Friday, March 14, 2014

Garage upgrade: new concrete pad

Once the building was suspended about 6" over the work site, I built forms with 2x6 lumber, held in place with wood and metal stakes.  I brought in half a yard of 3/4-minus crushed rock, and compacted it with a gas-powered compactor my neighbor just happened to be using the day before I needed it.  I have a hand compactor, which is basically a 15 lb iron plate on the end of a handle, and that would have been a hour-long workout.  Instead it was five minutes of guiding this machine around and I'm sure it did a better job, too.  The main pad is 4" thick, but it goes down to 8"+ around the edges to form a footing.  Yes, that's enough for frost depth around here.  I ran a single piece of #3 rebar around the perimeter, in the lower middle of the footing, to strengthen that portion, but I didn't bother with anything in the center of the pad.  Yeah, it might crack, but it's just a garage floor.  I didn't do any control joints, either.  I'm livin' on the edge!  I did put down a sheet of 6 mil plastic under the central part of the pad, to reduce the amount of water vapor moving up through the slab.

The concrete truck was scheduled for 10:30am.  I finished the rebar at 10, and got the plastic cut and laid down by 10:20.  Phew.
Ready to pour the concrete
The actual pour wasn't too dramatic.  The truck's delivery chute reached nearly to the back of the garage through the main door, so I just had to push the mud around a little with a rake and jiggle the corners.  Pulling a 13' screed board by yourself is a lot of work, but I'd been mentally preparing to scoop a few yards of concrete from the middle to the back of the pad if the chute hadn't been able to reach over my lifting beams.

Finishing it was no fun.  A strong storm forecast to roll in off the Pacific started dumping rain about the time the truck left.  Most of the pour was under the garage's roof, so not a big deal, but I had to run around and put up pieces of plywood to deflect areas that were dripping from the gutters or blowing in under the gap around the edges.  My lifting beams made bull floating the surface a huge pain in the ass.  I couldn't get the handle where I needed it half the time, and wound up digging in a few spots.  I managed to give it a quick once over in one direction and then gave up.
Using the Bull Float
After a couple of hours, I came out and edged the slab, and then hit it with a big steel trowel I bought the night before.  I guess I should have had a "fresno", which is bigger, thinner and has round ends.  I've never used one, but maybe I'll get one next time.  I tried to do a lot of the work hanging from planks laid on the lifting beams, but that was a tough angle to work from, and I was constantly moving the planks around so I wouldn't fall off.  A much better method was the usual way, which is to take a piece of plywood and use it as a work platform.  Thick plywood distributes your load better so you don't dent the surface, and you just clean up the spot where the plywood was previously sitting as you go.  I had a ~3'x2' scrap of 3/4" that worked really well.  I screwed a piece of nylon webbing to it so I'd have a handle to pick it up with as I moved along.  You need a strong handle, because the wet mud really sticks.  From down low, it's much easier to control the angle of the trowel and see any imperfections.  Anyway, my troweling skills are sub-par, but I got it relatively smooth and flat, so whatever.
Smooth Enough
A few days later, I formed and poured a couple of little ramps to get the car from the sidewalk grade to the garage slab.  I mixed up ten bags of concrete by hand and made the pads about 4" thick, with a couple of pieces of rebar in there.  To me, rebar is always a balance between making the concrete shape strong enough to last, but not impossible to break up later if (when) you realize you screwed something up or your wife changed her mind about how things should be.

After a week of keeping the slab damp and letting it cure, I lowered the garage back down, and parked the car inside.  I can't tell you how nice it is to finally have a floor I can SWEEP.