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Post by zenrat on Nov 20, 2011 6:54:07 GMT -5
Some (but not all) of the builds I have cleared with automotive acrylic clear lacquer are suffering from cracking in the clear coat. Can anyone enlighten me as to why? I'm using a matching brand of thinner, in the recommended (for 1:1 use) ratio and putting it on through a single action airbrush. I'm applying 2 mist coats before applying wet coats and leaving 5 minutes between coats. The worst instances of cracking have been when i've put it on over decanted acrylic rattle can paint (actually satin finish touch up paint for steel sheds - I liked the colour OK  ) or over Zero Paints acrylic candies (which were applied over enamel though). I have however also got cracking in one instance when applied over genuine Toyota touch up paint. One of the builds affected is less than a year old so i'm not putting it down to an aging thing. Any thoughts? It's driving me crazy and i'm on tenterhooks waiting to see what is affected next. |
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Post by draggon on Nov 20, 2011 11:31:14 GMT -5
If it looks like the clear coat has sort of pulled away from the edge of the crack, it could possibly be that the wet coats went on too heavy, especially with the recent paintjobs, or perhaps too fast drying thinner. If it looks like a fine hairline crack, then I think the lacquer is too brittle, a warmer environment might help. Those are my best guesses.
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Post by thumb on Nov 20, 2011 11:33:55 GMT -5
Probably not but is it the same brand clear that you used on all of the ones that are cracking or even the same batch? I have builds that I've done 25 years ago(rc jets) that are still fine. Can you show a close up pic of a couple of them so we can see?
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Post by davkin on Nov 20, 2011 13:48:20 GMT -5
You can only apply laquer over laquer, putting it over anything else is asking for trouble. Some people have got away with it over other paints but I personally won't take the chance. I think your problem is incompatible paints. Just because a touch up is "Genuine Toyota" does not mean it's a laquer, it could be enamel as well.
David
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Post by zenrat on Nov 20, 2011 18:56:11 GMT -5
Hmmmmm. Thanks guys.
The cracks are sort of like crazy paving.
I don't spray unless it's warm enough and not too humid.
Everything that has cracked has been cleared with the same tin of clear thinned with the same tin of thinners - so all the same batch but I have nothing to compare. Taking pics is hard as under natural light they don't show up that well - but i'll give it a try.
I'm was starting to think along the incompatible line as well David as nothing i've cleared over rattle can car touch up paint has cracked (yet!).
Thanks guys. I have a badly cracked '69 Charger on the mantlepiece which i'll try to get some pics of tonight.
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Post by Bryce on Nov 20, 2011 19:34:11 GMT -5
I think David is right. You can only put lacquer over lacquer - the solvents are too hot for anything else. And none of the colour paints you have described actually sound like lacquer, more likely enamel to enable an easy gloss finish. Which begs the question - why are you putting clear on anyway?
Stop being a tight arse pom Fred and spend some money on decent paint...LOL
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Post by thumb on Nov 20, 2011 21:16:31 GMT -5
Not knowing those paints and from what everyone else has said about them not being lacquer I also agree now that it's incompatibility.
