Technical HVLP paint gun - clearcoat problems

15-20 years ago I did a few garage paint jobs. I had two guns - one siphon feed, the other gravity. I don't recall the gravity gun being marked as HVLP, so I'm not sure if it was. Of course the siphon gun was not. Back then I was able to lay down some pretty slick finish, both single stage & base/clear. A little wet sanding and polish and I had some dang good paint. Sadly both those guns are lost to time...

After getting away from painting for 12 years or so I've done a few garage jobs in the last couple years, I'm just wrapping one up now. My new guns are HVLP. I cannot get clear to lay down worth a damn. Worse than the typical orange peel, I get areas with a surface texture almost like 40 grit sandpaper. First time I chalked it up to lack of practice/operator error. But it's happened to me a couple more times. I've tried different clears, different gun settings, more pressure, etc. - nothing has worked. I spend hours & hours wet sanding to get a decent finish. The one constant is the HVLP gun. This leads me to two thoughts:

1. My basic home compressor setup cannot supply enough volume to atomize the clear properly. It's just a 5hp 30 gallon craftsman compressor I've had forever, 1/4" hose, desiccant filter/dryer. I also use a disposable filter at the gun, along with a regulator. The most air presume I can get out of the regulator is about 40 psi, which I understand should be plenty. Startingline gun with a 1.3 tip.
2. The high solids clears I've used are two thick to be properly atomized with my compressor setup. Note none of the clears I've tried call for any reducer, just hardener. I've tried a few including SPI universal clear - I like it the best but I'm still not getting a decent finish out of the gun.

Note that when I spray primers or basecoats they lay out just fine. It's just the the clear that is giving me fits. Anyone have any thoughts/suggestions as to what I'm doing wrong? It's frustrating - I've done it successfully before, not sure why I struggle now.

 

I'd agree with point #1 above. I don't think you're keeping up with the required air volume out of your 30 gal compressor. Something else to consider is air pressure at the tip, not at the gun inlet. You can use an inlet regulator to get the right tip pressure, but that's what matters most. Too much pressure will definitely affect the atomization.

 

I would try a little reducer and use one slower than recommended. Just be aware that can cause runs if you don't allow plenty of time between coats. Also agree with the possibility of not enough air flow. What is your compressors output compared to the guns need?

 

I’ve never attempted any painting with a 1/4 inch hose
HVLP likes large fittings.
Sounds like ya need more volume of air and nothing choking it down. 3/8s mimimim.

 

I don't believe a 30 gallon tank and 5 HP can provide the volume needed to use a HVLP gun successfully, maybe the first few seconds of spray time then the compressor starts and tries to keep up with volume of air flowing but can't and air in tank starts to drop in pressure and then the compressor runs steady until you stop spraying. I have what sounds like the same sears comp. as you have and i find i've been able to paint with a siphon gun but not HVLP. Ralphie

 

High volume, low pressure. Far be it for me to say what the problem is because from where I'm sitting, I can't see the results or past what you've mentioned is a problem.

I will say this however... you have options.
Doing more or doing less.
Reducing for fast or for slower flash times.
Moving faster or slower when spraying.
Closing in or pulling away when spraying.

Universal Clearcoat 2.1 | SPI (southernpolyurethanes.com)
"Gun Tip Size - 1.4"
"Can Reduce with SPI reducers 0voc reducers up to 5% using slower speed than activators"

 

1st thought: you can thin clear 10% and not suffer any negatives that I have incurred. 2nd: I agree on the 3/8" hose and fittings completely. I would suggest you put a regulator at the gun only that is made for a paint gun. A regulator at the tank does not reflect the pressure drop in the system. Before you spray a part, do you take a piece of cardboard and check your spray pattern? I have an 80 gallon tank and a 5hp pump that won't keep up with a finishline 4 gun. When the tank gets below 125psi, the pressure starts to fall at the gun. I need better fittings but eventually, I need for the pump to be running to keep up with the gun and the constant airflow.

 

I was thinking I had a volume problem...I've tried a couple different guns- 1.3 tip & 1.4 tip. Made next to no difference; granted, they were pretty inexpensive guns. I haven't tried reducing the clear, but I'll give it a shot.

I am using a regulator at the gun - the tank regulator is set wide open. I read somewhere online (or maybe it was YouTube) that turning up the pressure will help compensate for lack of volume, but it's not helping me get a better finish, that's for sure.

