mottling, explained in detail?

hi guys,

if you get mottling then say you clear the car....how can you determine what actually caused the mottling? striping seems straight forward, but how do you determine if you applied the base too dry, too wet, maybe the air pressure wasn't right, etc? When I first started out I'd spray basecoat way too dry causing a gritty surface and it would mottle, and it seems like i've never put it on too wet to cause it, but how can you determine what's actually happening in the base? Are the flakes supposed to stand up, lay down?
Also for drop coats I've seen people not change air pressure but just move back from the panel, drop the air a few pounds, and I've also seen people raise the pressure....what's YOUR best procedure from experience? When I went to school they said lower the pressure and come back some to get "bigger droplets" but i never understood how that technically effects the metallics causing them to lay even.

Thanks in advance!
 

Chris_Hamilton

Trying to be the best me, I can be
This may be a long answer because some of your questions lead into other things that need explanations. I'll try to keep it simple although I don't always succeed in doing so.:)

What you should focus on is technique. Modern basecoats when used with a quality gun are extremely easy to apply. One reason I'm not big on going to a School to learn to paint is that most of the Teachers don't know how to paint either. Case in point drop coats. Drop coats do not apply to modern basecoats. Erase that crud from your mind.

Technique and proper materials = Success. What do I mean? If you learn the proper technique to spray and use quality correct materials you will turn out quality work.
Keys to success when spraying base.
1. Overlap. You should overlap each pass 50-75% depending on the base and your speed. You need to be consistent with this from start to finish
2. Straight passes. You should break up what you are spraying into imaginary straight lines. Follow those lines when making passes. Do not follow body lines or curves.
3. Gun distance. Keep your gun distance the same at all times and keep the gun parallel to the surface at all times. Most modern guns like 4-6 inches.
4. Medium coats. Ideally you want to shoot medium coats. Not wet and not dry. But if you are using a quality slow reducer light coats don't hurt anything. Tricky metallics shoot easier with light coats. I'll often shoot light and do 4-6 coats, solid colors no reason for that but on tricky metallics light coats help. There is a difference between light and dry though. Dry is usually the result of holding the gun too far away.
5. Slowest Reducer possible One of the biggest causes of issues when spraying base is using too fast of a reducer and not using a quality reducer. Too fast and the metallic does not have enough time to orient itself correctly before flashing off and you get issues with mottling, clumping, striping. When you use too fast of a reducer you will also notice roughness and dry overspray on the panels. Using a quality slow or very slow reducer solves these issues. Using a low grade reducer will cause these types of issues as well. Dry rough surface. Metallic not laying down correctly. SPI is the highest quality reducer out there. Example, I've shot a lot of PPG DBC over the years. The PPG DT reducer is a quality reducer but when I substituted the SPI reducer I immediately noticed a difference in how DBC sprayed and how it layed down. Surface was also much more slick. Only thing I did different was substitute SPI for the DT reducer. From then on I only used SPI reducer in DBC. Bonus is it cost $20 less a gallon than DT.
Always use a quality slow or very slow (in warm conditions) reducer when doing a overall or multiple panels.
6. Air pressure. Follow the base manufacturers recomendations. As I have been doing this for a long time I pretty much know what pressure I like to spray at. Just enough to atomize properly and no more. WIth my Sata HVLP Digital it usually reads about 12 psi at the cap (10 is maximum in regulated areas) I usually experiment some on masking paper to find a nice balance between atomization and too much air.

Those are some of the basics. Learn the technique and apply it correctly and you'll have success. It takes time and practice though. You can't expect to shoot the same as someone who has shot everyday for 10 or 15 years. But all the same if you learn the techniques you'll have good results.
 

AAE

Learner
Since I don't paint a whole lot, I watch a lot of videos and almost every one of them, the painter uses an drop coat of some type. These Cromax videos are pretty good.
 

Chris_Hamilton

Trying to be the best me, I can be
Since I don't paint a whole lot, I watch a lot of videos and almost every one of them, the painter uses an drop coat of some type. These Cromax videos are pretty good.
I stand corrected AAE. Although I like JC I never do it nor have I found a need for doing it. Acrylic and synthetic enamels used to need drop coats but I have never had to with a modern basecoat. I guess what I'm trying to say is if you are doing it correctly there is no need for it.
 

AAE

Learner
I stand corrected AAE. Although I like JC I never do it nor have I found a need for doing it. Acrylic and synthetic enamels used to need drop coats but I have never had to with a modern basecoat. I guess what I'm trying to say is if you are doing it correctly there is no need for it.
Not corrected at all. You've found a way that works for you and that's the important thing. I just though this was an interesting way of doing it. I have heard painters say that drop coats leave dry spray that leads to adhesion issues. My Standox tech sheets recommend drop coats.
 

Chris_Hamilton

Trying to be the best me, I can be
One thing that changes things because it's like comparing apples and oranges is that he was spraying waterborne base. That changes everything. Solvent doesn't want the wet on wet application like a waterborne does. Mist coats and drop coats apply with waterborne because of the long open time and style of application (wet on wet).
In my post above I was speaking only to solvent borne basecoats. I have very little experience with waterborne basecoats.
 

