Varnish spray booth

I received inquiries for further details on the "spray booth" I
referred to on a few weeks ago (Conservation DistList Instance:
17:38 Tuesday, October 28, 2003). These might be better described as
"walk in down draft varnishing cabinets". The first of these was
conceived of by me and engineered by consultant engineer Peter
Mathieson in 1997-8 and installed in an off site conservation
facility we occupied while our main building was being renovated
over a 4 year period. It was so successful we constructed two
identical units in our renovated facilities which we have only just
now returned to.

The units are approximately 4 meters wide, 3-3.5 meters high and two
meters deep. The entire front of the unit consists of 2 bifold
doors, allowing unfettered access. Temperature and humidity
controlled makeup air is delivered through the 4 x 2 meter roof
through common F-5 paint spray booth filters at a half meter
(approximately 1.64 feet) per second velocity. The velocity is
determined by Australian occupational health and safety
requirements, but given the choice, we would have installed a
continuously variable speed control. The airflow is drawn straight
down through a metal grill floor raised 1 foot above room level. It
would be preferable to have the exhaust air plenum sunk into the
floor, but this proved impractical in our buildings so we have a 1
foot step up into the booth.

The air flow should be as smooth and even as possible. The balance
between the delivery fan and exhaust fan is critical and the two are
designed to operate so the unit as a whole is in slight negative
pressure. F-5 filters are also in place under the floor which helps
even out the air delivery/exhaust cycle and traps overspray.

By not calling the unit a spray booth and assuring our Environmental
Protection Agency we are--in comparison with industrial
users--dealing with only occasional use and with extremely small
amounts of solvents, we avoided having to meet their stringent
requirements which would have required much higher air flow.

The units are more economical to build and maintain than
conventional designs because though they are 4 x 3 meters or 12 sq.
meters in usable size, the face area of the air outlet is only 4 x 2
or 8 sq. meters. Filtered makeup air going straight down through the
floor makes it unlikely residual dust or overspray will contaminate
wet varnish and the unit can be operated with doors closed, further
reducing the possibility of dust contamination from adjacent spaces.

They have proven ideal for spray and brush varnishing paintings as
well as for cleaning paintings and frames with solvents.

Peter Mathieson can be contacted at <mathiesonp [at] conwag__com> for more
specific engineering details.

Tom Dixon
Chief Conservator
National Gallery of Victoria
Melbourne Australia


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                  Conservation DistList Instance 17:42
                 Distributed: Friday, November 14, 2003
                       Message Id: cdl-17-42-004
                                  ***