Building hearth extension for insert

[Gooserider]

Well determining the thickness of my floor components isn't going to be all that easy. I tried to check along the edges of some of the rooms, but they are either covered by baseboard heat, or multiple moldings.

I checked in the drop ceiling of the basement, and I can see a layer of plywood (the sub-floor?) above the joists (2x10s). I see no planking, but between the joists running down the middle of the floor are some wood cross braces. If there was planking, I'm guessing I would see it looking up through the drop ceiling? I did notice that right underneath what I assume is either the actual firebox or hearth there is a triple 2x10 joist.

The only way I can get any indication of the thickness of the sub-floor vs. hardwood is by measuring the holes I've drilled through the floor to run electronic/computer cables. The thickness of the entire floor looks to be 1.5". Peaking into these holes as best I can with a flashlight, the sub-floor looks to be about 1/2", which would put the hardwood at about 3/4". Does this sound right?

I can just hear my wife if I wind up ruining the hardwood and sub-floor by calculating wrong :bug:

Well, it doesn't sound like the floors that I'm familiar with, but it doesn't sound unreasonable either (Though you seem to be missing 1/4" - .5" plus .75" = 1.25" not 1.5"... I would suspect you might have 3/4" ply in the subfloor. I would say to make your cut on the hardwood floor with the circ saw set at about 7/8" - won't make to much of a groove but would cut the hardwood nicely. If you wanted to get fussier, try drilling with a small hole saw in the area you will be removing, this will give you a "core sample" that will let you see what you have and get some dimensions off it.

However I'm not a house construction guru, you might see if Elk or one of the other "trades guys" might be more specific.

Gooserider

 

[Dunadan]

I meant 1 1/4" - (1/2" sub-floor plus 3/4" hardwood) to my best guess - but it could be some other variation to come to 1 1/4".

I may decide to build the extension up about 3/4" to allow for carpet, in which case I'd be looking at adding about 1 1/2" to what I cut out. Any reason I can't take some of that up with plywood so I don't have to use as much cement board? I assume the tile/stone will be about 1/4" but will know for sure once I pick it out.

Should I allot a thickness factor for the layers of quickset?

 

[nshif]

Usually plywood sub floor is 3/4" T&G;, which would make your flooring 1/2" If your going to build it back up why not just leave the hardwood down? Put the metal down and then the cement board or just the cement board if your not using metal.

 

[jqgs214]

If I recall the durarock comes 3'x5'. should be plenty for 2 layers. If you cut out the hardwood, (say 7/8"-1") mine was really old (80 years)and about 1" thick so the durarock took up the hardwood floor layer and the tile and mastic took up the carpet so its just about flush. My hearth was exactly 5' wide so it worked out perfectly for me.

 

[Dunadan]

Put the metal down and then the cement board or just the cement board if your not using metal.

I thought about this last night but in places my hard wood does not seem level, and in others it tends to have some flex to it.

I was worried that it wouldn't provide as stable of a base as cutting out the hard wood (leveling things as needed with mortar?) and building up with several layers of rigid boarding.

Am I wrong?

 

[jqgs214]

Thats the way I did it and it seems to have worked well for me, I can jump up and down on my tile and there is no flex.

 

[nshif]

Well you could level it out with fixall and screw down the areas that flex. If you feel you need to take it up drill a 1" hole in the area that you are going to take up and you should be able to determine the thickness from there. after its up you can plug the hole in the subfloor with fixall. Once you know the thickness drop cut it whith a circular saw set about 1/8" deeper. Youll still have to chisel out the corners and end cuts.

 

[Gooserider]

I meant 1 1/4" - (1/2" sub-floor plus 3/4" hardwood) to my best guess - but it could be some other variation to come to 1 1/4".

I may decide to build the extension up about 3/4" to allow for carpet, in which case I'd be looking at adding about 1 1/2" to what I cut out. Any reason I can't take some of that up with plywood so I don't have to use as much cement board? I assume the tile/stone will be about 1/4" but will know for sure once I pick it out.

Should I allot a thickness factor for the layers of quickset?

