Spraying Questions

[Mark Stutz]

I have never done any spraying before. I'm going to be moving to part time in a month or so, so will finally have enough shop time to actually build some furniture. I have an Earlex Spray Station Pro that I got on a going out of business sale about 8 or 9 years ago and have never had the opportunity to use it. Life and work always seemed to get in the way. This seems to have been renamed the 5500. I have been using General Finishes products for a while. Arm-R-Seal and the water based poly. The request is for light colored wood, maybe even whitewashed. I'll be doing some sample boards for approval. I'm expecting to use both the Enduro-Var as well as the Water-Based poly. To be honest, one of the aspects of spraying that made me shy away for many years was the cleanup, so I really would like to stay with the water based products.

Now my question. How long can the gun sit before you need to clean it? In other words, can it sit for the 2-3 hours needed between coats for the water based poly, or do I need to clean it between coats. Since I've never sprayed before, I figured doing samples would be a good way for me to get familiar with the gun, technique, clean up, etc.

Thanks for your patience with rookie questions. I'm sure this won't be the last.

[John TenEyck]

You can leave the finish in your gun as long as you want, with a couple of exceptions. Post catalyzed finishes have a defined pot life, so you have to use or dispose of them before the set up in your gun; probably not a type of finish you will need to worry about for awhile anyway. The other exception is any finish that contains pigments, flatters, etc. that quickly settle out. For normal clearcoats I leave them in my gun until the job is done, sometimes a couple of days.

I recommend you limit the products you spray to WB and maybe shellac unless you have a proper spray booth. If you don't have a #4 Ford viscosity cup you should get one and use it to pick the right needle/nozzle for your spray gun and to adjust the viscosity of anything you want to spray that has a higher viscosity than compatible with the N/N's you have.

John

[Rob Young]

I second John's recommendation of a #4 Ford viscosity cup. Very useful. Add to that a box of paper filter funnels (the ones from Harbor Freight are about as inexpensive as I've found and work just fine). Also, the plastic mixing cups from the big-box hardware store work pretty well too. Have a few on hand.

I spray mostly waterborne and shellac. To clean after both I use household ammonia mixed about 50/50 with water. Run that through and things are darn clean. Follow up with just water.

I've had no issues with materials like waterborne or shellac resting in the gun for a few hours so long as I take a rag and clean the nozzle well. You can get a build up on the tip which just doesn't help anything.

Finally, take good notes about dilutions, N/N pairing and materials. Try to change only one variable at a time.

[Jim Becker]

I will add emphasis to something that John mentioned....sticking with water borne and shellac. Aside from the serious safety concerns and considerations one must make to spray solvent based finishes like lacquer that most hobbyists are not setup nor prepared to pay for, slow drying finishes like oil based varnishes/poly are also not the best choice for spraying because of the sticky mess that results from overspray, etc. Spraying water borne finishes can be a pleasure once you get the hang of adjusting the gun for optimal performance with the specific finish you have in it at the time and the relatively quick dry times mean you can get whole projects sprayed in a day with good planning. Enjoy!

[Mark Stutz]

No chance of anything but water based or shellac. That is what veered me to wipe on finishes over 20 years ago. I didn't like the look of the first water borne polys. I think things seem to have come a long way since then, and a non-yellowing finish is what I need at this point.

My concern was more about the needle and tip. I seem to recall stories about throwing away guns because finish dried in the needle or something like that. Hadn't even occurred to me about going bad sitting in the cup.

Rob. N/N? Needle and ??? I will definitely pick one finish and manufacturer to start, and get comfortable with that product.

Jim. I recall you talking in a recent thread about waterborne and water based. Sounds as if the coatings you were spraying are water borne but not water based. Is clean up still with soap and water?

[Gordon Stump]

I worked as a professional itinerant musician/woodworker for many years doing big stuff. I jumped on the waterborne bandwagon early using Campbell WB lacquers. Waterborne finishes have really evolved into durable fast drying topcoats but........I coated my shop with a thin coat of hard overspray. I breathed in all that non VOC glycol stuff without a mask and without a good evacuation system. I was foolish. All I am saying is protect your lungs and your tools and have fun. I was able to compete with the big boys without burning down my 100 year old farm house by using professional WB products and an HVLP system.

[Jim Becker]

My concern was more about the needle and tip. I seem to recall stories about throwing away guns because finish dried in the needle or something like that. Hadn't even occurred to me about going bad sitting in the cup.

Water bornes are pretty forgiving around "pot life" if they have not had a catalyst/cross-linker added as has been noted above. Those additives have a specified pot life and you must empty and clean the gun prior to the end of that pot life. (And dispose of any remaining finish that has the additive, um...added...) There's no issue keeping the gun loaded all day long for frequent re-coating. The gun (should be) is sealed when the trigger isn't pressed. You may need to flick a tiny little bit of stuff on the outside of where the needle exits the air cap with your fingernail before spraying subsequent coats and pay attention to the air pattern holes in the air cap, too, in case any finish splashed in them...they cannot be clogged or your pattern will suffer. Finish drying in the gun, including in the needle/air cap interface shouldn't happen. Proper cleaning after use is obviously require with any finish and if you notice any dried material anywhere, it can generally be removed with solvents...in a well ventilated space.

[Rob Young]

Rob. N/N? Needle and ??? I will definitely pick one finish and manufacturer to start, and get comfortable with that product.

Needle and nozzle. They are typically paired. The third part is the air-cap. Some guns allow you to mix and match different air-caps to get slightly different patterns. In my case, I have a 4-stage system from SprayFine. Their N/N sets and caps are not interchangeable (or at least are not advertised as such). So if I use the 1.3mm needle, I need to also use the 1.3mm nozzle and associated air-cap. Looking closely at the smallest set I have (1mm) and largest set (2mm) I can see a difference in the passages of the air-cap. But haven't tried measuring them.

Most systems/guns will come with recommendations for which N/N set to use for which viscosity materials. If you have the #4 Ford Cup (or another similar viscosity cup) you can tweak your material to match and give it a try. Then make adjustments either with additives like flow enhancers, additional solvent or reducers. But always try to change only one thing at a time.

A couple bit sheets of cardboard make good test targets. I also keep around un-printed newsprint in large sheets. Many uses including having a neutral surface to spray and look at patterns. Being newsprint it tends to wrinkle a bit but works for me. Practice on the cardboard and maybe get a sheet of inexpensive plywood. Sand it well and shoot some practice finishes on that too. Good for learning gun adjusting so you don't get a drip/run. Can always be cut up and used for jigs and stuff later.

My biggest issues is just finding the time to spray. Since I spray outside on my driveway I have to wait for weather. Typically work in the afternoon (driveway is on east side) so I have shade. But also need to monitor the wind. Can usually work with the wind to my back but still, can't do much if the wind is much higher than 5mph. Finally, I have to deal with temperatures over 90F in the summer but crazy thing, this week we were 62F on Xmas day. And on the 22nd it was about 57F so I was able to drag out a project that needed its topcoat of "milk paint" sprayed. No problems at all spraying the GF acrylic on a day like that.

Just pick a few materials to learn with (plain water is great for learning gun adjustments) and practice.