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Spray booth build


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Built myself a spray booth in the garage this week and thought I'd share what I've done and learnt so far!

When my dad and I replaced the garage door with the stud wall several weeks ago, I got myself an explosion proof axial fan and we built it into the wall. I was planning on a negative pressure booth -  Means the pressure in the booth is lower than the surrounding room, so it's sucking air out of the booth at a higher rate than air can enter the booth which has it's pros and cons:

Pros of a neg pressure booth being that it's safer IMO , because it won't push fumes out into the room if there are any bad seals etc so it's not a risk to me when I'm doing other work in the shop, paint is less likely to end up in light fittings, switches etc (which could be very bad) because air is being sucked towards the extraction. The cons are that it's sucking air and potentially dust into the booth before it's sucked out through the extraction which means there is the potential for dust landing on the work. I'm not too worried about this because I used to spray my guitars in my old garden next to a dusty building site and got pretty good results by the time it was sanded and buffed.

With a positive pressure booth, the fan would be on an internal wall pushing air in at a greater rate than it is being forced outside so dust etc from outside can't get in therefore a better quality finish in theory. But the potential for fumes to work their way into the rest of the shop and electrical stuff if seals are not perfect.

Stud wall with the fan in situ

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Grill on the outside

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Wall insulated and plasterboarded around the fan

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Drew the layout on the floor and started on the studwork, used 2x2 that my good old dad cut down for me on the table saw from 4x2 (all I could get from the yard) he also mitred a 4x2 for me so I had 45º to make the door frame studs.

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it's 2.1m from the back and 1.8m from the left wall giving me 3.78 sqm minus the 45º door way but I'm not splitting hairs. The height is 2.4m so there is an overall volume of around 9 cubic metres which is important to know this as it indicates how efficient the fan will be at clearing the booth - This fan is specced to moved 30 cubic metres of air per minute, so in theory, my booth is < 1/3 of that volume so all the air in the booth should be displaced in < 20 seconds... in theory, and without filters as filters will slow down air flow. 

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once all the stud work was done, I began cladding the walls, I got some twin wall polycarbonate which is normally used for conservatory/green house roofing etc. rationale being that a clear wall would let a lot of ambient light in from the rest of the workshop and reduce the amount of light I need to put in the booth. For the rest of it 

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For the rest of the walls I used left over offcuts of plasterboard and ply that I had from the rest of the conversion project, I wanted to leave at least one wall partially plasterboarded in the event that I might need to add an inlet fan if I couldn't get good airflow, from what I had designed

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Made a timber frame door and carcass for the exhaust chamber. I had to change my plans here, I was going to have a filter on all 5 faces with the hope it would provide better extraction by pull fumes form all directions, but there wasn't enough suction so I ended up boxing off the sides and just having the front open. 

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Used some mesh grill screwed on to the frame, then filter, then screwed some baton around the edges to hold it in place, much better suction now, if I let a piece of paper just in front of it, it sticks to the exhaust :) 

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Had to do a bit of trial and error with the inlet (which I incorporated into the door), at first I had half the door as inlet but there wasn't really any negative pressure - while it cleared the booth, it felt like it took too long, so I reduced the size of it with an extra noggin and some more ply . Now I can noticeably feel air being pulled through the inlet. Got the filters in there to prevent workshop dust making it's way in. 

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It looks kinda dark in this photo but it's actually suprisingly well lit and light from outside the booth made a big difference, those two LEDs in the ceiling are in exactly the right spot (happy accident). Regarding the lights, they're not "explosion proof", they're IP65 which means they're fully dust proof and water resistant according to the spec they are fine unless full submerged 🤪  so to be on the safe side, I have siliconed around the edge of them were they meat the plaster board and also around the edge of the glass that meets the plastic housing, hopefully that will make them explosion proof...

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I went round and sealed every join I could find until I ran out of silicon so need to do more of that, but the act of sealing has made a noticeable difference too. Check out my "smoke test" below. I gave the back wall a coat of primer this arvo. Hoping that white walls will brighten it all up further. 

Still got a little way on my current build before I'm ready to properly try it out. Looking forward to hopefully not exploding myself. 

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1 hour ago, ADFinlayson said:

Looking forward to hopefully not exploding myself.

I can't say I've thought of it in just those terms....but now that you mention it, I'm looking forward to that as well.:D

That is very nicely done BTW. Thanks for sharing.

SR

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41 minutes ago, MiKro said:

Just remember to move the car or you may have over spray from the vent. ;)

mk

I park it round the front of the house now anyway because I went out to it the other day and it was covered in tree sap :( we're surrounded by a tone of tall Ash trees. The vent and the parking situation was always a consideration though. 

