Control joints in shop slab??

[shibaura_4043]

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.

 

[bspeedy]

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.

 

[jb1390]

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.

+1. Concrete will crack - it's up to you whether you care where it cracks.

Also, ideally cut the slab about 1/4 of the way through. For a 4 inch slab, that's a 1" cut. The deeper you go, the more likely the crack will follow the joint. If it's just scored on the surface, it might not follow the line. 1/4 of the way through pretty much guarantees it from what I recall.

 

[Shaneard]

Our shop floor at work doesn't have them. It made its own. The one that looks like it's been sawed in is actually where they poured half the building then did the other half.

 

[shibaura_4043]

Our shop floor at work doesn't have them. It made its own. The one that looks like it's been sawed in is actually where they poured half the building then did the other half. <img src="http://www.tractorbynet.com/forums/attachment.php?attachmentid=497141"/><img src="http://www.tractorbynet.com/forums/attachment.php?attachmentid=497142"/>

Are you suggesting I cut them too or it doesn't matter? Also, the saw lines will be cut directly in center or off center a couple of feet in the bay areas ( doors are on the 40ft side) im worried it will look like crap.

 

[Argonne]

My 30 x 70 shop was poured in early June (7 months ago). After curing the concrete, I added up the hours and materials to cut control joints, and decided to put that money into electrical stuff, so no control joints. About 3 weeks ago, the first crack appeared, running front to back across the width of the slab and about 20 feet from an end wall. The crack is about 1/8 inch wide and 1/16th height offset at this time.

So far I am happy with my decision, as I don't much care what the floor looks like.

My soil is all clay and famous for it's instability....cracking and settling were assured. I did pour a gravel base and let it settle for 4 months before building, and the construction is dug (as opposed to driven) 6 inch posts with all framing 2x6 stick built, so the building is not built on the slab, but the slab poured in the building. Had it been otherwise, I might have been more concerned with predictable cracking.

Anyway, so far so good. Still satisfied with my decision.

 

[Shaneard]

Are you suggesting I cut them too or it doesn't matter? Also, the saw lines will be cut directly in center or off center a couple of feet in the bay areas ( doors are on the 40ft side) im worried it will look like crap.

I am suggesting you cut them. If they are done right, straight and even you won't pay any attention to them after a while but you will if you have cracks. I been here 21+ years and these cracks annoy me, lol.

 

[Snobdds]

This is a no brainier...cut the joints. I had no idea people actually opted to not add control joints. This is the first I've ever heard of that...

 

[shibaura_4043]

This is a no brainier...cut the joints. I had no idea people actually opted to not add control joints. This is the first I've ever heard of that...

People just don't cut them around here because they will inevitably crack outside the joint lines

 

[4570Man]

My floors are cut. There are a few cracks outside the cuts, but they are small and hardly noticeable.

 

[shibaura_4043]

Well doesn't look like it's going to happen, he standing me up today, says he can't make it until tomorrow. I'm pretty pissed off about it too.

Update: he said he'd be here in 1 1/2 hours. I think you guys convinced me they are a good investment... I hate looking at cracks... lol. Now on the 40 foot width there will be two cut lines running the 60 foot length. Where Would you place them, remember I have 2 bay doors 12' wide . Would you just run them equally spaced even if it puts them offset in the bay drive-in areas?

 

[Gunny]

One pretty steadfast rule when dealing with concrete is that it's going to crack, doesn't matter about your sub base, the temps, how thick it is or anything, it's going to crack.

You can control a lot of that by putting control joints in

 

[nybirdman]

I worked on big construction for 25+years and they always sawed control joints.My last personal pour for my garage I made it in two pours and left the form(3/4")between and it has never cracked(10 years)

 

[fried1765]

Well doesn't look like it's going to happen, he standing me up today, says he can't make it until tomorrow. I'm pretty pissed off about it too.

Update: he said he'd be here in 1 1/2 hours. I think you guys convinced me they are a good investment... I hate looking at cracks... lol. Now on the 40 foot width there will be two cut lines running the 60 foot length. Where Would you place them, remember I have 2 bay doors 12' wide . Would you just run them equally spaced even if it puts them offset in the bay drive-in areas?

You have a choice!
Do nothing = spider web cracks.
Cut control joints = neat looking job

 

[Birdhunter1]

The floor in my 30x50 shop is 5" thick and was poured in September 2010. The cut lines are in 12' x 12' squares about an inch deep. So far there are no cracks in my floor and we have temps ranging from just below 0 in the worst of winters to about 110 in the worst of summers.
For what it's worth if you're worried about the lines in your floor being grooves just caulk them shut. It takes about a case of caulk but in 7 years I haven't complained about my floor one bit or even noticed them when rolling stuff around. Also the lines make great reference points when laying out the misc large frames that end up being built in the floor.

 

[bspeedy]

Well doesn't look like it's going to happen, he standing me up today, says he can't make it until tomorrow. I'm pretty pissed off about it too.

Update: he said he'd be here in 1 1/2 hours. I think you guys convinced me they are a good investment... I hate looking at cracks... lol. Now on the 40 foot width there will be two cut lines running the 60 foot length. Where Would you place them, remember I have 2 bay doors 12' wide . Would you just run them equally spaced even if it puts them offset in the bay drive-in areas?

I would space them equally. You won't notice them after two weeks.

 

[RNeumann]

You need them cut! In general we would go a max of 15'x15'- some really big stuff we would go bigger. If worst comes to worst you can cut them yourself with a chalk line and skil saw with diamond blade. They should be 3/4" deep. If you have steel posts use those as starting points. You want it done in the first few days.

Most of the time a slab on grade house doesn't get control joints as it is covered by carpet or other flooring. Anything that is exposed like shops, garages, sidewalks and driveways get expansion joints. I always prefer the cut joints but it does require the contractor to return the next day. That's why some do the wet joints that are "cut" in as the concrete is finished.

 

[6sunset6]

I put control cuts in myself . 10' centers The day after the pour Diamond blade in a skill saw. As deep as it would go . Followed a chalk line. 2 20' and 1 30'
Could have flooded it with water but just went dry. Other than a hugh amount of dust it worked great. With a double insulated tool and a little care water is ok. I have cut stone slabs with the same set up and water.

 

[RNeumann]

I put control cuts in myself . 10' centers The day after the pour Diamond blade in a skill saw. As deep as it would go . Followed a chalk line. 2 20' and 1 30'
Could have flooded it with water but just went dry. Other than a hugh amount of dust it worked great. With a double insulated tool and a little care water is ok. I have cut stone slabs with the same set up and water.

Too deep and you cut the rebar- not good! A skil saw cuts about 2" deep at max depth

 

[6sunset6]

Good point it was a 5.5" slab I did not cut the rebar.