Honestly, I don't even remember what kind of volume my air compressor can supply. I've had it about 20 years, and the tank stickers have long since fallen off or have been obliterated. I really need a bigger compressor, but I'm unsure I can get enough compressor in my home shop. Space is not the issue, it's the electrical requirements. The compressors I really think would work require 3 phase power & my rural subdivision is not set up for that. I could go for a 60 or 80 gallon tank, but my experience with tanks that large is they take forever to fill when all you have is a single stage pump run by a single phase 220v motor.

Or try find an old school gun. I hate to take a step backwards, but it would be better than what I'm doing now.

 

I have a Belaire 218e that is 220v, two stage. I have it set at 150 psi limit. I think it's about 15 years old and has been excellent.

 

They make hose fittings that have different sizes of holes. Most people use the generic fittings with small holes. I'd buy a larger diameter hose and equip it and your gun with some large diameter fittings. Turning up the pressure can increase volume, but you need low pressure with lots of volume, and a bigger hose and bigger fittings will do the job. The fittings are externally the same size, just have a bigger flow hole.....not the huge industrial fittings. Thats where I'd start. Then its up to your compressor to keep up. Also works better for your air tools.












You can find a Milton Catalog online and look for what you need. I'd also spend the money to get "push in" hose. You don't have fittings at eah end of the hose. You just use a "push in" fitting. They virtually never go bad...but if one does, you just cut the hose off and reinsert the push in fitting. No more listening to a leaky air hose and they last forever. Yep, they cost more, so check around for a reasonable source....maybe Amazon. Parker is rediculous.......

 

I also have a Starting Line gun set, and to get it to pattern well with thicker paint I had to go to a 3/8" hose. What is the gun regulator gauge showing when you pull the trigger? Mine dropped to less than 10 psi, so I knew immediately I had an air supply issue. Also need to use industrial fittings rather than automotive ones.
You don't need 3 phase current to get adequate air, just enough amps. I am running a 7.5 hp single phase motor running an old two stage Quincy on a 120 gallon tank.

 

Most of the clears I have used recently are high solid products and they need a 1.4 or 1.5 cap and 26-30 psi at the HVLP. I like a wide fan, medium material and I use the internal pressure valve on the gun butt to turn down the air for tight corners and jack it up if the coverage is orange peely.

Practice makes perfect but only if it is perfect practice...a little something a b-ball coach taught me many decades ago and it remains apt today in my garage.

 

I am just now going out to shoot some high solids clear Tamco 2104 which is much higher solids than the big 3 sell & I have no issues with using the HVLP gun I have (Tekna Copper 1.3 tip, Iwata 400. 1.6 tip & my old original Devillbis Finish line FLG 1.8 tip)

Most of the normal issues have been mentioned above & since none of us are there with you, it is really tough to fix without seeing what is happening. Different guns like different air pressures, fan width, product volume, etc. The only other thing that I don't think was suggested was moisture in your lines & tank...Are you using one or more good filters? You might try a bulb type cheapy at the gun just to see if it makes any difference.

God Bless
Bill
https://www.jalopyjournal.com/forum...ar-transport-hauling-open-or-enclosed.614419/

 

With my “too small for painting” compressor, I added a second 50 gallon tank bolted to my shop wall. The compressor runs fairly steady during painting but the I have not run out of air.

 

Another thing for HVLP.
Spray technique. A 75-90% overlap with the gun wide open moving faster than with a conventional gun.

 

Far be it for me to comment further, but I will anyways.

I was thinking about this problem of yours. While I think you can watch enough videos to eventually get this, ask enough questions or read enough good advice given to get it, what you need is to know a guy. Seems I'm also in Edmonton. Message me I'll send you a number.

That said... so you think you have a volume problem? My guess, you have a supply problem. Not supplying the CFM for the volume your using and that depends on how hard you work.

Let me ask you a question. You mention tip size. What's the purpose of the larger tip opening?
Spray more paint?
Allow for thicker paints to be sprayed?
Create a bigger fan pattern?
Widen the fan pattern?

You read somewhere online (or maybe it was YouTube) that turning up the pressure will help compensate for lack of volume?

Sometime I wonder if I'm making it up as I go but... I asked how hard do you work? Squeezing the trigger of the gun releases the air from the tank. The only way to not notice the drop in pressure will be to not release as much of it.
You could spray a line, stop. Admire. You could take a moment to visualize your next line. You could get in position, dry run it. Go back, squeeze the trigger and go again. Stop, Admire. Visualize and repeat. Over and over, your compressor will keep up too that I'm sure.

