Concrete 101

Today’s the day the RETROpad finally gets its pad. And not a day too soon, with a rainy forecast ahead.

Gary arrived early to set small plastic pylons under the rebar, to keep it elevated. We had measured the RETROvan’s wheels and concentrated the rebar under those stress points, where the concrete will support up to 2,500 pounds per square foot.

The Oregon On-Site Concrete truck arrived at 12:45 and Mike was happy to help again with the project. He explained that all the mixing happens just as the materials enter the chute. Apparently the days of the spinning cement mixer trucks are numbered. Modern trucks are really just storage compartments. Our mix even included hot water, since it was barely 60° when we started.

Gary started from the back using a wheelbarrow, since the truck is wider than the gate. From there it’s a race against time, especially for a one-man band like the Jackson 1.

The first pass at leveling is done with a 2×4. We had snapped blue chalk lines along the inside of the curbs as a guide for the drainage grades. We wound up using 3-3/4 cubic yards of cement mix, at a cost of just over $500. But the 9×30 foot slab is four to five inches thick.

The next step involves working the mix with a long-handled smoothing tool made of magnesium, called a bull float. This coerces the “fat” to the top and helps the gravel aggregate settle in.

It takes hours of edging, troweling and brushing to complete the finish. Stress cuts are pressed in using a special tool held against a straight board. These lines give the concrete a chance to crack cleanly if it should ever settle.

Oh no — someone’s damn horse ruined everything!

The RETROpad will be usable in six or seven days, once it turns white. Gary says the coming rain is a good thing, because that will make the concrete cure slower and become that much harder.

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