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?
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.
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.
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
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.
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
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 &
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"
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
But for adhesive installations one wants a slip fit with a small bond
line (minimizes material usage & improves stiffness)
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
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.
Bottom posted below top posting to try and preserve SOME kind
of reasonable flow of conversation. Hint: Start right below
this post, follow it down to the bottom. Jump back up to the
top, then end here. But wait, you have to start here to get
the instructions on how to read after the top posting, so
start here, then follow my other directions.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.