Help with Concrete Seams / Expansion Joints

[regularguysc]

Hello,

I know very little about concrete. I'm getting a 24x36 (3 car wide - 24 foot deep) slab poured next week. A foundation was poured, and a 4 block high cinder wall put up. The will be grading the inside, putting clay down, laying a vapor barrier, and then pouring a 6 inch slab.

It occured to me that they mentioned putting in expansion joints. I have no clue whether these are the same as "seam" so please correct me if I'm off the rails.

Question : if they put 2 seams in - one every twelve feet running from to back (that would make 3 separate 12 x 12 sections) then there will be a seam right about where I'll be putting in a lift. If they put 3 seams about every 10 feet (one seam centered in the middle of each garage door) then the lift's posts would be on different "pads" (not sure that is the correct word). Is this possible ?

The other option would be to run the seams across the 36 foot wide (left to right) about every 8 feet (making 3 separate 8 x 36 foot sections) then the lift posts (2 post) would be on the same "pad".

Any experience you may have would be helpful!

 

[tcianci]

First of all the feature you are talking about is called a control joint. It's purpose is to provide a place for the concrete to crack due to shrinkage as it cures. When shrinkage forces are not channeled to a weakened area via the control joint, random cracking of the slab is possible. You are probably correct in arranging the control joints to keep them away from the lift base plates, however I would still be inclined to run them in the short direction of the slab. There is no problem in having one base plate on one slab and another plate on another slab. A properly compacted and well drained base should not exhibit any compressive setteling or frost heave. Be sure to use a mix that is specified by the lift manufacturer as far as compressive strength and thickness for the anchor bolts.

 

[ConCretin]

tcianci laid it out very well. The only thing I'd add is to keep the 'panels' created by the control joints as square as possible. The 8x36 panels you suggest are likely to crack in the short direction.

You didn't ask but if it were me install some rebar in the area that will support the lift. This would mitigate any potential weakening created by the control joints.

 

[regularguysc]

Thanks for the feedback. I spoke with a local dealer / installer for Bendpak and Direct Lifts and he stated that you can have a control joint between the posts, just not between the bolts of a single post.

So I plan on having a control joint down the center of each garage door. 3 control joints total. So at 36 foot wide (35 foot inside dimension) each control joint would run front to back (24 feet). This would make 4 panels, 8'9" by 24'.

I plan on asking for rebar, though they are going to be using fiber, so I shouldn't have any problems with a "hobby" lift (@ 9000 lb two post).

Any other advice would be appreciated.

 

[Ryze]

Did you ask the installer about how close they can bolt the lift to the control joint?

We had a lift installed here at the shop in May and the installer mentioned it not being a good idea to install in within so many inches of a control joint.

 

[regularguysc]

Yes, the installer said 1 foot away from a control joint. My plan is to have the control joint run down the center of the garage door, so it'd be 5 1/2 feet from either lift post base plate (or 6 feet if I get a 12 foot wide lift).

 

[Dan in Pasadena]

Concrete cracks in approximate square as the shrinkage TENDS to be consistent across the entire slab. This assume you don't have deeper sections for footings, etc. Which brings me to my point. If you can decide in advance where you want to place your lift, pour the footings for it first, quite a bit deeper with a 2'x2' pad, then pour all the other floor as a separate pour. Then you will NOT get slab cracks from the weight placed on the lift.

 

[justsam]

Hello,

I know very little about concrete. I'm getting a 24x36 (3 car wide - 24 foot deep) slab poured next week. A foundation was poured, and a 4 block high cinder wall put up. The will be grading the inside, putting clay down, laying a vapor barrier, and then pouring a 6 inch slab.

QUOTE]

I am about as far as you can get from being a concrete expert, but the notion of putting clay down first does not seem right. I would think you woud want something that drains, like tamped down crushed gravel.

Perhaps it has to do with your soil condition?

 

[regularguysc]

Concrete cracks in approximate square as the shrinkage TENDS to be consistent across the entire slab. This assume you don't have deeper sections for footings, etc. Which brings me to my point. If you can decide in advance where you want to place your lift, pour the footings for it first, quite a bit deeper with a 2'x2' pad, then pour all the other floor as a separate pour. Then you will NOT get slab cracks from the weight placed on the lift.

I had thought about that when I was playing with the layout on graph paper. But honestly couldn't decide on the lift placement (front / back / distance from the wall etc.) and all the different sizes / wheel bases of the vehicles with enough accuracy to be effective. So I figured just go with the 6 inch slab and figure out the placement later. And while that would appear to be more money, I think under the circumstances the way my contractor operates the needed accuracy and multiple trips / stages / days needed to pour separate deeper sections would be more expensive. But, I'm meeting iwth him again tomorrow and see what he says.

 

[regularguysc]

Hello,

I know very little about concrete. I'm getting a 24x36 (3 car wide - 24 foot deep) slab poured next week. A foundation was poured, and a 4 block high cinder wall put up. The will be grading the inside, putting clay down, laying a vapor barrier, and then pouring a 6 inch slab.

QUOTE]

I am about as far as you can get from being a concrete expert, but the notion of putting clay down first does not seem right. I would think you woud want something that drains, like tamped down crushed gravel.

Perhaps it has to do with your soil condition?

Thanks. I'll double check about the drainage issue. I would serious doubt I'd have a problerm though. We've lived here a year and in that time we've had at least a couple of storms that drop 4 + inches of rain. The soil here is almost completely sand, and there is never as much as a puddle in our yard after a downpour. Very different from the Philadelphia and Chicago that I'm accustomed to.

 

[joes169]

Thanks for the feedback. I spoke with a local dealer / installer for Bendpak and Direct Lifts and he stated that you can have a control joint between the posts, just not between the bolts of a single post.

So I plan on having a control joint down the center of each garage door. 3 control joints total. So at 36 foot wide (35 foot inside dimension) each control joint would run front to back (24 feet). This would make 4 panels, 8'9" by 24'.

I plan on asking for rebar, though they are going to be using fiber, so I shouldn't have any problems with a "hobby" lift (@ 9000 lb two post).

Any other advice would be appreciated.

You don't want this either, as someone else stated above, you want to keep the sections as close to square as possible. The industry "standard" is no more than a 3:2 ratio, or in other words, a floor section 8'9" wide should be no longer than 13' long.........

 

[regularguysc]

You don't want this either, as someone else stated above, you want to keep the sections as close to square as possible. The industry "standard" is no more than a 3:2 ratio, or in other words, a floor section 8'9" wide should be no longer than 13' long.........

Thanks for the feedback / advice. I've been playing with graph paper to try and figure out a solution. I think I've solved it, the dotted lines are the control joints, the garage is 36 x 24, I have a 2-post lift in the first (left) bay and a 4 post in the middle bay. With the three control joints in the middle of each bay and two running across, none of the pads are larger than 11 x 8.

Any comments about this or the general layout would be a huge help. Hopefully they will be putting the slab down Monday or Tuesday.