What pressure for spray gun?

[hamster]

Hi all,

I am spraying some household acrylic onto MDF and was wondering what pressure setting I should use on the spray gun. The gun is the generic $70 one you see around the traps.

I'm currently using about 45psi - I tried a higher setting but I got overspray. At 45 there is a "orange peel" effect visible in the finish.

Any suggestions?

Marcus

[Shane Watson]

Your problem will no doubt not lie with airpressure, rather the viscousity of the paint. House paint is not meant to be sprayed therfor is too thick to flow easily through standard spray equipment.
FYI - To ask what airpressure to use is like asking for what insurance policy is best. It all depends on different circumstances. Heres a few things that change the airpressure needed - type of gun, operator preferences, fliud to be sprayed, finish required etc etc. Actually I never ever look at the pressure settings - I work off sound and feel, but years of spraying have helped with that technique
But like i said above your problems sound like there from using house paint.
HTH
Cheers..

[hamster]

Hi Shane,

The acrylic I am spraying is a general purpose acrylic undercoat (the top coat is going on tomorrow) which specifically notes that it can be applied by spraying so I don't think that is a problem. The supplier recommended thinning by 5% and by doing this and using 45psi the result is OK, if not stellar.

Before I do the top coats I wanted to check what other folks use, it seems the biggest problem I am having is overspray - the boxes I am spraying are about 1ft square so there is a fair bit of overspray on the edges which manifests itself as a "rough" feeling on the dried, painted surface - any way to mitigate this?

I feel stupid asking such FAQ type questions but I cannot seem to find an online source of info about this and the few books I have seen don't have much practical info in them.

Marcus

[Shane Watson]

Marcus,

Although it says it can be sprayed, it still isnt designed to be sprayed. The overspray you talk off is probably caused by the paint drying to quickly as it comes out the gun. To overcome this you will need to add a retarder to the paint, this will slow the drying rate down so the paint stays wetter longer and any overspray 'melts' into the paint. You may need to thin more than just 5%, as a general guide spraying consistancy is only slightly thicker than water. ( but again - that is guided by application etc )
Again, really there is no science for air pressure settings. If the instructions on the tin suggest 45psi, then you should be pretty close if you stick to that.
See how you go. Ya cant get any better experience than getting in and giving it a go
By the way - Welcome to the Board. And never feel stupid about any question you may want to ask. We wouldn't be here answering questions ( and asking some pretty stupid ones myself I might add ) if we didn't want to

Cheers

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Shane Watson..

Combine Love & Skill & You Can Expect A Masterpiece!

[This message has been edited by Shane Watson (edited 06 January 2001).]

[RETIRED]

Gooday.

Normally when they say "spraying" with Acrylic they mean airless type guns set up to spray acrylics.

My .02c worth.

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Ian () Robertson
"We do good turns every day"

[Rod Smith]

Yes, I think is correct in referring to airless spray and he probably means the serious proffessional stuff that runs at about 2000 psi or somithing like that. I have had some success spraying fences and sheds with a handyman airless, but plenty of overspray and imperfect finish. Cheers. Rod

[Shane Watson]

Argh, thats what I have been trying to think of all afternoon. Airless! Thats what they use to spray household/industrial paint, I couldn't think of that this afternoon . But yeah the machinery is commercial. Plus the tips they use on the airless for household/industrial paint are bigger tips to allow a higher flow rate due to the thicker paint. Geez if you watch those backyard renovation shows you may have seen them use airless guns to paint fences etc. The fan they use can be over a metre in height. The range of tips ya can get for an airless is amazing. It all depends on the job at hand.
But damn this is getting away from what Marcus asked... Don't think Marcus would be too interested in tradeing in his lil suction cup on an airless...

[STEPHEN MILLER]

To confuse the issue more ,the types of spray guns around is big ,high pressure guns low pressure high volume etc ,if the cup is sealed they are low pressure the air pressurizes the cup forcing paint out ,higher pressure guns use air passing through the nozzle to draw paint out but then there is low pressure types like CIG Eager Beaver quite good for acrylic when thinned 50/50 with water. There are lots of cheaper airless guns on the market than industrial types . But back to air pressure over spray is some thing you will get with most spray painting regardless of the pressure but a good pressure range is 30 to 45 psi plus a good supply of air so pressure remains constant.
Happy spraying Steve