Thread: We're not fancy but dirt cheap

The mens shed needs a Q&D spray booth as the previous spray painting location (in the open air on shed driveway) got nobbled after a few of the members cars got spray on them.

I said if they purchased a small tent or gazebo and put 3 sides on it I would rig up an extractor fan and hood.

A few years ago I picked up and old fume hood extractor from a skip where I used to work and replaced the small 3P motor with an SP washing machine motor and gave it to my son who has not used it so I got it back and knocked up a small 2 x 2 ft hood for it.

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The galv sheet metal for the hood is from the backs of a couple of old stoves I took apart a few years ago.
The galv mesh is part of large roll I extracted out of a same skip I got the extractor from .

The hood is attached to the fan via a PVC threaded coupler.
A couple of PVC 90º bends and a bit of 6” duct will be used to lift the hood up to ~ table height level.
We have a big roll of filter media suitable for spray work at the shed so we'll just cut some pieces off the roll and clamp it to the front of the hood.


I won’t claim the hood itself to be accurate or square but it should work OK for small jobs.
Hood is ~2sq ft in area.
At 600 cfm the linear air speed through the filter will be ~300 feet per minute.
Tent will be ~500 cu ft so it will be vented ~every minute.

I am wondering if you could use this on the mesh as filter screen to trap the paint? https://www.bunnings.com.au/earthwoo...-roll_p0810890

Originally Posted by jackaroo

I am wondering if you could use this on the mesh as filter screen to trap the paint? https://www.bunnings.com.au/earthwoo...-roll_p0810890

I reckon it would be too dense

Originally Posted by jackaroo

I am wondering if you could use this on the mesh as filter screen to trap the paint? https://www.bunnings.com.au/earthwoo...-roll_p0810890

In this video you can see the thickness and openness of the filters typically used in spray paint booths.
https://youtu.be/NJ8Sot4Lvbo
To save time go to the 2:40" mark and from there on you will see examples of different paint arrestor filters.
Note how thin and open the filters are. They have to be like this or the paint will clog too easily.

This is what makes me think the rock wool won't be that good, not to mention the air stream will pull some glass fibres out the back and into the air stream.
If you are far from neighbours this might not matter but then you probably don't need a spray booth either.

There's nothing especially fancy about spray paint entrapment filters and almost anything with a coarse mesh that requires the air to travel in a tortuous path through the filter will trap some paint. The coarser the mesh the thicker it needs to be to trap then majority of the paint.

This is why better filters are made with a very open weave on the side facing the booth to traps the bigger droplets and then a finer weave on the side facing the extractor side to pick up the remainder. This allows the overall filter to be made thinner and increases the time the filters remain unclogged so that they don't need replacing as often.

A good filter also has a coarse absorbent (usually paper) front and a polyester finer weave back. Some filters have a graded weave that changes continuously from front to back.

Cost is an important issue for commercial operators which is why they use the dedicated stuff but this is less of an issue for DIY paint smaller numbers of smaller objects.

Air con polyester filter media can be used but it's relatively expensive unless you buy it in a bulk roll but then you will have a dozen lifetimes supply.
I use graded polyester air con filter media on the exit of the spray booth in my shed. I was fortunate to grab a bundle of these from work where they were replaced every few years. They were pretty dirty but I just put them in the washing machine and they cleaned up fine. They typically last 12 months in my shed before I chuck them out.

Better than the rockwool might be something like drain matting.
https://www.bunnings.com.au/everhard...tting_p4770243
You might need a couple of layers to get better paint trapping.

Originally Posted by BobL

T

A fe and knocked up a small 2 x 2 ft hood for it.







Hood is ~2sq ft in area.

MMM if its 24" x 24" its 4 square feet ...not 2

an alternative to filter media off a roll, are disposable filters used in the air conditioning industry

24x24 is a standard size
you can get them in 1", 2" or 4" thick frame. media is of concertina style.

Originally Posted by eskimo

MMM if its 24" x 24" its 4 square feet ...not 2

Sorry it should be 2 x 1 ft (It's actually 560 x 340 mm = 2.05 sq ft)

an alternative to filter media off a roll, are disposable filters used in the air conditioning industry
24x24 is a standard size
you can get them in 1", 2" or 4" thick frame. media is of concertina style.

If you can get them cheap enough that's fine because they do clog more easily than the graded filter media.
What the air con filters are really good for is you are setting up a dedicated booth and prefiltering the air coming into the booth.
This reduces the dust levels of the incoming air and produces a better finish.