speedracerntrixie

My Feedback: (29)

I know some of the classic pattern guys are using this finish method. My question is: how long are you letting the Lacquer base gass off before applying the clear?

doxilia

My Feedback: (3)

SRT,

In my case, a week but just because of weather. Technically lacquer is ready for clear after as little as an hour. Unlike enamel or urethane base, the solvents in lacquer evaporate on contact. One can literally see the paint dry in realtime - recoat in 10 min but less than an hour. One of the great things about lacquer..., it's fast!

David

countilaw

It's always best to clear coat as soon as you can to get good adhesion. If you wait too long, the clear won't stick. I usually apply 3 coats of base coat at 15 minutes apart, wait 15 -20 minutes then apply a wet coat of clear.

Never below 55 degrees and over 95 degree temps.
If below 70 degrees use a fast activator
If above 80 degrees use a slow activator

Frank

doxilia

My Feedback: (3)

Frank,

are you assuming a single system finish? I haven't had adhesion issues if the 2K clear is applied in two coats; the first is misted and allowed to tack. The second is then flowed on.

I think 2K urethane pretty much bakes into just about anything. The application of clear after ~15 min of final basecoat also precludes any kind of wet sanding which I think is key to not only levelling and lightening the finish but also to provide a smooth surface for the clear to not "soak" into the base further keeping things light. This approach may well not work with 1K urethane clears though which may need some basecoat tooth to adhere.

However, the myriad of base and clear coat types all call for different approaches.

David

sensei

DuPont Croma Systems Base Coat is also very fast to work with, you can spray a color every 30 minutes @ 70 degrees F. The great thing about the Croma Systems Base Coat is if you wind up spending a month or even longer spraying base colors, then come back and spray the clear coat, there will not be any issues with adhesion. This stuff is pricey but it is also the only thing I have allowed to be used in business for the last 15 years.

Bob

doxilia

My Feedback: (3)

The interesting thing about Chromabase is that it is a urethane that applies very thin and mat. In some respects it behaves much like lacquer as it requires only 10 min flash time between coats and as little as 15 min before clearing.

However, I noticed that DuPont also states that the maximum time allowed before clearing is 24 hrs. I assume this is all keeping within the chromabase system though. The short time between chromabase and chromaclear is likely due to the fact that they are catalyzed 2K products which require cross-linking in order to adhere. Bob, it would be interesting to find out from DuPont what their opinion is on 2K clearing post 24 hrs of chromabase cure. Clearly, on complex body paint jobs, exceeding the 24 hour window is a common situation.

That said, 2K clear urethane over lacquer behaves quite differently.

I think the main issue today with using non water borne automotive basecoats is that the EPA has disallowed them. As such companies like DuPont and PPG are transitioning their urethane customers to water borne products (e.g., Chromax, Nexa, Envirobase). While water borne paint is somewhat more delicate in application, manufacturers claim their products are as easy to apply as solvent or catalyzed based systems.

Personally, what I like about 1K basecoat systems (i.e., evaporative solvent based systems) is that they generally don't contain isocynates which makes them less hazardous for our health. Water borne naturally goes a step beyond this in terms of lowering health concerns and as such will likely be the way forward. The beauty of water borne, among other benefits, is that it generally results in a light basecoat.

David

sensei

I know what the DuPont spec states but I/we have been utilizing several hundred gallons of Cromabase each year for many years now in the fashion I stated in my last post in and in the aerospace industry with great success, so I will most likely continue with what works for me.

Bob

doxilia

My Feedback: (3)

Bob,

paint products are often more flexible than their manufacturers state so I don't doubt you're getting great results with the urethane base and top coats beyond their 24 hr window spec. Other than its toxicity, urethane is great paint to work with.

The main thing I wanted to point out is that not only urethane but also lacquer automotive basecoats may soon no longer be available in the US and Canada (we've passed similar laws to those now enforced by the US EPA. I believe Europe did do earlier yet). In Europe that may already be the case.

If I understood well, I think SRT is concerned with lacquer flash off time prior to top coating with a catalyzed urethane clear.

David

speedracerntrixie

My Feedback: (29)

Interesting comments guys. Bob, I have sprayed tons of the Chroma system and yes it would be my paint of choice however this project has to be done on the cheap. Not to mention I can't even get Chroma system in the county where I live. Staying with the Chroma system here for a bit, I too have waited as long as a month before spraying clear without any issues. I don't know exactly why Dupont states to clear that quickly but I have a couple of theories. The first is that the base is quite porous and can absorb contaminates easily. The second gets a little technical. There is a current trend in the composites industry to plasma etch the faying surfaces to be bonded. What that does is removes electrons from the surface and creates an imbalance between electrons and protons. The adhesive will naturally be attracted to the surface on a sub molecular level thus giving a better bond. I'm going to speculate that when spraying the base this same imbalance occurs. That imbalance will do 2 things, It will attract the clear that has a different charge so the clear will go on easier and it will increase the bond. Again not 100% sure about this. Personally I feel that for our purposes we really don't have to worry about this much as our airplanes are not exposed to anything near what a car is.