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3 minutes ago, ADFinlayson said:

I park it round the front of the house now anyway because I went out to it the other day and it was covered in tree sap :( we're surrounded by a tone of tall Ash trees. The vent and the parking situation was always a consideration though. 

I get that, I have a large Pecan tree that I park under. The squirrels use my truck for target practice when they shit while they eat the pecans.

Little bastards. :)

MK

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That's a nice booth you've built there! The clear walls for ambient light are clever!

IMO negative pressure is better as it pushes all the fumes outside. With a positive pressure booth you'd be inhaling the fumes forever in the rest of the workshop.

There was times I thought I'd mention a thing or two but as I read further I noticed you already had sorted them out, including the filtered air inlet in the door and keeping the car away from the outlet grille.

Very nice!

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2 hours ago, Bizman62 said:

That's a nice booth you've built there! The clear walls for ambient light are clever!

IMO negative pressure is better as it pushes all the fumes outside. With a positive pressure booth you'd be inhaling the fumes forever in the rest of the workshop.

There was times I thought I'd mention a thing or two but as I read further I noticed you already had sorted them out, including the filtered air inlet in the door and keeping the car away from the outlet grille.

Very nice!

Yeah I was just rereading the UK HSE guidelines and it seems they actually prefer a negative pressure booth. The refer to a positive pressure booth as a spray room and less sophisticated. https://www.hse.gov.uk/pubns/priced/hsg276.pdf

They also state that a positive pressure/air fed mask should be worn, well those cost a lot of money.  I know you can't put a price on your safety but A LOT of money. 

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8 hours ago, ADFinlayson said:

a positive pressure/air fed mask should be worn, well those cost a lot of money. 

In a negative pressure booth, preferably equipped with a what-do-they-call-it filtered sucking cabinet so you can keep the fumes in an even smaller area, an active carbon mask adds quite a good layer of protection. I bought one from China for about 7 euros including mail. The better version with glasses is just a little more. - When buying a mask for painting, make sure that the vent isn't right in front of you! The moisture from your breath tends to condense and drip on your fresh finish.

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43 minutes ago, Bizman62 said:

In a negative pressure booth, preferably equipped with a what-do-they-call-it filtered sucking cabinet so you can keep the fumes in an even smaller area, an active carbon mask adds quite a good layer of protection. I bought one from China for about 7 euros including mail. The better version with glasses is just a little more. - When buying a mask for painting, make sure that the vent isn't right in front of you! The moisture from your breath tends to condense and drip on your fresh finish.

I ordered a new mask this morning actually. The mask I've got is alright - it's the GVS P3 full face mask, but as a glasses wearer it's a PITA and I don't currently have any contact lenses so I've ordered a Moldex series 7000 from Spraygunsdirect which I can wear glasses over the top of. I'm thinking I might shell out for some proper prescription goggles because I've been wearing my glasses as eye protection which isn't good enough, really. The mask I really want is the 3M versaflo positive fed mask and turbine but that's around £1000 all in. Maybe I'll see how I get on this year and how much spraying I do. It's a lot of money but if I'm spraying a lot and I can wear glasses and not have to shave the beard off. I was also looking at the Trend Airshield pro, which I thought was bang on the money at £230 but it's only p2.

 

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I got a coat of primer on all the walls and the ceiling this morning, just needs a coat or 2 of emulsion over the top, nice and bright. That dodgy dangly wire is the power, my dad left me with a temporary connection so I could get up and running while he's away on holiday and it's gonig through a 20mm hole in the back wall to the socket outside, he wants to put it through some conduit so it's sealed off properly (although it is fairly well sealed at the fan anyway) then there is going to be a switch just outside the booth.

I've read about downside of negative pressure booths being that they're great until you open the door and all the dust gets sucked it, so I was thinking I might put a switch inside on the back wall, so that I can wait for the room to clear, switch off extraction, step outside and switch it back on again. I got a IP66 rated switch to do it (the most sealed I could buy and more sealed than my lights on spec) but the explosion risk is of creating a spark and a switch creates a spark (it's only the act of switching lights on or off that might spark), so I was also considering just having the switch just outside and having a little hatch on the back I could open to flick it off and walk out, but to be honest there is not that much pressure, I really don't think any of this stuff is necessary, when thinking back to where I used to spray.

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Anyway, I couldn't resist having a go this afternoon so I sprayed 6 coats of rattle can cellulose sealer on this tester. It wasn't sanded particularly well but I'm very impressed with how little orange peel there is from a rattle can considering how much I used to get spraying it in my old garage.  

I sprayed, stepped out and shut the door, no sign of fumes anywhere else in the garage even when I sniffed at the filter in the door. Sprayed a load more and nipped out the front and couldn't really smell anything either, but more importantly, I haven't exploded myself yet. Looking forward to trying it out with the spray gun :) 

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