A friend of mine has suggested to me that heating Polyeurethene (sp?) before spraying makes it flow much more smoothly. He heats the poly in a vessel set in water.
It makes a certain amount of sense to me but I’m relatively new to finishing techniques so would like you folks inputs.
Regards,
Bob @ Kidderville Acres
A Woodworkers mind should be the sharpest tool in the shop!
Replies
I have heard that gelcoat sprays better and doesn't sag as much if it's at about 100ยบ F. The person who told me this uses an old Nesco cooker, which is like an oval crock pot, so it holds larger cans. It's worth a shot.
I have been thinking of trying this but I'll need to come up with a container to heat the finish in.
I've never heard of poly specifically being applied this way, but in the furniture factory where I first was exposed to finishing in the early 80's we heated the lacquer and sealer instead of reducing it with solvents. The heat makes the material less viscous so that solvents or reducers aren't needed. But it also cools down pretty quickly which definitely helps it hang on a vertical surface. There we were spraying it out of a big commercial Graco airless pump system. So I've never tried it out of a conventional pressure pot. I see no reason why it wouldn't work, though.
I have heard of, but never actually seen, folks putting an entire (small) pressure pot into some sort of water bath so that the entire pressure pot is heated up along with whatever is inside it. Which I should think would be safer than trying to more directly heat something flamable.
I think the first question is why ever would you want to spray poly, when there are lacquers that are as durable and more amenable to spraying?
********************************************************
"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
Spraying poly works pretty well, as long as it's thinned properly and the temperature, humidity, etc are agreeable. I sprayed my kitchen cabinets with poly and they look great, the finish is exactly what I wanted and it was a lot less work than brushing or wiping it on.Also, re: heating the finish, only electric heat is OK, never open flame. We know that but we also know that there are some out there who just use whatever is available, including gas burners, hot plates, etc."I cut this piece four times and it's still too short."
Edited 4/27/2007 7:51 am by highfigh
I don't doubt that sprayed poly will yield a nice finish. But given the longer drying time, I just don't get why anyone would prefer it over a fast drying lacquer. I always use one of the pre-cats from ML Campbell (mainly because it is readily available locally), and I honestly can't see any difference in durability between this stuff and poly -- at least from a practical point of view.Then there is the overspray problem with poly that Howie mentioned.********************************************************
"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
You mean the overspray that covers the sprayer's arms? Yeah, there is that. I haven't done any lacquer with a real gun yet, but I plan to ASAP. Lacquer is so repairable it's ridiculous and most of the others are harder to do that and not see it.
"I cut this piece four times and it's still too short."
I predict you will really like it. Not only does it dry fast, but it is easy to clean up the gun.********************************************************
"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
Lacquer is so repairable it's ridiculous...
Abso-friggin'-lutely. If anything that's an understatement. I think you're going to like spraying lacquer.
A tip, if you can get ahold of both of these solvents: Instead of using lacquer thinner to reduce with, use MEK and PM Acetate instead. MEK flashes really fast (but not as fast as it's cousin, Acetone) and helps to hold on a vertical surface as well as modifies the surface tension so that the lacquer flattens out much better. PM Acetate is a mild retarder which aids in flow-out. Both are primary solvents for nitro lacquer. So, knowing that one is a hot solvent and the other is a slow solvent, you can adjust the ratio to meet ambient conditions. I'd start with 50/50 and go from there.
You can use this same blend for touch-ups too. Sand a run or sag down flat with 320 and simply mist over the repair a couple times with this blend and it will reflow to a flawless finish. It works incredibly well.
Good luck!
yeah, methyl ethyl ketone works well, but is quite toxic of all solvents/thinners. Use with care and double ventilated windows, and using a dedicated hvac line is best.
I worked with wth two plexi mechanics who developed liver cancer from exposure.Expert since 10 am.
Hey kevin, can you use mek to fix overspray lacqure say on a large dining table or inside a cabinet box (as a flowout agent)?
MEK flashes too fast to be a good choice for flow-out. However, assuming that what is on your table is nitro lacquer, you don't necessarily need it to flow out. All you need it to do is to remelt back into itself. Blending with a slower solvent does help, no doubt about it. But it's not strictly necessary... it's just easier.
How bad is the overspray? Is it like orange peel or is it pretty slight? If the former then I would sand it out with 320 and then go over that with something slightly finer if you have it and then try misting it with MEK. If the latter then you might be able to clean most of it off simply by rubbing the affected area the backside of a piece of sandpaper. You'd be amazed at how well that works on slight overspray. Then you could always mist over it with MEK if it leaves detectable marks (which it shouldn't), but I find that often just rubbing it down works just fine.
Now you could probably try blending MEK with regular lacquer thinner and that should flow a bit better than straight MEK since the thinner will have some slower solvents in it.
No matter whether you blend it or not, it's important to start out with just misting. You may have to put it on a bit heavier, in fact you probably will. But you really don't want to put it on any heavier than you absolutely have to. So start with a light misting and then modify that based upon your results until you achieve a good result. What you don't want to do is to flood the surface so much that the solvent pools up on the surface.
