Pouring concrete floor for new garage - what to do about control joints?

[ez at nova]

My garge floor slab is being poured Friday. It will be 24x24 with a 1 percent grade down to front, using 3500 psi mix.
My question lies in teh control joints though. The cement guy suggested we do a "cross" of two control joints cut in...effectively making a + on the garage floor if looking from above. He said if I was against all that cutting, we could get away with doing just one cut, either -- or |
I guess I'm leaning towards the | since that would sort of "divide" the garage, but I don't know.
Anyway, I will be epoxy coating the floor when it's done so it looks purdy, but what will I do with that godawful line cut in the floor!? I don't think I should fill it BEFORE doing the epoxy since it probably wouldn't stick to whatever I fill it with. So, anyone have any suggestions?

 

[ChrisCairns]

I'm not a concrete expert...just reciting what the concrete guy who poured my 24x36 foot told me.

Cut the hell out of it .... lol.

Those cuts are apparently controlled cracking cuts. The floor will crack so you want the cracks there.

Hell, after a few years the cracks will be filled with crud anyway.

 

[b4black]

Do the | cut, and the -- cut will just make itself in a few years.

But it will be morel ike this ~~.

 

[bishir]

It's up to you but if your garage floor IS going to crack. You're going to have to decide how much you can handle. To do it correctly, you'd actually have to put in more control joints than suggested. Though, many do as your concrete man is suggesting and do a big +. My garage is going to be about a 40x40 so I'm going to have about a ++ on my floor with maybe an addition joint thrown in.

James

 

[ez at nova]

So what the heck do I do about the joints afterwards? I acn see them being REAL pain with screws, nuts, sockets, etc, not to mention liquids, falling down in there!

 

[TDS-84]

The cuts don't really need to be that big. I don't think they will be as bad as you're imagining. Maybe 1/8" wide, by inch or so deep at the most. You could caulk them if it would make you feel any better. I'm not sure how epoxy coating would take to the caulk sealant, though. But in my opinion, you would benefit from at least the 2 crossing cuts, and more would be even better. Concrete will crack, guaranteed. More cuts will keep it at least under control when it does, it should only follow the cuts.

 

[idaho gn]

you dont have to cut concrete

your concrete man should know that you can put fiberglass in the concrete and not have to cut it my fried who has a 50x50 shop has no cuts and it hasent cracked in 4 years and it get cold here in the winter and hot in the summer


shawn

 

[KEVINS]

A buddy had a new garage built and his concrete man made the + cut but lightly trowled over them again essentially filling them in just enough so it was perfectly smooth but the floor would still crack along the +. It worked PERFECTLY and the cracks are so minor that you don't see them and you can roll your creeper across them and never know it. I'd look into doing this!

Regards
ks

 

[Phatman]

I go along with your concrete man, IIRC code here in the South is no more than 144sf or (12'x12') and the fibermesh in the mix is a nice idea. The mesh is usually added instead of wire mesh and is in some cases a cost savings, I'd use both in mine if I had the option....

 

[ez at nova]

He already layed down the wire mesh stuff. I told him to go ahead and do the + cut. I'll just fill it with some acrylic caulk when the epoxy coat is done.

 

[Lee_Burough]

To reduce future cracking....

Take your garden hose and wet the entire floor surface three or four times before they pour the concrete. Hand water it just like you'd water a lawn: A deep watering if you can. Don't make it muddy, but get it wet so it will settle NOW instead of LATER. When you notice a couple sink spots, you'll know where to concentrate your watering.

Wetting the soil will encourage quick settling before the pour. Quick settling now will allow fewer cracks in the future. Fiber in the mix is good, but, not necessary.

