> On 4/8/2010 8:42 AM, Edison Coatings wrote:
>> > Maybe it's been covered here before, but I'd be interested in comments
>> > regarding removal of paint from an historic bridge using Sponge Jet.
>> > Anyone here have experience with that? The paint is not lead-based,
>> > and seems to have been effectively removed in a test area.
> Mike,
>
> I am familiar w/ the sponge blast technology but have not used it.
About fifteen years ago I was the historic building specialist on a
project to test paint removal methods for the US Army (USA-CERL). The
test was using SpongeJet to remove a very heavy paint buildup on the
General's quarters at Ft. Benning near Columbus, Georgia. My job was to
document and analyze the effect on the the historic building. The
General's quarters was the the old 19th century Benning plantation
house. The plantation and house was given to the Feds during WWI, and
the house had been painted at least every other year since then. It had
a paint buildup that was over 3/8" thick in some places, peeling off in
plates about 4"x6" to 8"x12". The joke at this military base was that
the place was painted with pierce-resistant ballistic armor plating.
This testing project was just part of a bigger program. USA-CERL was
testing 20 lead-paint removal methods on historic army buildings all
around the globe.
The SpongeJet system is quite amazing, with all kinds of adjustments and
blast media variations, compressors, generators, hoses running in every
direction, fuel supplies, controller central, controller remote,
nineteen types of nozzles, etc, etc, etc. If we need more of anything
just call the plant in New Hampshire. In fact, it looks like it could do
just about anything, and that's the way they market it. One whole end of
the plantation house was enclosed within a lead-safe containment and
scaffolding, with suit-in and scrub-out chambers. For two weeks we
tested SpongeJet on the General's paint. But, no matter how they rigged
the SpongeJet equipment, or what media was used, the substrate was
significantly damaged when a paint chip came off exposing bare
substrate. Substrates included wood and brick masonry. The result was
the same on both, significant damage to the substrate.
I documented the historic significance of the General's quarters and the
importance of the exterior woodwork and bricks. I documented the methods
and materials of paint removal. I documented the skills of the SpongeJet
operators and the knowledge of the three other specialists involved. I
documented the paint and the substrate. And most of all I documented the
damage to the substrate, with macro and micro photos with my handy but
heavy field binocular microscope. I measured missing wood with mico-dial
indicators and made measured drawings of cross-sections of damaged wood
showing softer early growth wood and harder late-growth wood, indicating
loss of important historic fabric in four colors, with a key to the
colors in the upper right of every page. I took samples and hired Susan
Buck to do cross-section micro paint layer analysis with ultra-violet
light, polarized light, cross-linear di-fracted light, and probably a
few other kinds of light. (silly me, I had always thought there was
light and there was dark) My analysis of the General's paint was that
anytime the substrate is less resistant to the blast than the paint
there will be damage to the substrate because the blast cannot be
controlled well enough to keep from blasting the substrate. In this case
all the wood and brick masonry was much less dense and less resistant to
abrasion than the paint. Substrate damage was the inevitable result with
this SpongeJet method, and probably any other blast media method.
On the last day at lunch I was at the site alone and the General made an
appearance to ask what was going in with his house. He had been
conspicuously absent for the previous two weeks. I was a little nervous,
but he was really nice, quite friendly. I explained what we were up to
and what my findings were. He put his hand on my shoulder and asked,
"John, you look like a practical sort, if it was up to you, how would
you get the paint off?" We walked over to the wall, I took out my pocket
knife, and popped off two or three of the gigantic paint chips with with
the screw-driver blade. There were a couple of privates nearby doing
yard work and he called them over, and gave them an order to round up
four screwdrivers. I dress all of us up in lead-safe gear, and in half
an hour we had 6 sq.yds. of paint removed down to bare wood with little
or no damage.
John (his middle name is Practical) Leeke
www.HistoricHomeWorks.com
--
**Please remember to trim posts, as requested in the Terms of Service**
To terminate puerile preservation prattling among pals and the uncoffee-ed, or to change your settings, go to:
<http://listserv.icors.org/archives/bullamanka-pinheads.html>
|