I'm pretty cautious . . . and lazy . . . I hate doing the same job twice.

 

[summit]

I would not do glue underneath a stove. From top to bottom: tile, thinset mortar, 1/2" hardibacker (it holds together better than regular cement board), 3/4" advantech, 1 x 4 strapping 12" on center. gives an airspace underneath (when none is needed, big + 4u: it will help to dissuade discoloring of the existing floor underneath), and allow you to run 1 3/4" screws (without being terribly accurate to hit, cause 4" strapping is 3.5" across) into it all to hold it all without hitting your nice floor underneath.

 

[wendell]

Well, I learned something today. I talked to a friend who is in construction and he told me my plan would probably end in disaster. As you may be aware, Pergo is a floating floor and thus, must be allowed to float. (Duh!!) Anyway, he told me that even with taking lots of precautions, cracking would still be a possibility but more of a problem is that since the weight of the hearth pad and the stove would pin the floating floor in one spot, having some of the joints in other parts of the floor pull apart is quite likely..

So, I will now be cutting out the floor and putting in the hearth pad directly on to the sub floor.

 

[summit]

problem solved!