Spray Booth Design Requirements #1: Exhausting (the purpose of a spray booth) attracts unfiltered air

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Blog entry by CatiaMan posted 10-05-2009 08:14 PM 2546 reads 0 times favorited 1 comment Add to Favorites Watch
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Hello everyone, I know there is much talk on this subject but I have not seen anything related to establishing proper design requirements of a spray booth so here goes. As you can see in one of my projects I built a spray booth (concept 1) based on a simple design requirment, to exhaust the overspray so that the finish improves, and to that end it worked. However, now that I am thinking about this in more depth, the process of exhausting the overspray also pulls fresh air in, air that may be laden with dust. So let’s say I want to achieve a super mirror like finish, I suppose this basic concept is flawed.

Perhaps I have it backwards, the fans, which are fitted with furnace filters to provide filtering, should blow towards the workpiece. It also means that whoever is doing the spraying would be exposed to the overspray much more so than concept 1.

Another approach might be to make the spray booth zone over pressured by a small amount, just enough to keep unfiltered air out. Then within this over pressure zone, another fan is used to exhaust the overspray. This sounds like a winning approach except if you want to work outside.

My workshop is small so I plan to build a spray booth outside. It will need to be heated or the finishes will not dry. I am thinking of an insulated outter box (shed) with an spray booth inside. The outter box is where the heater air is created. The inner box is the spray booth proper and is overpressured (by fans that draw air accross filters) as described above. This way the same air is recirculated without loosing it to the outisde (to keep costs under control).

Am very intersted to hear your comments especially if they lead to a better design.

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19 posts in 3256 days

#1 posted 10-05-2009 08:44 PM

If the overspray is exhausted outside then you risk loosing all the heated air if you do a lot of spraying. If you only do a little then I suppose exhausting to the outside would work. In my application I spray 4 coats of polyurithane totalling about 5 minutes per coat. I expect I would loose all the heated air in a small shack in less than 5 minutes. That’s why I am thinking outside exhaust is not the right approach. Instead I think relying on the furnace filters to trap the overspray and keep the heated air. In my spray booth project, I mentioned that before I built the booth I sprayed (HLVP) a frech door and my workshop air was thick (like London fog), after building the booth, the air was very clean (normal) and there was no residue on horizontal surface the next day, also the leading edge of the fan blades were clean so I am sure the filters are doing their job. Of course not exhausting means you better be wearing an approved mask !

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