HVLP question regarding high build primer

[Tom and Vipers]

The problem is that I can't get a nice heavy paint flow thru the gun. To get any kind of flow, I find that I'm turning the pressure up way beyond the HVLP range. To get any kind of wet application, I have to spray 2-3X slower than normal. This results in taking over 5 minutes to put a coat of primer on a Viper hood.

I think the cause of this problem is that I don't have a large enough cap for my gun (its a 1.5mm) and am wondering how I can workaround this problem since it is only primer. (The gun is Sharpe SGF98HVLP and a cap kit is $150, money that would more than buy a decent primer gun.)

I am using Sikkens ColorBuild as a Surfacer
which is 3:1:1 (CB:Hardener:Activator)
and recommends a cap of 1.9-2.1mm

I was thinking of attemping to thin this mixture with Reducer, however, Reducer is only used when this product is used as a Sealer:
10:5:3 (CB:Hardener:Reducer)

I'm thinking this may not be a good idea because the Reducer (solvent) can get trapped in the successive layers of the CB as a filler.

I've just realized there is a Slow Hardener - I guess that would really have helped trying to nurse a small cap gun.

I'm afraid all I can do with what I have is turn up the pressure and paint when it is as cold as possible.

Thanks in advance,
Tom

 

[C O D Y]

Go with 1.6 or 1.7 cap. Paint and your time is worth the extra cost of the cap.

 

[Tom and Vipers]

HOW TRUE!!!!

But I'm inclined to get at least a 1.9

I'd rather have to contend with too much paint flow

Thanks
Tom

 

[dansauto]

you should use a differant gun for primer, def at least a 1.7, I use a 2.0 in a Sharpee HVLP gravity gun

 

[Mopar Steve]

Buy a "cheap" devilbis gun for primer. You will be sanding it eventually. Use a different gun for primer and a different gun for base clear.

 

[Tom and Vipers]

That's the plan Mopar Steve. I might get even an Astro or a Finex for primer, but I'm going to get a Big Pig cap, 1.9 at least.

I figure with primer, you can always cut back on the paint flow.

Latest problem/discovery is hilarious. It appears it is not possible to block sand a 17 lb carbon fiber hood sitting on sawhorses. I'm only using 16" blocks and if I get anything near a good bite, I slide the hood off the horses. Sanding the sides is almost impossible due to this. I'm tempted to put it back on the car just to sand it. That does have some appeal because you can position the hood all over the place.

 

[RAYSIR]

The pressure at the regulator going into the gun should be set to about 40-60# on HVLP. They give the pressure at the cap/nozzle usually 10#. Some guys don't know and set in pressure at 10-12. I've sprayed with no problems with 1.6 tip and surfacer from HVLP all the time.

 

[Tom and Vipers]

Raysir, that could be part of the problem.

This Sharpe says something like 43 psi inlet for 10 psi at the cap.

I don't have a pressure gage on the gun ( I know this is a nono) and found that setting the regulator on the 50' line to 60-70 was essential to get anykind of fan pattern.

The fan pattern was poor, basically elliptical with air and paint valves wide open. I'm used to a nice linear, even fan pattern.

This Sharpe gun is supposed to be a good one I was told.

 

[RAYSIR]

You will also get a pressure drop from regulator on the compressor or wall to your hose then gun inlet. Been there done that. NAPA or others have a real small regulator that fits right at the inlet of the gun. I use one and sometimes notice 10# difference on a 50foot hose from my water drier on the wall to the gun and Have to set the wall reg at 60#. The main thing about the pressures is atomization. So you set the gun to what the specs say for different paint. Don't try to overthin it but go by the mix directions. Most paint manufactures have the mix sheets on the internet now.

 

[Tom and Vipers]

I'm sticking with the paint specs, but they do specify a 1.9 to 2.1mm cap and I'm using a 1.5mm.

I'm thinking a $30 1.9 would actually work better for me.

Let me ask this question, what are the downsides of having too big a cap? I think someone said for finish coats, you get less orange peel with smaller tips, however, I do't know if this is true. But for primer, I'm thinking it would have had to have a cap that was too big.

_____________________________________________________

Another piece to the puzzle, it turns out this Sharpe produces only 8 psi at the cap w/43 psi input. Sikkens specifies 10 psi max. So for 10 psi I would need 51 psi input if linear.

Another indication that I simply didn't have enough pressure was that I could **** the air out of replacable cub insert.

 

[Tom and Vipers]

Latest developments:

Looks like massive pressure loses in system.

I had the following:

delux, large micron filter w/regulator
50' 3/8" hose
disposable carbon filter

I found a small "gun-size" regulator w/gauge and added it to this series.\

At 80 psi at the micron filter, was I was only getting 30 psi on the gun regulator.

I removed the disposable carbon filter and picked up 11 psi.

