Polyester finish? - created 06-07-2011

Meyers, John - 06/07/2011.13:14:53

Does anyone know what types of paint can be used for pigmenting and base coating in and under Polyester? I would like to try using polyester instead of Nitro and wanted to know what type of paint will be ok to use as a base coat to spray clear polyester over. Also what pigments are safe to use in polyester for making it the color coat? I still may stick with Nitro but like the quickness and ease and strength of the polyester.

When I've had situations like that I've called the manufacturer of the finish I was using or wanted to use. The manufacturer's technicians who answer questions on the phone tend to be overly cautious (they have to cover their ...) so if they tell you something will work, it normally will. If they tell you something -won't- work, it might work anyway.

Thank you John. I was looking on Semtec's site and they had a comment that said you could spray the polyester over color coats from House of Kolor. So I looked up what they use and it does not tell you what kind of paint that is made of, only what can be applied over it Acrylic Lacqure or Enamel. I like a lot of their colors but not all and I do not know what their paint is made of to look for other paints that are the same but in different colors. Also I have tried asking questions to Simtec and they will answer back once then not again. Again thanks for the info.

There's usually an 800 or 888 phone number to call. You might try calling House of Kolor and ask them what their product is.

HoK is probably all polyurethane.

Solid color polyester is sometimes known as "gelcoat". Most fiberglas boats are cast inside a mold. The mold is first treated with mold release agent and then sprayed with a thickish coat of gelcoat and then the fiberglass mat is layered in with resin and the whole thing cures as a unit. When it's popped out of the mold the gelcoat becomes the shiny, tough outside surface.

My computer is too slow to get answers from google but John's suggestion to call seems like a no-brainer.

My guess is that some tints will be compatible with a wide variety or media from epoxy to polyester to polyurethane.

Check out this link I found searching the web. It is a chart for paint compatabillity. http://www.nasascale.org/howtos/chem-compat.htm I know this is off the subject but could be a good reffernce for others. David, Thanks for the info.

Does anyone know if you must use a sealer when using Polyester? If so what type, that is clear?

There was a polyester rosewood sealer that was for use on oily woods under the McFaddens system, I don't know if Seagraves Coatings took it up or not. Generally polyester can go right on the bare wood with no issues, many places use it as a basecoat and filler and then shoot polyurethane over it to speed up the buffing.

Thanks as always David. I think I am going to try the Polyester by Solarez. That is the stuff that will fully cure in the sun in 3 minutes. I spoke to the guy that owns or runs it and he had told me it would be ok to use on bare wood. So I am going to use it for the finish or at least as the sealer/primer coat for the color and maybe the top coat. It seems anything can be sprayed over it just not the other way around. So if I can not find a paint that is ok to be finished with Polyester over it, I may end up going with Nitro or Acrylic Urathane as the color and top coat. I will let everyone know how it goes using this stuff. You can tent and/or pigment the Polyester but I also want to do metallic like Lake Placid Blue and others. So trying to find a color that is safe to be sprayed over with Polyester is now the hard part.

Also the guy at Solarez told how to make the gloss polyester a satin finish. He told me about Microspheres by 3M. They are white or gray ceramic bubbles that you add to the polyester and when you spray it on they will float to the top and cut the sheen and leave that satin to the touch feeling. Also it will make the finish supper hard and scratch resistant. I am going to do this on the necks.

I am placing my order for this today and as soon as I get it I am going to do some test samples and I will let everyone know how it goes and if it is picture worthy I will post them. Until next time.

Trans-tint works fine to tint polyester. Just add and mix it like you would with Nitro. If you're used to using Nitro be sure to measure your finish thickness as you're finishing with polyester. It builds ~4 times faster. My first polyester finish was almost 20 mils thick (before I stripped and re finished)

I suppose some colors could interfere with the UV curability of Solarez. (actually they say so) For UV curing you add the photoinitiator, as well as 1% MEKP. You can add 2% MEKP for a complete chemical cure (~30 minutes)

