As part of a remodel project and reconfiguring an exterior wall, I need to drill some 7/8" holes in my foundation to epoxy in 3/4" threaded rod. So I got an SDS rotary hammer and an 18" long 7/8" carbide hammer bit. I've never done this job before, so I'm looking for some advice.
For example, how will I know if I hit a piece of the foundation rebar? Hopefully this won't happen as long as I keep the new holes in line with the existing anchor bolts. If I do hit a piece of rebar, is there a way to drill through it? Most of my holes I could just move over a bit, but two of them are tightly constrained and would be a major design headache to move.
I done this a LOT, that is, drilling into concrete with rebar.
"For example, how will I know if I hit a piece of the foundation rebar?"
The bit will stop advancing. With a good rotary hammer (Hilti, Miluakee) the bit will make steady progress into the concrete. Don't push hard on the tool, let it do the work.
You CAN drill by the rebar IF you only hit it "partially". If you hit it dead on it will be nearly impossible to drill through with a rotary hammer (unless it's only a #3 or 4 bar and you are very stubborn)
But do you reall want to sever the rebar?
Most epoxy anchoring goop allows for oversized holes, not a great idea since it can lower the tensile valves if the hole is REALLY big but much better (IMO) better than severing the rebar.
The worst thing that can happen is that you just barely nick the rebar & the bit "corkscrew" passed it.
When you go the withdraw the bit, the drilling debris will cause the bit sieze up in the hole.
A pair of vise-grips will be helpful but clearing the hole as you go by withdrawing the bit often is the best bet. Even better blow & vac it..
You'll get a feel for the rebar depth so you'll know when you in the "danger zone".
Getting a bit stuck is a major PITA and can take a long time to futz with to get out.
If you hit rebar with a bit I suggest that you stop, re-drill the hole with a larger bit such that the smaller bit now can be "moved over" & sneak passed the rebar.
SImpson & Sika both make good products for this sort of app; Sika works in a regular caulking gun, Simpson needs a special one ($$'s)
Both products spec hole sizes; the SImpson website gives info about oversized holes
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SImpson reports no stenght reduction for holes up to 150% larger than desired hole. The SImpson website (& Sika for that matter) has a wealth of info
Long winded answer.........my bottom line, avoid severing the footing rebar, work around it, over size the holes if need be & load them up with goop. :)
Make sure you blow AND brush the hole.............the correct sequence is brush, blow, brush (at a minimum) but ALWAYS end with "brush".
Thanks for all the info. I just received the item requiring the precisely placed 3/4" threaded rod (a Simpson Steel Strong Wall SSW12x8). I now see that the bottom holes to bolt it to the foundation are oval shaped, so I do have some leeway to move the hole if I hit some rebar.
BTW, is drilling a 3/4" hole any easier than drilling a 7/8" hole? Most of the holes I need to drill are for anchor bolts, which only have to be 5/8", so they would only need a 3/4" hole. But I figure it would be simpler to just do everything with 3/4" rod in 7/8" holes.
Cheers, Wayne
P.S. Why does everyone use epoxy to grount in the anchors, instead of a cementatious grout like hydraulic cement? Is epoxy stronger, or just easier to work with?
You know you hit when it seems you aren't drilling anymore. Just use less pressure and you'll go right through it. Takes a bit longer than concrete is all.
Too bad you already got you StrongWall I would have suggested a ShearMax
anyway
"is drilling a 3/4" hole any easier than drilling a 7/8" hole?"
Slightly but it depends on the capaciyt of the hammer, I have a Hilti TE-52 that can drill up to 1 1/2" so 3/4 or 7/8 not much difference but my Milwaukee Falcon (nominal 3/4" capacity) would struggle witha
7/8" bit
"Most of the holes I need to drill are for anchor bolts, which only have to be 5/8", so they would only need a 3/4" hole. But I figure it would be simpler to just do everything with 3/4" rod in 7/8" holes."
Use the rod size they suggest, the smaller rod with be more forgiving with respect to placement & fit up
"Why does everyone use epoxy to grount in the anchors, instead of a cementatious grout like hydraulic cement? Is epoxy stronger, or just easier to work with"
PourStone, PourRock, etc are fast setting cementious anchoring compounds that work well. I've used them in some situations but never for uplift on shear elements. I have no idea of the tensile properties. I have experience with epoxy; construction & testing. I know it works
IMO the epxoy goop is easier to work with, esp the Sika AnchorFix that goes in a standard caulk gun The strengths are in the 5000psi+ range
they sell it at HD in the masonry section, the two parts come in a single standard caulk cartridge (two plastic "bags" inside the caulk cartridge)
There is a fast (~5 minutes) & a slow set (~30 minutes) AnchorFix1,
2 or 3 I don't remember the number. Read the tubes.
The fast set stuff with harden in the nozzle for you don't keep dispensing new proucts every minute or so. I've lost lots of nozzles by being delayed & setting the gun down; only to find the product setup!
If you use the fast set, ....................you've got to ready, setup & quick!
The short answer is that my approved permit plans call for epoxy anchors. The long answer is that while I haven't checked the numbers, I am under the impression that epoxy anchors are much stronger. I'm in a seismic zone.
ShearMax is a wood shear panel? I'm actually using a metal shear panel with attached wood side bucks, the whole thing is only 12" wide. Shearmax's website is rather rudimentary, but it seems to indicate that their smallest product is 16" wide.
Right, the Simpson Steel StrongWall calls for 3/4" rod, so I know I have to do 3/4" rod. The other holes are just for anchor bolts for the 2x6 mudsill (at least every 4', and 6"-12" from each end), which are required to be at least 5/8". I was planning to use 3/4" anchor bolts for simplicity.
Wayne, I saw you going with Simpson products. Their wedge anchor is tested tested under ICBO's AC01 Acceptance Criteria for Expansion Anchors and is rated to withstand seismic,wind, tensile,and shear loading as are other anchors. The epoxy bond strength is greater than wedges, but the tensile strength of the rods are another story. Of the rod that Simpson has, 2 out of 3 are weaker than wedges. The other is about 15% stronger.
Wedge anchors are indeed tested & approved for tensile (wind / seismic) loads
I've done cyclic testing on wedge anchors and I would never use them for tensile loading; for shear they're fine but not tensile.
Chemical anchors (epoxy / vinyl esters) are the way to go.
With chemical anchors you drill down deep into the meat of the existing foooting & improve their performance by de-bonding the top few inches of the rod
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