A.John Leeke, a
preservation consultant from Portland, Maine,
responds: The first step is to investigate the
masonry to determine what type of bricks and mortar
was used. Repressed bricks that are very square,
with even sharp edges, and laid with narrow mortar
joints, are usually fired hard and intended to hold
up to the weather on their own. Some buildings were
made of softer bricks with rounded edges; these
softer brick were intended by the original builders
to be painted. You wouldn’t want to leave
this type of brickwork exposed with no paint,
because the surface would absorb too much water,
causing serious problems over the long term.
If the bricks need a coating, determine if the
existing coating is still performing its intended
function. If the bricks will have to be recoated
for the good of the building, the owners will want
to reconsider their decision to expose the
bricks.
We do testing and development on every one of
our paint-removal projects. We usually test at
least three removal methods and materials, starting
with the least aggressive methods. Mechanical
methods like scraping, chipping, and dry blasting
are more likely to damage the masonry than chemical
methods.
Blasting methods that use any kind of grit
usually damage the bricks by taking off the
weather-resistant surface, exposing the more
absorbent core of the brick. Blasting can also
remove mortar, leading to the need for repointing.
Even high-pressure blasting with plain water can
blast out softer but perfectly good mortar.
Although blasting must be approached with caution,
we still sometimes test and use blasting methods,
which can work well under certain conditions.
In recent years, our tests have usually led us
into using wet/chemical methods with low-pressure
washing. With these methods it is easier to control
the hazard of lead-containing waste. Generally,
solvent-type chemicals give better results than
caustics, because un-neutralized caustics seep back
out of the wall to damage paint coatings (even on
adjacent woodwork).
To determine which removal methods and chemicals
work best, we begin by testing small 1x1 foot
patches. Then we select the best performing method,
and try three or more variations on methods and
materials on successively larger test panels.
Why is testing necessary? Because the conditions
on these older buildings are so variable and
unknown. On a recent project, a tradesperson who
knew better skipped testing and development and
signed a contract for a paint removal project on a
masonry building. It turns out that back in the
1970s, an owner of the building (who was a chemist
at a local industrial plant) painted the house with
a special chemical-resistant epoxy coating. The
removal took six times longer than expected and put
the guy out of business.