Be careful. Use a good resporator. Polyester contains vinyl benzine. There's currently ongoing arguments among scientists about whether vinyl benzine (styrene) is, or isn't carcinogenic. IMHO a good respirator is a good idea reguardless of who wins the "carcinogenic" argument. Wear safety glasses with messing with MEKP. Buy your MEKP locally (fiberglass hardner from Lowes, Home Depot ect) I'm pretty sure there's a big haz-mat charge if it's shipped. There's also arguements about how dangerous MEKP is. Don't get any in your eyes. 1% (for the UV cure) is 3 drops per ounce. Double that for a chemical cure. I've been using Polyester (Ilva) (with 3M microspheres) on my necks for some time. After a bunch of testing I use ML Campbell Exotic woods sealer. Several barrier coat sealers worked, but I buy the ML Campbell stuff locally. The sealer isn't necessary for most woods, but I use it all the time anyway. (better safe than sorry) I've got some Solarez I'm experimenting with now. I love the 3 minute cure, and the price is good too.

I helped a friend lay-up a white water canoe once and he handed me a respirator that had old cartridges. I can't remember much from the week that followed except that I could taste the styrene all the time. I'd say the immediate loss of brain cells was a bigger factor than any future cancer risk for me. I wouldn't go near the stuff without supplied air now. Just exposed skin will allow the fumes to get into your blood stream.

Woodrow, thanks for the info. I am glad to see someone here has been using this stuff and you are trying the Solarez as well. Where did you get your 3M Microspheres? The only thing I have found on line is a gallon or more and I don't want to spend $50 on the Microspheres at this point. I would like a pint at the most for now. You mentioned tinting was ok but what about pigments like Mixol or the colors Stew Mac sells. Can these be added as well? Thanks again for the info. David I will do like you said and cover up my self before spraying this.

The "ColorTone Liquid Stains" from Stew Mac are Trans-Tint. I know they'll work to tint Polyester. I also know that the MEK based dye concentrates from LMI will also work. I suspect the "ColorTone Liquid Pigment for lacquer" from Stew-Mac will also work, but don't know for sure. Most any finish can go over Polyester, but using stuff under Polyester can be tricky. I suspect that Mixol would also work to tint polyester, but don't know for sure. I believe it would be best to tine the polyester instead of using a color coat, either under or over it.

I got a cup full of 3M microspheres from a friend at a local automotive paint supply store. You can probably get some, or some other type of flattener from any auto paint store. I'll reply to your e-mail, but I figured I'd post this much here. We're not that far apart.

Thanks for the update Woodrow! I did not think about an auto paint store having the Micro spheres. I did get an email back from Kustom Shop about paint compatibility with polyester. I am going to give them a call tomorrow and I will let everyone know what they say. The reason I ask about base coat/color coat under polyester is to do metallic colors which I have no idea on how to mix those.

Just give everyone an update/ contact for finish supplies. When I spoke to the guys at Kustom Shop/tcp global he let me know that him and his partner are the instrument finish division for the company. The guy I talked to Joe had to call me back because he had an appointment at the Fender factory, what a ruff job. Any way they are the finish supplier for Fender, Carvin, MusicMan, Taylor, DW Drums and a lot more. He told me they have every option of finish for instruments and they can do any color out there including the Fender colors. So I am setting up an account with them now to get pricing and everything going. Also they let me know the paint you want to use for color coats under a Polyester top coat is Urethane. Anyway let me know if any of you would like their contact email? So it looks like I am now set to do a polyester finish and when I get these guitars done I will post pictures and comments on the finish.

I'd like that contact email address if you don't mind, John.

I'm currently interested in spraying some poly color/metallics and what to clear coat with and such, but I am in no way set up to spray any kind of two-part polyurethane. I'm scared by all the things I've heard and really don't want to spray anything that I can't get away with spraying with my lacquer equipment.

Problem is, I have a customer who wants anything but a lacquer finish.

Paul,

2 and 3k polyurethanes are closer to lacquer (spraying-wise) than polyester will ever be. Not sure what fear-inducing things you've heard.

Gosh, I gotta be honest, I'm baffled with all the different "polys" there are out there. I don't want to take this discussion too far off topic, but perhaps I can ask a few questions here.

Are 2K polyurethanes two-part product where I have to mix the color with a hardener?

Are there any good non-lacquer clear coats (besides shellac/oils) that are as easy to use as lacquer?

