Concrete Floor Expansion Joints

[Cemoto]

My floor will be poured next week and the concrete will cut expansion joints no charge.

Do I need them?

And what size?

The floor is 34'x30' inside the foundation.

Any advice is well appreciated - Thank you!

Regards,

 

[bobscogin]

They're going to cut control joints, not expansion joints. And yes, you need them. I'd recommend two saw cuts on each axis, which would make the panels 10' X 11'-4". They need to be sawed as soon as the concrete is hard enough to put the saw on. To be effective they should be no less than 25% as deep as the slab thickness.

Bob

 

[ForceFed70]

They're going to cut control joints, not expansion joints. And yes, you need them. I'd recommend two saw cuts on each axis, which would make the panels 10' X 11'-4". They need to be sawed as soon as the concrete is hard enough to put the saw on. To be effective they should be no less than 25% as deep as the slab thickness.

Bob

Bob has got you covered there with some excellent advice. Isn't really anything more that needs to be said.

 

[Cemoto]

Thank you very much. I will pass this along.

Best Regards.....

 

[1949 caddyman]

Are you putting a lift in? If so cut so that posts are on same cut slab.

 

[Highbeam]

Mine were only about an inch deep for a 5 inch slab but worked perfectly. In the bottom of each cut a crack formed, that's the idea. Crack in the cut, not in the floor.

 

[James E]

Bobscogin nailed it. I worked for a mason who also did concrete work. He told me he never let a slab span more than 12 feet without a cutline. We did mostly driveways and sidewalks, very few garage floors.

 

[bobscogin]

Bobscogin nailed it. I worked for a mason who also did concrete work. He told me he never let a slab span more than 12 feet without a cutline. We did mostly driveways and sidewalks, very few garage floors.

A good rule of thumb is that the size of the panel in inches should be about 30 times the slab thickness in inches.

Bob

 

[Cemoto]

Thank you sir.

But, my new dilemma is that because the door openings are off set and the left to right cuts will fall in the middle of the bay.

Any suggestions here please?

Thank you very much.

Regards,

 

[bobscogin]

But, my new dilemma is that because the door openings are off set and the left to right cuts will fall in the middle of the bay.

Doesn't matter. The purpose of the control joints is to induce cracking in the joint rather than at random. Having a straight, thin saw cut in the middle of a bay is better than sawing the panels the wrong size to accommodate the bays and ending up with big cracks meandering randomly across the surface.

Bob

 

[wssix99]

Thank you sir.

But, my new dilemma is that because the door openings are off set and the left to right cuts will fall in the middle of the bay.

Any suggestions here please?

Thank you very much.

Regards,

The control joints can be on the doors, but if you are going to install a lift - you may need the joints in specific places. If you need to do this, you can add joints. As long as the longest distance between two contraction joints is less than 24-36 times (American Concrete Institute Recommendation) the depth, then you are fine. (The closer you are to 24, the smaller the chance of getting cracking outside of the joints. The closer you are to 36, the larger the chance to getting cracking outside of the joints.)

 

[joes169]

If I were the contractor, I'd saw it at 9' by about 8' squares. The door openings ARE important, as any 90 degree corners is a potential for a re-entry crack. Concrete doesn't like to be bound by a solid foundation as it cures and shrinks, so either have them place additional cuts to the door jambs (they can angle from the last intersection), wrap a foam expansion material around the door jambs, or ideally, do both.........

 

[skulldrinker]

you don't want to cut deep enough so the rebar or wire mesh gets cut. Take a look at the sidewalk out front. Those lines are 5 feet apart. No matter what you space the lines at chances are some of them will crack in the middle.

 

[HotrodHR]

Thank you sir.

But, my new dilemma is that because the door openings are off set and the left to right cuts will fall in the middle of the bay.

Any suggestions here please?

Thank you very much.

Regards,

I'm not a concrete expert, but I would have the contractor put in two cuts... one vertical in center of doors (at the divider) and one horizontal centered on the 32' wall...

or same vertical and two horizontal cuts space equally on the 32' walls (10.67' sections)...

I think either way your floor wil have very few "cracks" if any... plus you know you're gonna want to epoxy coat it anyway!

 

[Cemoto]

Ok, so I came up with this for a plan based on the advice given.

There will be a 4' apron on the front so I didn't want a saw line running into that.

The floor will be 4" w/ steel mesh but in spots thicker due to penetration into the stone. So using the 30x thickness rule I should be good at 11' - right?

Thanks again for all the help.

Regards,