Drilling concrete for Seismic retrofit tips tricks please.

[skylarkguy]

So I decided that my house, originally built in the 1930's, needs a seismic retrofit. Basically the premise it that keeping the house on the foundation is the best way to have the structure survive a slip fault earthquake. Before 1974 there were no requirements to bolt the sill plate to the foundation, thus the need for a retrofit.

What is required it basically screwing/bolting a series of plates to the foundation and sill plates. I'm using a simpson strongtie UFP10. The bolts require that 2 holes 1/2 inch diameter by about 2.5 inches deep be drilled in the concrete foundation for each bracket. An expansion bolt then is placed in and bolts the plate down. Each plate requires 2 bolts and I have 40 plates for the size of my house.

Drilling has been a difficult and tedious affair. Keep in mind I'm working in the crawl space on my belly or side. I've managed to install 8 plates in about 10 hours...brutal. So I need some suggestions on how drill concrete. What I have is a Porter cable PC70THD, hammer drill (7amp, 2 speed), I've tried several different bits (standard concrete "ace" brand, a dewalt branded one, and a dewalt with 4 cutting surfaces. I've tried just using the 1/2 inch bit, I have also tried drilling with a 1/4 inch bit first. Most of the time I have been spinning the bit fairly slowly, a couple I when full speed and it really chewed the concrete...but man it got hot.

Any suggestions would be appreciated.

 

[KevT]

Try using a small SDS drill such as a Bosch Bulldog. What you have is made for occasional concrete, use a drill dedicated to concrete. Your arms/hands wont tire as easily either.

 

[Egon]

As per KevT on the drill. You may also try and make a support or hanger for the drill to take the weight off your arms.

 

[skylarkguy]

Thanks guys. I did find out there is a difference between a hammer drill (what i have) and a rotary hammer (what i need).

 

[Paddy]

Renting or buying a real tool will be quickly justified. My drill will drill 1/2 holes 4 in deep in 10 sec.

 

[skylarkguy]

Paddy...do you recall a make and model?

 

[EddieWalker]

Like already mentioned, you need a SDS drill. They are fairly cheap at the box stores. I have a Makita from Home depot and it just melts through the concrete. Get a good quality bit and you will be amazed at how easy it is. I also have Makita bits, which I highly recommend. But for such a small number of holes, you should be fine with just about any name brand.

One of the nice things about the SDS drills is they can be used as small jack hammers, or for digging in really hard clay. It is a tool that has multiple uses that makes it very worthwhile owning. I also have a SDS max drill that is the same thing, just a lot bigger, heavier and more powerful that I use for holes bigger then half an inch, but mostly for jack hammering out concrete on remodel jobs. It also has a nice attachment for driving in ground rods that makes that a fun project

 

[Cord]

I upgraded from a Hilti TE30 to a TE76 and I can't believe the difference in power. The bigger drill is a SDS max and it pounds 1/2" holes through concrete like you were drilling in wood. No joke. These are too expensive to buy new so try shopping on Craigslist or Ebay. Otherwise just rent the tool for a day.

 

[skylarkguy]

So do you guys think something like this would be sufficient...

Makita 8-Amp 1 in. SDS-Plus AVT Rotary Hammer-HR2621 - The Home Depot
Milwaukee 7/8 in. SDS D-Handle Rotary Hammer-5262-21 - The Home Depot
Bosch Bulldog Extreme 1 in. Rotary Hammer-11255VSR - The Home Depot

Or move up to something like this...
Bosch 1-1/8 in. SDS-Plus Drop Down Rotary Hammer-RH328VC - The Home Depot

or this:
Milwaukee 1-1/8" Heavy Duty Corded Electric Rotary Hammer

I don't usually do the pawn shop route but could in this case.

 

[Cord]

My Hilti is a 15a unit; here are the specs for a similar model: https://www.us.hilti.com/drilling-&-demolition/combihammers/r1021424 You can always get by with something smaller, but as you have discovered it comes at the cost of time.