Material to make up for slight fluctuations in concrete floor

[Jakee]

I have slight level flucuations on my concrete floor that I'm about to put a 30"x30"x3" thick piece of bluestone on which I will set my Napoleon 1100 stove. It's not much flucuation, a 32"nd here and there, possible slightly more. I'm concerned that when I put the stove on top whether it could possibly crack the bluestone even if the flucuations are small. Maybe I'm over thinking it, but wondering if theres a material someone knows about that would fill these slight voids without adding height where it's not needed. Sand would just cause problems. Any ideas?

 

[Riteway]

I have slight level flucuations on my concrete floor that I'm about to put a 30"x30"x3" thick piece of bluestone on which I will set my Napoleon 1100 stove. It's not much flucuation, a 32"nd here and there, possible slightly more. I'm concerned that when I put the stove on top whether it could possibly crack the bluestone even if the flucuations are small. Maybe I'm over thinking it, but wondering if theres a material someone knows about that would fill these slight voids without adding height where it's not needed. Sand would just cause problems. Any ideas?

It's called different things, depending on the brand, but look for something like "self-leveling underlayment." It's a cement-based product for leveling floors, generally used before installing tile. Should work fine for your application.

 

[EbS-P]

It's called different things, depending on the brand, but look for something like "self-leveling underlayment." It's a cement-based product for leveling floors, generally used before installing tile. Should work fine for your application.

Just used this and it would work fine BUT you need to pour the entire area and it will add minimum 1/8” thickness. Don’t trowel it but rake it. Not sure how you would keep it contained just to the area under the stone. You could grind the high spots, messy but doable with a 60$ wheel for a right angle grinder. Wet grinding makes less of a mess if you can contain the splatter still not clean.
Outside the box here padded underpayment for a click down floor would reduce pinpoint pressure but it’s probably not thermally stable enough. Steel wool but would not really be stable long term.
Dam it up and use this. best answer I have. Self Leveler Plus 50-lb Indoor Self-leveling Underlayment https://www.lowes.com/pd/MAPEI-Self-Leveler-Plus-50-lb-Indoor-Self-leveling-Underlayment/50293201

Evan

 

[bholler]

Thinset

 

[Jakee]

Thinset

I thought about that but the height variations are almost not worth using it. Maybe I'll run some type of caulking just in those spots before putting it down, move it around a bit, and squishing down on it. I don't think temperature will be an issue. It's got a pedestal base and the bluestone is 3"
Any more sugestions are welcome from anyone

 

[bholler]

I thought about that but the height variations are almost not worth using it. Maybe I'l run some type of caulking before putting it down, move it around a bit, and squishing down on it. I don't think temperature will be an issue. It's got a pedestal base and the bluestone is 3"

Why not use the product designed for the purpose? That product is thinset.

 

[Jakee]

Just used this and it would work fine BUT you need to pour the entire area and it will add minimum 1/8” thickness. Don’t trowel it but rake it. Not sure how you would keep it contained just to the area under the stone. You could grind the high spots, messy but doable with a 60$ wheel for a right angle grinder. Wet grinding makes less of a mess if you can contain the splatter still not clean.
Outside the box here padded underpayment for a click down floor would reduce pinpoint pressure but it’s probably not thermally stable enough. Steel wool but would not really be stable long term.
Dam it up and use this. best answer I have. Self Leveler Plus 50-lb Indoor Self-leveling Underlayment https://www.lowes.com/pd/MAPEI-Self-Leveler-Plus-50-lb-Indoor-Self-leveling-Underlayment/50293201

Evan

Thanks

 

[Jakee]

Why not use the product designed for the purpose? That product is thinset.

Would it squish down to almost zero where it wasn't needed?

 

[bholler]

Would it squish down to almost zero where it wasn't needed?

If you mix it to the proper consistency and use the right size trowel yes.

 

[Nealm66]

I’ve used it 4 or 4 times where I’m putting in tile flooring. I find I have to mix it a lot thinner to get it to flow to level. It lays thin and chips easy if left with nothing over it

 

[Highbeam]

Self leveling is not self leveling, that stuff will leave you with just as much variation as you’re hoping to solve. You don’t want that here. You want to bed the big slab into thinset and then clean around the edges with a wet sponge.

