Control Cuts?

[shooon]

Building a 24 x 31'5" shop. Slab on grade with 14x14" thickened edge and 5" thickness in the middle. Using a 12 x 16" rebar grid with 15mm rebar.

I have a sump set in concrete in the middle of the shop. The box is 16x16" with 8x pieces of rebar welded to the sides of it (inline with the rest of the grid) to support it from settling, and there is 2" angle iron welded on top of the box to allow for grating- the angle measures 18x18 at the top. (see awful drawing)

So it's somewhat tiered. My concrete contractor is trying to talk me into control cuts, he says it will for sure crack around my sump; but I've had other advice saying I'll most likely be fine and if it does crack it won't be a problem.

Personally, hate the look of control cuts. Also the box is square and got twisted slightly... so doing control cuts will only make this flaw massively noticeable.

What do you guys think ? Control cuts a must or are they optional / not likely needed?

 

[willymakeit]

Concrete will usally crack at a inside corner [called a reentrant corner]. Its one of the items I look and ask for on all slab pours. Your luck may vary but I would make the cuts and then fill with backer rod and caulk such as sika flex ect.

 

[shooon]

Thanks willy.

So for future a round sump is the only way to avoid control cuts / potential cracking. Good to know!

 

[Finky198]

Willy is 100% correct and know his stuff Sika Flex is top notch we repair cracked chimneys with sika products its gives but its super strong... great product for concrete work...

 

[reader2580]

The garage floor in my last house has multiple cracks in it due to control cuts not being done. The basement floor also had cracks near the sump even though the sump was round.

 

[matt_i]

Another way to look at it...saw cuts = you control the cracking (mostly). No saw cuts = you are allowing the crack to propagate randomly at the "weakest link".

There's nothing that says they can't be diagonally out from each corner. Ala \ /

 

[Falcon67]

FWIW - I don't do control cuts and haven't had any issues. They don't do control cuts here on house slab-on-grade foundations. The 40x60 slab next door that was slated for a metal building uses 18x18 footers, re-bar 24" OC and had no control cuts. And no faults either. Spider cracks, but that's common here. Control cuts won't stop that - not when your slab runs 130~150F in the summer sun.

 

[Finky198]

In the north east with the ground heaving hoeing due to the weather changes that same 40x60 slab would crack in a few years... the control cuts just make it look Cleaner down the road as there Straight and not random, also if you work with sika or any good caulk, there are plenty of tricks to hiding and or blending the seams... not to mention if you put a coat of paint or epxoy down they will be even less noticeable...

if you ever look at HD or lowes most of their floors are cut every 10'x ??'

 

[Falcon67]

Yea, and they saw cut the drag strip in 2003 every 20'. Those 25' x 900' x 12" thick lanes cracked every 10' in between the control cuts. Most likely due too the lack of extensive base material.

 

[pmiranda]

I suspect the high shrink/swell clay soils we see in many parts of the south rival the freeze/thaw seen in the north, but it's easier to control soil moisture than temperature!
Having said that, I'll probably get control cuts in my 40x60 (or maybe 45x65... or 45x90... or..)

 

[GSRinmyCRX]

concrete will crack on average every 10 ft. try and space your cuts out to about 10x10 and I think if you do diagonal cuts form the corners of the sump it would look fine.

Levi

 

[willymakeit]

Thanks willy.

So for future a round sump is the only way to avoid control cuts / potential cracking. Good to know!

Round is less likely. If you haven't poured the concrete add rebar around and transverse bars on the diagonals. All need to be tied together.
I have added slip dowels at expansion and or cold joints.
Concrete behaves in funny ways,
Different parts of country use methods suitable to there soil conditions and final use.