I suspect there is 10-15psi drop at the gun regulator. (What is typical dP at these regulators? I think I am going to put the gun regulator upstream of the filter regulator to get its dP measured.)

It appears I was nowhere close to getting 51 psi at gun to get 10 psi at cap (gun spec: 43 psi for 8 psi @ cap.)

Tom

 

[HP]

Tom - what are the specs on your compressor? With HVLP the flow rate is critical at the gun.

 

[HP]

Ditch the 50' hose and go with the shortest hose that will work.

 

[Tom and Vipers]

I'm still tracking down the pressure drops.

I have 100 psi at the line (shop has mega compressor capacity).

My big micron filter w/egulator appears to be about a 25-30 psi drop and I know the 1/4" couplers are adding maybe 7 psi per coupling and there are 3 of those in the system.

I'm going to plump the micron filter in with 3/8" to eliminate that bottleneck.

I just tried a Lowes Cobalt spray gun adjuster valve w/gauge (said high efficiency low dP) and at 90psi input, I get 50 psi at the gun. So that pressure drop is due to a single 1/4" coupling and the valve, no hose anywhere, just a series of fittings. The adjusting valve was increasing pressure even during its last 1/2 turn.

I'm going to ditch the valve a plumb a 1/4" T at the gun for a gauge.

I'm thinking there might be better 1/4" couplers than those Sears/Chinese ones. I know one body shop that was plumbed with a different type - the "yellow tape" style at Lowes.

I figured the high volume would reveal weaknesses in my rigging and boy was I right.

Onward...

 

[Tom and Vipers]

I've got something workable:

3/8" coupling
micron filter w/regulator
1/4" coupling
35' 3/8 hose
1/4" coupling
T w/gauge
gun

After using this gun in another paint booth with a Binks micron filter/regulator, it was instantly clear that the micron filter/regulator has no CFM capacity - should have known, Harbor Freight knockoff of a REAL product. I suspect the regulator is the culprit.

Anyhow, I can get 41 psi at the gun with shop air drawn down to 82 psi. I get 55 psi at the gun at 110 psi shop air.

I am eyeing up a Devilbiss Finishline 3 2.2mm and a chinese W-71 2.0mm for primer. My friend tried to shoot maximum thinned Rustoleum enamil thru this Sharpe 1.5mm and it clearly was too small a cap.

One observation is that guns that require less pressure at the input do have a real advantage. Requiring 43 psi was a problem for me. If it was anything in the 20's I would have been on my way.

Just goes to show you how low the pressure can be at your tool when any CFM is involved.

 

[HP]

1/4" connections at the compressor end of the hose kill CFMs

 

[EllowViper]

I run about 70-80 psi into my in-line oil/water separator which under "load" (aka use)...gives me about 40-50 psi at the gun. I then step the gun pressure down to around 30-35 psi under load. I used a DEBEER high build primer/sealer with a 1.5 HVLP in the 3:1:1 ratio just fine. The oil/water separator really restricts the air flow, but without it, I was getting a lot of crud (moisture) into the gun leading to some fisheye problems in the final clear.

 

[Tom and Vipers]

HP: Yeah, I found out about the 1/4" connectors, I was getting something like 7psi loss per connector with various setups. Actually, the 3/8" connectors do a pretty good job with 3/8" hose but they are bulky.

EllowViper: This Sikkens ColorBuild I'm using recommends 1.9-2.1mm while PPG NCP271 is 1.4-1.6 so there you have vast differences between high build primers. Your DEBEERS, what cap size do they recommend?

 

[EllowViper]

I believe a 1.4 - 1.6 but I don't have the application sheet nor product information sheet anymore. When I explained to the paint shop what I was using for equipment, they indicated I would be fine with a 1.5. I actually used the 1.5 for all my work (primer/sealer, base, and clear).

 

[HP]

Best to watch the weather and pick a low humidity day, or rent/borrow a refrigerant-dehumidifier when spraying the final coats.

 

[EllowViper]

Oh HP did you hit that one correct!!! I totally messed-up one side sill when the clear actually started to set-up in the gun within about 10 minutes of a standard mix. It looked like cotton candy coming out of the tip. After than, I reduced the activator by abut 2/3rds, increased the reducer amount, and shot first thing in the AM before the heat/humidity set in. MAN-O-MAN what a mess. It actually turned out much better than I expected so in hindsight, I wish I would have used that approach on the entire project. Thinning the clear actually was not recommended by DEBEER but I found that in the heat/humidity, it kept things flowing.

 

[Tom and Vipers]

I know when I painted acrylic enamil I got the glass finish by using the slowest reducer AND retarder. You simply couldn't get the paint to dry slow enough. Of course, you have to watch for the runs.

I want to find out more about Sikkens water base system, AutoWave and AutoClear WB.