One of my earliest childhood memories was a job that I had remarking the white lines on the local tennis court.
My recollections are that I had to mix up a fine white powder with water, pour it into this weird looking three wheeled contraption, pump it up with a hand pump, and then as I walked down the lines pull on a lever which squirted the white stuff onto the line.
This was, of course, whitewash – at least one form of it. In years gone by, before sophisticated paint formulas had been developed, and before pastels had even been thought of, people used whitewash to paint just about everything, but mostly houses and fences.
So what is whitewash? Well of course we have all read about Tom Sawyer and his famous account of tricking people into whitewashing the fence. But we aren’t told how Tom Sawyer made up his whitewash.
Mostly, whitewash appears to be hydrated lime. According to Wikipedia, it is a mixture of hydrated lime and calcite (which is limestone, or calcium carbonate). The idea is that when you paint it on, the hydrated lime reacts with carbon dioxide in the atmosphere and is converted to calcium carbonate (limestone), and the mixture hardens, or cures.
Ca(OH)2 (lime) + CO2 = CaCO3 (limestone)
The trouble is that I don’t know anywhere where you can buy calcite, or chalk as it is commonly known, in powdered form. So that leaves us just with the lime, which I’m pretty sure is what I put on the tennis court. But the problem with this is that it will take longer to cure than it would if it already have some calcite in it.
So how do we make it up? Fortunately, our friends at Cockburn cement can help us out. They have produced a series of formulae for use in different applications. The one for cement looks particularly interesting, and would probably be a nice way to finish the surface after cleaning off oil stains. I’m not sure why they put salt in there, but it’s probably used as a thickening agent to help the lime stay in suspension, and make it easier to get a consistent coating when you paint it.
If your cement driveway needs rejuvenating, give it a go and let me now how you got on.