AAE

Learner
One thing that changes things because it's like comparing apples and oranges is that he was spraying waterborne base. That changes everything. Solvent doesn't want the wet on wet application like a waterborne does. Mist coats and drop coats apply with waterborne because of the long open time and style of application (wet on wet).
In my post above I was speaking only to solvent borne basecoats. I have very little experience with waterborne basecoats.
I use solvent, and as I mentioned, the TDS recommends drop coats for blending. Maybe, some makers have more confidence in their product. Boils down to do what works for you, right?
 

Chris_Hamilton

Trying to be the best me, I can be
I use solvent, and as I mentioned, the TDS recommends drop coats for blending. Maybe, some makers have more confidence in their product. Boils down to do what works for you, right?
I think you and I may have a different definition of a drop coat??? Never heard of a drop coat for blending. Can you refer the TDS to me?
 
thanks for all of the replies. I use cromax chromabase and 5 star medium reducer. I've heard a lot of guys on here say that reducer is terrible, and i'm beggining to belive that's usually my root cause...because I've sprayed a good bit and sometimes it lays out great with no mottle at all, and other times it mottles just a little bit. I've worked as an apprentice painter and used water and solvent and usually have pretty good results, but once it starts to fight me I think I start doubting everything and changing it up, making it snowball.

I've heard chrome premier needs a special basemaker, but would you guys use SPI reducer in Cromax Chromabase? the 5 star stuff I use I believe is nothing special, just another urethane reducer.
 

Chris_Hamilton

Trying to be the best me, I can be
Looked at the TDS and I will say that I seem to have an antiquted idea of what a drop coat is. Probably goes back to when I first started and there was still some of the acrylic and synthetic enamels shot. I have always equated a drop coat to a mist type coat. The "droplet technique" that Standox talks about in that TDS seems to be similar to the blending techniques that I'm familiar with.
Sorry for any confusion.:)
 

texasking

Active Member
I have found that some basecoats are much more forgiving than others at metallics laying out even. Some seem to want a wetter application (SW Ultra) and some seem to want a drier application (Deltron). I never had any luck trying to fix a mottled metallic with an old school drop coat (lower pressure, gun backed off, larger droplets). Usually mottling occurs because the base dries too quick for the temperature, or it is flooded on trying to get it wet with a reducer that is too fast. Slow, or extra slow in high temperatures, prevents lots of issues.
 

AAE

Learner
I have found that some basecoats are much more forgiving than others at metallics laying out even. Some seem to want a wetter application (SW Ultra) and some seem to want a drier application (Deltron). I never had any luck trying to fix a mottled metallic with an old school drop coat (lower pressure, gun backed off, larger droplets). Usually mottling occurs because the base dries too quick for the temperature, or it is flooded on trying to get it wet with a reducer that is too fast. Slow, or extra slow in high temperatures, prevents lots of issues.
What you described as not working is what is recommended. Point is to just be you and do what works.
 

texasking

Active Member
What you described as not working is what is recommended. Point is to just be you and do what works.
Agree 100% with doing what works for you. All I said was I, personally, have not had success trying to fix a mottled base that way. Spraying a base as the video shows goes against everything I have ever been taught in many certification schools, as well as Barry's advice, on flash times. May work with waterborne, but solvent base sprayed like that has a big chance of delamination. I know this from first hand experience, after listening to a certain major's paint rep on flash times before clear. He was trying to make the company look good to the body shop manager by rushing me through flash times, saying 15-20 minutes after base was not necessary, and 5-10 minutes in a downdraft booth was plenty. After seeing my brothers truck I sprayed complete, blow off in sheets in less than 2 years with their premium products, I called the same rep and had him come look at it. He couldn't find any clear less than 2 mils anywhere, and 99% was over 2.5. You could still faintly smell the solvent when peeling back a section of clear, and the rep said that is probably what caused it, even though I was going on his recommendations.
 

Chris_Hamilton

Trying to be the best me, I can be
Thought about this a little more, Texas I'm glad you posted that. I would like to see a video of someone doing a drop coat on a solvent based base coat and successfully fixing a mottling/clumping/striping issue. With many of the base coats I've sprayed it I can't see how it would work. I read a bunch of manufacturers base coat TDS's today out of curiosity and found it interesting that only Standox recommended it in their TDS. I would love for the Standox tech rep to show me exactly how it's done.
But I think it's completely unnecessary especially with all of the Manufacturers making a "blender" of one form or another these days. A far safer and super effective technique is to reduce your RTS base 1:1 with the manufacturers blender and shoot one or two more coats. That would solve any metallic issues and eliminates the "guesswork" that using a drop coat would. Wet on wet with solvent base's is not something I would ever want to do.

Id just like to say that today i painted a fender and it was 96 degrees...if i had worn a suit like the video id had a heat stroke...
Welcome to the life of a Production painter. Summers in the paint booths I've shot in it gets over 100 degrees pretty easily. Gotta constantly be drinking fluids or else....I used to strip down to my boxer briefs, no shirt, no pants..... :eek: and put the suit on. When I would leave my shirt and jeans on it was like I took a shower with my clothes on when I would take off the suit. Fun. Only have had one time where I had heat stroke though. That was enough.
 

texasking

Active Member
The worse it covers, the less it mottles, and the easier it is to blend. SW had some high hiding metallics several years ago that could not be sprayed on anything larger than a sprayout panel without mottling. They got rid of them.
 
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