Spraying Satin Polyurethane with an Entry-Level Gun

      Can a beginner get decent results spraying poly with an "El Cheapo" gun? Pros chime in with advice. May 17, 2005

I cannot seem to get an off-the-gun suitable finish. Are you supposed to buff it out? Buffing seems to give a higher gloss than satin. I am new to spraying and don't know all the tricks. I have a cheapo gun. I am spraying Defthane and have tried thinning it with mineral spirits. Narrow boards buff out ok with steel wool, but the wider boards take on the higher gloss. Is buffing necessary? Are there any other suggestions? The material flows out nicely, but there is a sprayed look when dry.

Forum Responses
(Finishing Forum)
From contributor A:
It sounds as if you may be dry spraying. Open your fluid valve and try to get a little more on the piece. You certainly should not have to buff or rub the urethane.

From contributor B:
Are you spraying with a HVLP turbine set up or a conversion type? My thoughts are also that you may be dry spraying. This may also be occurring if your fan is too large. Narrow up your fan pattern and also cut back on your air. If you are spraying with a cheap HVLP setup, is it a full bleeder gun - does air come out of the type of your gun at all times? I find that you should not have to buff poly either. Keep working at it. It sounds to me like there is an application problem and not a material problem.

From contributor C:
Things to consider:

Gun quality and cleanliness, type of coating delivery to gun (pump, cup) Can you remove air cap on gun, trigger and get solid stream of coating through fluid tip? If not uniform and full stream, hold gun triggered and remove fluid tip. Inspect cleanliness inside fluid tip where fluid needle seats in orifice.

Size of orifice in fluid tip in relation to viscosity of material being sprayed (gun mfg. should have this info).

Quality of air and its pressure to gun (most HVLP operate best @ 40-45lbs). Dry air or/and filter water with water trap.

Gun adjustment- fluid and air pattern relationship and spray technique.
Temperature of part being sprayed (are you in a cold shop?)
Rate coating dries (retarders are sometimes needed)
Air flow across part from fan or draft

Sounds like material is drying too quickly during atomization leaving a rough finish that then appears to need buffing out - and no, buffing should not be necessary. Try going to a coating company such as Sherwin Williams, Campbell, or others, and get advice. Take your problem sample with you! The formula is very important and to change it by adding spirits can cause bad effects. Try one ready to spray out of can from professional paint store as listed above. There are many knowledgeable finishers on this site and I'm sure you'll get good advice.

From contributor D:
It always has seemed to me that spraying poly is a pain compared to the different finishes like lacquers and the newer high quality waterbornes that have properties that make them easy to spray.

My suggestion would be that if you want to have professional results and make money doing it, that investing in a good gun, even one of the $80 Astro's or an $80 Porter Cable, combined with switching to a finish that sprays great while drying fast enough to prevent every speck of dust in the room to settle on it will make finishing a much more enjoyable job.

From contributor E:
I'll be the one to state the obvious. What you need is a coating that dries faster. Even if you setup everything perfect, unless you are spraying in an absolutely dust-free environment you going to get crap and have to rub it out. Look into properly setting up for spraying lacquer and buy a quality product and you will be amazed before you are half-way through.

From contributor F:
A turbine HVLP is best suited for this job, but I have yet to get a Class A finish with poly. It is thick and takes too long to dry. The turbine does a good job of heating the material and makes it flow better, but a consumer grade poly is designed to stay wet even when brushed. Expecting to get great results from poly is like trying to cut your teeth and may be a high expectation. If you want to stick with poly, go to a professional paint store and look into conversion polyurethane. You will have to learn to mix parts, but the finish will be more durable and better suited to spraying.

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