I Recently purchised an hvlp gravity feed sprayer. Although I have had some experience years back in technique i know very little in set-up and working w/ mediums ie. polys, lacquers, sealers.
Problem is, I have a job fabricating choir bell cabinets. Normal finish for me would be a sealer and several coats of polyurethane. this job is way to big for that. over 50 bells in three cabs. @ 82″*36″*32″. I need to spray
I bought a minwax high build polyurethane for job. with no ins. or recomendations on application / thinning / temp range. Minwax has not returned emails on subject. Could Someone please help
Also this is my first experience in this field of communication and am a little unsure as to how it really works.
Thank you
James
Edited 3/13/2007 6:51 pm ET by JAHughes
Replies
Minwax, in fact most oil based manufacturers, do not recommend their products for spraying. That's the reason you will find little help from them.
Spraying oil based finishes is problematic because of it's slow drying time. The resulting overspray is in liquid form and when it lands on other items in the shop, a crust is formed. If you want to spray oil based finishes you would be best doing it outside in in an effecient spray booth.
Thinning is dependent on your equipment. Pressure, needle size and air volume all come into play. You will need to experiment with your equipment to get to the optimum point.
Air temperature for spraying oil based finish is the same as it is for brushing.
Thank you howard,
i have built a spray booth w/ exhaust installed. So what would be a better solution and hard finish for something that will be used at least twice a week w/ bells and carts going in and out of it? Vanish?
Edited 3/13/2007 7:19 pm ET by JAHughes
Poly is varnish. It's varnish made with some amount of polyurethane added to the resin. The poly supposedly adds some "toughness"--scratch and abrasion resistance.Personally, I like non-poly varnishes for appearence reasons. For a hard non-poly finish I generally use Waterlox Clear or satin on darker woods or Behen's Rockhard for lighter woods.As always, test your finishes out on scrap or in an inconspicuous spot before committing to the real project. No tears.Howie.........
JAHughes,
Consider shellac! fast drying, (15 minutes for first coat, 30 minutes for the second and an hour for the third) low overspray and safe to spray. (It's used to coat candy and drugs) You can buy it cheaper than you can buy most other finishes. It's harder than poly and extremely easy to fix if damaged. With spray equipment you can follow the mixing direction right on the can, just be sure to use denatured alcohol
Denatured alcohol! OK? Oh, I suppose if you insist you can add a little single malt scotch ;-)
It used to be the most common floor coating so it's plenty durable. My 150 pound dog doesn't hurt it..
Water will damage it but only if you leave it on for a while.. splashed water wipes right off without damage.. don't go spilling booze on it if you're going to leave it either.. but considering the application I suspect that won't be an issue.
Oh and considering it's thousands of years old it's historical in case that enters the discussion..
In another post someone is complaining about getting the shellac off a 120 year old floor, so it's plenty durable.
If damaged take a rag soaked with denatuured alcohol and rub it back and forth a bit and the scratch goes away. If you want to remove it for some reason denatured alcohol again and it comes right off..
With all due respect, with a high-build finish I think he'd find sprayed shellac unsatisfactory in terms of appearance. I know that I do! The thicker it gets the worse it looks unless it's rubbed out afterwards.
Kevin
Not so much rubbed out,, but sanded.. color sanded yields the deepest finish. You've got to get it flat inorder for it to show real depth but poly's have the same issue a thick coat of poly just looks like plastic untill and unless it's sanded flat.
The way I show that is to paint a piece of glass with whatever finish is desired. Darn few can spray perfectly flat and brushing produces even worse results.. but color sanding flattens everything..
now I am lost in the term "color" sanded. I have used rotten stone on shellac tops after six to seven coats. Up to 600 hundred grit sandpaper hand sanded for polyrethane. What is color sanding?
JA Hughes,
Color sanding is the process of flattening a finish . If you look carefully at a coat of paint, sprayed or brushed you'll notice dips and rises plus in all likelyhood orange peel and maybe dry spots..
Color sanding removes those imperfections untill the surface is perfectly flat and then by stepping up in grit you slowly remove the scrathes you made when you sanded it flat.. start at 320 and work your way to 2000 grit or higher.
A remarkable thing occurs as you color sand. The finish gets glossier and glossier as the grit gets finer.
When you are finished with sandpaper you can go to polish and then to wax.
Not so much rubbed out,, but sanded..
You say pot-A-to, I say pot-AH-to. It's the same thing in the context that I meant it. Sprayed shellac at any meaninful build level has to be worked to look acceptable.
color sanded yields the deepest finish.
In your opinion. As I'm sure you know, that kind of thing is 100% subjective. And it involves a lot more extra work.
but poly's have the same issue a thick coat of poly just looks like plastic untill and unless it's sanded flat.
Again, that is totally subjective. And there are other alternatives besides just poly and shellac. Alternatives that neither look plastic nor require a fraction of the labor that shellac does to look decent at any meaningful thickness.
And for the record, straight off the gun poly looks vastly better in terms of leveling out. You may not like the way it looks. But that's a totally different issue.
Darn few can spray perfectly flat
With all due respect, that is a strawman fallacy. There is a world of difference between perfectly flat and the kind of surface texture that sprayed shellac yields.
Unless there is some trick that I'm simply not aware of... I've sprayed everything out there and I have never in my life sprayed anything that left as unsatisfactory of a surface appearance "off the gun" as shellac at any meaningful depth of build. Literally everything else I can achieve an acceptable "off the gun" finish with. But not shellac. The only time it looks decent right off the gun is when it's really thin.
Now I know that Steve Schoene has said something to the effect that normal approaches don't work with shellac and so I am open to the possibility that there is a trick that I'm not aware of. But if so then that simply reinforces my view of shellac. It's not the simple, idiot-proof finish that some make it out to be. That doesn't mean that it's therefore bad and folks should avoid it. But don't sell them a bill of goods that isn't real.
JA, get in contact with Target Coatings. (http://www.targetcoatings.com) They make a water based finishes from laquers to conversion varnishes to spray on stains to shellac to hybrid varnishs. The lacquer can recoat in 20 minutes. Super durable and water resistant. I am currently using there Hybrivar and I love it.
JK Wood
Thank you for the info JK,
Certainly like the sound of recoating topcoats w/in twenty minutes.
ja
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