Hearth to subfloor interface

[kamill]

Hello friends, I'm renovating the flooring around my fireplace and found some issues with the concrete pad and subfloor. It looks like the subfloor settled over time and separated from the brick that was installed on top of the concrete pad. The pad itself is also ~1/2" higher than the subfloor.

I'm planning on installing porcelain wood look tiles on schluter ditra laid over the plywood so I have to level this area out. I don't want to raise the subfloor up with concrete board because I'm installing ~600sqft of tile and the height of the floor is a concern. Can I get away with filling the void under the bricks with some backer rod then taking a grinder to the pad and leveling it down to the subfloor? I looked at the joists under the fireplace and they're in great condition, no signs of sagging. The floor should support the tile, I calculated the deflection to be L/427. Any thoughts or feedback would be appreciated, thanks!

Joists:

 

[bladeofanduril]

That'll be fun to correct... it might be a little easier if you use Detra XL. It's 7mm thick and would eat up a bit more of the difference than the regular detra. If you're able to work the underlayment up to be even with the cement, or at least close, that's less you'll have to grind off. You shouldn't need to use detra on the cement, just mortar the tiles directly on.

 

[rwhite]

I'd do something like you mentioned. I'd probably just tuck/point completely under the hearth. I'm no mason so take this for what it's worth. I wouldn't try to grind the entire concrete down. Not only messy but probably uneven too. I'd score lines a bit deeper than floor level, chisel it out then use leveling compound to build it back up to level.

 

[mcdougy]

My guess is chipping the concrete down to or below subfloor level won't be too hard....often those slabs do not pose much of a problem and are often above the subfloor. A 15lb demolition hammer with a point and chisel should do the trick and shouldn't be very dusty in the grand scheme of things...wear safety glasses.

 

[EbS-P]

What size are the tiles?

 

[kamill]

They will be 6"x24" tiles

 

[EbS-P]

Glad you didn’t say 8x48. I tried to grind down high spots for an lvp on concrete. It was dirty messy and I just could not get it flat across 3-4 ft. You are going to have to remove material and then use self leveler.

I should have leveled 800sq ft but didn’t to save money. Floor has places where the lvp moves under foot. Ehh is a second space price was more important that doing it right. I wouldn’t make the same choice for my living room.

 

[rwhite]

And if you have one, air chisels work great! Many years of pulling green chain ruined my hands. If I use a hammer to long my hands go numb and soon enough the damn hammer flies out of my hand because I can't grip it a any longer.

 

[mcdougy]

I was referring to a 15lb electric demolition hammer if you have access to one or rent. Something like this....

 

[kamill]

Glad you didn’t say 8x48. I tried to grind down high spots for an lvp on concrete. It was dirty messy and I just could not get it flat across 3-4 ft. You are going to have to remove material and then use self leveler.

I should have leveled 800sq ft but didn’t to save money. Floor has places where the lvp moves under foot. Ehh is a second space price was more important that doing it right. I wouldn’t make the same choice for my living room.

Yeah I installed lvp in my bathrooms, it goes down easy but I'm not a big fan of the feeling under foot. My dogs hate it too, too slippery for them.

I'll give it a shot, trying to chisel it down slightly below the subfloor and level it back up. I don't have an air hammer but I have an angle grinder with a diamond blade so I'll try to score it and knock out chunks

 

[mcdougy]

Yeah I installed lvp in my bathrooms, it goes down easy but I'm not a big fan of the feeling under foot. My dogs hate it too, too slippery for them.

I'll give it a shot, trying to chisel it down slightly below the subfloor and level it back up. I don't have an air hammer but I have an angle grinder with a diamond blade so I'll try to score it and knock out chunks

That should work too......I would suggest having a helper that is holding the hose of a shop vac very close to the grinder as you cut to help with the horrendous amounts of dust the grinder will create.
If your ok with the dust in the house then go for it.......if not, I suggest renting a demo hammer from anywhere that is close to you. Lowes,HD, or similiar will all have one for a fairly minimal cost.