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Old 11-11-2007, 06:53 PM
DGW DGW is offline
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Urethane Clearcoat Reducer

Is using a reducer suppose to help prevent solvent pop?
Or will using a reducer just make matters worse?

I build and paint guitars for a hobby and have had a big problem with solvent pop.
I've tried low temp, med temp, and high temp reducers as well as no reducer at all and still ... I have problems.
Up until recently, I was using Dupont Chroma Clear and it was horrible.
At the advice of a friend, I tried the cheaper clearcoat from TCP Global and it did seem to help, but still it could be better.

I'm using a HVLP gun with a 1.4 nozzel.
Air pressure is set at 40 psi at the gun (before trigger is pressed).
And no, I'm not spraying too heavy.

Just curious using reducer helps or is it best to do without,

Thanks.

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Old 11-11-2007, 07:01 PM
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Most likely it is insufficient flash time between coats that is causing the problem..Reducers are not usually the issue with solvent pop..

Sam
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Old 11-11-2007, 07:04 PM
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Use a slower reducer (or add a little retarder), a lighter coat and increase the flash time between coats. The slower reducer will make it flow out nicer without excessive heavy spray and make the surface stay open longer.
Solvent pop is caused by the top surface of the clear skinning over before enough solvent can escape from the coat. Too heavy of a coat drying over too fast and being recoated too soon. urethane clears are usually a two coat system. Often any more than two coats will solvent pop especially in high humidity. Increase the amount of ventilation. leave the fan on longer after finishing so more solvent can escape the booth. If baking(force drying) the clear with heat, let the paint flash longer with the fan on before baking it.

If the wood or the under coats/base are absorbing solvent they will give it back up and can add to solvent pop. Try 1 coat of Sikkens "base fix" over the base even on sold colors. It's great barrier coat. Will stop the wood from sucking up solvent. Also stabilizes metallics and pearls before clearing. In fact you find Sikkens Autocryl superior to Chroma Clear in every way. If you want to build a quality Guitar use a quality paint system on it.

Last edited by F-BIRD'88; 11-11-2007 at 07:14 PM.
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Old 11-11-2007, 07:12 PM
DGW DGW is offline
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Thanks Sam, but the solvent pop happens on the first coat as well.
So my thinking is that adding reducer, thus thinning out the viscosity, will help it lay nicer and allow the solvent to escape.
But I'm guessing that's not the case ... I dunno.

So how do I avoid solvent pop?
Besides heavy coats and not waiting between flash times, what causes it?
Contamination? Lack of airflow? Too much airflow? Wrong temperature activator? Water in the lines? Improper air/fluid mixture adjustments? All of the above?

This had been a big problem.
Any information would be a big help.
Thanks!
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Old 11-11-2007, 07:15 PM
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Quote:
Originally Posted by F-BIRD'88
Use a slower reducer (or add a little retarder), a lighter coat and increase the flash time between coats. The slower reducer will make it flow out nicer without excessive heavy spray and make the surface stay open longer.
Solvent pop is caused by the top surface of the clear skinning over before enough solvent can escape from the coat. Too heavy of a coat drying over too fast and being recoated too soon. urethane clears are usually a two coat system. Often any more than two coats will solvent pop especially in high humidity. Increase the amount of ventilation. leave the fan on longer after finishing so more solvent can escape the booth. If baking(force drying) the clear with heat, let the paint flash longer with the fan on before baking it.
Good info.
Thanks!
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Old 11-11-2007, 07:18 PM
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You don't want to add more reducer (dilute the clear). You want to slow down the flash over time so it will flow out nicer and stay open longer. Then you can really back off on your coat thickness. Add a little retarder to slow it down. Use the recomended amount of reducer.
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Old 11-11-2007, 07:18 PM
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A couple of things you can try.
First, air pressure for the clear you are using is about 10 Ls too high.
That will cause a dry spray and could be some of your problems.

Does the clear call for reducer? If not don't use it. First if you use a 70 degree reducer and it is 70 degrees by reducing the clear you will speed it up as you are cutting the solids down and this could also be the problem.
Fast flashing is not always good.

Are you using a low grade reducer? Lower grades tend to have a higher water content and they tend to forget to put in the tail solvents to save money and both of these items can cause the problem you are having.

Some clears if the first coat is tack coat or dry sprayed, they can pop no matter what you do after that point. What does the instructions say how to spray.

First thing to do is read instructions and if the clear does not ask for reducer, leave it out until a last resort and then go with a slower grade.
Also how do they ask for the clear to be sprayed, such as, wet and wet, medium and wet.
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Old 11-11-2007, 07:28 PM
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If you really want a nice finish on your guitar clear it with two coats. Next day wet sand it with 1200 and then give it 1 more coat of clear. The last coat of clear will really flow out over the smooth fresh sanded previous coats.

Will only need minor denubbing and polishing. I like using Farecla polish + the G mop buffing pad. It's water based. Use water on the pad and paint surface as you polish.
Farecla
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Old 11-11-2007, 09:35 PM
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Quote:
Originally Posted by BarryK
A couple of things you can try.
First, air pressure for the clear you are using is about 10 Ls too high.
That will cause a dry spray and could be some of your problems.
Good to know.
I'll try backing off the air pressure.