I'm probably going to have a bajillion other questions, so if the mods feel like I should start my own discussion, please let me know, and I will.

Paul the email is jmcgowan@tcpglobal.com his name is Joe. Look on there site and use the Urethane 2 part clear if you do not want to use polyester as the top coat and use a urethane base/color coat. You can do like PRS and do a polyester sealer coat put it on thick and sand it back until it is thin and level. next add urethane color coat then do the urethane clear coat. Sand and buff within 24 hours and you are done. You should be able to spray everything with any normal paint gun. I want to do polyester because it is much harder and quicker to spray then Nitro and will cost about the same. I am also not one who thinks that Nitro is the holy grail of tone.

Paul yes the urethanes are 2 part finishes paint and hardener. You just need to buy a mixing cup for automotive paint and fill to the lines provided stir and spray. That contact I gave can do any color in any finish so if you decide on something other than urethane they should be able to do the color in any other finish. You could try acrylic lacquer and I think most of them are single stage paints.

Thank you very much John, I'll email you privately about proper etiquette for emailing Joe.

Is it fairly easy to clean up a 2-part urethane? I'm using an HVLP gun, not a standard air compressor setup. I don't want to ruin my gun.

Paul, You'll have better luck cleaning a gravity feed gun all around, if you are still using a syphon gun it's a whole lot more problematic. You won't ruin the gun if you clear it and clean it within a half hour or so of when you mixed your paint/clear-coat.

You need to take the air-cap off and soak it in a little cup of thinner.

I wash down any over-spray on the gun with a piece of old, cut up bath towel soaked in thinner. You can buy disposable cup liners from 3M for most models. The cups are almost always the problem as a thin sheet of cured resin will form over time and then slough-off into your fresh resin and make a mess of your finish. I'd just run thinner through as you usually would and then disassemble the gun to see what the condition is on the inside. Any goop in there you can brush out with the brush kit that came with the gun. Some guns clean up without issues others don't but you want to find that out right away, before the stuff starts to kick off.

A syphon gun will probably need a new cup and a new syphon tube at the first hint of trouble. I used one for years but every time anyone else used it I would end up having to toss it out.

I have only used a gravity feed or traditional style with the paint held below the gun. Both clean up easy with thinner as long as you do it before it starts to harden. So as soon as you know the guitar has enough paint for that session dump and clean asap and you should have no worries. I do not know if you have a Harbor Freight store near you but they sell paint guns for cheap and my Dad says they are very good for the price and when they do go bad just trash it and buy another. I have never used an HVLP system to know if it will work ok with these finishes. I will look for your email and reply.

Paul, I was talking to my Dad tonight and he said the HVLP system may not spray the clear urethane or some other clears to well because it does not have the pressure that a air compressor has to brake up the clear because of the thickness of the clear. He was saying it could come out clumpy and not have enough time to level out before it sets up. He said it is good for the color coat so you loose less paint in the air and more goes on the instrument. I hope this helps in some way.

Harbor Freight sells a low volume low pressure (LVLP) gun for as little as $13 on sale. You still need a small compressor, but I have used it to spray contact cement with, so it will handle heavy bodied fluids.

Well I got the Gloss Solarez Polyester in yesterday and I did a test on a scrap piece of wood that I had sprayed with Testor's Blue acrylic lacquer color coat and toped with Watco gloss Lacquer. I have heard you can not add Polyester on top of this finish but nothing bad has happened yet. So this morning I sanded the polyester smooth to 1000 grit and sprayed it with more of the blue Testor Acrylic lacquer. When I get home today I am going to pour more on and see what happens. I will let everyone know. I also need to pick up some MEKP/hardener to try it and see how it works. I still need to test it spraying from a paint gun and I will do that as soon as I can. As long as this comes out good enough for a sealer coat I will use it from now on because it self levels really well. When I poured it on and moved it around with a foam brush it filled it self back in really well. So I think this will be great for pores woods as well. So maybe you can say good buy to grain fillers. Anyway more on this as soon as I can give you another update.