I'm sure this compressor would paint a car eventually. Key word eventually.

The tip size will dictate the products ability to flow thru it.
To thick it just won't.

Squeeze the trigger often enough to earn a buck squirting cars and you can expect from the compressor size that with a smaller CFM model, it's volume will diminish quickly, it failing to keep up in CFM within minutes. All due to a constant drain on the available supply.

If you didn't reduce your clear, you have a thicker product to spray.
Like measuring the suction to pull on a thick milk shake up a straw, vs. a fountain drink in comparison. Then think about how changing the straw size effects that. That's the tip orifice difference. Small straw is even harder to draw up or push thick out.
It no longer is transferring paint from the gun in a droplet with a ratio and proportion to adhere without running, it's splatting it out. In a hard to judge wet clear. When in doubt wait it out. Then hit it again. It helps to avoid runs.

I mentioned that mentor thing...as it has been mentioned...

It's ok not to get it. I'm not sure if I do past the point 3 phase is more efficient...? But the amps part...Amps, volts, resistance. Think paint, pressure, reduction. Spraying a product, the thinner the product the finer the mist. To get a thicker product to create a fine mist you need higher pressures to push it.
Post some pictures of what you have for equipment, what you've squirted to a panel. I'm not convinced you need a old school paint gun, but Princess Auto sells one last time I looked.

 

Checking paint viscosity is such an old fashioned idea that has been superceded by measured mixing cups. Or has it? The TDS lists the viscocity, or it does on the paints I've used recently. Might be worth looking into? Also, being at or near the limit of the temp range of the activator can cause problems. I've recently got back into painting after many years (ain't retirement great, and completely mistitled! I've never previously achieved any noteworthy results however), and found the el cheapo lvlp primer gun id gotten simply chewed through the air. Devilbiss gpg gun fixed that, and I'm running an air fed mask all off a 3hp, 14cfm compressor. Also got a devillbis gti Pro lite for colour (straight paint) and am getting glass like finishes. Im more than happy!

Chris

 

How far away is the gun from the panel? Get closer, overlap at least 50%.
Sounds like it's dry (not enough clear or too much air) and too far away.

Test your fan pattern before shooting, should be cigar shape and wet throughout. Adjust your fluid control knob.
You can balance the air on the gun, "air micrometer" is on bottom of a lot of guns.



I shot several brands of clear with an HVLP and 30 gallon oil less compressor. Use a regulator at the gun, good water separator - the compressor runs all the time.

Thinner - Depends how you shoot - can you lay a wet coat and get it to hang without running / sagging ?

 

Is it an oiless compressor? I have one I bought from Sears around ‘95, 5hp/30 gallon. I can still make out the ratings on it (I think). Not sure if it would be rated the same as a normal compressor.
I’ve used it for my HF purple gun but only for matte black and primer. Don’t recall if I used it with a Sharpe Platinum, gun I loaned out and never got back, rust oleum primer and paint.

 

Had to feed the horses before turning in, mine is 9.1 scfm@40 psi and 7.1 @ 90. Thinking Craftsman was optimistic. But never tried to paint with it when it was new(er).

 

First, we need to quit caring so much about the size of the pressure tank on a compressor. Even marketers use this spec in their ads as though it has anything to do with the performance of the air supply rate. The ONLY two specs that really matter is 1) CFM, and 2) pressure at that CFM. All the size of the tank indicates is how often the compressor will cycle on and off, has zero to do with capacity of the system. 5HP sounds like enuf but appears to be a bit too small. Your compressor is too small for your gun. Period.

I run $9 Harbor Freight HVLP purple guns (one with the 1.4 tip it comes with for clear and color and one with a 1.8 for primer) and get fantastic paint jobs. Key to my success is my Harbor Freight 2-stage, 6hp, 10CFM @ 120psi compressor. Feeds thru 3/4" copper pipe distribution system to a HF dessicant dryer,/regulator, 25', 3/8" HF hose. Pay attention to the length of the hose to the gun. Keep it as short as practical, there is significant pressure loss per foot there. I never fool with the pressure setting at the regulator, leave it at 60psi for everything.

Point is, even though I use bottom of the line, junk equipment, poor gun setup technique, low skill level, I get show room results because I have good air supply.

