Advice on spraying equipment

[PJL]

As well as my recently acquired Decola, I have an HMV radiogram both of which need a re-finish. I'd like to try to do the job myself using nitro-cellulose so I am looking to get some spraying gear.

There are alot of small compressors about mostly with 25l tanks and plenty of cheap spray guns but are these going to be up to the job? Other than waving spray cans around I've not used professional equipment before...Peter

[GMB]

Are you sure you want to use nitro-cellulose - it's really dangerous.

Small compressors are more than up to the job but you might not want a cheap spray gun as this is the critical part. You should consider adding filters to remove water and oil from the air.

My experience is that when set up correctly you can get very good results but if you don't use this kind of equipment often then you will have to experiment to get things right and you can still completely mess up on the real item. I think you might find that results are not necessarily much better than a spray can.

You could also consider an electric airless spray gun which I guess doesn't blast the paint everywhere, i.e. more of the paint goes on the item - but I haven't tried this technology.

[Mullard]

I have an HVLP spray gun that I have used for paint. I haven't had it long and have not yet got around to trying varnish and lacquer, but I will sometime. HVLP (high volume, low pressure) spray guns push out more air at a lower pressure and as a result suffer less bounce back i.e. more of the paint/varnish goes on to the item and less lands everywhere else. I have not tried an airless spraygun and these may give a similar benefit.
Hope this is useful.

John

[Sean Williams]

A 25 litre tank might be a bit small if you are doing large panels, and flooding a lot of lacquer on in one go.

Guns are a different issue - Speed costs money, how fast can you afford to go? A second hand Devilbiss gun is likeley to be much better than a cheap diy model. Suction feed guns (with the pot at the bottom) are good for vertical serfices, but not so hot for horizontal, or detail areas, for this a gravity feed is much better.

Air wise, the hoses and fittings supplied with most hobby compressors do not flow enough air, so a change to 3/8 inch hose and pcl fittings will make vast improvements, and will also help to keep the air dry (by avoiding heating up and forming condensation)

The most important thing with air for paint is to keep it clean - most piston compressors use oil to lubricate, with wear and tear the oil makes it into the air stream, this manifests itself as tiny little bubbles in the applied paint.

HTH

Sean

[Mike Phelan]

Hmmm ... I have had quite a lot of experience with paint spraying, using small compressors. A few comments:

• What GMB is saying about using a decent gun and some sort of filtering are paramount.
• You must have a temperature of at least 20C. Any trace of damp will give 'blooming' on the results.
• Overspray (except HVLP which I haven't tried) goes everywhere.
• There must be no dust anywhere in the room or on your clothes.
• Good light
• A lot of testing needed before actually doing the job.

There are many variables, which must all be right:

• Proportion of thinners to paint.
• Nozzle size.
• Pressure.
• How quickly you move across the panel (the most important bit).
• Distance from gun to panel.

That said, although I am quite conversant with spraying panels on my cars in the past, using a compressor, for radio-related and other small stuff, I use 'rattle cans'

[PJL]

Thanks all for the very helpful input and I will try to summarise:

1. Nitro-cellulose is dangerous due to low flashpoint?
2. Need a room you can keep at 20degC, is well ventilated and expect a complete mess. This could be tricky in winter!
3. 25l tank should be OK (oil-less compressor?) but I will need a quality gun and possibly replacement hose. The HVLP systems are cheap but not much on the web on how well they perform - also used for spray tanning!
4. It's probably not worth it for smaller jobs as spray cans will do.

The HMV (I have a spare cabinet to try first) is no more than 3m2. I'll need a filler and finish presumably gloss? This has multi-coloured veneers so I presume no toner? Using 400ml cans I reckon 2x filler and 4/5x gloss? At £8/can it quickly adds up...

[Station X]

I thought that nitro cellulose was an explosive. Gun cotton?

I'm reluctant to google that sort of thing nowadays for fear of the front door being kicked down at 4:00 AM.

[GMB]

The tank size is not really an issue unless the compressor is pathetic and can't keep up with the supply requirement, which is only 3-5 cfm for spray painting.

Don't forget that air compressors fill up with water and have to be emptied from time to time. The problem here is that water droplets condensing in the tank can get swept out and into your spray gun, hence larger pipes helping and having an oil/water separator is better. I suspect this is the main reason why you see quite large tanks on professional systems - it gives the air longer to rain out the water.

Small jobs are a pain because you have to clean the gun to perfection when you finish, or buy a new one.

At £8/can it adds up quite slowly because you will be spending as much on gallons of thinners and a load of wasted paint and that's before the cost of the equipment.

I only bought mine because I had the job of respraying a vehicle which had been resprayed with a paint that wasn't compatible with the spray cellulose cans so I had no other way to do it.

[Aerodyne]

HVLP systems are ideal for cabinet work, not so good for automotive finishes. Try Axminster. You can get a variety of lacquers and finishes on-line. Here's a firm I use:

http://www.rydenor.co.uk/

Needless to say, no connection - they've just given good service in the past. There's numerous other sources on-line too. If you use gunwash to clean the gun, dismantling is unnecessary. Just open the valve and spray until clear. Wear a face mask at all times.
-Tony

[Telleadict]

Hello

Some of the regulars on here -- in the "Bodywork" section should have some tips on spraying although in a car repair context.

I got some help there which proved to be sound when I needed to do some touching up on my motor.

Just another contribution.
William

[Ian B]

Before getting a compressor, check that you can still buy cellulose based finishes! Under an EU directive, from this earlier year their manufacture has been banned (not for safety reasons, but because if the effect on global warming of volatile organic compounds (vocs)). At least, this is the situation with car paints, but it's probably still posible to buy it if you know where.

Mike's advice is good, but I would add that "antibloom" thinners are (or were) available which help enormously to prevent the blooming caused by damp. And remember that it's the relative humidity of the air that matters, so the problem is usually worse on hot days!

I tend to use spray cans for small jobs, it's a lot easier than cleaning the gun out after every use, but I don't like them, they vary so much in the quality of the spray pattern.

I know some restorers who have done all the filling, staining, toning etc on their cabinets, then have a friendly car bodyshop to spray them in the spraybooth with 2 pack clear laquer. If the groundwork is good, this can look stunning, but it won't hide anything!

Ian Blackbourn