Rebar sealant in Concrete.

I have removed an 18" section of concrete under my garage door (cut with a diamond saw) because it was crumbling. I also removed one row of foundation blocks under it. The concrete was only 2" thick at that point and the obvious reason why it crumbled. I'm getting ready to pour a new entrance. I drilled a bunch of 1/2" holes 4" deep into the old floor and I'm going to insert 1/2" rebar 18" long to tie the new to the old.. My problem is what type of sealant to use when I ram them in. King Sealants have a product for bolts but recommends a hole much larger than the bolt (Rebar in my case) It is not to be used in wet areas however but I supposed that it won't be wet when the concrete is dry. Loctite has a range of products and one of them might be the ticket. Has anyone had a similar experience? Ben
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Ben wrote:

First of all, we dowel into existing concrete to tie a new slab to it all the time and don't use any type of sealant or actually adhesives. If you drill a half inch hole into the existing concrete, you will usually have to drive the #4 dowels into the hole. You will probably have trouble pulling them back out.
Having said that, in instances where an adhesive is needed, we use an epoxy anchoring system. There are many on the market, but we use one from Hilti which is a two part epoxy that comes in a caulk tube. The parts are mixed in the nozzle and injected into the holes, then the dowel is inserted.
There are two part types that require a special caulk gun (quite expensive) but you can find some that come in a single tube that you can put in any old caulk gun.
Contact your local concrete products supplier and they will have what you are looking for. Again, I would recommend going more that 4" into the existing concrete and just driving the dowels in. You might try one and see how you like the fit.
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Robert Allison
Rimshot, Inc.
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There is a special epoxy that is used. I don't know the name but they were using it on my construction just the other day. The hole has to be the right size for the rebar and then must be blown out with an air compression to be completely clean. I am sure your local concrete supply place will know the right type of epoxy.
Mike
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Someone suggested a 1/2" hole and drive the #4 rebar into it. If the hole is in the edge of a 4" slab and I drove a bar like that into it, the slab would split. The hole needs to be 5/8", not 1/2". It doesn't need epoxy though.
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In Florida the epoxy is required for hurricane protection I guess
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vMike wrote:

Sometimes we have to use epoxy because it is engineered into the design. Most of the time, the epoxy is not required. Sometimes it is definitely wrong to use epoxy, such as in expansion joints (as in curbs). There we use smooth dowels with one side of the dowel sleeved to allow movement between the separate concrete sections.
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I may have missed something in the OP but isn't the edge of the concrete that he's talking about only 2" thick?
At 2" I doubt epoxy or no epoxy will make much difference. But it the epoxy makes you feel better, go for it.
OP, if you want to use epoxy I suggest SIKA AnchorFix #1 (available at HD, at least in SoCal)
fits in standard caulking gun, gels in 5 minutes & cures in an hour or so; great stuff
If you're going to epoxy, I would suggest 9/16 or 5/8" hole
followed by brush, blow, brush hole cleanout / prep
Stick the nozzle in & load hole from the bottom.......only a few pumps since the rebar will take up most of the hole & you don't want to waste this stuff at $16 / tube.
insert rebar, rotate the rebar in a twisting fashion, back & forth to spread epoxy
Have all your holes prepped so you can fill & insert rapidly.......the stuff cures so fast, it can harden in the nozzle if you hesitate.
The Hilti products are also great (I used to use them but switched to SIKA, got a free sample & loved it; esp since it goes in a standard caulk gun) Hilti now makes product that also goes in a standard gun.
All the "epoxies" (after not epoxy but that's what everyone calls them) on the market made by major companies are awesome products.........they have to be since the market is so demanding & competitive.
On the issue of a 1/2" rebar in a 1/2" drilled hole..... 1/2" rebar is ~9/16" over the "bumps" but it has the total cross section of 1/2" smooth bar.
A 1/2" rotary hammer bit will tend to drill "slightly large" ........so one can easily hammer in rebar, the rebar broaches it's way in, with the shaved concrete material filling into the rebar deformations.
But for adhesive installations one wants a slip fit with a small bond line (minimizes material usage & improves stiffness)
cheers Bob
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Thanks for all the info guys. I decided not to use a sealant. The old floor was 3 to 4 inches thick. The 2 inches was at the entrance of the garage because the foundation blocks had been brought up too high 35 years ago when the house was built.That is why the concreted had crumbled over the years. I removed one course of blocks which means the concrete is now 8 to 10 inches thick at that point, since I am now have a 2 inch slope in 1 foot. No more rain backing into my garage.
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Glenn wrote:

Wow! Maybe I shouldn't have done that the last 4 or 5 hundred times. You mean that I may split the concrete? Man, I never realized that. I had better go back over the last 200 or so jobs that were done like that and check for split concrete.
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