As far as my original question, I know that what will be happening is a mechanical bond as Lacquer and Urethane are very different chemically. Lacquer will outgass for quite some time after spraying. Spraying the Urethane clear over Lacquer base just as soon as the base is touch dry will result in a clear that will shell over but remain soft further in. The reason that Lacquer can be oversprayed with more Lacquer for almost an indefinite time is this slow outgass. What I was really looking for was someone what has used the Lacquer/Urethane system with good success that can tell me how long they waited between the base and clear. That being said I think the thread has good info and I'm betting even more useful info will come forth. Thanks guys!

Stuart Chale

I used to use lacquer followed by a Urethane clear back in the early 90's. A friend sprayed the clear so it was often at least a week later and we had no issues. I don't remember which clear we were using back then. I am sure it is no longer made but it was catalyzed. We had no issues and it was obviously more fuel proof than lacquer but if you got a small crack or fuel crept in from an edge you were in trouble. It would craze and was very hard to repair.

Stuart C.

speedracerntrixie

My Feedback: (29)

Thanks Stuart. That is pretty much what I was thinking. In my case it is going to be a few weeks until I can get to the clear. The airplane in question is a 40% Extra so the clear is really there for gloss and durability. I will be finishing up on the base orange today and then will apply a lacquer clear with gold pearl added. Then I have to wait for some vinyl graphics that will go on before the clear. I plan to block with 800 grit to get a good adhesion between the base and urethane clear. My worry was if the urethane was sprayed too quickly I would end up with something that would never fully dry like I had in the past.

MTK

Whenever I used 600 or finer for clear coat prep, it seems I had some small areas where clear PU could lift. Now I use 400, dry usually, and have had no more lifting.

To add a little to SC comments, I found the hard way that PU must be allowed a long time to fully cure (cross link), in cooler conditions(60*). Avgas, regular gas or glow fuel would eat the clear if insufficient cure time was allowed. No scratches required

speedracerntrixie

My Feedback: (29)

Matt Mixing up the PU and letting it sit and activate for 1/2 hour before spraying will help with that.

countilaw

Lacquer is getting very hard to find these days. There are two suppliers that I know of, one in California and one in Oklahoma. The reason I know is that I had a 68 Cadillac that was damaged by the owner when he rubbed some lacquer thinner on the hood. He wanted the hood restored, and he wanted the original type of paint used. Lacquer. This was about 3 years ago and the car only had 8 k original miles on it. It even had the original tires on it which blew out when he rolled the car out of my shop.

I am building a Vertigo II which I will use Polyeurathane base coat/clear coat on. The maximum time I allow for recoat or clear coat is 24 hours. I really like having the previous coat in the curing process when I apply any top coat. That way I am assured that the two coats will bond.

If you are going to have to wait for any considerable time before recoating, you can clear coat over the new finish. When it comes time to add the trim colors, you can scuff the surface with scotchbrite and then add the trim colors. After all the trim colors are applied, two or three coats of clear can be applied followed with wet sanding with 600 grit. This will remove all the tape lines and the three coats of clear will protect the finish so you won't sand through the clear into the base coat. After sanding and all the tape lines are gone, One more coat of clear and your are done.

It's a lot of work, but it results in a beautiful and slick paint job.

I miss K & B Super Poxy, it was the best.

Frank

speedracerntrixie

My Feedback: (29)

Frank, I will 100% agree with you on the flash time of a compatible system. What you are getting by shooting the clear within a short window is a molecular bond. When using two different systems like I am the best you can get is a mechanical bond. Keep in mind that this is a 40% Extra and all that clear application could easily add a pound to a pound and a half of additional weight not to mention the additional cost.

countilaw

You're right about the weight. However, a lot of the paint that is applied is reducer that gasses off. The clear is the culprit, it contains a lot of solids that build up the clear film that makes it so nice and shiny. Another fuel proof paint is automotive single stage with activator. I dries to a hard shiny gloss without adding the clear coat.

Frank

speedracerntrixie

My Feedback: (29)

I appreciate all the feedback. I have learned a few things that is going to help. The paint is Duplicolor that comes pre-reduced and ready to spray. It took 3 quarts of the oragnge to cover the whole airplane. I'm in the process of spraying some super reduced lacquer clear with some gold pearl mixed in. I got curious and read the can instructions on color sanding and buffing out the clear. The can states that it can be rubbed out in 6 hours so my original question has been answered with that one. I figure if it can be rubbed in 6 hours then it has pretty much gassed off in that time as well as wax would seal it. So by the end of today I will have all the color and pear shot then I will be waiting to the vinyl graphics and clear coat to show up.

countilaw

Looking really good. Lighter colors of lacquer take a lot of coats to cover. When using yellow apply white first. When using red, apply yellow first. I know it sounds strange, but it does make a lot of difference.

Frank

speedracerntrixie

My Feedback: (29)

Makes perfect sense, if you notice the canopy my primer was yellow. Getting excited to get it finished, that orange with the gold pearl is going to pop. Now I have to start thinking about ordering 11 300 oz + servos. It's well worth it as because the airplane was badly damaged it was pretty much given to me.

speedracerntrixie

My Feedback: (29)

Getting more work done, I have a few parts in clear now. the pictures show the gold pearl really well but the shine is under rated in the pics. I could not be happier with the color. I've decided that I will need to block out the clear with 2,000 grit and buff back out. Not that there is a lot of orange peel, I just feel I have to go the extra mile on this one.