If one layer of Durock meets the R-value requirement, there is no reason you couldn't build back up w/ plywood, but IMHO you are better to use the cement board. Cement board is cheap, less than a lot of plywood last time I checked. It also gives that much more protection, which never hurts, and could be of value if you ever upgraded to a different insert that had more stringent requirements.

As to the thinset layer thickness, I don't know the exact answer, but I would guess not very much, assuming that you aren't trying to build thickness...

I used a 3/16 x 5/32 triangle notch trowel when putting down the layer of thinset to attach the Durock to the subfloor, and will probably be using a 1/4" x 1/4" x 1/4" square notch trowel to attach my slate to the Durock. Since both are essentially giving me 50% coverage of the area, and assuming that: A, the stuff has to go somewhere, and B, that it doesn't shrink significantly, that the approximate thickness of the thinset layer would be about 1/2 the thickness of the notches in the trowel you use...

I believe 1/4" is a pretty good guess for the tile thickness, assuming you aren't going to be using anything strange for tiles - the 1/4" seems to be pretty much of an industry standard from the little that I have seen.

Gooserider

 

[Dunadan]

Thanks all....these forums are great.

Now the hard part...picking my tile :shut:

 

[jqgs214]

OH I never "glued my durorock" I just screwd it to the subfloor. It doesnt move so I think i'm ok

 

[Hogwildz]

I didn't glue my cement board down either, did screw the hell out of it.
Hasn't budged.

 

[Gooserider]

I don't know just how much difference it makes to cement the board down, but it seems to me like it might make things a bit stiffer by filling in any gaps and "laminating" the layers together. I glued and screwed mine, but mostly because the Durock technical literature said to...

If I don't know just what I'm doing, my general rule is to look for the most authoritative source I can find, and follow it's advice unless I have a definite reason not to. This is especially the case if the incremental cost is low compared to the total job. I figure that thinset is cheap.

Gooserider

 

[Dunadan]

So you know what I'm working with. Here's my hearth now.

 

[nshif]

Well its obvious you need some front protection. Frankly I wouldnt burn that stove again untill its installed. Any of the above mentioned ideas will work just get it done before you start burning.

 

[Dunadan]

I don't burn with it as you see it. I have a couple large pieces of 1.5" thick slate that I lay down in front. I just moved them out of the way to take the pic. I'll post pics once I'm done.

 

[elkimmeg]

How complicated or easy do you want to make the hearth? Do you want to match the height and brick work and make it look like it was always there?
Did you know with wire lath an mortar one can lay down bricks in a bed of mortar and pretty much match your hearth? You can also lay tile and match floor height slate,
endless possibilities All of which will reg quire cutting out the oak flooring BTW 3/4" thick

What I would do is lay out the tile pattern with gout spacing on a piece of plywood or even in place in front of the stove. It does not hurt to be a bit larger. I would let full tiles
determine the final size .where no tile would need to be cut. Now that you have the layout size mark it out on the floor on the oak you are going to cut.

Before doing so it is so much easier to make the hearth to match taking out a full width of oak flooring You might be able to adjust the grout spacings and still finish
up on a full with oak flooring You may need to only make the parallel cut in front of the fireplace.

Now for the tip that will ensure a straight cut Like goose said adjust blade height a smiggeon over 3/4" Measure the saw frame to the blade say it is 1.5" set pieces of strapping or straight pieces of pine the distance from the saw frame 1.5" larger and use thes strapping pieces to ensure a straight cut .It also takes the worry out of over cutting.

Excuse me I missed a step You have to nail the straight edges in place 4 penny finish nails will probably do After done a little wood filler and putty the holes.
A small price to pay for the straightest, professional looking ,cut possible.. Good planning usually brings better results If you did not follow or want more info just let me know

This is my real profession carpentry

 

[Dunadan]

Thanks Elk. I believe more information is always better.