Quote:
Originally Posted by BarryK
Does the clear call for reducer? If not don't use it. First if you use a 70 degree reducer and it is 70 degrees by reducing the clear you will speed it up as you are cutting the solids down and this could also be the problem.
Fast flashing is not always good.
The instructions say ...
"No reduction is required or allowed in areas where 2.1 VOC is the legal limit.
Up to 4oz. per quart of reducer is permitted in areas where the 3.5 VOC National Rule applies."


So, I guess I won't use the reducer.

Quote:
Originally Posted by BarryK
Are you using a low grade reducer? Lower grades tend to have a higher water content and they tend to forget to put in the tail solvents to save money and both of these items can cause the problem you are having.
I didn't use any reducer with the TCP Global clear and the results were a little better.
I think the lowering the air pressure and making some fluid/air adjustments at the gun will help alot.
I just need to practice and get it right.

Quote:
Originally Posted by BarryK
Some clears if the first coat is tack coat or dry sprayed, they can pop no matter what you do after that point. What does the instructions say how to spray.
First thing to do is read instructions and if the clear does not ask for reducer, leave it out until a last resort and then go with a slower grade.
Also how do they ask for the clear to be sprayed, such as, wet and wet, medium and wet.
The instructions say wet and wet coats.

If I use a med temp activator (70 degree) and spray in a room slightly cooler, would it speed up the cure time and cause solvent pop?
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Old 11-11-2007, 09:40 PM
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Quote:
Originally Posted by F-BIRD'88
If you really want a nice finish on your guitar clear it with two coats. Next day wet sand it with 1200 and then give it 1 more coat of clear. The last coat of clear will really flow out over the smooth fresh sanded previous coats.

Will only need minor denubbing and polishing. I like using Farecla polish + the G mop buffing pad. It's water based. Use water on the pad and paint surface as you polish.
Farecla
That's pretty much what I've been doing.
Most of my paintjobs are masked, so alot of the clear is used to level out the surface.
Here are a couple examples ...



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Old 11-12-2007, 05:26 AM
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Are you sure you're getting solvent pop and not fish eyes?
You said you get it with the first coat, so I would guess it's
more likely fish eyes. If so, what are you spraying the clear over?
Could you be getting a contamination problem? that would be
easier to explain.
If it really is pin holes........never mind
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Old 11-12-2007, 06:30 AM
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Some of my lessons from these guys here.

Cleanliness - How do you clean before painting? If you did some sanding of the base coats, you have to use something like a wax and grease remover to get the sludge out of the sand scratches, no matter how microscopic the scratches are are

Air pressure - 40 PSIG??, Most HVLP guns call for 20 - 23PSIG at the inlet for 10PSIG at the nozzle for proper atomization. My Iwata is 14-16PSIG and with some paints, has been down as far as 10 at the inlet while my DeVillbiss and Sharpe guns call (and work)at the 20-23.

Speaking of pin holes - I've got a few tiny ones that will never be seen in about a 2" square repaired area on one of my car's splash shields. Fixed? Someday? Maybe!! (......... Dammit!!)

Dave
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Old 11-12-2007, 07:23 AM
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Are you sanding the color coat before clear? I think this is a big no no with all paint manufacturers. If it is popping on the first coat, i am thinking it is silicone ro some other contaminant on the surface. Any silicone in the area will attach to every surface in there and cause lots of problems. I once detailed a car in my garage about thirty feet away with one walk through door open from the one I was going to paint the next day and it fisheyed like crazy because of the armor all I used on the interior of the completed car. Never again, or so I thought. Next occurence was the same situation with vehicle location and we were using silicone sealant on a speaker enclosure same end result. Nothing containing silicone is even allowed in my shop any more.
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Old 11-12-2007, 07:44 AM
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How fast is this pop occurring on the first coat? If it is just as you paint, imeadiately, then it is likely not pop at all but a fish eye. I have used clears that on the first coat if you don't apply a full wet coat it will have "voids" here and there that look like pop or fisheye, could this be it? I am talking kind of a "dry" spot here and there where the clear doesn't flow together.

Soooo, you are saying the base goes on fine, but the first coat of clear pops?

Brian
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Old 11-12-2007, 10:29 AM
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Thanks for all the tips guys ... I really appreciate it.

I'm using a Dupont epoxy primer/sealer on the wood.
Then I prep that with 320-400 grit before shooting my basecoat (Dupont Chroma Base).
The primer and basecoats go on nice and smooth with absolutely no problems.
I do not sand the basecoats, nor do I handle the bodys alot after shooting them so I wouldn't think contamination would be an issue.
Of course, I could be wrong.

I always keep my guns clean.
I use a water/oil separator and air pressure gauge at the gun.
I drain my compressor regularily of any condensation that may have accumulated.
I even run a room de-humidifier to try to keep the humidity to a minimum.

And yeah ... I'm sure it's solvent pop and not fish eyes.
To me, this is sounding more and more like the problems could be from improper air pressure and/or fluid/air adjustments. Clearcoat always seems to want to "spit" out of the gun as it has a much thicker viscosity. So to help compensate, I purposely increased the air pressure instead of using a reducer. I think I remember reading somewhere that adding a reducer would only make solvent pop worse, so that's why I asked that question earlier.

I'll try to get some pics posted of the solvent pop.
It really looks horrible.
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