nealtw

Look for screws on each side of the fireplace near the front, they will be black, I would just remove the drywall and see what you have. You can always do something with the size to hide floor problems. You could rebuild the box a little smaller to allow for rock to line up with fireplace, if the fireplace can't be moved out a little.

condoowner

hey guys

so being maybe a bit crazy and adventurous I went ahead and stripped down the drywall. then I noticed the whole thing was shaking and not strong at all... probably the worst framing job ever done.. they nailed everything crooked, they used scrap wood shims to shim the lumbers when not long enough to be nailed to the others, not a single bar was straight and true...

anyways I demolished everything!.. now I have the fireplace insert standing on the concrete floor with next to nothing around it.. on the picture below you will see some leftovers of the wood box but tomorrow they will be gone.

since the fireplace is loose on the floor, and since I will need to build a new box, I have some questions:

should I bolt or screw the fireplace to the concrete floor?

should I use steel or wood frame?

should I glue or screw or nail to the concrete floor?

can I use only backerboard or do I need drywall or plywood underneath?

finally I have never installed backerboard and worked with concrete slabs.. i also have never worked with steel studs..

can you give me advices and how-to??

thanks!!!!

condoowner

so I went ahead and started drilling the concrete to install the concrete screws but after 2 screws I noticed something funny. basically after 1 1/4" while putting pressure on the drill I feel a big relief as if I was going through the concrete slab and into something much softer like wood or an air space..

no sure if it's normal. don't the floors are supposed to be 4" thick in Canada???

I tried inserting a small steel rod into the hole to feel if it's open ended but as far as I can tell it's hard and feels strong.

CallMeVilla

You may have a light weight concrete floated floor. Are you planning on using TAPCON screws?

condoowner

I am using cobratap concrete screws (the blue ones) 3/16"x1 1/4"... is that ok?? See picture.

Also for my personal education, what is a light weight floating floor? They just poured a small layer of concrete over the floor to act as a barrier against fire & noise??? If so whats underneath? Am i gonna drill in a water line or worst the gas line for the fireplace???

Finally when i removed the conctactors concrete nails some of them pulled fairly easy but 2 made a mess and wrecked the concrete around th nail hole. Its what i believe civil engineers call cone failure... how do i screw close to that???

CallMeVilla

Sure, those screws will work. They are comparable to TAPCONs. Here is a video that show a hand poured light weight floor. Sometimes the cement is mixed with foam stuff . . . Strong but light floor found in many applications:


The subfloor will hold the screws but I think your pilot hole should be small, not large. Screw down adequately, to feel, but do not over-drive. Since your new structure is not load bearing, you should be fine.

Dos this help?

condoowner

Very much so!! But what about the craters left by the old nails? Can I drill just beside where its still flat? Any chance of having too many holes in the same area and having cracks in the future?

Ill finish drilling and hope I wont hit anything in the subfloor like pipes, wires, gas line.. ouch! Would the gas line run in the floor by code or run in the outside wall??

CallMeVilla

Another tip . . . use construction adhesive (PL Premium) on the underside of your floor plate to adhere them to the concrete (nice sine wave pattern the length of the wood). Yes, move the pilot hole away from the crater and re-drill. Space your holes about every 12" - 18" and you should be fine. Remember - you are not supporting a 2nd story on this wood, just some backer board and tile/stone.

Go for it!

nealtw

The area behind should have been drywalled, all of it. so close that up before building your new box.

condoowner

So ive drilled and installed the concrete anchors. For now all sole plates are installed and the left side of the structure is done. So far so good! Tomorrow i will finalize the right side and normaly the structure should be done.. next will be the backerboard.

I will post some time soon with some pictures

Btw the floor *has* to be a lightweight floating floor.. last hole i drilled about a quarter inch longer than the screw and next thing i knew the hole was about 3 in deep!! Must be a cavity of some sort.