Spaying lacquer and proper ventilation
I am in the process of using a HVLP sprayer to spray clear lacquer on some bookshelf’s, crown molding, and wainscot in my living room. I use a little over a gal of material per coat.
How much ventilation should I have in the room and what is a good way to get it?
I put on the first sealer coat and there was quite a bit of overspray that settled on the horizontal surfaces(not much ventilation). That’s not a problem now because I will be sanding it off, but as I get to the finish coats it will be a problem.
If I increase the ventilation will I run into a dust problem? How do you determine the trade off between more ventilation and dust vrs. more spray/fogging and overspray settling on your wood?
Some general information…. The room is 13’ by 23’ with windows on one 13’ wall and the dinning room on the other 13’ wall. There is another doorway in the middle of the 23” wall.
Any insight into this would be appreciated. Thanks
Replies
When you're feeling good but still not taking your clothes off you've got about the right amount of ventilation.
With laquer spraying, there are a few rukes:
1) There can never be too much fresh ait;
2) The air can never be too clean; and,
3) You can never mask too much or too well.
Laquer is nasty, and will explode in a heartbeat. On the plus side, it makes for a really nice finish, lasts long, and dries fast. Rather than sucking the air out, I suggest blowing filtered air in - say, by covering the windows and doors with bedsheets.Let the fans suck air through the sheets, or through a furnace filter, and direct it against the ceiling to disperse it. Act like you're spraying gasoline, and keep ANY source of ignition - smoking, most space heaters, the water heater igniter - well clear of the spray area.
For those who are setting up some manner of spray booth, I suggest that you spray against a 'water wall.' The constant flow of water will catch much of the overspray.
Lacquer spray and ventilation
Thanks guys,
sounds like ventilation is the key (clean/filtered).
how much ventilation
You are spraying one gallon of lacquer per coat. How long does it take to spray each coat?
For each gallon of lacquer, usually about 80% is volatiles; acetone, MEK, butyl acetate, etc. weighing about 5.25lb (0.8 x 6.6lb). You need to move enough fresh air through the room that those vapors remain below about 2.5% of the air volume.
1 cu ft of air = .08 lb, so to move 40 times the amount of air as there is lacquer thinner vapor, you need to move 2625 cu ft of air in the same time you spray one gallon of lacquer. For safety sake, you'd probably want to move at least twice that amount, so shoot for at least 5,300 cu ft of air exchange during that time.
Dilution of vapors with fresh air works only if you pull in fresh air while you expel vapor laden air, so you need a filtered intake on one side of the room (to avoid pulling in dust) and an exhaust on the other. Put cheese cloth or furnace filters over one or more windows and a big fan in a door or window on the opposite side. Choose a fan that can move a sufficient amount of CFM for the rate of spray and remember that the cheese cloth will restrict flow somewhat, so the fan rating needs to exceed the necessary air volume.
The only way to control overspray in the situation you describe is to cover those surfaces that you aren't spraying and work from air intake side toward the exhaust side to minimize overspray onto partially dried surfaces. Fortunately you are using HVLP, so the overspray will be less than with a conventional air atomized gun.
dealing with lacquer overspray
Any sprayed project is best done in one continuous process keeping a wet edge the whole way.
Trying to wipe lacquer with a rag soaked in lacquer thinner is a recipe for disaster. You will ruin the lacquer under the overspray. you can wipe the area with a soft rag soaked with mineral spirits or VM&P naphtha, but whatever is partly melted into the underlying lacquer will not come off.
Are you using nitrocellulose lacquer, not catalyzed? If so, you can melt in the overspray where one section joins the next by spraying the surface with a thin wet coat of N-butyl acetate or maybe a rich lacquer thinner that has good tail solvents. Ask your paint supplier what they have to offer.
The idea is that nitrocellulose does not cure, it just dries by evaporation and can always be re-dissolved. Pure butyl acetate is both strong and medium slow evaporating, so it can re-dissolve the overspray and melt it into the surface of the underlying lacquer. Acetone or MEK would re-dissolve the overspray too, but they evaporate so fast that there wouldn't be time for flow and leveling.
Cheap lacquer thinners have the maximum amount of hydrocarbon diluents and so will not have the solvent strength after the acetone and MEK flash off.
Practice a bit on some scrap material before working on your finished projects. You are going to have to experiment quite a lot to get the spray pattern right. Ideal would be a misting spray with low fluid flow for best control.
Good luck