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Subject:  Re: stained concrete Date:  2/12/2004  1:12 PM
Author:  Goofyhoofy Number:  46133 of 137307

Watched a show yesterday on the construction of the Mount Rushmore National Monument. Back in the 30's/40's, they used a paste of white lead, granite dust, and linseed oil to seal cracks in the sculpture. New cracks are sealed with something else, but all are monitored for movement.

The sealant is now silicone based. The object isn't to stop the rocks from moving (because that would be a vain hope) it is to keep water out of the cracks so it doesn't freeze and thaw and exacerbate the destruction of the rocks.

Silicone has the ability to "stretch" and bend and keep the crack sealed, shedding the water. The older mixture did not, and while it worked when it was first applied, any movement of the rocks caused a fissure into which the water could penetrate.

(I have relatives in Deadwood and Rapid City SD, and have visited MR quite often, most recently on September 10, 2001. Not hard to remember the date, really. It was closed the next day.)
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