I've been asked out to visit a lighthouse on the East coast that has the
following problem as related to me over the phone:

A while back the masonry (sandstone) structure, a significant landmark, was
painted with a breathable (?) coating by a chimney company. Prior to the
coating the structure was cleaned with baking soda blast. Currently the
coating is adhering to the mortar joints, but not adhering to the sandstone.
The coating resounds hollow over the sandstone. The coating manufacturer and
the installer are telling the lighthouse group that it is not their problem.
The lighthouse is located in a coastal exposed location with a high degree of
Nor'Easter weather.

My questions to BP: Is it possible that the baking soda blast saturated the
sandstone with salts such that the coating would not adhere to the sandstone?
How would one determine the baseline content of salts prior to soda blasting,
after the act? If there were salts present in the sandstone prior to the soda
blasting, are there masonry coatings that would adhere to the sandstone
regardless of salt content? Would it make sense to take a masonry drill and
take a preliminary dust sample of the sandstone?

I imagine walking around to the landward side of the structure may not be a
bad idea.

Lastly, why do people clean masonry with baking soda blast? I've never yet
seen the technique not result in efflorescence. Seems to me
impregnating/saturating masonry with anything is somewhat contrary to the "do
no harm, think reversible" methodology.

I'm worried over a few issues that I am not looking for answers to here: 1)
do they need to remove the coating and 2) what will that, or no action,
result in to the historic fabric and 3) do they have any case to go against
the manufacturer and installer for the cost of correcting the situation?

A portion of the problem, I suspect, is the relatively isolated and possibly
naive lack of information on the part of the lighthouse group and that they
may have been blindsided by the coating installer. I'll be taking w/ me a
copy of the NPS Lighthouse repair handbook.

For now I'm out collecting information.

Thanks,
][<en

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