Don, thanks for your response to my question about white wash, but I must ask. What is the purpose of the 3lbs of salt? Wouldn't that rust the nails and such? Just wondering. Thanks again.

-- Red Neck (Secesh@CSA.com), November 23, 2001

Answers

The salt is there to slow the peeling of the whitewash off of whatever you apply it to. Chemically, the dried whitewash in the first recipe looks like NaCl + Ca(OH)2*(H2O) (bi-directional arrow) CaCl2 + NaOH + H2O . The understandable explanation is that the salt and the slaked lime will release water to the air(called "the water of hydration") when the whitewash is too wet, forming Calcium Chloride, Sodium Hydroxide (AKA lye), and free water. The process slowly goes back and forth depending on the water content in the air. This keeps the whitewash at the optimum water content, which prevents the whitewash from forming cracks and falling off your fence. Eventually the Chloride ions get washed away and you have to call Tom Sawyer's boys over to get the fence done again. If you use galvanized nails (steel coated with zinc), the zinc and free chloride ions form zinc chloride, which is white: no problem. However plain steel nails form ferric chloride, which is a nasty dark brown chemical that will stain. That should be enough freshman chemistry for one evening...

-- Paul D. (pd-personal@qwest.net), November 24, 2001.