Ask the Expert Question-and-Answer Archive

by Ron Joseph

February, 2005

Selecting Between Dry Filter and Waterwash Spray Booth

Q. If we have high productivity (for example from 50 litres of organic materials such as polyurethane or NC paints per day) is it possible to use dry booths or dry pressurized rooms for painting of wood parts for example doors, panels, windows? If it possible what kind of dry booths (rooms) could you recommend for us?

A. Thanks for your question: Your usage of 50L/day (13 gals/day) is high for a "small" dry filter spray booth, but not too bad for a "large" dry filter booth. By "small" and "large" I'm referring to the facial surface area of the exhaust plenum and not the physical size if the spray booth. For a dry filter spray booth, the larger the surface area of the filters the more paint you can use, provided that the paint overspray is well distributed over all the filters. If you paint in the same spot every day and load up the same filters all the time, then what I've written does not necessarily hold true.

For all other paints I probably would not hesitate to suggest dry filters, but since you intend to use nitrocellulose (N/C) lacquers I'm concerned that if you load up the filters extensively before replacing them, you run the risk of having a spray booth fire. Such fires can occur at any time, even at night after all the painters have gone home. In the USA N/C lacquers are no longer used as frequently as they used to be prior to the 1980s when spray booth fires were more common, but in recent years with the change to other coatings we hear of such fires less frequently.

Therefore, in my opinion I would suggest that you consult with the spray booth manufacturer and discuss the pro's and con's of dry filter v. waterwash booths. I'm inclined to suggest the use of a waterwash booth, even though it has several disadvantages.

If the painters predominantly point their spray guns in the direction of the exhaust plenum, you should consider a side draft booth. If they walk all around the doors, windows, etc., and spend much time spraying in different directions then a downdraft spray booth is preferred.

I hope this helps.

Best wishes,

Ron Joseph