tech request..tell me about basecoats.....

Most of the stuff that I've painted at work has been single stage paint....no problems there.

But I have a few questions about basecoats.
What exactly is it? I know there is a color and a reducer, but is it a two part air dry like lacquer, or is it catalyzed like the urethane...or something else?

What is in the reducer?

If you drop some of the basecoat on something, will it clean off with lacquer thinner?

If left uncoated, does it allow moisture to get in like primer?

Any help would be great.
Thank you.

 

Base coat varies from brand to brand. Some are polyester. Overspray could probably tell you more spacifics, but here's some general info.
In most cases the reducer is a mild solvent. It allows it to be sprayed, then evaporates.
It can be removed with most any solvent including thinner, and even wax and grease remover.
If not clearcoated it's a pretty weak film, not much moisture resistance, no uv protection.

 

Tinbender, you pretty much nailed it in the proverbial "nutshell". Like most other automotive paints, you need to choose the reducer/thinner that will work best for your shop conditions-temperature, humidity, etc. The new basecoats are pretty easy to spray. They are similar to lacquer-but not the same. They are applied similar to spraying the old lacquer type paints- try to get an even medium-wet coat, then let the reducer evaporate (flash off) between coats. You can "crosscoat" metallics (change the spray direction)-"dropcoat"- (lower the spray pressure and spray a lowpressure mist coat, but not "dryspray") to get even distribution of the metallics. If you screw up a spot or get some specs in the basecoat, most systems will dry in a few minutes to a couple hours enough to sand the bad spots and redo the area. You HAVE to respray any sanded basecoat or the sand scratches will be "magnified" when you apply the clearcoat. The blend edge should lay out flat unless you spray too dry which can show up when you clear also. Usually base "melts" into itself pretty well. A little practise and maybe watch someone else spraying will really help get you on track. Most basecoats are designed to "encapsulate" the metallics. This means that the droplets of paint land on the surface and stay round for a short time then flatten out and leave the metallic particles laying flat instead of on edge. Flat reflects light and on edge doesn't-big difference in the look of the paint. This is usually done by a parafin type substance in the base color or reducer which helps the droplets of paint stay round and "orient" the metallic particles in a flat position on the panel. The parafin also helps keep the paint film firm so the metallic doesn't shift when more solvents in the clearcoat are sprayed on top. Metallics reflect light-pearls are like little prisms and refract light as it passes through them. They need to be distributed evenly in the paint film to get the desired effect of the color. Basecoat solvents are more "agressive" or powerfull than the solvents/reducers in the clearcoat. "Taildragger" had problems with wrinkling after trying to repair a couple spots on "Daisyduke's" Pickup. The resprayed basecoat over the sanded clear let powerful basecoat reducers attack the clearcoat film, which was probably not to full cure, and wrinkled the disturbed (sanded or featheredged) clearcoat. Each system has a way to repair areas that need to be resprayed. Some need to be sealed off with another sprayed on sealer, some can be baked or heat cured to let the clear film harden further so the solvents don't penetrate the clear film. This is where experience and information with a particular base/clear system is necessary in order to make the repair. Check with others familiar with your particular system and the manufacturer's recommendations for repairing the paint film. Most urethane or polyurethane clearcoats used over base colors handle like spraying enamels or acrylic enamels. Again-pick the reducer for the shop conditions and spray even wet coats at the recommended air pressure and spraygun settings. This information should be available from the manufacturer. It is usually very helpful to watch someone else spray and then practise on a smaller area than a complete car. You can get some real "show quality" results even in the "home shop". Even with limited experience with base/clear, you can spray color, clear coat-if it isn't as smoothe as you like- you can sand the clear to flatten the texture out, (make sure you have enough clear on the base first) then spray a few more slightly thinner coats on, then finely color sand and buff the clear to a high-gloss smoothe finish. This is a little more work but the results are nice. Always remember to use a good spray mask and follow the safety directions for the products. overspray

 

Overspray, thank you very much for taking the time to reply, both you and Tinbender have been very helpful.
Thanks to you both.

I have worked in prep, and have done my share of buffing, lol. I currently work in a fabrication shop, and I spray mostly Nason single stage, and some Hy-Lux Industrial coatings on the equipment, trucks, and trailers that we are making. But, I now free reign of the shop in the off hours, and I picked up a great "practice" side job. A base clear spot in on a quarter panel. I am familiar with the prep, and the appropriate blending areas, and things like that, but I've always worked under a painter, (some were REALLY good), and other than a few bike parts, I haven't sprayed any real base-clear.

I'm confident that I can get the clear down, and mostly confident that I can do the blend. I was just trying to get as much information as I could before I get to the "practice" part.

Let me ask you this, I prepped the area with a catalyzed urethane primer, and am spraying chroma base with Nason clear. Any recomendations on primer? Also, on some cheap car lot jobs that I helped with in the past, we used laquer primer. What are the problems with using this with a baseclear system such as the Chroma base, and Nason clear?
Or even with a single stage urethane paint?

Thanks again,
Brandon.

