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Discussion Starter #1
This guide is intended as a collection of suggestions for anyone contemplating a DIY spray job on their car in an average garage. There's a lot of subjects to consider but the results can be good if it's all taken carefully and slowly.

As everyone's situation will be different, it is appreciated there can be no “one solution fits all”, but a lot of research went into my own project (and a few mistakes!) and hopefully I can pass on some of my discoveries on the subject.
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Discussion Starter #2 (Edited)
Health & Safety

Two types of paint were used, metallic basecoat (solvent based) and clearcoat (2k).

The solvent gives off unhealthy fumes and the 2k contains extremely unhealthy isocyanate, so serious attention must be given to the quality of breathing air especially for the clearcoat.

Breathing requirements for 2k spraying are for the user to have an air fed mask, usually in the form of a branch off the feed to the spray gun via a belt mounted regulator to a full face mask that seals completely around the face.



There are filter masks advertised that claim to be able to filter out the isocyanate for up to 40 hours of use (Gerson 2k disposable masks - about £20), however given the severe danger to health and the fact that isocyanate is odourless I couldn't bring myself to take the risk and decided instead to go down the air fed mask route to be completely safe.



The air fed mask gives us home sprayers a bit of a problem in getting enough air from a general DIY compressor.

A typical spray gun uses 9.5 cfm of air, and the air masks typically require about 7cfm, so the compressor would have to supply 16.5 cfm of air working flat out to keep you breathing and paint the car at the same time. This figure is the “Free Air Delivery”, which is about a third less than the “Displacement” figure of the compressor quoted in its specifications, so I would need to buy a compressor with an air displacement figure of over 24 cfm in order to breathe and spray at the same time! Compressors like this are either 3 phase, two single phase motors or petrol/diesel driven and cost a lot more than I can afford.

The air from the compressor will contain droplets of water and oil and must be filtered out both for painting and breathing. Filters for painting can be down to 5microns and are easily obtained. Filters for safe breathing must go down to 0.1 microns, which are obtainable but get expensive as you need the flow rate to be unimpeded in order to get enough air through to the spray gun. One solution I haven't seen implemented would be to take off the spray gun feed after the 5 micron filter but before the 0.1 micron filter. This would lower the flowrate through the breathing filter and allows the use of a smaller less expensive filter.

This combination of filter and compressor requirements makes it all a bit expensive for a one-off DIY project to spray your car, so compressor air fed masks are really out of the question unless you have an industrial compressor and good filters already installed.

The solution I found in the end was to buy an air fed mask from Aliexpress (£75) which included a belt mounted rechargeable motor driving a small two speed fan that supplied air to the sealed mask. The motor pack has a filter that screws into it, but if removed will allow a 20ft extension breathing hose (£28), which was then connected to a 10m tumble dryer ventilation ducting which brings in a constant supply of fresh air from outside the garage with no need for oil and water filtering. This has worked very well, the mask seals well and is well made. I can stand in the middle of the garage surrounded by a mist of spraying droplets and solvent and not smell anything except fresh air.


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Discussion Starter #3 (Edited)
Dust-Free environment

The floor was 40 year old dusty concrete. Pre-sealing with 20% PVA solution and then painting with garage floor paint worked well. The dips and bumps meant roller application was going to be patchy, so a fence brush was used to “scrub” loads of paint into all the dimples and give a good coverage.

The brick walls and exposed rafters were a good source of dust and cobwebs, and have been covered with sheets of polythene stapled to the woodwork. The sheets are 2.7m x 3.7m thin polythene (Prodec PDPY001 from CPC, £1.55 each) and seven were needed to cover the ceiling, sides and ends of just over half of my double garage. These cheap poly sheets are very thin and the first staple didn't hold the sheeting, so 25mm reinforcement tabs of black duct tape were used at each staple point for added strength.

The first few spray sessions produced lots of dirt specks in the clear coat. This was traced to a piece of hardboard used as a table top. Even though it had been vacuumed and wiped, it still gave up lots of bits when the gun was blasting anywhere near it, so be aware of anything that can give off bits of dirt when painting. Apparently newspaper used for masking can give off fibres when hit by strong air blasts.
Clear coat is known to build up static electricity when sprayed, which explains why my basecoats are speck free but nearly every clearcoat has a few dust nibs. I tried mopping the floor before a session, and misting the polythene clad walls very lightly with a water spray bottle, and this made a great difference.