I didn't want to build up the extension to the same level as I figured I would have a hard time matching the brick and hearth stone, and since the hearth stone is rough cut on the edges, without a lot of work (assuming I could find a match) I was worried any extension would look "added on". An entirely new hearth was an option, but not financially possible at this time. Also, because we have a 10-month old, and my wife does daycare, we will be surrounding the stove with a Hearth Gate. In order to have enough room inside the gated area to load the stove, we'll need to be able sit right in front of the stove, and a flush to floor (or added carpet) installation would allow for this - where a raised hearth wouldn't.

I plan to layout my tile on the floor to get the spacing - letting the tile determine the size (more or less). I was thinking it might be easier to end on a seem in the hardwood, so I'm glad that you are saying the same. I hadn't thought a single parallel cut might be all I need, so I'll plan to do that first, and see if everything else slides out.

As for making a straight cut, let me repeat back in my own words, as I think I'm clear on what you are saying when you say -

Now for the tip that will ensure a straight cut Like goose said adjust blade height a smiggeon over 3/4” Measure the saw frame to the blade say it is 1.5” set pieces of strapping or straight pieces of pine the distance from the saw frame 1.5” larger and use these strapping pieces to ensure a straight cut .It also takes the worry out of over cutting.

My circular saw has an adjustable base so I can control the depth of my cut. This is what I would set a bit over 3/4" (measuring from bottom of base to edge of saw). I was thinking of then measuring the distance from the edge of the base frame to the blade, nailing a piece of wood this far from where I need to cut, so that I can use it as a guide. So long as I can keep the edge of the base along the guide, I get a straight cut. The only thing that didn't make sense in what you said was that this would help prevent an over cut. I'm not sure how it would do that. Do you propose two straight pieces nailed into place that the saw would go between? That would ensure the saw didn't leave the proper line.

The only other information that would be helpful is whether you had any suggestion on tile color/style. We have a rustic country home and are planning to put in a darker color carpet - not sure what color yet so I can't match it and don't want to wait until we get around to buying it. I was thinking either a dark color tile (like gray) with some browns/purple in it to accent the existing hearth, or a lighter color tile (like the lighter bricks) with the darker brown/purple in it from hearth. Not sure which would look better in the long run, and wife tells me she doesn't care

 

[jqgs214]

Have you been to the tile store yet? You'll gag at the choices and still not find the perfect tile.

 

[elkimmeg]

If you hand is not steady and you wist the saw it could cut on the other side of the line creating an over cut or cutting out too much
using a straight edge guide will prevent this. You also could set up blocks or guides to prevent cutting more behind the saw or in front
After 3 pages of suggestions time to make the operation as easy as possible. I guess that's why I get big bucks ..

my job today is to install the trim that yesterday I custom cut for this job. Using my molder cutter router and bench saw, I custom cut the moldings on this job to
closely match what is existing.. Many of these moldings have been discontinued. The hardest molding to match, was the window side stops. I ended up making them in two pieces

 

[Gooserider]

I just registered on the John Bridge / Tile your world website that seems to be a very good source of tile info - they seem to do for tile what Hearth.com does for wood burning :coolsmile: The explanation that they gave was that the reason to put down thinset under and between hearthpad layers is to fill in any gaps and ensure that the backerboard is 100% supported. As the response I got put it "The screws hold the backerboard down, the thinset holds it UP... Makes sense to me.

Also the question was asked about how much thickness to allow for a layer of thinset. I had guessed at about 50% of the trowel notch size. The response I got was that there were a number of variables such as surface irregularities, the exact angle one holds the trowel at, and so forth, but that my guess was a reasonable one, just don't put bets on it.

Gooserider

 

[Dunadan]

Ok, I think I've decided that if I'm going to go through all the work to build an extension, I might as go all the way and just replace my hearth (which I don't really like). After thinking it through, while it will be a lot more work, I don't think it will add that much cost to my project.

The only question I'm still pondering, is once I remove the hearth, I'm going to need to build something back up to support the portion of my insert that sticks out. Unless removing layers of brick from inside the firebox is an option.

The fireplace firebox is raised about 6" above the floor, so I'd either need to tear out this much "stuff" after which I'd need to probably buy a new surround for my insert and figure out how to reconnect the liner to lower insert, of I need to build up about 6".

