Spray technique?
 

Share your spray technique! What has worked for you? What hasn't? What kind of spray equipment have you used?

As some of you are probably aware, I've been having trouble getting a nice sprayed clear coat. I've used by Nelson's Flat Çlear and Minwax water-based PU both with similarly unsatisfactory results. A "light misting" technique results in an unacceptable "orange peel" effect. If I spray more heavily the paint/clear coat runs. I'm using an HVLP type spray gun with a small compressor -- small in the sense that it can't really keep up with the gun for continuous spraying but is ok as long as a take small breaks. Anyway, I don't think this is primarily a compressor problem.

I'd really appreciate hearing your stories about spraying -- even if they are horror stories.

RE: Spray technique?
 

With WarbirdColors, I spray light mist coats, gradually increasing them to a final, wet coat.

Sounds like you may be omitting the "wet" coat. Try it on a test panel, and see if it gives satisfactory results.

In any case, your compressor needs to keep up. You don't want to be waiting for air pressure to build, while in the middle of a painting project.

RE: Spray technique?
 

Spray technique really depends on the paint being sprayed but you could try a two coat process. Make a initial "mist" coat and allow it to get tacky. Then go with the "wet" coat. The initial mist coat will give the wet coat something to hang onto until it sets up. Should help the issue of running in the wet coat.

SunDevilPilot

RE: Spray technique?
 

Did my kitchen cabinets with water based polyeurathane, and the only way I could get a "decent" finish was using 60# pressure at the gun (conventional auto type). The finish was not super glossy, more like semi gloss, what was what I wanted anyway.

Les

RE: Spray technique?
 

My spray equipment:

Devilbiss Finishline II Automotive large HVLP gun for spraying large areas.
Sata Minijet III HVLP gun for large and small areas.
Paasche VL double action airbrush.
Iwata Custom Micron airbrush.

Craftsman 1 HP 7 1/2 gallon tank compressor for use with the airbrushes.
Craftsman 6 HP 30 gallon tank compressor for use with the HVLP guns.

I used hobby paints for many years and thought I was happy with them. When I had to repaint an outer wing panel on a JMP T-33 which had originally been painted with Chevron Perfect Paint, I used an automotive paint for the first time since there was no other way to match the custom color I originally used. I was absolutely amazed at how well the paint flows out and got a perfect finish the first try! I am now committed to using only automotive paints for almost all of my r/c painting needs. With the automotive paints, you really have to make a huge mistake before you get it to run.

Another thing I like about automotive paints is that they have data sheets out on the net that tell you what mixes to use and what air pressure to use with a particular type of spray gun. Another particularly nice characteristic is that about 20 minutes after spraying the paint, it can safely be taped over to paint on other colors.

I have found automotive clearcoats to be far superior to other types. PPG has a really nice clearcoat product called Flexed and Flat. OH my God, what a fine finish this stuff provides! As the name suggests, it already has a flex agent and the flatener mixed in. If you want a little bit of sheen or a satin finish, you have to add gloss clear to it. Really great stuff. I have already used it over Testors Model Master flat paints with success using multiple light coats rather than any heavy coats.

RE: Spray technique?
 

If you want to do it right the first time do what Steve Collins does! However, if you are cheap like me a $65 Passche VL airbrush should be enough volume for a 1/6 scale plane and won't require a compressor upgrade. Mask off areas at natural breaks to spray individually so you can concentrate on surface finish and not be distracted by repositioning, cup volume remaining, etc.

Automotive paints are wonderful. It's all I spray on my car model bodies. The two-part clear systems contain potentially deadly fumes and should be used outside or with a respirator. I've been using the DuPont ChromaClear system with good results.

RE: Spray technique?
 

My spray gun:

I use a Sata Minijet 4.

I chose it based on the quality of the equipment as well as the low CFM of air it requires. The smaller "touch up" style guns need far less air than their full size companions. The Minijet runs at 29 PSI at the gun and consumes about 4.1 CFM.

By comparison, the Satajet 2000 also uses 29PSI at the gun but requires 15.2 CFM. The smaller compressors most people buy at local hardware stores generally will not keep up with the 15.2 CFM.

The actual spray gun may cost more but the savings on the compressor will make up for the price ten fold. And you get to have professional quality spraying.