 

A good catalyzed primer should be good enough to be final sanded (400-600 wet or 320-400 dry) and do the repair on. I use a blend-prep for wet scuffing the area to be cleared ( the rest of the panel that doesn't get color/base). I think it's SEM scuff and clean. They are usually a mild abrasive paste that you scuff with a 3M gray pad and water to prep the area for clearing. (RINSE THOURUOGHLY with water) There are some blending sealers that work very well too. Just remember to leave yourself room for the blend. If you need to go to 1 more panel it's easier if you plan ahead for that. Lacquer primers are soluable. They soak thinners up. When you do base/clear you are painting the car twice and using twice as much solvent which makes it more succeptable to shrinking and swelling with lacquer based primers. Catalyzed primers, good quality ones, should not let the thinners/reducers soak into the repair if they are fully cured. You'll get better results with the catalyzed primer. Also anytime you put catalyzed products over uncatalyzed products you run the risk (almost always) of trapping solvents under the paint film in the soluable primer. When those solvents try to escape they can do all sorts of weird stuff--including bubbling, shrinking, and lifting. overspray

 

Damn overspray, you are generous with your time. I always love your posts.

 

Thanks for the kind words "PTL". I get a lot more out of this board than I give. There are a lot of very gifted, knowledgeable and talented people on this board. I'm very flattered that Ryan posted a couple tech threads I started in tech-o-matic and PM'd me with some nice compliments on my contributions. Those tech's were added to by more talented individuals increasing the knowledge and information we are able to share here. I LOVE IT!! This is the coolest place for car people ever!! (Now I wish I could type with more than 2 fingers) overspray

 

Overspray, I've been using laquer primer for a while. Could I use a Catalyzed primer over it before the base color coat or is this asking for bigger problems, what about a sealer before the base coat. Last time I painted anything emron was the rage don't even think they make that stuff any more.

 

Hey slider, you must be as old as me. Like I said above, you run the risk of problems with catalyzed products over uncatalyzed products (lacquer primer). Some of the new paints don't even reccommend use over lacquer primer. If you have a lot (thick film build) of lacquer primer that may cause problems. The lacquer will act as a sponge and absorb solvent from whatever you put on top. If it's just a thin coat and you are concerned about the finished job, just sand most or all of it off and use a 2 part primer to redo the area. The nice thing about -GOOD QUALITY- catalyzed primers is most of the time you don't need a sealer, especially if you have primed the whole job. OK, I better put some GOSPEL up about sealers.
Most sealers are used wet on wet-this means that you spray them on just before you spray paint. They usually require a "flash" time (20 minutes-1 1/2 hours dry to let the solvents evaporate) then you apply the finish (color). This means the sealer may be dry to the touch-but not cured. They usually have an optimum time to dry before they need to be recoated or sanded in order for the paint to still
bond (stick). The solvents in the paint are usually the same or more powerful than the ones in the sealer. This means that they will soak in and penetrate the sealer film at least somewhat. So, they really are a "tie coat" that helps the paint bond with the undercoats (primer/old paint) or a color coverage coat to make everything 1 color before paint. If you really want to "seal out" the solvents from the (topcoat) paint, the best thing is a fully cured catalyzed primer-or fully cured catalyzed paint system that will not let solvents penetrate the film (properly prepped and sanded-of course). The only exception I can think of to this would be using a "water-borne or water based" primer or primer sealer. Solvents usually don't penetrate water based primers. The drawbacks are: they aren't compatible with all paint systems-they usually dry slow- and there aren't many real good ones for the way we use todays solvent based auto paint systems. Solvents-thinners-reducer, are the key to all painting. The thinners/reducers in paint are made specifically to work in the paint film for flow and gloss-and then LEAVE (evaporate). If they soak or penetrate into the undercoats, then they don't leave (evaporate) and can come out later when the paint has cured causing bubbles, die-back-low gloss, shrinking or swelling, amoung other things.
There are lots of good 2 part primers on the market, in all price ranges. When changing from the old lacquer primers to 2 part catalyzed primers, remember to mix smaller batches-YOU CAN"T LEAVE IT IN THE GUN-(it hardens up and your paint gun is now a shop wall ornament) and 1 coat of high-build 2 part primer will equal the build of 2 to 6 coats of lacquer primer, depending on the brand/type. overspray

 

Thanks Overspray lets just say I've been riding harleys long before they were the thing to ride and a basket case could be bought for a few hundred bucks. It was (still is) a hardtail with a 8" over front end and so low that you can't roll a beercan under. Anyways thanks for the info. I'm roughing in a 46 chevy and covered the bodywork with laquer primer to keep it from rusting until the truck is the way I want it then I'll tear it all down and do the finish work. Think it'll be ok to sand most of the primer off and cover it with the 2 part? I'm sure there will still be a bit of primer left but it shouldn't be to thick. One other question I heard/read that most of the catalyzed type paints need a forced air resparator, know of any kind that doesn't or is at least not to deadly?

 

Thank you for digging this post back up.

I am happy to report that the side job went very well.

The guy at the paint shop said that I could have used regular urethane reducer with the Chroma Base, but I popped for their Basemaker after reading the can (!) and it did just what it said it would with getting the flakes laid down like they should, and the blend was seamless.

Thanks again for sharing, it's great info like this that makes wading through these pages of drivel worth while....

 

slider-- you should be good to sand off most of the lacquer primer and use 2 part. Ask around in your circles, and see who's using what kind of 2 part primer. Check with someone that does more than one job a year and see if you can look at the results. You heard right about the mask. The main thing to watch out for is if you are "sensitive" or "alergic" to the chemicals. Some people can break out in hives or their airway can close up like really bad asthma. Most of the time, if you don't do it every day, a good quality charcoal respirator is pretty good and remember to leave the spray area when you are not spraying to limit your exposure, with good ventilation, of course.
hemi--I'm glad my fingers conjured up some useful information for you. Thanks also to Tinbender, his info was right on the money.
If any one else has some base coat info they need, there's a lot of expertise here on the H.A.M.B. I'm sure the paint guys, on the board, will all help out with any other questions or concerns. overspray.