Nikkiwood,
Many years ago I sprayed lacquer for a small custom shop. I didn't and still don't understand the chemisty behind the benifit over varnishes. My old boss was a retired chemist from the oil industry.. He knew though. I did find that the lacquers we used were easy to spray, but assumed that varnish were easy too. I've been spraying varnish for a few years now. I've been using spray cans because the projects I've been making are small. Ussually single pieces of furniture, one at a time. Now I'm building a kitchen with 14 cabinets, and various trim stock. I'm getting set up for HVLP spraying now. I don't have a spray booth. I plan on building a room of plastic sheeting in my garage and venting out a window with a box fan with a furnace filter. I'll be experimenting with this exhaust to make sure the fumes don't get out of hand. I'll have to use this until I can work out a real spray room. (my woodshop is not in my garage)
Now that I've layed the ground work. (time to stop babbling) Do you think I should use lacquer instead of varnish? I would prefer a polyuethane lacquer for this kitchen. ( I assume that polyuethane lacquers won't get watermarks when exposed to moisure) If so, is there a type of lacquer you suggest, and do you have any techical details you would be willing to share? (cut/sanding/sanding sealers/post polish rubbing/cleanup/addition hazards/ect.
Thanks in advance..
GRW
I am by no means the best person around here for comprehensive advice on what and how to spray. Your choices in various lacquers are many; I happen to use a product from M.L. Campbell called "Magnalac" because it is readily available locally and it is simple and pretty much idiot proof. It sprays well, dries fast, is very durable, does not require a sealer coat, and I have used it for just everything (furniture, casings, etc.). http://www.mlcampbell.com/pages/starpage.asp?star=MAGLike you, I don't have a spray booth and do all my spraying in a large detached garage. The great thing about an HVLP system is that overspray is less of a problem than with conventional spray set-ups. I open the main doors, use a couple of cheap box fans, and never bother to cover anything with plastic sheeting. Most of what little overspray there is lands on the floor in dust form and is easily swept up. Spraying an occasional project in these circumstances is, I think, perfectly safe and acceptable, but I would not recommend doing large volumes of work -- like on a daily basis. Having said all this, and since you are just getting started with your own HVLP system, I would urge you to read up on the new generation of waterbased lacquers that are available. I haven't done so only because I'm lazy and the above has worked well for me. One of the best places to get started is the link below. Jeff Jewitt is a frequent contributor to FWW, he sells these various products, and is known to be both pleasant and helpful to folks like yourself who are just getting started. You can call him on the phone, but he also maintains a forum on his site where you can pose questions, and the site is a treasure trove of good information. http://www.homesteadfinishing.com/In sum, the main reason for using lacquer is drying speed. If you have enough room to spread everything out, you ought to be able to complete the entire finishing process with your 14 cabinets in a single day. Good luck.********************************************************
"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
GRW, The best place to pose this quetion is over in the Breaktime forum where you'll get answers from pros who do this for a living. I advise you to use either CAB-Acrylic lacquer, a pre-catylized lacquer or a catylized varnish. Most of the cabinet pros use catylized varnish. The advantage of CAB-Acrylic lacquer is that it will give you very good service, it's very durable and easily will withstand the rigors of a kitchen envirnoment, plus it is as easy to repair (when necessary) as nitro. Catylized lacquer, and especially catylized varnish are even more durable (many times so) but if repair is necessary it's much harder to accomplish and quite a bit of experience is necessary to pull it off well. Rich
Edited 4/28/2007 10:22 am ET by Rich14
GRW,
I think you should be cautioned about spraying highly flammable and poisonous finishes like lacquer and conversion varnish in a makeshift spray booth such as you describe. It could be dangerous for you, your family, and any neighbors who happen to live anywhere near you.
Rob
Pre-cat laquers are, IMHO fine for furniture not subjected to heat or moisture. On kitchen,bathroom or laundry doors & timber tops we use only 2 pack poly. Easy to apply, dries fairly quickly but whilst harder to repair than pre-cat it is more durable. You do need a good booth or extraction system coz they don't hand out medals if you die in the process of completing the job.
Regarding heating of paint - our paint rep told me some of the industrial (ie metal fabrication) painters who heat paint before applying it on cold mornings. Cold here is still above freezing so I assume it is to get a days work in.
Dondownunder,
What is "2 pack poly"?. It may be a product I know by a different name. But I haven't heard of anything called this.
Thanks.
Finishes that have a separate catalyst that must be added immediately before use are two-pack or two-part finishes. Most commonly available to non-pros in the US is the marine finish made by Interlux called Perfection which comes pigmented and clear versions. Additionally, there is quite a range of two-part or post-catalyzed finishes available to professionals. They mostly contain solvents or other materials that you DON'T want to breathe so they must be used in proper spray booths, etc.
In addition to what Steve said regarding what we refer to as lacquers (possibly some geographic nomenclature) where pre & post catalysers are used, I was refering to, in this case, 2 pack poly as an epoxy polyurethane (where Part A (the poly) has a hardener (Part B) added to it). The end result is a mar resistent finish which pros favour because it is basically consumer proof, goes on fairly easily & doesn't give a 'plastic wrap' finish (although the purists will disagree). Unles you are familiar with it's application & health issues best avoid it & use a single pack polyurethane or oil based varnish.
Don
Let me say first that heating the varnish will produce no better results than merely thinning the finish with mineral spirits or naphtha.
Second, spraying oil based finishes is problematic for most shops. Because it dries so slowly, the overspray is liquid and when it settles on things in the area is leaves a thick crust. If you want to spray, I strongly recommed using a spray both.
In winter here I have found that the pre-catalysed lacquer behaves better if warmed up first.I just keep mine in a 2 litre glass wide neck bottle and warm it in warm water first.
I suppose that poly would also be better if treated like that in cold weather.
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