Saturday, May 02, 2009

Gunite is in


Kathleen is spraying water on the gunite, Anya is directing, while Ava looks on. We're supposed to keep the gunite wet for the next two weeks.

I stayed home for the day to watch the crew shoot the gunite. We used Aqua Gunite (here is their web site), on the recommendation of our consulting engineer Charlie Adams. I found a listing for them here. It's listed as a two-person company, which I suppose would be Jose Aguayo and Sergio Garcia. For a two-person company this place has a lot of assets: at one point I saw three and my neighbor reports five trucks lined up to deliver the sand/cement mix. Those trucks had Aqua Gunite logos and Charlie tells me they cost $260k each. They also had what my friend Wes Grass reports to be the largest air compressor he's even seen (it was all of a large truck). Maybe the company is owned by those two guys.


They got here at 7:30AM and had the gunite going by maybe 8:00AM. That gun was shooting almost continuously until something like 5:45PM, and it took them another 30 minutes after that to finish up. We used almost five truckloads of gunite (our pool is 46 feet by 18 feet, and has a big cover vault at one end). Sergio, the foreman, told me that was 78 to 80 cubic yards of gunite, but I can't see how that's possible:
  • The shell surface area is 2015 square feet that average around 8.5 inches thick (53 yards^3).
  • We have about 38 feet of internal dam walls that are about a foot thick and average 4 feet tall (5.6 yards^3).
  • There is maybe 3 cubic yards of gunite in the steps and two pedestals.
  • We have a gusset which holds up the diving board that is 2 feet by 2 feet by 6 feet, so that's another yard.
  • 10% rebound would be another 6 yards, which is consistent with what I observed getting dumped and hauled away.
  • Total: 68 cubic yards.
Those trucks were claimed to hold 15 cubic yards, but they just did not look big enough. Maybe that's the volume of the containers, which they perhaps don't usually fill completely. For comparison, a 10-wheeler holds 10 cubic yards.

The cement and sand is mixed in the truck right before delivery, and the water is only added in the nozzle at the end. As a result, they don't have the usual concrete problem of having to order exactly the right amount of mix. Instead, they have the problem of disposing of "rebound", which is the portion of the stream that does not stick when it hits the wall. Sergio says they usually have 7 to 10% rebound. Aqua Gunite carefully arranges not to have the capability to offhaul the rebound -- they want to dispose of it somewhere on site. We had a nice big hole in which to dump 2 or 3 cubic yards, but after that we piled it up on what used to be our lawn and had some other folks cart it off for recycling the next day. In retrospect it probably would have been a good idea to negotiate this ahead of time with Jose.

It doesn't much matter, we had a fixed-price contract: $13145, $733 of which was for using thicker masonite so that we wouldn't have to strip the forms to make the form edge straight. This last bit is an artifact of our having a bond beam raised 15 inches out of the ground -- the sides have to be straight so that the masons can lay the siding stone properly.

One of the first things Sergio decided when he got here is that we didn't have enough rebar in the cover vault dam wall. The wall is 12 inches thick, and had just a single curtain of #3 rebar on 12 inch centers on the water side, plus four #4 rebar at the top. Sergio added another curtain of #3 rebar on 12 inch centers on the vault side. One nice side effect is that this will make the vault floor even more resistant to cracking from the applied torque should the gravel under the pool settle and leave the pool hanging on the soil under the cover vault.


Here's the top of the gusset that holds up the diving board. You can see the four two-foot bolts that actually go up to the diving board base. In retrospect, I should have had the gusset rebar tied into the vault wall rebar better, as that would help transmit loads between the two.



So now we wait four weeks for the gunite to harden, and shrink, and maybe crack, while we race to get the plumbing, electrical, and solar installations finished, and get the trenches closed up and filled in preparation for the new landscaping. In the meantime, the maintenance crew is keeping the shell wet.