Concrete control joint question

[Macinnis]

I have a 60x60 pole barn. All posts are 10,000 psi concrete posts set in ground with concrete and dirt material filling the 4 foot hole they are set in. At 6 inches out of ground they are 3 2x6s screwed together up to the truss.

20x45 of this space will be used as an apartment with the remaining 15 foot as a covered patio. The remaining 40x60 will be used as a barn/shop.

I had the concrete guy out today to do a final inspection of the grade (now that I finished my plumbing) and control joints came up.

Concrete guy said: the living quarters does not need to do any control joints, we will just do one on your long wall (separating the shop from the apartment).

They will be doing cut in control joints in the 40x60 shop side. He was trying to be nice I believe and not show any control joints in the living quarters side.

My question is...should I have him put in some control joints in the living quarters side, regardless of what they look like?

The barn sits on level ground with 4-6 inches of compacted gravel with fines and then 4-6 inches of clean gravel on top of that.

Edit: the slab will be 4-5 inches thick, over 4000 psi, with rebar on chairs and fibers.

All opinions appreciated.

Thanks,
Bill

 

[mikester]

Control joints are meant to put cracks where you want them. All concrete cracks, especially in large monolithic slabs.

I can't picture your setup, but if you get a good concrete job done on a well compacted base it probably doesn't matter if you put control joints in or not if you plan on a floating floor material like engineered wood or carpet. Terrazzo might be different. I have no control joints in my house and ceramic tile and haven't had any problems in 23 years.

I've seen new builds where lazy contractors don't compact properly, then the concrete guys pour wet runny cement because its less work for them, and a year later your beautiful concrete floor with control joints has cracks in it and is heaving in unexpected places.

On an aside I strongly recommend putting insulation under your concrete floors. Recently I've seen contractors using closed cell spray foam on the floors upto and onto the walls. Makes a great vapour barrier and thermal break.

 

[fried1765]

Control joints are meant to put cracks where you want them. All concrete cracks, especially in large monolithic slabs.

I can't picture your setup, but if you get a good concrete job done on a well compacted base it probably doesn't matter if you put control joints in or not if you plan on a floating floor material like engineered wood or carpet. Terrazzo might be different. I have no control joints in my house and ceramic tile and haven't had any problems in 23 years.

I've seen new builds where lazy contractors don't compact properly, then the concrete guys pour wet runny cement because its less work for them, and a year later your beautiful concrete floor with control joints has cracks in it and is heaving in unexpected places.

On an aside I strongly recommend putting insulation under your concrete floors. Recently I've seen contractors using closed cell spray foam on the floors upto and onto the walls. Makes a great vapour barrier and thermal break.

A major reason for concrete floor cracking, is the amount of water added to the concrete mix.
The stiffer the mix (less water) generally the less cracking (shrinkage).
Concrete contractors do not like using a stiff mix, because it is more difficult for them to work with.
Tough chit!
I would put lots of control joints in the entire floor.
The joints are best being cut in, and done so within 18 hours of the pour.

 

[dougtrr2]

When my garage floor was poured they used a different technique for the control joints. I didn't see them do it, the contractor pointed it out and explained it to me afterwards. They poured the floor. Then at some point before the concrete completely set they used a trowel? to slice a control joint in the floor. The they lightly troweled over that joint to hide it. As it dried I had very fine cracks at those points. It served me well.

Doug in SW IA

 

[s219]

Remember that saying, there are two types of concrete: concrete that has already cracked, and concrete that will crack. I'd put standard control joints the same everywhere. There are methods that might look a little neater in the living area if appearance matters.

 

[Macinnis]

Here is the layout...he was going to do one control joint along the wall separating the apt from the shop, then all throughout the shop.

 

[Rustyiron]

Isn't there a reccomend s/f for control joints in a large (60x60) slab? I know there is, just don't want to mis state it.
The last slab I had done I had them use a vinyl "T" shaped strip that got pushed- tapped into the concrete after the first trowling. Then the too of the "T" got pulled off leaving a very minor visual, and it worked as a control joint and is near invisible.

 

[fried1765]

Here is the layout...he was going to do one control joint along the wall separating the apt from the shop, then all throughout the shop.

View attachment 686325

I would also cut a cross joint every 20ft.
I guarantee you will have cracks with the layout you show.

 

[Macinnis]

Thanks. I will look into the vinyl thing or have him just cut them into the living space side as well. Thanks all!

 

[rademamj1]

That's what I would do. Saw cut the expansion joints on your living area. You can always put down tile, vinyl or wood flooring to hide the expansion joints.