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Post by RodBurNeR on Nov 20, 2011 21:28:10 GMT -5
I haven't read all replies. I only have to say.....you CAN put laquer clear over enamel. I had a phone call with Dupli Color after doing it myself. I asked them if it was possible....because so many modelers said it wasn't. When they told me it wouldn't work, I told them "well I just did it" and wanted to tell them.  They didn't believe me, I asked for email to send photos to and they said it would be pointless without seeing it in progress "live"....so I agreed. The THING is.... You can do it. You just can't shoot the clear on like you would normally. I did it on a non-trakable build so the angles will be for reference only. It doesn't matter what brands you use. In order to use laquer over enamel, you have to shoot it very lightly. First few coats will have to be "overspray" amounts....just enough to get overspray appearance on the enamel....leaving the surface looking almost frosted with dots of clear. Once you have covered the enamel with the dots of "overspray" what I like to call "oops coats".... , then you can put your first light coat of clear on....not very wet, just a light coat. Let that cure up and shoot it wet! Why go through the trouble? I did it to prove a point AND so I could still polish my laquer clear while using the particular red paint I could only find in enamel.   I learned years previously, that doing it with normal coats....it will wrinkle enamel up and crack it. I learned ....but now I know how to do it without ruining the paint job! |
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Post by Bryce on Nov 20, 2011 23:19:14 GMT -5
You can also smoke while painting too Bob but like putting lacquer over enamel they are incompatible and it's not a good idea...LOL
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Post by RodBurNeR on Nov 20, 2011 23:26:09 GMT -5
You can also smoke while painting too Bob but like putting lacquer over enamel they are incompatible and it's not a good idea...LOL lol true! Just think it should be known it's not "impossible".  |
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Post by zenrat on Nov 21, 2011 2:06:54 GMT -5
Yes Bryce, but (similar to Bob) I could only get the colour I wanted in the White Knight colourbond touch up rattle cans (have you tried asking for a colour match to a shed in automotive paint?) and they do say ACRYLIC on the cans. And anyway, I don't have money to burn. Here's some pics (forgive the unTRaKableness). This is Automotive clear over Zero Paints Candies over automotive metallic. It looks a hell of a lot worse here using flash than it does in the flesh under artificial light.   |
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Post by RodBurNeR on Nov 21, 2011 2:11:41 GMT -5
Fred, that's not as bad as the one I effed up.
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Post by thumb on Nov 21, 2011 8:26:59 GMT -5
I've never had that kind of reaction to putting lacquer over enamel or any other type of paint. The results I get is almost like a melting type of cracks. That looks more like it got frozen and cracked which I know it didn't...right?
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Post by reedeezel on Nov 21, 2011 11:18:51 GMT -5
I'm thinking that the cracking issues lie more in the solvents that carry the finish than the actual type of paint. Years ago I painted motorcycles with acrylic laquer; this was state-of-the-art for custom finishes, as it was quick-setting and additional colors and effects could be applied in short order. The thing about acrylic laquer was that each coat would "melt" into the previous coat because of the solvents, unlike enamels or the now-popular catalized finishes. Dick Scritchfield's '32 roadster had one of the first Metalflake paint jobs, and it was said that when the clear coat cracked due to weathering (mind you, this was over the course of years), the fix was to spray straight laquer thinner over the finish to "melt" the clear and remove the cracks. The only time I experienced cracking under a clear coat was when I sprayed clear over laquer that had been applied at least a year previously by someone else. It was surmised that I had used too "hot" a thinner; I kinda think that the other guy had used inferior product to save a buck. Bob, I can see your technique working because the thin coats allow the solvents to flash off before they can eat into the base coat.
Zen, I'd look at the thinner, it might not be flashing off quickly enough, eroding the basecoat layers (actually eating through the top coat into layers beneath). As far as acrylics go, I used to apply clear acrylic laquer over murals brush-painted with artist's acrylic paints with no evident cracking.
I used to "cheat" a lot with painting processes and rarely got bit, but nowadays my main problem is my own impatience!
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Post by zenrat on Nov 21, 2011 16:10:24 GMT -5
No freezing Tim. My builds live in my shed but it doesn't get that cold here - probably down to 4 degrees C in the shed on the coldest night.
Thanks for the info Rich but as this is decaled over the clear I don't want to start spraying thinners on it just in case (also real rubber tyres - they could melt?). The cracks are definitely in the clear but you can't feel them even with a fingernail.
I have a confession to make though.
I was thinking about this last night at a club meeting (they were arguing about money so I had switched off). I actually used a metallic enamel as the base coat on this not an automotive paint.
What reminded me was that the build I took with me last night HAD been painted with this clear over acrylic candy over automotive metallic at about the same time and is showing no signs of cracking.
For me this confirms the "incompatible paint" hypothesis (sounds like an episode of Big Bang Theory!) - don't trust what it says on the can!
Incidently the paint job that hasn't cracked is the 2nd one on the build in question - the first time I used enamel as a base under the acrylic candy and while it looked fine (without clear - didn't need it) the candy didn't stick and peeled off when I tried masking over it to paint black rubber side trim.
This has been a good process - thanks folks. I can now stop looking at my display cases worrying about what will crack up next (answer - probably me!) and will try to identify my paints better. Enamel clear (I have Tamiya) goes on OK over anything right?
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