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-   -   Metallic Base/Clear Issue (http://www.hotrodders.com/forum/metallic-base-clear-issue-218182.html)

johnyIROC 04-15-2012 09:04 PM

Metallic Base/Clear Issue
 
I am shooting a fender and bumper cover using PPG Omni with metallic base (silver) and clear. The base laid down fine, and after the final coat I let it flash off for extra time (2 hrs at the recommended temp).

When I shot the clear, the first layer when down... second layer had a few runs. I thought no big deal, I'll wetsand that out later. So I proceeded to throw down the third and final layer, then let it cure for 2 days.

So today I went to knock the runs down with 1000, and after levelling the clear, I can clearly see where every one of the runs was, the metallic is reflecting differently. I did not break through the clear... it is almost like the basecoat was absorbed up into the clear coat or the base sagged after the second coat of clear. Is this even possible?

MARTINSR 04-15-2012 11:01 PM

It is absolutely possible and you will need to shoot some color over the top and re-clear the whole thing to correct it properly.

The run in the clear coat was full of solvent and it soaked into the base.

Brian

Stu D Baker 04-16-2012 06:21 PM

What he said ^^^^^^^^^^, Stu

johnyIROC 04-19-2012 11:55 PM

Quote:

Originally Posted by MARTINSR
It is absolutely possible and you will need to shoot some color over the top and re-clear the whole thing to correct it properly.

The run in the clear coat was full of solvent and it soaked into the base.

Brian

Thanks... so how do I prevent this from happening? Would letting the base flash longer help? The window before clear is up to 24hrs... Or do I just need to make sure I don't put any runs in it period? I have always been told that runs in the clear are no big deal because they can be wetsanded... so I was more concerned with getting a wet coat than avoiding a run or two.

MARTINSR 04-20-2012 07:39 AM

You avoid it by not getting runs. Letting the basecoat flash further is going to help, but not much. That run in the clear is FULL of solvent and it's going to lay there on the base and loosen it up. Just don't get the runs in the clear.

Brian

johnyIROC 04-20-2012 11:24 AM

Quote:

Originally Posted by MARTINSR
You avoid it by not getting runs. Letting the basecoat flash further is going to help, but not much. That run in the clear is FULL of solvent and it's going to lay there on the base and loosen it up. Just don't get the runs in the clear.

Brian


Okay, I will be extra careful with the clear this time.

Is this something that the new low VOC paints are more succeptible to? In the past I would always do a heavy final coat of clear to make sure there were no dry spots. Before this job, I have never had any issues with the base mixing up into the clear even if I had the occasional run. Previous experiences were with with tri-stage candy, so maybe the midcoat isolated the metallic?

MARTINSR 04-20-2012 11:32 AM

I don't have any technical explanation but the way I see it is the more high solids products of today don't flash as fast so they are just laying there wet and soaking in. They also use things like acetone and oxhall (spelling?) as a solvent because they are heavy and don't go up into our atmosphere, thus "low VOC" (or NO VOC actually) and they just sit there in the film taking a long time to leave.

That's how my brain sees it anyway. :sweat:

Brian

johnyIROC 04-24-2012 11:13 AM

Quote:

Originally Posted by MARTINSR
I don't have any technical explanation but the way I see it is the more high solids products of today don't flash as fast so they are just laying there wet and soaking in. They also use things like acetone and oxhall (spelling?) as a solvent because they are heavy and don't go up into our atmosphere, thus "low VOC" (or NO VOC actually) and they just sit there in the film taking a long time to leave.

That's how my brain sees it anyway. :sweat:

Brian


I re-shot it, and was extra careful with the clear... the first 2 coats were basically dusted on, and the 3rd and 4th progressively wetter. Came out perfect.

I think you are right in that it has something to do with the new paint. This is PPG Omni MBX, which is essentially a 1K.... there is no hardener, only the base and reducer.

When I shot tri-stage and did other jobs in the past, I always used DBU or DBC with DX57 hardener, which when cured will not allow the base coat to "re-melt" as easily if there was extra solvent from runs in the clear.