I'm thinking something that is slightly larger than the footprint of the insert that extends onto hearth. The rest of the hearth will be built to be flush with future carpet that will be in this room.

Any ideas of the easiest way to build up something under just the front of the fireplace?

I've got lots of idea (i.e. brick, wood framing covered with cement board, cinder block, plywood/cement board layers, etc.) but in a real world I'm not sure what would be best.

The bigger part of this question is what can I cover it with? The rest of my "new" hearth will be ceramic tile, I'm looking to use Mohawk's Riverstone - Cotto tile.

Can I top whatever I build up with tile like this? Or will the weight of my insert break it?

As always, thanks for the help!

 

[Dunadan]

I think I've got my answer. I've been doing so many searches in these forums and over at the John Bridge tile forum (to make sure I understand exactly what I'm getting into, especially on the tile side) that I forgot to re-search on building a hearth here (after deciding to remove my entire hearth).

Once I get the exact measurements for what I need to build up I'll finalize my plans, but based on this thread, I'm thinking either metal or wood studs, topped with tile will work. I'll just need to be a bit careful when putting my insert back in so I don't crack any tile.

 

[Gooserider]

I think I've got my answer. I've been doing so many searches in these forums and over at the John Bridge tile forum (to make sure I understand exactly what I'm getting into, especially on the tile side) that I forgot to re-search on building a hearth here (after deciding to remove my entire hearth).

Once I get the exact measurements for what I need to build up I'll finalize my plans, but based on this thread, I'm thinking either metal or wood studs, topped with tile will work. I'll just need to be a bit careful when putting my insert back in so I don't crack any tile.

Looking at the John Bridge Site, use their "Deflecto" calculator to check, but I'm not sure just a Durock and tile floor would be strong enough. Given the small size you are after, I suspect you might be better off just to stack up some bricks or blocks, cover w/ Durock, and tile over it. Alternatively I would definitely use steel studs as opposed to wood, and be sure to put enough beef on top of them to support the weight.

Gooserider

 

[Dunadan]

Looking at the John Bridge Site, use their “Deflecto” calculator to check, but I’m not sure just a Durock and tile floor would be strong enough. Given the small size you are after, I suspect you might be better off just to stack up some bricks or blocks, cover w/ Durock, and tile over it. Alternatively I would definitely use steel studs as opposed to wood, and be sure to put enough beef on top of them to support the weight.

Gooserider

Hey Goose.

My floor passes the Deflecto test, and below where the platform is going to go it's either solid concrete or plywood over 3 - 2*10s. Once I get my floor built up with plywood and Hardibacker, I'll know exactly how high to make my riser. I'm leaning towards using either brick or some type of cement block, since it will require less construction and tile can go right on the outside. Still have not decide on the top portion yet.

Also, I went with Hardibacker. I was all set to get the Durock at Lowes, but when I was going through trying to find a nice looking sheet, and all were somewhat crumbly on the edges I changed my mind. The HB looked so much nicer sitting in a pile right next to the Durock. All the edges are square, nice stamped layout for drilling, I couldn't resist.

BTW...the Hardibacker site says

"Non-Combustibility
HardieBacker™ cement board is recognized for use in non-combustible construction in NER-405."

Since all I'm looking for is non-combustibility...I couldn't resist.

 

[Dunadan]

Hi all,

The hearth replacement is going well. No pictures at this point, but here is what I've done to date -

- Removed old hearth (not surround), including concrete slab and brick underlayment.
- Cut out hardwood where new hearth will extend.
- Replaced 1/2" sub-floor under old hardwood with new 1/2" plywood, then built up with 3/4" plywood and 1/4" Hardibacker to be slightly above floor.
- Floated a deck of mud (masonry term for 4:1 mixture of sand:cement, though I used Quikrete's Sand/Topping Mix as a shortcut) to fill in the concrete area under old hearth and bring it level with Hardibacker.

I am at the point where I need to build the raised portion of my hearth (to support insert extension).

In the end, all horizontal and vertical surfaces will be covered in 6x6 natural stone slate tiles.