I believe one of the problems with using Polyester over another finish is expansion/contraction rates. (but I don't understand why it would be OK to use Polyester under the same finish if this is true) I recommend getting your test piece hotter than a guitar will ever get, as well as colder. I'd also recommend taking a razor and cutting an "X" on it, through the finish. Stick a piece of tape where you cut, then rip it off to test adhesion. I'd also knock a big ding in it to see if it delaminates around the damage. It would be bad to have the finish start falling off a 3 year old guitar.

Woodrow, thank you for the advice and I will do this. You mentioned you got some of this. Have you had a chance to test it yet?

I did another sample run this morning with the poly on lacquer. This time I did not use any of the Watco clear as a mid coat for the color and just put the polyester right on the blue metallic lacquer. I poured the polyester on and moved it about with a foam brush to spread it out some. It did get a couple of fish eyes in it and I am not sure if this was a chemical reaction or contamination. Also in the fish eyes I tried to remove them before curing and I noticed it did soften the blue underneath. I pushed the paint brush down on white cardboard and it left some blue. So I do see this as a problem in the event you try and do something to the finish prior to it curing. After the poly self leveled out as much as it was going to I stuck in the sun for 15 seconds at a time and did this for a few minutes then let it sit for 30 minutes and it seemed cured. I hit with some 1000 grit wet and hand buffed it and it came out to a nice shine in just a second of rubbing. So I will now do what Woodrow said and see what happens and when I get time to go to where I paint everything, I will try it out in the paint gun. Talk to you soon and here is a picture.

I sprayed some Solarez gloss polyester on a piece of Rosewood. It was sealed with ML Campbell Exotic woods sealer. It was a little cloudy when I done it. I use the "dual" cure, using the photoinitiator, as well as 1% MEKP. I thinned it with 30% MEK before spraying. You have to make sure the thinner if evaporated before curing if you thin it. It cured fine under the cloudy skys. The thickness of the finish after buffing was .004". I let it sit overnight after curing, before buffing. The marks are cuts I made through the finish to test adhesion. I put tape on the cuts, and jerked it off. I'll post some more on it after more testing. I'm working on an acoustic for a client who wants a Polyester finish. I may use Solarez. I'll post pictures after the guitar is done.

Woodrow, that looks real nice and shiny.

Do you recomend thinning the poly before spraying?

Also how do you know when the MEK has evaporated enough to let it cure in the sun?

So I take it, it passed the tape test?

How does the finish feel at this point, nice and hard or rubbery?

Thanks for the update and pic!

My rule of thumb is to put the try to put the harder finish under the softer one. My thinking is that you don't want the undercoat to start squirming around with a brittle topcoat.

It's hard as a rock. David's point about different hardness finishes is why I'd be careful what you use for color coats. A hard finish on top of a softer one could cause crazing, or delaminations. (Maybe other stuff too, David knows his stuff) I don't think thinning is "necessary", but it's necessary for my spraying equipment, and the way I want to spray. Polyester cures from the bottom up so trapped solvents, or thinners probably wouldn't be a problem, but I think it's best to let the thinners evaporate. MEK evaporates pretty fast, but I let it sit ~10 miuntes to flow out. I dug up my old PDF's from Mcfaddens to see what they used to say. They recommend letting the UV cured finish sit 45 minutes before exposing to the (high intensity) UV, but it would cure in seconds instead of minutes like this stuff. They also say

"4) Spray 2-3 coats (4 wet mils each) R-1778 (or R-1797), allowing 20-30

minutes air flash between coats. Stir the R-1778 slowly before using – DO

NOT SHAKE. After final coat has flashed 45 minutes, cure and sand with

280 grit.

5) Apply color coats if needed. Use 2K urethane for best results. Allow

overnight dry before going to next step. If longer than 24 hours, scuff

sand with 280 grit.

6) Spray 2-3 coats (4 wet mils each) R-1778 (or R-1797), allowing 20-30

minutes air flash between coats. Stir the R-1778 slowly before using – DO

NOT SHAKE. After final coat has flashed 45 minutes, cure.

7) Let sit overnight, the rub and polish."

The HOC finish you've mentioned for color coats is a 2K urethane.

Woodrow what type of finish is the R-1778? Thanks for your process? I did a few of the test you recommended and everything is good so far. No cracks or peeling. Also you mentioned the 2K finish for best results. I was talking to a guy at the paint supply and he said using a 2K color coat will come out hard as a rock. Do you think it is best to put the clear poly on top regardless?