FYI: I use a DeWalt 15 gallon compressor and in spraying the primer for my Cowl, Wheel Pants, and Canopy on my 29% Edge I only had the compressor come on once to recharge. The compressor recharges at 150 pounds and stops at 190. In reality, I could charge the compressor and unplug it. I would have enough air to complete a sequence of spraying in less than one charge.

Just something to think about,

SunDevilPilot

RE: Spray technique?
 

I painted both of my WW1 planes with Behr outdoor latex thinned about 25% with plain water, no other additives. I used an old Passche airbrush for all the painting and have been very happy with the results. It does, for me, a completely adequate job covering the 1/4 scale models and I have felt no need to buy a hvlp spraygun. (Of course, we don't miss what we've never had!) I have cheap no-name 2 gallon, 1/2 horse compressor and run it at about 30-40 psi.

When painting, I start with a latex white primer coat and let it dry overnight. Then a light mist with color, wait a few minutes and apply a wet coat. I let it dry overnight and do the same again. Two coats like this are usually enough. I have found the paint can be masked with good quality tape after 24 hours without problems.

I haven't yet clear coated either of these planes as I was intending to run gas engines in them, and have been in the DR1. The DR1 is four years old now and the paint is still in very good condition. I will probably clear coat my new Nieuport 11 both for the experience and the possibility of putting a large glow four stroke engine in it. Also, a lot of the Solartex covering on the wings will not be painted and the clear will make it easier to keep them clean. So I'm interested in the experiences of others with clear coating.

RE: Spray technique?
 

FWIW - When spraying latex or a waterbase paint (Minwax Polycrylic, Nelsons, etc) I have gotten my best results at 25 - 30 psi. Under 25 psi and I dont get the coverage and over 30 psi I start getting the orange peel.

Hope this helps.

RE: Spray technique?
 

Here's what I use. I'm set up for spraying either epoxy, or polyester. Perfect finish ever time.

This is the polyester spray system.
Two lines go into the gun.
- From the compressor - red
- From the pressure pot - black

Notice that the gun has another side mounted reservoir. That's for the MEK. Regulated at 2% flow rate.

This is a typical industrial set-up. Has a chopper attachment but I don't use it very much, because the work is mostly with fiberglass cloth.

I can spray a job, put the gun down, come back the next day, pick it up again and start spraying a second coat if needed.

I don't usually clean the system out until the job is finished, which might be 2-3 days down the road.

Plane is the XP-67 Moonbat, with removable outboard wings.

RE: Spray technique?
 

I'm feeling very amateurish here! I have a cheap 6L compressor of indeterminate HP and a HVLP gun I picked up for $19 (at Rockler's). I also have a "Mr.Hobby" $30 airbrush that uses canned air. The compressor has a guage with a knob on it that doesn't seem to do much of anything. Based on Campi's description, the pressure is probably too high so I'll see if I can do anything about that.

But to be perfectly honest, I don't plan to spend $300+ on spray equipment. Not when I can get a pretty darn good looking result on sort of models I made with a $1 foam brush. I just thought it might be convenience to spray on the clear coat -- and still think it might be. But I think unless I can do it with the equipment I already have I'll just have to stick with the brush.

Since I only do WWI models I don't need to be able to do a "slick" finish and I generally hand-paint all markings. I'd like to learn to use the airbrush a bit more for small detail parts and weathering effects. And I'd like to be able to "seal" my weathering effects with a simple sprayed clear coat. That's about the extent of my need for spraying.

RE: Spray technique?
 

Don't feel amateurish. I use an electric HVLP system I bought of EBay for $89 (several years ago) and I also have a "Husky" 1 1/2 gallon compressor (Home Depot - $99) to use with my 20 year old single stage badger airbrush. They do a reasonably good job. Much as I would like one of these "high level" systems, I can not justify the cost to myself (or the wife) for painting 1 or 2 planes a year.

Check Sears. They used to sell pressure regulators that you could install in the line (or at the compressor). Last I knew (several years ago) they cost about $20.

RE: Spray technique?
 