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Discussion Starter #4 (Edited)
Ventilation

As the garage was sealed in an effort to minimise dust particles, there was no flow of air in the garage to dry the paint. The solvents need to be removed to bring down the solvent vapour pressure, clear the air, and allow drying and hardening. Two kitchen/bathroom ventilation fans are used, one for inlet and one for exhaust. The inlet fan is mounted in the eaves at the northwest corner, above the sealing polythene, and feeds air through a 3m tumble dryer ducting from outside to a cardboard box fitted with a flange left over from a Screwfix tumble dryer kit. This box is wall mounted inside the spraybooth with one side of it cut out and replaced with air filter material.

The exhaust fan is mounted on the rafters at the southwest corner, collecting air from inside the spraybooth with another length of tumble dryer ducting leading it to the outside eaves at the southeast corner. After a few sessions I cleaned it out to find it had nearly seized with all the paint build up. A modification then added a large rectangle of filter material in front of a box housing the fan to catch the paint, and this filter should be renewed before every session.

These fans could have done with being a little stronger, as quite a fog builds up when spraying clear coat.
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Discussion Starter #5 (Edited)
Lighting

My regular garage lighting really didn't make the grade, with barely enough light to just see the car let alone work on it. I needed a lot more light, and being able to see well from all angles when painting is a must, otherwise it may look good in the garage but turn out like a patchwork quilt when rolled out into daylight!

There are so many cheap led lights available I managed to get a good light coverage without much expense.

There are cheap floodlights available and I fitted four along the the centre line of the booth ceiling (CPC Pro-Elec PEL00547 20W at 6000k, 1600lumens, £5.34 each). These really are bright and the colour temperature will help with any paint matching you may need to do.

To illuminate the sides I bought six T5 led tubes (CPC ProElec PEL01621 8W 800 lumens) and fitted three each side in a 3m length of round white guttering from Screwfix. Not as bright as the overhead lights but good enough to help light up the sides of the car. They are hung by adjustable cords with toggles to raise and lower them to the optimum position.

Spraying the bumpers revealed a problem with lower down vertical surfaces, I had to get down on the floor to see any reflections to guide my spraying. I added two portable 20W LED floor standing led work lights (CPC PRO ELEC PEL00947 )

Lots of light sources spread around the place are needed as you can catch the reflections at different angles and see how the coverage of the spray pattern is going. Without these reflections you are spraying blind.

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Discussion Starter #6
Spray gun

These two items used up a lot of online research before committing to the items. There's a lot of spray guns out there at prices from £20 to £700 and they all appear to be extremely similar. Most of the reviews are from professionals who depend on these guns for their livelihood , so need qualities such as toughness and reliability, ease of disassembly etc which aren't as important for cash strapped diyers. You don't want to find out your poor paint job was due to using a dodgy spray gun, but do you really want to lash out on a top of the range job if it's not necessary?

I found a great informative site from an Australian painter called The Gunman: The Gunman | Spray Painting

Among his dozens of Youtube clips are comparisons and evaluations of different sprayguns, showing them in action. You can learn a lot from this guy and he has so many topics covered about painting and all with excellent videos.

I settled on a Devilbiss FLG5 as the best all round spraygun, and in the affordable part of the range (£106). It seems to work very well indeed.
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Discussion Starter #7
Compressor

I had sold my tiny “Jumbo” compressor (3.5cfm portable) and 24L tank as it really wasn't up to the job. Great for general cleaning etc but I had used them to spray the underneath of the car body last year, first with Rustbuster EM-121 epoxy followed by a coat of Tetrosyl underseal (aka “tins of flying snot”), and ended up doing one minute of spraying followed by five minutes of waiting for the tank to re-fill and it seemed to take forever. After a few of these cycles, the hose heated up and popped off the compressor nozzle. So something bigger and better was definitely needed.

The choice of compressor and tank is hard and will be a compromise for most of us. What I really wanted was a three phase industrial compressor costing over £1200, but what I could really afford (and have room for) was considerably less.

