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Old 04-04-2010, 12:04 AM   #1
Sawbladz
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Default Connecting two existing concrete slabs

I am posting this to try and get some advice from people who may have done this before or have more experience working with concrete. The situation is that we have two existing slabs. They are directly in line with each other and at the same height and have the same width (12ft). One shed is 8 feet long while the other is about 6. They are separated by a distance of approximately 6 feet. Is it possible to have a slab poured between these two existing pads to make one larger one? How would one tie them together or is that the best idea? The building on the larger, front shed would lose its back wall the roof line and existing side walls would be extended to cover the rest of the new slab.

Essentially, this plan is to make a usable, small garage out of two tiny sheds for limited cost. If the plan for the foundation is feasible the rest of the work could be done in a weekend. Let me hear your guys thoughts.
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Old 04-04-2010, 12:23 AM   #2
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Default Re: Connecting two existing concrete slabs

This should be a pretty straight forward job. What you want to do is drill horizontal holes in the two slabs and epoxy some rebar into it, then have some sticking out. You should be able to continue to tie the rebar together. What you are tying to do is what some people have to do when they want to install a hoist but their floor isn't good enough, and they cut out a section of the floor and then put in a new and stronger section.

Derek
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Old 04-04-2010, 12:59 AM   #3
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Default Re: Connecting two existing concrete slabs

The only problem with pouring a new section in between the two existing ones is to avoid cracking/chipping at the 2 seams , you would have to cut/groove expansion joints in at the 2 seams. doing that you wouldn't have a completely flat floor, also use rebar as said earlier
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Old 04-04-2010, 01:19 AM   #4
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Default Re: Connecting two existing concrete slabs

There is a concrete bonding paint that will keep the joint from opening. All supply houses HD, Lowes carry it. I used it when I had to cut a slab out for a lift. It does work.

Without it, concrete will never adhere to old work.
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Old 04-04-2010, 01:39 AM   #5
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Default Re: Connecting two existing concrete slabs

Hope the 2 slabs are plumb w/each other.
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Old 04-04-2010, 02:07 AM   #6
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Default Re: Connecting two existing concrete slabs

Quote:
Originally Posted by hilld View Post
This should be a pretty straight forward job. What you want to do is drill horizontal holes in the two slabs and epoxy some rebar into it, then have some sticking out. You should be able to continue to tie the rebar together. What you are tying to do is what some people have to do when they want to install a hoist but their floor isn't good enough, and they cut out a section of the floor and then put in a new and stronger section.

Derek
X2

Also, add expansion joint foam(NOT TO BE CONFUSED WITH EXPANDING FOAM) to the 2 existing slabs...it is about 3-1/2" tall & about 3/8" thick-it is perforated about 3/4" along it's length(guessing on the measurements). You nail or tack it to the existing slab-or slabs in your case with the perforation near the top. After the new slab is poured between your existing slabs & cured, you rip out the 3/4" foam & seal with a product called Deck-O-Seal, it's self leveling. You also need to get silica sand & pour it in the joint prior to using the Deck-O-Seal-what the silica sand does is take up all the voids to avoid using extra D-O-S.....keep pouring silica sand til you have a SOLID bed of sand about 1/4" or so from the top of the slabs-THEN use the Deck-O-Seal.

This will allow the slabs to move a little & not let water between the joints & possibly rust out the rebar dowels. I've bought the Deck-O-Seal at wholesale pool supply houses, though might be available at Home Depot under a different name. Good luck.


Check www.deckoseal.com for deck-o-seal & deck-o-foam.....not cheap but work great. Even though they're geared toward the pool industry-this system works with any concrete job.
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Last edited by g6f6y6g; 04-04-2010 at 02:26 AM.
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Old 04-04-2010, 10:22 AM   #7
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Default Re: Connecting two existing concrete slabs

Excellent. Thanks for the great advice. I will be checking to see if the pads have shifted but when they were poured they were plumb and level to each other. I'm sure they have shifted slightly over the years but I hope not by too much.

The expansion joint foam you are talking about. Does that come in a roll? All I can find is the type of sealant that comes in a caulking type tube. I can picture the product you are referring to in my head but I can't find it. Have a link?

With the expansion joint foam, would I want to have this in place before I drill and install my rebar? The way I read that is that you want the foam to protect the rebar from water and I only see that working if the foam were in place first with the rebar running though it.
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Old 04-04-2010, 11:14 AM   #8
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Default Re: Connecting two existing concrete slabs

Yes, it does come in a roll & deck-o-seal comes in a caulking gun cartridge for small jobs & a 2 part pourable mixture-which I think would work best for your app. Check link @bottom of my previous post. I would drill & epoxy the dowels first & make small notches in the foam. The website has a lot of good info.
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Last edited by g6f6y6g; 04-05-2010 at 12:07 AM.
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Old 04-04-2010, 11:22 AM   #9
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Default Re: Connecting two existing concrete slabs

The approach of using the rebar and then the foam, tear out and self leveling sealer is right on. The only thing no one has mentioned is depth. You really need to find out how deep the other slabs are footed and create a similar situation for the piece you are planning to add. If the other slabs have a deep perimeter footing and you just pour a slab on grade between them, the different pours will react differently to frost conditions (heaving) and you will see cracks where one floor is trying to move the other. Even if your existing slabs seem to be less than perfect as far as how deep they go, do the new one the same way. Everything will "fly in formation".
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Old 04-04-2010, 11:43 PM   #10
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Default Re: Connecting two existing concrete slabs

That makes sense. Thanks for the input everybody. When this finally gets done I will be sure to make a thread to show how it turned out.
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