building concrete form to extend existing hearth

[oshen]

I am having a regency hearth heater woodstove installed and need to extend the existing fireplace hearth.
The current brick hearth is 16"x5' and 1/2" above the adjacent wood floor so I want to pour concrete (flexibond) to make a 3x5' hearth that is all level. How do I make a form for the concrete and what do I put in the existing fireplace opening to contain the concrete at the edge. I assume I use 2x4's? What do I put at floor level to keep concrete from seeping under the form? I was told the concrete will automatically settle to level. I intend to put durock board overtop and then tile? Any advice is much appreciated!!

 

[fossil]

I think I'd look at cutting the wood floor down to the underlying plywood subfloor and pulling out the finish flooring from the area of the hearth extension, then working up from there. You can probably build something by layering non-combustible materials and not get into pouring anything at all. Trim out the exposed edges of the sandwich with more of the same tile as you're putting on top. Pay close attention to the R-value requirements and build accordingly. There have been many discussions on here about doing the job in a number of different ways. Rick

 

[oshen]

Thanks for the quick post but I don't have the tools to cut out the wood floor and I'd have to tear out the existing brick hearth too. Just putting down concrete sounded much easier and would level itself nicely. I was just going to put wood trim around the edges after tiling is done. The fireplace store said the concrete, and 1/2" durock and tile would be plenty of non-combustible and not to get to concerned with the r value in the manual as that is really overkill and not necessary.

 

[fossil]

The people in the stove store are not the Authority Having Jurisdiction. If you have any question about whether or not it's OK for you to deviate from the stove manufacturer's stated requirement, you really need to run that past the local building safety inspector or the Fire Marshall, or whoever it might be where you live. Welcome to the forum! Rick

 

[oshen]

Thanks Rick, but they are a located in my town and do many jobs in our town and assured me that is acceptable. I will make sure to confirm with the building inspector. I just need suggestions on how to pour the hearth. Thank-you!

 

[fossil]

Okey Dokey, if you've got all the stove-specific details worked out to your satisfaction, and all you're looking for are tips on pouring a liquid underlayment, then you oughta put a post up over on the "DIY and General non-hearth advice" forum here on Hearth.com. All sorts of things like that are discussed ad naseum over there. Perhaps one of the moderators will move this thread over there for you. Good luck with it. Rick

 

[kd460]

If I understand your description correctly, why not just add the extra by using durock? But I question the k factor (r value). Once again, if I understand you correctly, you want to pour a 1/2 inch of concrete over a wood floor? Seems like durock would be easier, BUT, it is not enough non combustable material to meet code. Trust me, I had a 1/2 inch of durock, a 1/2 inch of stone, and I could feel the underside of the floor from the basement. It was not enough. Now I have 4 layers of durock laminated together with 1/8 inch (each layer) of thinset and then 3/4 inch stone on top of that. Now it is enough.

I would add the durock to the width you need, use the durock tape (fiberglass tape per durocks instructions) to join the seam, then add mor full sheets on top of that to get the required k/r factor, then tile or stone it.

Not sure what you mean by "what do I put in the existing fireplace opening to contain the concrete at the edge". I am thinking you are putting concrete on top of your existising hearth that is flush with the fireplace floor (going higher?). If so, I don't understand why or if this is permissable. Not trying to give you a hard time, just trying to understand. KD

 

[oshen]

the problem is the where the existing hearth meets the wood floor in front, the wood floor is tapered to come up flush with the hearth but the hearth sits up about a 1/2" higher then the floor overall (on the sides of the hearth it is an abrupt 1/2 change(give or take a couple 1/8's of an inch). So I can't just butt up the durock and have a level surface. The question about the fireplace opening is just that if I am pouring cement I need to have a form edge there, not that I will be raising the height at that point(not with cement) there will just be a thin layer of cement there which will basically covering any non-levels area between bricks where they are grouted and where the bricks themselves may be out of level by a bit. In the end the hearth will sit higher that the fireplace bottom(because of layer of durock and tile) but the hearth stove sits on the hearth it is not an insert so I don't know if that is a problem or why it wouldn't be allowed. It will have a surround piece around it so you won't be able to see in the fireplace. Thanks for you input!

P.S. Rick, just to make it clear the area I am extending is just the additional clearance I need in front of the stove plus a few inches extra. The existing hearth brick should already be to code as far a r value which the stove will sit on. Do I still need to have to worry about r value for the additional clearance in front of the stove.

 

[oshen]

I posted to dyi board, I hope someone can give me some advice

 

[Hogwildz]

Wood 2"x's are used to make concrete forms, but your adding alot of weight in that area with the concrete.
Best make sure its supported well underneath the floor joists etc there, or you may be doing more than adding concrete for a hearth.

 

[backpack09]

And if you are looking to "self level" with concrete you are going to need a very wet mix, which will be very messy. You will atleast need to screed the surface to help get the bubbles out.

 

[oshen]

the self leveling concrete gets bubbles in it? And how do I screed?