Hi Abu, I have two compressors, one is a small purpose made compressor for my little airbrush. With a Pasche or Badger it doesn't need a tank. It's good for plastic models and detailing parts. I usually use regular acrylic model paints in it. For big jobs I have a 60 gallon (100+ liter) 5 hp compressor. My other hobby is old cars and I used it to paint my Austin Healy Sprite. Before I got the big tank my compressor was an upright compressor from a 1950's refrigerator connected to one of those 4 gallon portable tanks and powered by a 1/2 hp motor from a swamp cooler (evaporative air conditioner for those of you who are not from the southern US). Total investment $35. For painting models I use the "touch up" gun with the 6oz cup that they sell at various chain stores. My paint guns are the high pressure type. When I bought them the HVLP stuff was still pretty pricey. I spent a lot of time researching the HVLP stuff and found out that the V in HVLP stand for volume and lots of it. My understanding is that you cannot substitute pressure for volume with these guns. Your 6ltr compressor may do the job but the regulator and the hose will have to flow the necessary cfm to operate an HVLP gun. Your orange peel effect may be coming from running too much pressure and drying out the spray. SunDevilPilot's comments about mist then wet coat are correct. Some paints, including the automotive paints, require that the second coat be sprayed with the first coat is still tacky. If you let it set up then you have to wait until it is fully hardened and may even have to sand it before the second coat. Other paints, dope for instance, are much more tolerant. I've read a lot of your posts and if I remember correctly you live/work in Japan. A lot of things that I can get away with in rural Texas may not go over well in other places. I can walk in to the local auto parts place and they will sell me a quart of Imron (rather toxic stuff) without batting an eye. HVLP equipment is good stuff in that it requires less thinner, has less over spray and is generally more economical when spraying expensive paint. It is generally better for the environment but to make it work it is important for all of the equipment to match up. BTW if the orange peel is on a sandable surface you can use successively finer grades of sand paper and then buff it to whatever level of gloss you desire.

RE: Spray technique?
 

At this point I've essentially given up on the HVLP gun. I haven't even had minimal success with in in any of my experiments. I'm now trying out my little airbrush running on canned air. The results are more hopeful but still inconsistent. I would really like to be able to spray IF I can get a smooth (almost invisible) effect. So far, that's not happening. Either I'm getting a speckled effect or the clear coat runs.

It seems ridiculous that I can get a better result from a $2 spray can.

RE: Spray technique?
 

Here is where I am at in my current paining project. PPG K36 sprayed with the Minijet 4. Smooth as glass and this is just the primer.

Unfortunatly, the cold weather outside is halting my progress.

SunDevilPilot

RE: Spray technique?
 

Cold weather? In Mesa, Arizona? Surely you jest! :D Seriously, that looks great. Since I wouldn't be using this more than one or twice a year it really doesn't make sense to invest a lot of money. I wish I had the skills to make something out of old refigerator and AC parts but I can just barely find the oil dip stick on my car!

All of the model airbrush compressors I've seen in Japan are from $200-300. I might be willing to pay $100 for one but no more. Anyway, I think unless I can figure out a workable airbrush technique, I'll just have to hand brush the clear coat.

RE: Spray technique?
 

Don, I started out nursing an external mix Badger airbrush and propellant cans with lousy results. It seemed the cans would fluctuate in pressure as the propellant boiled. The propellant also super-cooled the paint, thickening it so it wouldn't "level out" properly on the surface. I needed an air compressor anyway so my first upgrade was there. I skipped the rotary airbrush compressors the hobby industry tries to sell you because they had no tank and they were way, WAY, WAAYY overpriced. I ended up buying a small "pancake" compressor for about $150. The motor/compressor sits on top of a round tank that looks like its squished giving the unit a low center of gravity for roofing work etc. Since I bought mine the price for these has dropped to about $100. They are loud when they activate but deliver consistent pressure adjustable from 5 psi up to 100! My airbrush performance improved markedly. No longer did my pressure peter out intermittently in the middle of a session.

Last year I hadn't used my Badger in a while and the seals had dried out. I couldn't find parts and a friend was waiting on me to spray a model car body for a contest deadline. He loaned me his Paasche VL and I immediately stomped on my Badger and took it to the trash!! The VL is a dual action brush that is internally mixed. The design is old but works incredibly well. You push down on the trigger and air starts to flow through the tip. Then with air flowing, you slowly pull backward on the trigger and paint mist begins to flow in perfect proportion to your trigger. The amount of control is much, much better than a single external mix airbrush. For about $65 the VL comes with three different needle/nozzle combos for using with different viscosity paints, several mixing bottles/cups and a 6 foot braided hose - a great value.

