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Discussion Starter #1 (Edited)
Here is how I am fixing my drive way slabs that have opened too far for self-leveling sealant.

This is how it looked before I started. The gaps range between 1 inch to 1 1/2 inch wide. Too wide for backer rod and Sika sealant.


I cleaned out the old crumbed expansion material and loose dirt.
Then I cut strips of Lowes blue polystyrene foam to fill most of the depth, and also to support the repair motor that I will fill in later.


I had a whole bunch of old rubber foam mats that used to be in our laundry room. This stuff is really tough. Can't pull it apart, it has to be cut with a utility knife. Seems like a great material for expansion joints.


I cut the foam into strips about 1 1/2 inches wide. So that the edge would be flush with the top of the slabs. I cut the ends so that the strips would be butted up against one another. I used Gorilla glue to keep them attached to each other.


Here is how the gaps look before I backfill with the mortar repair.


Here's the repair mortar and bonder I used in the next steps. I wire-brushed the gaps and edges, then brushed on the bonder.


I will post the final result. I forgot to take a picture of the finished project.
 

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Anyone else think this repair is going crack within a year?
Those slabs are going to move at slightly different rates from freeze thaw, and just heavy rains.
 
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i'd bet it will crack,,, conc isn't flexible in this situation,,, a sealant should be used - that's what i'd recommend

:thumbsup: on the backer rod material - like that idea,,, the material's compressible so when the slab expands in summer heat, the sealant's still supported,,, you won't find the size you need at apron/vest stores,,, any const supply source will have it,,, OR go to the dollar store, buy the kids' pool foam tube wings, & cut them to friction-fit size :yes:

irc
 

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It won't make a year. It has to be a flexible material. The size of the joint is not a problem for joints, I have seen them 3-4 inches wide.

They make backer rod that big, and it needs to be a round backer rod, not flat, although in a pinch flat will work. The important things to remember for any flexible joint are:

The depth needs to be half the width.
The backer should be round, flexible, and provide a bond-break between itself and the sealant.
The joint needs to be clean, dustless, and dry.
 

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Discussion Starter #5
One detail I left out is that the driveway is on a bad slope. Using self-leveling sealant would not work for that reason as well.
Why does everyone think it will crack?
I don't think it will because all I've done is add about an inch of length to the slab. That inch is well supported underneath with tightly packed soil, gravel, and high compressive strength foam board. The repair mortar is structural and rated at 6000 psi after 28 days. I don't plan on parking on it for at least the first month. I also don't think the concrete will expand much, as it rarely sees direct sunlight. The position of my house and path of the sun takes care of that. And this is in Pittsburgh where it does not get very hot for very long.
 

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Discussion Starter #6
i'd bet it will crack,,, conc isn't flexible in this situation,,, a sealant should be used - that's what i'd recommend

:thumbsup: on the backer rod material - like that idea,,, the material's compressible so when the slab expands in summer heat, the sealant's still supported,,, you won't find the size you need at apron/vest stores,,, any const supply source will have it,,, OR go to the dollar store, buy the kids' pool foam tube wings, & cut them to friction-fit size :yes:

irc
I like the swimming noodles idea. That will work in other areas where I have level grade and wide joints between sidewalk slabs.
 

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that 1 detail you left out will cost you, soldier,,, DROP DOWN & GIVE ME 50 !!!!!

NOODLES - that's the word i couldn't remember :whistling2: tnx for that !

the conc repr you've done don't have enough tensile or flexural strength hence, as tscar posted, it will crk :yes: rather soon, too,,, it will have compressive strength however not enough 'bulk' for that quality to overcome the other deficiencies :no:

there, of course, is a limit on joint width - check the mfg's w/site for proper depth:width ratio,,, were these joints originally formed w/2x4's ?

irc
 

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It is a live crack, that is the dimension changes over time. If you use a material with a strong enough bond and tensile strength not to crack itself (like an epoxy), it will crack at the edge of the repair. You do not need to use a self-leveling product, the are plenty non-sag ones that will work just fine.
 

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Discussion Starter #9
Update:
In July 2015, at least a year after my OP there were no problems with the repair. No cracks or other defects. I have since moved to Florida and will have a new home to post topics for.
 

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cracks that are 'working' (joints) often exhibit sealant failure thru loss of adhesion (break away from the edge) OR cohesion (they crack down the sealant's middle),,, the 'trick' is installing it no thicker than designed + 'tooling' against the sidewalls - CLEAN sidewalls of course
 

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Actually, looking back at the pictures, you did it the right way. You left a live, flexible joint with the laundry room flooring material. I misinterpreted your posts originally.
 
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