pebbled paint causes

I was painting the hood today. Can't say I liked the results of my effort. Instead of the surface being nice and smooth, it seemed very pebbled. poor reflection, very granular. I'm looking to understand the to understand the cause so I can correct it.

Acrylic Enamel
Surface was wet sanded and very smooth ( 600 grit)
Pa int was thinned with paint thinner not lacquer thinner
pressure at gun was about 40lbs at the outlet.
Temp 83, humidity 80%, car in shade

I was wondering, paint too thick, pressure too low for good atomization?

Any help from you pros out there would be appreciated.

Dave

I'm no pro, but I'll say pressure too high, and the paint is drying before it hit the panel.

Pressure is good. I use 30PSI at the gun through a 1.2 tip for my urethane based clear.

Most problems are either "solvent pop", or too thick of a coat and it can't evaporate properly, or most likely it is surface prep. ANY wax/oil that is on the surface will have a "hammered" look to it.

If your talking orange peel?
if so it's either a pressure problem or not reduced correctly.

Pebbled paint ??? not quit sure what you mean there, but if it has the look of tiny holes,... then Robert is correct "Solvent pop" basically the top layer is drying to fast and the solvent causes little holes in the surface to escape. Fix for that is a much slower reducer on a hot day. Or what they call a "High Temp reducer"

Now if it looks like little round circles in the finish then that is what we call "Fisheyes" The surface is contaminated.

Also just so you know 80% humidity is a No, No, to paint on a day like that. 50% and below is perfect. I've done it in a 60% humidity day but anything above that the surface would need to be heated up to dry in a control environment, prior to painting.

I sprayed a car once outside 20 years ago on a humid day and 2 weeks later the customer came back and had this huge crack in the paint. I took a blow gun to it and it all came off in one huge sheet. Humidity sucks for adhesion. That fine layer of moisture on surface is not good.

My first thought was "Are you using the right reducer for the ambient temperature?" (eg: a medium reducer might be too fast for a warm day, requiring addition of a retarder to the mix.) Then I read the details and see you are mixing it with paint thinner? Is that what the manufacturer recommends?

What exactly is "Pa int" anyway? I'm not familiar with that one, I usually use one of the DuPont products (Centari, Limco, Chromabase) or PPG.

EDIT: I see now, a space slipped in there, you were writing "Paint", not listing a brand name!   Ok, what brand and systemof acrylic enamel are you using?

I went to the Auto paint store this morning.

His answers were:

Too hot, too humid. He mentioned the black surface in the sun was likely well over 200* , with no time for the droplets to spread out before drying, and they should not have been droplets .

I showed him my spray gun, not a HLVP gun, and he mentioned I need much more pressure than forty pounds at the tank outlet. He mentioned at least 60 at the gun inlet, so now I have an inline gauge for the gun to help.

In the meantime, the paint has to harden more to be able to wet sand it better than one day later when it's still soft.

Are you saying you didn't put hardner in the paint?

Yup,live and learn.

Suggestions?

lakeffect wrote:

Suggestions?

Well, you know what they say: when all else fails, RTFM.

Ok, maybe that's a little facetious, but there is a grain of truth in there too. BASF, PPG, DuPont, et. al. spend a lot of money trying to perfect their products. They even have different formulations for OEM application and the refinish market because the conditions are different, but the result should be the same. The field is highly competitive, constantly evolving and the formulations are closely guarded secrets.

What was true about painting cars in yesteryear no longer applies today. (Well, that's not exactly true -- preparation and cleanliness are still just as important.) Hopefully the clerk at the paint store has actually attended a factory seminar or two about the product he carries and enough sunk in that he's not just spouting something he heard a painter say years ago. Too often he was the only applicant who knew a carburetor from a fuel pump.

I'm concerned because you said you used "paint thinner" instead of "reducer" and didn't know about hardener. Acrylic Enamel is a catalyzed paint process -- it doesn't "dry" like house paint (other than the initial flash), it "cures" like an epoxy. It is important that you use all the components of the selected system as the manufacturer intended. Some paints need a hardener, some don't. Some paints can accept a plasticizer (for flexibility on plastics) or a blender (to suspend metal flakes) some can't. Certain reducers can be slowed with a retarder or sped up with an accelerator, others can't. A professional may know from experience that Brand A reducer will work with Brand B paint and/or Brand C hardener but the rest of us are better using the components made by the manufacturer of the paint for that particular paint. And they will happily tell you what you need via product data sheets and can labels.

