Spraying latex

[Joe Shinall]

Age old question. Spraying latex through hvlp guns. I have a Kobalt and a HF HVLP gun. I have a 80 Gallon compressor. The Kobalt has a 1.4mm tip. Not sure what the harbor freight has because it doesn't say. It's the famous purple one. I haven't been able to get a great finish with either one spraying latex. Not really that it's too thick because I have thinned to 10% and it seems to be coming out ok. But I'm ending up with a huge white cloud of dust all over everything when I finish and it's just not that smooth quality finish.

Any suggestions on either setup tips to prevent the cloudy mess or either a gun that's not outrageously expensive that will prevent this?

[Steve Schoene]

What finish, specifically are you using? There is a big difference in waterborne finishes made for brushing and those made to be sprayed.

Waterbornes are generally quite limited in how much they can be thinned since the coalescing of the finish "packets" doesn't work well with the packets seperated by too much thinner. I would also be concerned about finishes labeled "latex" unless the label doesn't also say something like 100% acyrlic.

[John TenEyck]

Joe, if you don't have one get a plastic #4 Ford viscosity cup. I'm pretty sure the purple HF gun has a 1.4 mm N/N also; it's probably printed on the air cap if you look closely. For a 1.4 mm N/N gravity feed HVLP gun you need a viscosity of about 25 seconds through the #4 Ford cup.

What paint are you using? I suspect the viscosity is still too high, but you can't just keep adding water to lower it because at some point the properties will go all wonky. You can try adding a few percent Floetrol, but I think the real solution is to see if you can get a larger needle and nozzle for one of those guns. Depending upon the paint, you could easily need a 2.0 mm orifice or even larger. What you have now is a little paint coming out and there's too much air for the flow so it's atomizing into droplets that are likely dry or nearly dry before they land so it doesn't have a chance to flow out into a smooth film. You need more paint coming through the orifice so a heavier layer gets applied and has a chance to flow out before it sets up. A larger orifice will do that. You can try opening the orifice up on your current gun as far as it will go, putting the gun closer to the work, and moving slower, but I don't think it will really solve the problem.

The best solution is to get a pressure assisted gun. I bought one recently and spraying paint that my old gravity feed gun would have struggled to do was as easy as spraying shellac. And no thinning was required.

There is a lot of good info. on spraying paint at this link: http://homesteadfinishingproducts.com/resources/articles/

John

[Joe Shinall]

Thanks for the info guys, and John I have thought the same thing about the tip being too small and though about going up to a 2.0 or 2.5 nozzle gun but just don't have much to spend at the moment and have multiple projects needing finished soon.

I have tried a few different finishes but mostly Behr Premium Plus Enamel. But I am about to go up a step to Sherwin Williams SuperPaint (acrylic latex) as referred by a long time cabinet builder and friend.

[Jason Roehl]

Try dialing back your atomizing air. I've sprayed a LOT of waterborne finish through HVLP. Waterborne finishes are made to have thicker films in general, so over-"atomizing" is counter-productive. That white dust is because the droplets are too small, moving too fast out of the gun, and drying too quickly.

I've always had the best results using a pressure pot setup instead of a siphon cup. A gravity feed is somewhere between the two.

[John TenEyck]

Joe, take a look at ML Campbell's Agualente Pre-cat Pigmented Lacquer. It's viscosity is only 35 - 45 seconds #4 Ford cup, so it should spray very well through a 1.8 mm HVLP gravity gun, and probably wouldn't take much thinning for it to work with your 1.4 mm guns. In the end, if you have a lot of projects that need to be painted, you either need to find a product that works with your guns or step up to a gun that can spray what you want.

John

[Chris Padilla]

I think everyone pretty much nailed it: larger tip/needle. I spray latex all the time with my Apollo 1000 (4-stage turbine) with the #5 tip (sorry, no clue the actual size) and I only 'thin' (not really) with Floetrol as it seems to help with the cheaper Borg type paints. I've always gotten very good results. It could be my system or simply tip/needle size or both. :D

[Joe Shinall]

Thanks guys, I have a line on trying a gun with a 2.5mm tip, gravity feed. I'm going to try it with your suggestions and better paint and see how it goes!