Preserving bricks

This is in response to Jonathan Farley's inquiry on preserving a
brick from 221B Baker Street:

The problem sounds very much like a soluble salt deterioration
problem (i.e. the brick has absorbed salts from the mortar and/or
groundwater). Unless you can keep the brick forever in a low
humidity environment, conservation intervention is probably
required.

If the brick is truly crumbling I would suggest you consolidate it
and then desalinate.  I recommend 15% Acryloid B-72 in acetone,
applied by percolation: In a fume hood, or properly ventilated area,
place the brick in a plastic lidded container or plastic bag with
enough consolidant to cover 1/3.  Close the container or bag and let
the consolidant "wick" up through the brick.  It generally takes
about 24 hours.  If all the solution is drawn up, add a little more,
close again. Leave the container closed for 24 hours after the top
of the brick appears wet.  Open the container, remove the brick, and
place it in a clear polyethylene bag.  Tie the bag closed and leave
it (in fume hood) for at least a week.  The solvent will migrate out
slowly through the bag, leaving you with a well consolidated, but
not shiny, brick.

Soak in changes (daily) of distilled or deionized water to remove
soluble salts. Monitor with a conductivity meter, or specific ion
spot tests.  You will probably need to soak the brick for 2-4 weeks,
as the B-72 consolidation will slow down the salt extraction.  The
brick should be clean enough when the conductivity reads around 25
microsiemens or you get negative results for chlorides and sulfates.
(I recommend the low conductivity reading because of the
consolidation).  Remove the brick and allow to dry slowly. Good
luck!

Stephen Koob
Department of Conservation and Scientific Research
Freer Gallery of Art
Smithsonian Institution
Washington DC 20560
202-357-4880 x276

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                  Conservation DistList Instance 10:71
                 Distributed: Monday, February 10, 1997
                       Message Id: cdl-10-71-002
                                  ***