Airless spray equipment for lacquers?

An in-depth discussion of HVLP and airless equipment and techniques. January 16, 2001

What type of spray equipment are you using? I spray ML Campbell Clawlock and Magnalac topcoats and am wondering if I should switch to airless. I use HVLP and have to thin out too much to get atomization.

Forum Responses
I have used Clawlock and Magnalac with HVLP, conventional, airless, and air-assisted airless, all with good results. Perhaps the problem is with your equipment itself rather than the type. I have found that HVLP equipment must be kept very clean. A very small amount of dry finish on or in the air cap will cause poor atomization.

Clawlock is a very different breed from the Magnalac. Youíre dealing with a high solids catalyzed primer in Clawlock that will need to be reduced to about 28 seconds in a ford #4 cup. Clawlock is shipped at probably above 50 seconds, hence the poor atomization from the gun. The reduction is made after catalyzation. You will need to slow down your application rate until you achieve the proper mil on the surface which is about 4-5 mils wet or about 2-3 seconds a foot with the gun. Get the MSDS sheets and the instructions from the supplier.

Magnalac is fairly simple to use. Just make sure you apply enough wet mil of finish, again 4 is about right on the mil scale. You want to end up with about 4 mil dry, which is about 4 coats. Pigmented would be 2 sealer, 2 topcoats. If you live in a humid climate, use a flow enhancer to minimize blushing.

When you get your coating to the viscosity you want, you must use the correct needle and nozzle (always a matched set because they are machined to fit together) in your gun for that particular viscosity. Is your turbine rated enough so that it can properly atomize what you are pushing through it?

If you are dealing with a two stage or even many of the dinky three stage turbines, then you will continue to have finish problems or be faced with always having to reduce your materials with solvents to make them thin enough to spray. You need to know the rating of that turbine in "psi @ cfm".

Find out where you should set the material adjustment knob on the gun and where to set the air flow adjustment control on that horribly thick turbine sprayer air hose (3/4" ID hose is kind of big, but there is no alternative for us turbine users).

There are many ways to make HVLP work with higher solids coatings. Unfortunately, they mostly involve reduction of the coating, which defeats the purpose of high solids. These coatings are designed to give quick builds with less passes while also reducing VOC emissions. By reducing your coating you are increasing these VOCs, while at the same time reducing your productivity. It is not solvent that you want on the wood, but solids. That's what is left when the solvent evaporates.

Using a higher pressure system like Airmix or Air Assisted Airless allows you to atomize most coatings, without reduction. Therefore you accomplish quicker build with less coats and reduced VOC emissions. I would not recommend straight airless as you loose a lot of your control in applying the coating due to excessive fluid pressure. This can quickly translate into runs and sags.

You might think about a conversion HVLP. The best one Iíve had was an Acuspray #10 gun on a 3/4 " hose to a conversion regulator with a pressure pot. As long as it was clean it worked great.

Airmix and A/A technologies use small Airless type tips with holes (.o11 to .021) to pre-atomize coatings before they get ANY atomizing air. Although larger tips are available, most Airmix and A/A applications are done within this range of tips.

Air Spray and HVLP use fluid nozzles, not tips. These fluid nozzles are used to convey fluid and air to the air cap where all of the atomization takes place. These nozzles usually range from (.o28 to .088). These technologies are better suited to adhesives and materials containing aggregate such as metallics. Because of their infinite adjustability, these technologies are more versatile than any air-assist, Airmix or Airless system. They are recommended for texturing, staining, shading and glazing and you can use them on sealers and topcoats as well.

That is why Kremlin also makes a diaphragm pump, the PMP150 and why they also make Air Spray, LVLP (low volume low pressure) and HVLP.

Diaphragm pumps are great for adhesives and stains. They are also inexpensive to manufacture because they are made out of plastic and not stainless steel like Airmix and other A/A fluid sections.

Any gun can be efficient at low flow rates and with low viscosity materials. Even Kremlin concedes this at flow rates under 4 ounces per minute. But when you start spraying higher solids at flow rates of 8, 12, 14, 16 ounces per minute, HVLP can't match the finish and efficiency of Airmix.

I do a lot of cabinet finishing and refinishing, all on site, not in a booth or controlled environment. That is why I own airless equipment, a conversion HVLP, and for the last two years an Airmix. Every job is different and each may require one or more than one tool to complete it. The Airmix gives me the advantage of using my regular airless equipment, so I only need to have separate guns, not full setups.

I sprayed lacquer and alkyds on cabinets for many years with airless equipment and did not like the hard edge of the fan, even with double orifice tips. Airmix, air-assist gives you that soft pattern, so that you don't see overlap lines. Many companies make air-assist guns, but the advantage for me working on site is the small air requirement of Airmix; I use a compact 1 HP compressor and it works great. Most other air-assist guns require 10-12 cfm. If you have a large shop compressor that may not matter, but the reduced fogging of small air use will.

The big advantage you will find with air-assist or airmix is production and the ability to spray higher viscosity materials. I have sprayed thick acrylic coatings with great results.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Have you tried Airmix, a product manufactured by Kremlin? If you choose the correct pump you will not need to thin the product down at all. Also, the system is designed and tested to run compliantly as it has a transfer efficiency of 81%.