> 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

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