Leveling concrete

[DrPizza]

I have 2 garages (side by side) that I'm going to level the concrete in. When it was finished, a drain was put in the center of each garage. The concrete is tapered nearly perfectly down to the drain, which sits about 1 1/2 - 1 1/2" below the grade near the perimeter of the garage. So, more or less, I'm filling in a very short inverted cone - 1 1/2" height, 5 foot radius. I wish to remove that taper and make it reasonably level. It will eventually have a thick carpet pad and carpeting over it, so it probably doesn't have to be absolutely perfect.

Any ideas for best product for such a job? It seems that it would be unnecessarily expensive to go straight for the self-leveling concrete - $30/bag vs. $4 per bag for regular concrete. Regular concrete first, then self-leveling? Or if I go with regular concrete, simply work that into a level surface?

 

[Greenman]

You could get away with mortar if you use a bonding agent between it and the concrete. I'd stop short of the edge and use fixall or self leveling for feathering it out.

 

[DrPizza]

Sounds good, thanks. I probably should have mentioned the bonding agent in the OP. And, first, I'll clean the surface with muriatic acid.

 

[Howard]

Drill in a matrix of concrete screws (e.g. Tapcons) for better mechanical bonding of the new layer. Basically it should look like the worst prank your kid could play on you, if you were barefoot and walking around the house at night.

EDIT: If you drill them reasonably plumb, you can set them into the concrete so that their heads align with your reference plane. Would make it pretty easy to level out the concrete. Flat-head screws would be better if you plan on doing this but they aren't as reliable as hex-head screws. use an impact driver to minimize damage to the Phillips drive surface.

 

[linuxboy]

EDIT: If you drill them reasonably plumb, you can set them into the concrete so that their heads align with your reference plane. Would make it pretty easy to level out the concrete. Flat-head screws would be better if you plan on doing this but they aren't as reliable as hex-head screws. use an impact driver to minimize damage to the Phillips drive surface.

This. Use some kind of a system where you can create a level top using the surface of the heads so you can trowel it to a single plane where you pre-check the level before pour. Laser can be useful here. Then pour and smooth with the float. The float will use the surfaces of the heads as a boundary so the level will be even. And then should be good to go.

 

[Howard]

Also you may already know this but never back out a concrete screw, even the tiniest bit.

 

[DrPizza]

Sounds like a great idea for mechanical bonding, though it seems that it wouldn't be an efficient use of time to get them close to level enough to make it worthwhile to use for that purpose. (Especially since you can't back them out.) Stopping, checking, and driving slightly farther would probably be a pain in the neck. I should be able to get it level enough by simply screeding it with a solid, straight 2x6 of sufficient length. I saw some concrete guys working over the summer, and thought, "that's brilliant!" They didn't look like they were from a higher end company with a lot of money invested in tools - they were using a shorter float - about 24" - and smoothing I think 10'x10' slabs. They simply had a concrete block off to each side, and put a piece of scaffolding across the slab and laid down on the scaffolding to reach the concrete. I just attached a couple of 2x4's to the bottom of a 2x8 to use as scaffolding to walk back and forth on while working on my ceiling. It'll serve a second purpose.

 

[Howard]

Sounds like a great idea for mechanical bonding, though it seems that it wouldn't be an efficient use of time to get them close to level enough to make it worthwhile to use for that purpose. (Especially since you can't back them out.) Stopping, checking, and driving slightly farther would probably be a pain in the neck. I should be able to get it level enough by simply screeding it with a solid, straight 2x6 of sufficient length. I saw some concrete guys working over the summer, and thought, "that's brilliant!" They didn't look like they were from a higher end company with a lot of money invested in tools - they were using a shorter float - about 24" - and smoothing I think 10'x10' slabs. They simply had a concrete block off to each side, and put a piece of scaffolding across the slab and laid down on the scaffolding to reach the concrete. I just attached a couple of 2x4's to the bottom of a 2x8 to use as scaffolding to walk back and forth on while working on my ceiling. It'll serve a second purpose.

Fine! Do it the easy way.

My dad used to use a piece of aluminum rectangular tube (had sharp corners, not rounded) as a concrete screed. Worked out pretty well.

 

[stormkroe]

If you have access, I strongly recommend hammering yourself a 'border' around the area to be filled. The super-thin edge will easily crack away if you just try to float it out like a drywall joint. Also, if you can give yourself a good 1.5 inches, you could use cheap quick crete without worrying if the aggregate will be too thick.

 

[Greenman]

Drill in a matrix of concrete screws (e.g. Tapcons) for better mechanical bonding of the new layer. Basically it should look like the worst prank your kid could play on you, if you were barefoot and walking around the house at night.

EDIT: If you drill them reasonably plumb, you can set them into the concrete so that their heads align with your reference plane. Would make it pretty easy to level out the concrete. Flat-head screws would be better if you plan on doing this but they aren't as reliable as hex-head screws. use an impact driver to minimize damage to the Phillips drive surface.

Overkilling by a factor of ten really isn't necessary. Mix up a few bags of levelquick, dump it in the low spot, wait half an hour and hard trowel the edge to get a nice feather on it.

The screws won't really help at all as a thin patch has almost no tensile strength. The bond to the existing concrete is what matters, and that bond is easy to achieve.

 

[DrPizza]

Besides, all that's going over it is a really thick pad & carpeting. Thus, I don't think any cracks are going to be much of a problem.