How about an HVLP update? - created 03-30-2004

Pole, Edward (Ed) - 03/30/2004.17:47:57

Got another question for the gang,

I´ve spent many hours in the library and gotten a ton of good info. Regarding HVLP, most of it is from ´97-01. After several more years of experience I´d like to hear what you continue to be satisfied with. I´m interested in spraying both lacquer and polyester, but I´m still not clear as to whether both can be shot through the same gun. Or should separate, dedicated guns be used?

I´m leaning toward a conversion, gravity-feed jamb gun to use with my compressor on solid-bodies, although I´m still open to the turbine. What units, either way, have you been happy with. There are so many guns it´s confusing. Still trying to put the puzzle together......Thanks....Ed.

You would need a dedicated gun for each material. Polyester is extremely nasty stuff and you have to have a special suit and hood and air unit for breathing (filters wont do) It's also not easily available to the consumer. I have sprayed it with HVLP unit with sort of OK results. Best to use plastic disposable cup inserts. You can put a mixed batch on ice between coats. Best suited for pianos or electric guitars but not acoustics since it's difflicult to control the thickness. The stuff can be 80% or more solids so you don't even need pore filler. Piano manufacturers shoot it on thick and heavy and UV cure it in 3 seconds then grind it down and polish it. Lacquer works great with HVLP units and is a lot less lethal.

"You would need a dedicated gun for each material"

Maybe, maybe not. If you know how to clean your gun properly and often this should not be a problem. It is easier to avoid some potential problems by using seperate guns. In twenty years of spraying polyester and acrylic lacquer through the same guns it was not a problem for me. I do pull the needle and tip to clean them after I finish spraying every time. I also clean my guns well, I have had lots of practice at it.

"Polyester is extremely nasty stuff and you have to have a special suit and hood and air unit for breathing (filters wont do) It's also not easily available to the consumer."

Polyester is no more nasty in my experience than many of the catylized finishes that are available today. I do not recall anyone becoming sensitized to polyester but it is possible I guess. Most polyurethanes are way more mean, some people have had a bad reaction many years later when re-exposed. The last time that I checked, I could get polyester at the local auto body supply. I recommend a spray booth and respirator for all finishes regardless, water based or any other kind. Even while mixing or cleaning your gun!

"I have sprayed it with HVLP unit with sort of OK results"

My results with polyester have been very good. Good enough for my boss to sign off on my work. Think of a shiny boat finish and you have what I was getting consistently. I was using both a gravity feed, pressure feed and a siphon. The gravity is much better in every way except for volume, the pressure feed rules here. A gravity is very good for heavy bodied finishes like polyester.

"You can put a mixed batch on ice between coats."

Polyester is hygroscopic, it will absorb water. I would not cool it off as it could condense water vapor into the finish. It is better to mix up what you need to spray for each coat.

I have never used polyester on an acoustic guitar but I see no reason that you could not use it, as long as you thin it properly so that each coat is thin enough. Now what it might sound like on an acoustic, I have no clue. I would not use it on someone else's guitar, but I might try it on one of my own. The worst that could happen is that I get to sand it off if it sounds like crap!

A compressor HVLP gravity feed is the most inexpensive way to go. A turbine set up can work well but I have heard that it does not do as well with lacquer.

I am not trying to pick on Brian but a lot of what he said has not been the case for me or my fellow workers so far. I have used siphon feed, pressure feed, gravity feed and HVLP, both tubine and compressor types so if you have any more questions I would be glad to answer them. I am pretty much sold on the compressor HVLP's, less money, more performance with more kinds of finishes. Plus you will have air in your shop, not an easy thing to get by without, at least not for me but I could be spoiled .

I have been spray finishing for many decades so others may not get the results that I get but, if you stay at it you should be able to get results like mine. Ask a lot of questions from as many finishers as you can, this has helped me greatly, and I still pick up cool tips and techniques. Some from the forum library and some from finishers, it is a constant learning process. It will take someone awhile to get up the speed that I work at but, it sure is not hard unless you don't listen well and don't ask questions.

Well, my experiences are alittle different Brian.

I have done alot of boat repair using fiberglas, gelcoat, and epoxy. I´ve always had a healthy respect for the chemicals so of course I always used a good respirator and nitril gloves. Never had any health problems. Actually, lacquer bothers me alot more than polyester, although both are foul. Also, polyester is readily available.

I´ve found that it sprays OK thinned, but of course for these finishes you have to wet-sand and buff to get the piano finish. And then it´s HARD! RP mentioned shiny boat fnishes. That´s what I am accustomed to seeing with my work in gelcoat. I believe PRS is just using a clear polyester and polishing to get their trademark finish quality. But knock a chip out of it and then you´ve got problems.

Most importantly, I was interested in feedback from experienced users on their favorite guns. I am getting ready to invest and am leaning toward a HVLP gravity-feed, conversion jamb-gun to use with a compressor. RP indicated this type gun was a good choice. Got any brands/models you especially recommend RP?

I just bought a SATA MiniJet 3 HVLP gravity feed gun, arrived yesterday. The thing has better nickel plating than a lot of guitar hardware I've seen. Feels solid, looks the part, seems easy enough to adjust. I need to go out and get a new air hose this weekend, and hopefully do some test spraying this weekend or early next week at the latest. Going to shoot some lacquer as well as some ColorTone (Oxford PSL v3, I believe), to get a feel for how it handles. It's a fairly pricey gun, but I bought it because a) I can run it off my small compressor and b) I have yet to see any negative reviews of SATA's stuff. Check the library, quite a bit on the MiniJet 2 in there.

