Saturday, July 28, 2007

Fortress Progress!

If you're a regular reader of my blog, then you've suffered through quite a few unhappy posts over my frustrations with getting a fire-proof “safe house” built. I started this product last October – 9 months ago – and it still is not completed. But today, for the first time in 8 months I can report some progress. Substantial progress – what you see at right is a slab, poured (14 yards of concrete) and finished! I just came back into our house from wetting down the slab, something I must do for the next few days as it cures.

The fellow at right is my contractor, Ruben Ponce. He hails from Chula Vista, which is roughly 30 miles from here; he does concrete jobs all over southern San Diego County. Don't even think about using him until you've read my previous posts – and feel free to contact me directly (through comments or by email). My experiences have been a very mixed bag – high quality work with an almost unbelievable inability to get the job done.

I've never had the chance to observe a concrete job from close up before; the process was more interesting than I expected it to be. The “pumper” showed up first, towing a diesel-powered concrete pump behind his pickup. This concrete pump would move the concrete from the nearest point to the project that the concrete truck could reach (about 100' away) to the project itself. Carlos the pumper told me that he owns several of these pumps, plus a “boom truck” – one of those impossible-looking articulated machines that looks a bit like a cherry-picker with a few extra segments. His pump is a piston pump, with two pistons working alternately to keep pressure in the hose relatively steady. One feature of the pump Carlos tried to explain to me, but failed – I had to Google it to figure it out. His pump has a tank of high-pressure nitrogen attached to it, and I had trouble imagining what that could be used for in pumping concrete! It turns out that the nitrogen is used to pressurize a surge chamber that helps keep pressure (and concrete moving down the line) during the brief time while the pump is switching over from one piston to the other.

Shortly after Carlos arrived, the first concrete truck arrived. This first truck was carrying 9 yards of concrete, and so was very heavy. He had to turn around in my yard so that he could back up my driveway and a small hill to where Carlos' rig was set up. The driver and Carlos worked together in a very practiced manner to get the truck's chute lined up with the big funnel that leads into the pump; it was obvious that both of them had done this little dance many times before…

Once the truck and pump were physically lined up, Carlos added some water to the mix (I'm not sure why), and then the driver positioned himself to control the rate at which concrete was fed into the pump. His job seems quite simple – just control the speed at which the giant drum spins so that the funnel on the concrete pump is mostly full. Something I didn't know before: the drum on the concrete trucks spins one way when they're running down the road (keeping the concrete well mixed) and the other way when they're unloading. There are baffles inside the drum that form a sort of Archimede's screw to pump the concrete out through the action of the drum's turning. It's an ingenious solution that eliminates any need to tilt the drum.

Carlos the pumper doubles as the “placer” – the guy who has the job of placing the concrete in the right place and in the right quantity. He started in one corner of the footing trench and worked his way around the entire foundation, filling the trench but leaving the slab itself empty. Ruben's son told me that this was done in order to allow the footing to begin curing before the slab was poured on top of it. It took Carlos something like 45 minutes to fill the entire footing trench.

At that point he started placing the concrete for the slab itself. He has an amazingly good eye – no doubt developed through much practice – for judging the amount of concrete needed to precisely fill the form. The other two workers (the fellow on the left is Ruben's son) attacked the concrete Carlos placed with pieces of scrap lumber, very quickly getting it flat enough to tell if any area needed more concrete, or needed to have some removed. There wasn't a single instance I observed where Carlos' estimate was off by more than a few cubic inches per square yard of surface…

The concrete placement started along one side of the slab, and proceeded toward the opposite side. The other guys worked immediately on the areas Carlos was filling, just moments behind him. They used nothing more than a piece of scrap lumber, worked very cleverly, to get a rough level just inches behind where Carlos had just placed concrete. Just after I took the photo at right, the first concrete truck ran out. Within a few minutes, the second truck was backed up to Carlos' pump, and the work recommenced as though nothing had happened.

After all the concrete was placed, the whole crew of four workers got very busy. After the whole slab was rough-leveled, they started on the detail – making sure the sidewalks sloped gently outwards (so rainwater will run off and not collect) and the inside floor was level. Then they went to work with in an interesting collection of odd (to my eye, anyway) tools to get the surface nearly perfectly flat and very smooth. The photos below are in sequence from left to right, showing the guys working on this phase of the project. The very last step was to use a broom to create a light texture on the part of the slab that will be a sidewalk outside the building.

No comments:

Post a Comment