When spraying clearcoat its difficult sometimes to see what the surface is doing. I like to spray in a darkened room with natural light coming in through a window so I can watch the surface reflection very closely. As material starts to build on the surface the sheen grows from dry to wet and its time to "move along".

Don, I've noticed you learn new techniques pretty quick. With the info that I and others have mentioned you should be spraying like a pro in no time!

RE: Spray technique?
 

Yeah, but not without a lot of whining! :) BTW, how would I go about connecting an airbrush to one of the small industrial style compressors. The one I have used the standard 1/4" connector. You're right about the propellant cooling and the pressure dropping.

I've read about the double action airbrushes and they are clearly superior. The thing is that I'd really like to find a solution to this problem in the next couple of days so I can get on with finishing the Snipe.

RE: Spray technique?
 

There is a 1/4" adapter that goes in the compressor and the other end fits the fitting on the hose for an airbrush.

A tip for you whether you are spraying or brushing waterbase paints - add 1 1/2 caps of "Flotrol" per quart of UNDILUTED paint. It retards the drying slightly so the paint levels itself out better.

RE: Spray technique?
 

I'll see if anything like that is available locally. The hose on my little airbrush looks like it has about a 1/8" female coupling that screws onto the aircan valve which itself appears to have something like 3/8" attachment.

I remember reading somewhere that Flotrol is essentially the same thing as windshield wiper fluid. I did this way back when I did my EIII but had forgotten about this.

RE: Spray technique?
 

I just discovered that the pressure guage on my small compressor has been busted probably for a long time. That's why twisting the nob didn't have any effect. I also found that I had to almost completely unscrew this knob to cut off the airflow.

Anyway, at least I know understand how to adjust the pressure -- and that opens the way for more experiments with the HVLP. But it looks like I'll need a new guage.

****

OK. I clearly don't get how the pressure guage/compressor/HVLP gun are supposed to work! I solved the problem of the busted guage by swapping it with the identical guage on the tank exit pipe. Now I can see how the guage measures airflow pressure. Unfortunately, there's no way of maintaining an even pressure for even a couple of seconds. The very moment I start the air flowing (with the trigger on the gun) the pressure starts dropping on the outlet guage (vs. the tank guage with also starts dropping but not quite as fast as the outlet guage). This is even with the 6L tank is "full." There is just no steady amount of pressure at all.

BTW, my guage is marked in Kg/cm2 so it looks like 25-30psi is somewhere around the 17-20 marks on my guage. For my first tests I must have been spraying as something like 60psi. Way too high! And when I think about it, both the spray can and the airbrush seem to use only a "gentle breeze" by comparison. That's probably been my problem from the start.

RE: Spray technique?
 

So is this 6L (2.2A -- whatever that means) compressor entirely useless for anything beyond blowing away balsa dust? What a waste of money that was! As they say in Spanish: "Quien compra barato, compra cada rato." ((He who buys cheaply, buys frequently.))

RE: Spray technique?
 

You're right about buying cheap stuff.

Try adjusting your air pressure with the gun's trigger pulled. The pressure will rise when the trigger is released, but you're not worried abnout that. You are only interested in the pressure while the gun is in use. I think you will find that the pressure will remain more constant, if you adjust it in this manner.

RE: Spray technique?
 

That's what I did. And you're right that the pressure does rise when I release the trigger. The problem is that when I pull the trigger it drops DOWN AND PAST the point I had set it at. So what I get is a sweep of pressure from about around 40psi down to about 15psi in a couple of seconds. That's no good at all.

BTW, I've been checking this with no paint (or even just water) in the gun. Do I need to adjust the pressure with paint loaded?

Frankly, it doesn't look like I'm going to be able to use this compressor. But I'd still like to figure out how these work in case I decide I just can't live without the larger $170 compressor.

RE: Spray technique?
 

So what's the relationship between paint viscosity and pressure. Is it: More viscious, more pressure, or more viscous, less pressure?