It's important to realise the cfm figure (Cubic Feet per Minute) quoted for compressors is derived from the piston displacement and is a lot more than what it can actually supply at the outlet (fad or Free Air Delivery) which is the usable delivery rate. The difference is the fad can be one third less than the compressor cfm, so if your spray gun needs 9.5cfm you will need a compressor specified at 14.25cfm. I learnt this some time after buying my new compressor (a Burisch 2.5hp 9.5 cfm with 50L tank) which although it's considerably better than the Jumbo, I have to admit isn't fully up to the job, but for DIY use I can wait for the tank to fill and just take small breaks while spraying. It tripped the thermal cutout after 30 minutes of on-off spraying on the first session so it's definitely struggling. I have adjusted the electrical pressure switch to lower the maximum pressure it can reach down to 95psi from 106psi. It's these last few psi that give the maximum load on the motor so hopefully it should now run a little cooler. I also have a desk fan pointing at the motor and leave that on whilst painting.

I have a brick built shed next to my garage, a leftover of a partly used electricity substation, and it's good to keep the bulky compressor/tank there with its own feed of clean air. I have made pipework (15mm copper) that goes through the two walls from the shed into the garage and mounted two filters and a long hose on the inside of the garage wall. These are 40 micron and 5 micron filters (for moisture, oil and dust), the first has a regulator fitted and is adjusted to maintain about 60psi feed to the hose. This means that as the tank loses pressure from 95psi down to 75psi (the cut-in point for the compressor) the hose supplies a constant 60psi to the spraygun. A gun mounted mini regulator allows pressure to be quickly adjusted to suit the paint requirements, commonly 20-25psi for the basecoat and 35psi for the clearcoat.

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Discussion Starter #8
Spraying tips

There are loads of Youtube spraying demonstrations and tips, some excellent and really helpful, whilst some are extremely slow, tedious and baffling. Take some time and search out the good ones.



As a simplification, I believe there are two main skills to be learned for successful spraying:



  1. Getting the right amount of paint atomised finely, and going in the right direction.
  2. Moving the gun around to lay down an even, optimum layer of paint.


The first is to do with the gun setup (paint delivery, fan control and gun pressure settings), the second is to do with your eye and hand co-ordination.

I had sprayed a lot of aerosol can jobs over the years, and I found using a spraygun turned out to be so different. The aerosol cans have very thin runny paints that need a quick hand and a very light coating of paint at a time to avoid runs. The spraygun by contrast gives a finer spray and can be moved slower, especially with clear coat. Runs and orange peel still happen, but it's a different technique and in some ways easier to manage than aerosol cans. It just needs practise and watch carefully all the time for signs of whether it's going well or not.

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Interesting guide, and you’ve obviously spent a lot of time setting this all up. Thanks for posting.


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Very helpful guide, though I'd be sh***ng myself using an Aliexpress mask!
 

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Fascinating read and a very impressive set up.
ive done some home spraying, primer and a bit of top coating, also and truck bed liner For the underside of the car. Must admit I did cheat without using air an fed mask. I seem to have got away with it.
my compressor constantly over heated.

I did wonder about going to much greater lengths, but came to the conclusion my neighbours wouldn’t be impressed with the noise and the venting of the gasses.

on that basis I’m sticking to professionals for the bulk of the spraying. My skills are not up to it either.
 

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You do have to be a bit careful here (I worked in a VW bodyshop for a short while).....there are some pretty strict laws relating to paint application and extraction of fumes especially in built up areas....also depending on the type of paint you use , once the air gets "saturated " with vapour/chemicalsenough no mask will help you....that's why proper spray booths have to have extractors and filters.
 

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Discussion Starter #14
Very helpful guide, though I'd be sh***ng myself using an Aliexpress mask!
You can buy them from UK suppliers if you prefer, but it's important to check, inspect and test any safety equipment before use. This mask has two very effective seals to keep the fresh air in and the fumes out.
 

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Rod, I spent nearly 20 years selling tools and garage equipment and I congratulate you on your detailed post which I cannot fault. Its a setup which would put a lot of 'body shops' working in sheds to shame. It cannot be stressed though the importance of proper H&S gear when using 2K. Prior to my time selling garage equipment I was on the other end of the tools and 45 years ago sprayed a van with 2K and I can atest to how ill you can get without the proper air fed mask. I do a little paint spraying at home, but not full respray, havent needed to. I use a fairly cheap LVLP (£80?) gun and it works well on a compressor the same size as yours. The benefit of using the gravity gun you have is that you can use very small quantities of paint for touch up work, working with a very narrow paint fan and barely squeezing the trigger.

Well done, so now, lets see the results of your hard work.
 
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