Some of my VERY AMATEUR paint jobs.
Sold at auction for $248,000


My daily driver


Grandson's project car

 

Meant to comment on the 3ph question earlier. Not important at all IMO, even though I have a 3ph compressor. It is a 5hp, 80 gal, about 16cfm unit, oldie but goodie. Chosen for price, not ph. Lots of good single phase 5h units that are capable of supplying enough air.

I use a Devilbiss GTI620G for urethanes. Supposed to use about 15 CFM but I think that spec is way high for my usage. All 1/4:", 'normal' fittings on a 3/8" hose. Works fine for me in occasional use.

125PSI at the wall, reduced to 25-30 at the gun, works for most everything even primers from my HF guns.

Important that the at the gun setting is with the trigger pulled though,,

On tank size, as long as the pump can provide enough air, it is not terribly important. But a bigger tank can get you through a cup of paint and then the compressor can catch up. But, that provides warmer air, (with more moisture in it) to the gun. Better to have some cooling time in the tank. At one time I had an extra 1000gal propane tank sitting outside the shop. I hooked it up to my compressor for storage for sandblasting. Worked! Even painted a car with that setup. Compressor didn't even come on until I was nearly finished.

 

Keep in mind that a regulator at the gun affects air volume. I used to paint professionally and have used various high end HVLP guns since 1992. My newest guns are Sata 2000 so were talking 20 plus year old technology. On an HVLP the pressure part of the pattern is configured into the tip. The smaller the size the better the atomization. When I use to have access to paint and gun company reps, I would discuss air pressure at the gun and the answers were basically opinions. no one person had the same as the other. And no one at that time, at least 2007 when I closed shop offered a gun regulator for HVLP specific guns. Some reps had access to them, but you could not by one. My guns cost over 500.00 a piece in 2000. But the only thing I ever came up with that worked for me regardless of the gun cost was test shooting said materials with different adjustment settings that gave me the pattern an atomization to get the show finish I wanted. The gun regulators we use now are the same ones I started with in the 70's except then they were made here and not in China. My guns and my spray technique like 45 to 50 psi at the gun regulator. 25 to 35 like many including gun reps suggest does not give me the atomization I want. And yes, my compressors are 4-cylinder 2 stage 10 horse units that supply my whole shop. But the wall regulators in my booth after my air dryers are set at 90 psi and i use 1/2-inch hose and wide mouth nipples and quick releases. Bottom line if you can get a constant 50 t0 60 psi at your gun and work with your adjustments you should be fine. Hell, I started out in 1970 with my dad's craftsman 5hp 30-gallon compressor and the spray gun that came with it. lol And I have received many best paint awards over the years. Oh, and in the immortal word of Jon Kosmowski " a man with a full pull is a man out of control." Restrict your trigger pull to about 50 % and adjust fluid and fan from there. Larry

 

I may have missed it but you also need hi flow couplers and at least 3/8" ID hose to get a decent CFM at the gun.

 

I still use my old Sharpe siphon gun with great results. My question is how do you measure pressure at the tip of the gun on a hvlp gun?

 

You can't, at least not without a special gauge. The recommended inlet pressure should max out a 10psi at the tip. In the case of my Devilbiss, that is 30psi. Other guns may vary. I sort of ignore that number and go by the test pattern..

 

I might have missed it, but I did not see a mention of a pressure regulator and gauge attached to the gun.

You should be running full line pressure (at my shop we set it at 90psi). The hose is an additional reservoir of air, and you need all you can get. If you regulate at the compressor, you lose some air volume access.

Your operating pressure, in almost all cases, should not be over 40psi at the gun, with the trigger pulled.

In may cases, as @Bandit Billy mentioned, it may need to be even less.

I was just pushing clear through a 1.4 tip, at 28psi, at the gun, trigger pulled.

 

I also learned a lot last month about temps and the effect it has on clear. I used a blow up booth outside my shop, when the sun was behind a cloud it was 70 degrees in the booth, when the sun emerged it climbed as high as 90 and fast! I was using 70-80 degree activator in my clear and it would not lay out. I switched to slow activator (80 plus) and the second the sun went away the runs showed up. I ended up frustrated and sanded down the clear "flow checks" and re-applied it my garage under ideal, controlled temps. Turned out very nice. Don't discount the temp and the proper activator. There is actual science happening in the booth.

 

True that!

My shop gets too hot, and while that does indeed suck for day-to-day work, it holds that heat.

I have to triple-stock 70º-80º activator for Summer, and Second-Summer.