The edging controls where the floor will crack when it settles. The edging IS important. Instead of using a concrete edger the day they pour, your contractor could use a concrete saw and make the + pattern a few days later (as long as he makes it half an inch deep). That way, it would be barely noticable and still function. Good concrete patch is available, you can fill the cracks with that and epoxy away. HTH

 

[EightSecV6]

My attached garage at my house is 28x32 with a 8x10 (office), it slopes 4" from back to front and one solid slap. I epoxied it 1 year after it was poured. I have no joints in my floor,no support poles and it doesn't even have a hint of a crack anywhere. Looks like an operating room floor! It is only 4 years old so maybe I can expect it to crack????? However when we built the house we hit water (G.D. Chesapeake Bay!) and the state required us to dig the entire area under the basement floor and garage and aditional 36" and fill it back in with #2 stone! It is a 6" pour as that is what is required for a Rotary lift that I intend to install one day....
I found out after the fact but you can have the concrete dyed to practically any color you want (CHEAP TOO!) and then just coat it with clear sealer, if I had to do it again that would be my decision.
Bill

 

[tom h]

There's "crack control" joints and "expansion" joints ... I assume you mean the former??

After the control joints have been either saw cut or edged in (special tool while concrete is setting up), and after the concrete has been epoxy painted, you can use polyurethane sealant to cosmetically fill in the cuts.

Polyurethane is far more dureable, adheres better, and is tougher, than any other caulk/sealant for this purpose.

There are special "self leveling" poly's made for this purpose, but can be tricky to apply (might run out of joint).

In either case, a flexible foam "backer rod" is inserted into the crack first ... then a thin layer of Polyurethane is applied over the backer rod ... thin layers of Polyurethane are far more flexible than deep, narrow layers.

The Polyurethane comes in several colors to match the concrete or paint color.

All this is fairly standard among commercial/industrial concrete contractors, but may be less familiar to the typical residential contractor.

I am a 100% advocate of re-bar (not mesh), placed on "chairs or "dobies" so that it is nearer the middle of the slab during the pour. Wire Mesh or rebar that is laying on the dirt is ineffective at prevent cracking & separation ... it must be embedded within the center part of slab.

Fiberglass fibers may prevent some types of cracking but do NOTHING to prevent growing separation of the crack, or uneven settling along the sides of the crack.

You didn't say whether your garage is subject to freezing, but there are methods to resist 'spalling' of the concrete in freezing weather, I think it involves the amount of air "entrained" or trapped in the mix back at the readi-mix concrete plant ...

Do it once & do it right ...

 

[8587GN]

A builder once told me this,1,your going to pay taxes,2 you will die someday,and 3 your concrete will crack. We poured my 30x50 garage slab 2 weeks ago with fibermesh,I found a crack in allready

 

[TurboDave]

I don't know what was layed in my garage floor, but it's about 25X36, and it has not cuts, lines, etc.
It's about 5 years old now and no cracks. (WI winters too).

 

[CHARGED]

My 40x40 garage slab was cut like this -l-l- dividing the garage into 6 rectangles(car spots) with no poles comming down on it.

Floor hasen't cracked in 2+ yrs

The only time I even notice the cracks at all is when I'm sweeping up and some dirt goes into it, otherwise after awhile you won't even know they are there(about 1/8" wide)

 

[ez at nova]

Well, it's done. They poured at 7 am and then came back to cut the lines around 5 pm. the lines are much much smaller than I was picturing. Not intrusive at all. And when I epoxy the floor they will dissapear even more. I'll probably polyurethane fill them anyway, just because I'm picky like that
I hope I'm not overly concerned about teh curing. The concrete guys wet the floor down well, then covered most of the door and windows openings (that are open now since the garage is still being built and they are not installed) with heavy plastic to keep the moisture in. But, they didn't lay down burlap or tell me to rewet it or anything.

 

[NASSTY]

My 30x40 slab is 3 weeks old and so far there are no signs of any cracking (keeping my fingers crossed).It's still early but sometimes it doesn't take long to start cracking.I have 3 relief cuts,2 cross cuts and one down the center running lengthways.
My garage isn't going up very fast.I'm far from a good carpenter but I'm the only carpenter I can afford to build it.