Slab-on-Grade control joints - align with columns?
Slab-on-Grade control joints - align with columns?
(OP)
Typically, consistent with the rest of the universe, we use diamond shaped block-outs in interior building slabs at columns to separate the column from the slab.
The diamond shape also allows slab control joints to intersect at the diamond corners, eliminating re-entrant corners and cracking from such corners.
In a project we have going, there is a need to align slab control joints with tile flooring joints. The tile, of course, will not align with our irregular column spacing so we are thinking of possibly laying down a control joint pattern that is independent of the columns so we can align the joints.
If we do that, we now have columns (steel tubes - 6 to 10" in size) extending through holes in the slab and we are concerned that this might cause cracking off the re-entrant corners of the "little" holes that are generally square in shape.
Has this been done before? Are the column holes small enough that re-entrant corner cracking doesn't occur? Can you use circular blockouts around the columns to avoid the corners and cracking?
Looking for ideas and experience - thanks.
The diamond shape also allows slab control joints to intersect at the diamond corners, eliminating re-entrant corners and cracking from such corners.
In a project we have going, there is a need to align slab control joints with tile flooring joints. The tile, of course, will not align with our irregular column spacing so we are thinking of possibly laying down a control joint pattern that is independent of the columns so we can align the joints.
If we do that, we now have columns (steel tubes - 6 to 10" in size) extending through holes in the slab and we are concerned that this might cause cracking off the re-entrant corners of the "little" holes that are generally square in shape.
Has this been done before? Are the column holes small enough that re-entrant corner cracking doesn't occur? Can you use circular blockouts around the columns to avoid the corners and cracking?
Looking for ideas and experience - thanks.






RE: Slab-on-Grade control joints - align with columns?
RE: Slab-on-Grade control joints - align with columns?
RE: Slab-on-Grade control joints - align with columns?
The problem is that the column spacing is totally independent of this large-format (24" x 48" porcelain) tile.
RE: Slab-on-Grade control joints - align with columns?
If that is not the case, then the extra reinforcement for crack control is the only other option I can think of at this moment.
RE: Slab-on-Grade control joints - align with columns?
Wow.... “large-format (24" x 48" porcelain) tile.” I suspect that big a brittle tile could have other cracking problems also, namely: cracking due to differential expansion or contraction btwn. the tile and the slab, either temp. or moisture induced; and if this tile isn’t perfectly set and bedded it could be subject to flexural cracking too. 2'x4' is a big bed to get perfect for each tile, and then that tile set perfectly, and then adjacent tiles to match too. I’ve seen tile over a void in the bedding punch right through under traffic. A smaller format tile is much more forgiving. And, you shouldn’t be blamed for any problems in this regard. Have you talked with the tile manuf’er. about these types of issues, for your own protection? How are you going to detail the top slab edge at a control joint, to support the tile edge? You might be better off to cast a .75 - 1" void around the columns and fill that with caulking/filler at a later date. Also, don’t let the slab bond to/around A.B’s. or nuts as this could be a crack starter. Seems to me that the Arch. is looking for trouble on this floor system, and you should put as much of that on him as is possible. How is he going to get those tiles around the columns without some unwanted joints?
RE: Slab-on-Grade control joints - align with columns?
RE: Slab-on-Grade control joints - align with columns?
RE: Slab-on-Grade control joints - align with columns?
RE: Slab-on-Grade control joints - align with columns?
Maybe it might have been better to use a "pinwheel" type of joint in this circumstance to alleviate cosmetic damage to this joint due to differential movement.
RE: Slab-on-Grade control joints - align with columns?
RE: Slab-on-Grade control joints - align with columns?
I would have the slab jointing pattern mimic the tile pattern as close as possible.
What soil? any differential movement? Can you use a structured slab? added cost would be small considering the floor treatment.
Dik
RE: Slab-on-Grade control joints - align with columns?
Dik
RE: Slab-on-Grade control joints - align with columns?
RE: Slab-on-Grade control joints - align with columns?
I think we will be wrapping the columns with 1/2" expn. joint material and then aligning slab joints with tile joints (i.e. the contractor will work out the alignment not us).
We also show additional ring reinforcement around the columns so if there are any projecting cracks from the small column "hole" we at least control their width a bit.
We'll see how this works.
RE: Slab-on-Grade control joints - align with columns?
Dik
RE: Slab-on-Grade control joints - align with columns?
RE: Slab-on-Grade control joints - align with columns?
RE: Slab-on-Grade control joints - align with columns?
Dik