Or just set it on the slab and hope it doesn’t rock or crack. With thinset, it’s stuck there.

You can also spend a few hours with a diamond cup bit on your grinder trying to make it flat but really, the bottom of the stone is not flat either so why bother?

 

[Jakee]

I think the thinset and cleaning the edges with a sponge is a great idea. Thanks for the reponse.

If you mix it to the proper consistency and use the right size trowel yes.

By right size trowl. you mean smaller notches, correct?

 

[Jakee]

I'll use the ideas, thanks

 

[Rob711]

Just had a patio and retaining wall installed. How about the “glue” they use to put the caps on top block walls. I never checked the tubes but it looked like a PL type construction adhesive

 

[St. Coemgen]

It's not much flucuation, a 32"nd here and there, possible slightly more.

To avoid cracking, best to follow the ANSI Standard:

For tiles with at least one edge 15 in. (0.38 m) or longer, the maximum allowable variation is no more than 1/8 in. in 10 ft. (3mm in 3 m) and no more than 1/16 in. in 2 ft. (1.6mm in 0.6 m) from the required plane, when measured from the high points in the surface.
ANSI A108.02 section 4.1.4.3.1 Sub-floor surfaces

If you are within those parameters, then you need no special adjustments.

And you want typically at least 80% to 95% mortar coverage on your tile or stone (stone requires minimum 95% always). Anything less is more likely to eventually crack.

One way to test, is to lay down some mortar, lay the tile and then lift it up (prying off the mortar) and check the coverage.

See this video for more info:

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[jetsam]

If you want to clean up some 1/32" dips, thinset is really fine.

Clean the slab, put down a little bit of thinset, and run a long steel straightedge (at least as long as your bluestone) over it, which will scrape almost all of the thinset off. Do that N/S and E/W.

What's left is your low points, done.

 

[Jakee]

To avoid cracking, best to follow the ANSI Standard:


If you are within those parameters, then you need no special adjustments.

And you want typically at least 80% to 95% mortar coverage on your tile or stone (stone requires minimum 95% always). Anything less is more likely to eventually crack.

One way to test, is to lay down some mortar, lay the tile and then lift it up (prying off the mortar) and check the coverage.

See this video for more info:

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For more detailed information, see our cookies page.

Accept third party cookies

I appreciate the resonse, the flucuations are pretty minor. The bluestone is 30 x 30 x 3" thick, so went go to put it down, it's for good

 

[Jakee]

If you want to clean up some 1/32" dips, thinset is really fine.

Clean the slab, put down a little bit of thinset, and run a long steel straightedge (at least as long as your bluestone) over it, which will scrape almost all of the thinset off. Do that N/S and E/W.

What's left is your low points, done.

Now that sounds like a good idea. I like that, thanks

 

[Highbeam]

You need to let the thinset harden after going n/s before going e/w with this “screed” or you’ll just dig out the thinset. This makes the floor flat but does nothing for irregularities in the stone slab.

Bedding in thinset absorbs irregularities from both sides but it’s effectively glued in place.

 

[David.Ervin]

Don't put it down with something adhesive like liquid nails because while it'll work AWESOME for what you want to do, it's also theoretically combustible (give or take the 3" of stone on top of it). A thinset mortar will both adhere well and take up any tiny voids. Just be sure you never want to move it again once it's down.

 

[Jakee]

You need to let the thinset harden after going n/s before going e/w with this “screed” or you’ll just dig out the thinset. This makes the floor flat but does nothing for irregularities in the stone slab.

Bedding in thinset absorbs irregularities from both sides but it’s effectively glued in place.

It's pretty much OK if it beds in place because that's the spot for the stove as long as I'm alive.
Th Bluestone is quarried and custom cut, I think it's going to be really flat. I've dealt with this company before.

 

[Highbeam]

It's pretty much OK if it beds in place because that's the spot for the stove as long as I'm alive.
Th Bluestone is quarried and custom cut, I think it's going to be really flat. I've dealt with this company before.

Can't wait to see pictures. Huge stone slabs always look cool.

 

[Jakee]

Can't wait to see pictures. Huge stone slabs always look cool.

Thanks!
It's supposed to come in a few days.
I'll definately post pictures. The stove I got was a rusty thing that I took completely apart and made a good as I could.