Old Fool 04-24-2012 05:25 PM

A lot of guys put a bit of activator in their base coat to help control the metallic even though the base coat does not call for activator.

johnyIROC 04-29-2012 12:05 AM

So this job never ends. We go the fender and bumper cover based and cleared, installed them on the car and went to cut and buff it today after sitting for 4 days.

I guess I had the buffer too fast and melted the paint where the fender meets the a-pillar. It went through the clear into the base.

I sanded it out, and then went to shoot base over top with an airbrush, but it keeps reacting and lifting along the feathered edge of the clear. Do I need to shoot a primer sealer across the holes where it broke through the clear?

MARTINSR 04-29-2012 07:42 AM

Often if you spray the base dryer, use a fast reducer and let it flash good you can get away with it.

If it's a real small place you can get away with murder, you don't want to push this out too far though the adhesion can be poor because you aren't spraying wet enough for it to stick to the previous coat good.

But I have pushed this to the limit, I am talking "dusting" a little base over, NO WHERE NEAR coverage, I am talking something like "overspray" no where near a "coat". Just dust some, leave it for a while and come back and dust a little more, leave it. Build up a layer over the top of that sensitive area one dust after another until you have it covered. Then a "light coat" to distribute the metallic properly and to get it a "little" wet so it sticks around the edges. Let that flash a long time, depending on the shop temp, we could be talking hours. Then come back and clear over it.

This is a gamble, but you would be surprised how much you can get away with. Like I said, it's cheating and if you push it with too large of an area you are going to have trouble though.

But think about it, if the solvent in the base is what is causing this lifting, the and no solvent (paint) painted there it doesn't lift, there is a point of solvent you could apply there, a very tiny amount that won't lift it. So you do just that, apply that tiny amount. Then again, and again, and again until it's covered. Once it's covered it is often a barrier.

The best way is to sand that area out and get some primer down. But that too can lift it, and you have to spray the primer real dry too. Or use a water borne primer which will cover just about anything.

Brian

mitmaks 04-29-2012 08:28 PM

Quote:

Originally Posted by johnyIROC
Thanks... so how do I prevent this from happening? Would letting the base flash longer help? The window before clear is up to 24hrs... Or do I just need to make sure I don't put any runs in it period? I have always been told that runs in the clear are no big deal because they can be wetsanded... so I was more concerned with getting a wet coat than avoiding a run or two.

Next time shoot a medium wet coat first and then follow with full wet coat.

johnyIROC 04-30-2012 08:44 AM

Quote:

Originally Posted by mitmaks
Next time shoot a medium wet coat first and then follow with full wet coat.

Thanks... thats essentially what I ended up doing.

I will never use a non hardened basecoat again. The cost savings are not worth the headache if things don't lay down perfect.

mitmaks 04-30-2012 05:48 PM

Quote:

Originally Posted by johnyIROC
Thanks... thats essentially what I ended up doing.

I will never use a non hardened basecoat again. The cost savings are not worth the headache if things don't lay down perfect.

Theres nothing wrong with non-hardened basecoat. You do have to follow instructions though and not rush it or else you'll mess up.

johnyIROC 05-02-2012 11:41 AM

Quote:

Originally Posted by mitmaks
Theres nothing wrong with non-hardened basecoat. You do have to follow instructions though and not rush it or else you'll mess up.

We talked to the local PPG rep, and he said to resolve the issue with it lifting the 2K clear on the feathered edge, I would need to add hardener to the MBX even though it is not called for. Without the hardener, even if you build up several dust coats, the first medium coat will saturate any base it is in contact with and keep lifting the clear. Without the hardener, the 1K is not an effective sovent barrier.

Shot it last night with the hardener and it worked like a dream. I am sure there are some people who can shoot MBX day in and day out with no issues, but for me the hardener makes the stuff a lot easier to work with especially if it is metallic.

This job is finally done. Thanks to all for the advice.


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