Control joints in shop slab??

[Snobdds]

I must have really gotten to you at some point. I'm just glad you talked your way out of the firewood thread, that was pure entertainment.

Go find your entertainment and PM to me. However I don't remember any earth shattering "gotcha" moment on your part.,

 

[shibaura_4043]

The fact that you were asking if you could cut the joints yourself seemed to indicate you were in charge of the pour to some degree, not a competent contractor. No competent contractors is going to tell you to go check the internet to see if you should cut expansion joints in your slab. Your welcome.

I never asked how to cut lines, I asked what would be the best placement.... So I could make sure the CONCRETE guy did it the best possible way. The contractor never suggested I go to the internet and ask what to do, it was this little thing called free will!! I'll give you the benefit of the doubt because I did refer to myself( only because it's my slab and I'm the direct contact to my contractor) in a couple posts but it looked pretty clear to me. Now I'm going to read the firewood post... My guess is you like to assume things without asking questions.

 

[shibaura_4043]

The fact that you were asking if you could cut the joints yourself seemed to indicate you were in charge of the pour to some degree, not a competent contractor. No competent contractors is going to tell you to go check the internet to see if you should cut expansion joints in your slab. Your welcome.

I'll let Louis know this guy on the Internet thinks he's incompetent, unless of course that was directed at me since you think I'm the contractor in charge?

 

[shibaura_4043]

Tractor Seabee,
Your post was informative thank you for posting that. Hopefully cracks will be "controlled" in my slab, if not oh well it was a pretty cheap chance to take. Since you seem to know a lot about concrete. What is your suggestion for a house slab? Overkill rebar. post tension with several beams? Several people tell me a lot of rebar is the way to go and several people have said post tension, I like the theory behind post tension. All these different opinions have made this a difficult decision? What would you suggest?

 

[hslogger]

The guys who did my slab made it smooth as can be. They then cut the joints in. THEN, after it cured a little, filled the joints in.

What I ended up with was a smooth finish floor, level as can be. The joints have small cracks in them as they had planned. It turnout primo and I really appreciate their craftsmanship.

 

[buckeyefarmer]

Cut them.

 

[Egon]

Very informative post Tractor Seebee.

Concrete is a very well engineered product with easily available information.
The quality and transport conditions are frequently different from what is expected as are the placing and finishing methods.
Quality controlled, tested and owner supervised conditions as in larger construction have a much better chance of being done properly.

It also has a great Folklore Following!

 

[bigtiller]

4. Control joints: Lay out in a grid pattern depending on size and penetrations. Over 16' in any direction requires two equal cuts that direction up to 12' per panel. 12' by 12' is a good grid goal to plan around with max of 14 x 14. Where ever a penetration exists, the slab will always crack at the corners unless you block it out with joints, again planning is needed to keep small sections minimized, every job is different. WHEN & HOW: As soon as finish is completed do it even if you have to work under lights, next morning or day you have wasted you time and money, it has already cracked where it wants to. Small jobs have the finisher cut with a jointing trowel, larger use what is called a soft cut machine right behind the finishers. Depth is 1/3 the slab thickness, less is iffy on results.

The soft cut or green cut saw really works. But around here not to many contractors have one set up. I wonder if it is because they don't want to wait the extra time for the concrete to cure enough that the wheels on the saw don't leave a mark.

 

[Cord]

Had a 40x60 4" slab with 24" beams poured yesterday afternoon. Should I cut control joints? I've got several contradicting opinions. I'd like to get suggestions from people who did and who didn't go with control joints. Also, I'm pouring my house slab in about a month. I, trying to decide on post tension vs rebar(5/8 rebar in slab and beams on 12" centers) Again I've got a lot of contradicting opinions. Trying nail down a decision and its proven difficult lol. Thanks in advance.

Definitely saw in control joints. For a 4" slab the max spacing would be 8' oc with 3/4" or smaller aggregate and 10' oc for larger than 3/4". The spacing changes because the larger aggregate will shrink less. The joints should be cut 1/4 of the slab thickness or 1" in this case. The joints should come off any reentrant corners because there will be stress concentrations at the corners.

Because of the expansive soils in Texas many will do post tensioned in that region. I will say that making modifications to a post tensioned slab is very difficult. If you have plans to remodel a kitchen or add onto the building, I'd suggest going with conventional reinforcement.

If you have expansive soils, be sure to have the contractors grout the gravel filled trenches. This will prevent the water in the gravel from running under the building and causing the soil to swell.

Regarding the ability to open up the spacings or even omit the joints... with the modern macro fibers I'm seeing some incredible joint spacings. Just did a 8" slab with a heavy dose of macrofiber, 3,000psi (lower strength shrinks less), water reducer and 1.5" aggregate and those joints were set at 60' oc!

 

[mike69440]

I would cut the control joints. The slab WILL crack. Looks a lot nicer when it's in a nice straight control joint than in the ugly zig-zag pattern.

And I think the window for cutting the joints is pretty tight. Better git er done.

Really pound the ground and wet it before you pour, Stone down and plastic over stone.

Cut the slab, 12'x12'. squares would be fine. Fill crack with self leveling Polyurethane.