It's good that you guys have no problems with polyester. Even sanding the hardened finish, if dust gets on my skin it irritates the heck out of it. Maybe if you are around something for a long time it gets easier. I once went in a room where some guys were screenprinting with some kind of ink and the fumes about knocked me over. They said they couldn't even smell it, they had been at it for years. Yes, automotive finishes are available in stores. The stuff the piano makers use is not. I feel a little sheepish about mentioning any finishing experiences now that I know there are professional spray finishers in our midst. I am, admittedly, a simple amateur.

Sometimes when posting I don´t remember everything I want to say.....must be the chemicals.

Polyester dust IS bad. I forgot to mention that I wear a tyvek suit when working with it.

I´m interested in knowing the differences between "boat-grade" polyester and piano poly. Is one clearer than the other? I had never even thought about it.

I´m probably going to stick with lacquer anyway. Catalyzed mixtures annoy me. And I have come to hate acetone.

I´ve heard nothing but good about the Sata guns. Are they worth the price....steep. Roll the discussion......Ed.

"Got any brands/models you especially recommend RP?"

Yeah, I do have a few favorites in the brands anyway. Devilbiss, Sharpe, Binks, and Satajets. My own gun is a Sharpe SGF98. I bought that quite a few years back and one of the reasons was that you could get the rebuild kits at the local NAPA store.They might have to order from the local distrubition center if if was not in stock, but that would be quick unless there was a back order on it.I was also told the air channels in the gun were more resistant to corroding over time than many other guns offered at the time.

I have never regetted buying that gun it is excellent in everyway, perfomance wise and quality. I just love the thing! I am sure that a comparable gun from the others that I mentioned should be good too. These manufacturers seem to want to outdo each other every year it seems. I am blown away every time I see the new guns!

The Sata is very expensive, but worth it. I have "access" to the gun Mattia posted on, and the quality of spray is unbeatable (I've used DeVillbiss & Sharpe suctions, and a "cheapo" PC gravity HVLP).

Unfortunately, I haven't developed a "feel" for the Minijet 3. This would be my own personal problem, and nothing to do with Sata. My full size PC is much more comfortable, so right now, it is my gun of choice. I've held Sata's top of the line digital (also have "access" to that one too), which costs more, but I may invest in (those with the most toys. . .wins!). I guess using the suction pots in the past has warped my sense of flexibility of using a jamb gun.

This is an area where you get what you pay for. The smaller gun works if you only do one instrument at a time (small pot).

Either way, gravity feed is the way to go. By the way, don't forget the filters.

Is the SATA minijet 3 suitable for Water based finishes? Is the plastic cup okay for waterborne? I'm thinking the 1.0mm set is the one to go with here too, right? Also, any hose and attachment recommendations i. e. (filters, regulators, gauges)?

I spoke with a representative about compressors and I was told the sata uses 3.5cfm@30psi. He recommended a Dual stage (for faster air compression) and at least 1.5 hp 25-30 gallon tank because a smaller tank will cycle more and possibly create moisture in the line due to the heat generated. Does this jive with everyone's experience? And does anyone have compressor recommendations?

Could I have more questions?! Thanks!

I wondered about this, and since I know so little about spray guns that I don't know which question to ask, I went to the Sata website. There is basic information (videos) about this subject that may be simplistic, but it helps me to think about the subject, and it might help you too. Also I think that it's better to learn good habits from the beginning.

I got the SATA MiniJet3, plastic cup, 1.0mm regular (not SR, or spot repair, nozzle). All the wet parts are stainless steel, so it's more than fine for waterbased finishes. I need to get a new hose (probably a SATA one, I think. My schedule is conspiring against me to prevent productivity on the spray gun testing front!), and I'd like to get an on-gun gague and a filter for moisture, but I can't afford those right this moment, so I'll have to make do. I'm going to be using it with a cheap oilless 1.5HP compressor with a 50 liter tank, so not huge. But I think if I run it for a while before shooting, I should be able to do a guitar finish just fine, especially since it's a fairly small surface, and I'm not shooting non-stop for that long at a time.

I just looked into filters from Sata, the dual stage one, wow is it expensive. Is it possible to get by without the filters when spraying waterborne? Or does anyone know of cheaper but good filters?

Peter, I can't speak to the Sata filters waterbourne issue, but I will say that unless you have a filter/drier system you will have some air line issues. They may not affect the finishes but your air supply will not be as clean as with the filter/drier setup. On the cheap filters question, I think they still make the "toilet paper" style ones. I bought one when I was contracting out my finishing/repair work and had to use the company supplied compressor. I will post a picture of it if there is any interest in seeing one.

Thanks for the info R P, I'd love to see the the toilet paper!

Check places like Mcmaster-carr for coalescing filters. If you're really worried about fish-eyes, they make silicone free units (no silicone used in either the parts or in the manufacturing process). In-line desiccant dryers can get the dewpoint of the outlet air to the -30 deg range (they work like R.P.'s toilet paper type filters, but much better and you can regenerate the desiccant in your oven instead of replacing the filter). If you can, my preference is to put a coalenscing filter and desiccant dryer before the tank (stops corrosion and crud pooling in the bottem) and a particulate filter after the tank, (or several small ones at point of use).

No experience with spraying finishes, but 15+ yrs dealing with compressed air in clean-room manufacturing. Take it for what it's worth.

Peter,I found the filters at, http://www.motorguard.com/air_2_2.html. Pictures and specs are there as well as the filter cartridge numbers. I have the M-60. A buddy told me about these filters a while back but he thought they were not made anymore. I had to find out myself because they were so cool and in a pinch you can stuff in a roll of real toilet paper for the filter! Take out cardboard center if you do this it might work better. I called my paint guy and worked out a trade for repair on his truck topper shell, (the things with the windows) so mine was free for the labor! I have had mine since the 90's. If I had the cash I would go with what Ian suggested in a heartbeat, my tools and spray guns would love me.