I've heard several times now that polyester finishes will not cure correctly over epoxy without a barrier coat between them. I just thought I'd toss that in there while I had it in mind.

R1778 is Lawrence-Mcfadden Gloss Polyester UV cured top coat. The information I posted if from their data sheet. I never used their UV cured stuff, but I have used their R-1775 catalyzed Polyester. Lawrence-McFadden is no longer in business. Their UV cured finishes (as well as all the others I know of except Solarez) required high intensity curing lights. I believe someone "(Bob Garrish???) told me it would cure in sunlight, but would take several hours.

David, (and everyone else) I don't fully understand what I'm talking about, but I believe amine blush from some (or all) epoxies can cause problems with alot of finishes. I don't understand the chemistry of all of it, so I ALWAYS do a bunch of tests when trying something new. I'm not much of an "epoxy" fan anyway. In the past I have used West Systems Epoxy for pore filling, under Mcfadden Polyester, but used Mcfadden's "Rosewood" sealer between the epoxy and polyester. I've used West System epoxy as a pore filler under oil based Varnish. For Varnish I've used Epifanes, but now use Sherwin Williams. My standard finish is oil based Varnish on (acoustic) bodies, with Polyester on necks.

Woodrow,

Amines are present in West systems finishing (105+207) epoxy, they are supposed to migrate to the surface during the cure and can be scraped or sanded off. I don't know if they are the only contaminant that affects the polyester cure.

Did Seagraves Coatings takeover the Rosewood sealer formula from McFaddens I wonder?

I was told the amines should be washed off with soap and water. I wipe anything I'm finishing down with Naphtha, followed by Mineral Spirits, then ammonia. A cabinet builder/finisher told me to do this years ago. When I've used epoxy I've always sanded it back to the wood, leaving it only in the pores.

It's my understanding that Seagrave has all of the old Mcfadden formulas but I'm not sure what they're actually selling. I called them shortly after the Mcfadden buyout, and they "didn't seem" real interested in talking to a little guy like myself. If I understand correctly LMI is buying barrels of "stuff" from Seagraves, then mixing and packaging the Nitro they're selling. (using the old Mcfadden formula) I've used ML Campbell Exotic Woods sealer as a barrier coat under several different finishes, including 3 brands of Polyester with good luck. It's a similar product to Mcfaddens Rosewood sealer. I buy it locally. Ilva has an isocoynate cured barrier coat that I've been told it good also.

I just wanted to add something to this thread. I spoke to the people at Mixol about using their tints in Polyester and they said it should work just fine and the same for the Metallic-Effects. They did say to always do a test first just to make sure the finishes are compatible by taking a small amount of the coating material and add some Mixol metallic effects, stir in thoroughly. The Metallic pigment must disperse all over the coating to know if it is compatibile.

For the color pigment, they said to brush some material on a paper and immediatley rub hard with your finger a part of the coating. If it turns a darker shade, the material is not compatible with mixol.

I am not sure about this last part and I am checking with them again for clarification and I will let you know if someone here does not already know the answer. Just wanted to share this.

Just a little clarification for some.

Automotive "2K" is actually a 2 part mix, however... 2K actually means two stage process- Meaning, you shoot a color coat of your choice, then you must shoot a clear coat over it.

They also make "single stage" paints which are designed to not use a clear coat over it.

Reading this thread just seems to complicate things so much more than necessary.

Try automotive 2k, and you wont want to use any other finish. You can get or mix any color you want- use "candies" for tints, flakes, pearls, etc, etc.

My last 2 builds were porefilled/sealed with west systems, automotive primer (real primer from a paint supplier- not rattle can primer from an auto parts store) then block sanded, color coats, clear coats, cut and buff. Paint looks perfect with a deep gloss and it's tough stuff too.

All of this stuff was sprayed with the $13 harbor freight guns. Whoever said hvlp cant spray clears is wrong. What do you think autobody shops use? $300+ Sata or Iwata HVLP's....

One of my next builds is going to be black single stage "aircraft" paint- (my customer demands it) And clear for the binding from the same manufacturer.

I never have, and never will use nitro.