I am not a pro, but have one or two paint projects per year. I just painted a motorcycle last week. The manufacturer had a chart plotting the size of the project against the temperature to select the correct reducer -- painting a whole car or high temperatures require a slower reducer than panels and cooler temperatures for best results. The manufacturer will also recommend spray gun nozzle sizes and pressures (for both HVLP and traditional guns).

That's my 2¢ anyway.

Your 2 cents of info is worth at least few bucks ( Canadian)to me. I'm not a pro, but I'm really good at shaking rattle cans.

The gentlemen in question has been in the business for over forty years. I trust in his wisdom. He had a " what a ph*cking idiot idiot " lookl on his face when no hardener came up.

In the lomg roof. I plan of having the whole car repainted within the next year , maybe over the winter. I don't mind that I'm learning.

By the way, I could not find a "cent" icon on my keyboard. How'd you get one on yours?

lakeffect wrote:

Your 2 cents of info is worth at least few bucks ( Canadian)to me. I'm not a pro, but I'm really good at shaking rattle cans.

The gentlemen in question has been in the business for over forty years. I trust in his wisdom. He had a " What a ph*cking idiot " look on his face when the point of no hardener came up.

In the lone run, I plan of having the whole car repainted within the next year , maybe over the winter. I don't mind that I'm learning.

By the way, I could not find a "cent" icon on my keyboard. How'd you get one on yours?

Yeah, our dollar seems to be slipping a bit this week.

Depending on the paint brand and system you are using, hardener may be optional, although IMHO, it's a worthwhile option for a single-stage paint. A friend of mine mixes custom single-stage colours to match OEM antique outboard motor colours. He supplies BASF Limco2 Acrylic Enamel, IIRC. He packages it reduced in aerosol cans for those without spray equipment and it looks OK. Obviously there's no hardener introduced into the rattle can! He also supplies the colour base in pint cans and the finish is not only more durable, I find it looks "shinier".

In the basecoat/clearcoat system I use (Dupont Chroma -- an acrylic urethane rather than an acrylic enamel), the hardener (they call it "activator") is optional for the base, but essential for the clear. They are two different activators; the base activator comes in 4 different speeds and the clear activator comes in 5 different speeds. I can't afford to buy gallons and gallons of activators, so I buy a medium and wait for the right day  

As for the ANSI/extended ASCII characters, you need a keyboard with a number pad. With the num-lock on, press and hold the ALT key while typing 0162 on the number pad, the ¢ sign will appear when you release the ALT key. At least in Windows, I don't know about other operating systems. Google "Alt+ codes" for a table of similar characters like µ, °, or £.  

You can also cut-and-paste the character from Windows charmap or similar. Some WYSIWYG editors for forums (such as tinyMCE) now offer a character map icon in the editor window, but I don't see one here. It's typically an omega (Ω) icon.

My 2¢.

It's right there next to the P:  

Cool, but if the ! character is above the ¢ character, what's above your 1 key?

( hold "alt" 0162 release "alt") ¢ ¢ ¢

Well I'll be damned! There it is!

Almost as much fun as watching paint cure.  

buickwagon wrote:

Almost as much fun as watching paint cure.  

This is the thread that never ends, yes it goes on and on my friend. Some people started posting in it, not knowing what it was, and they'll continue posting in it forever just because..This is the thread that never ends, yes it goes on and on my friend. Some people started posting in it, not knowing what it was, and they'll continue posting in it forever just because..This is the thread that never ends, yes it goes on and on my friend. Some people started posting in it, not knowing what it was, and they'll continue posting in it forever just because..This is the thread that never ends, yes it goes on and on my friend. Some people started posting in it, not knowing what it was, and they'll continue posting in it forever just because..

Shades of Sherri and Lambchop You know, as a moderator you COULD lock it.

        Where's the mint jelly when you need it.

NOOOO! You can't lock it yet, we're still hanging in suspense waiting to hear what shift-1 does on Greg's keyboard!