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Testors enamel paint not curing...


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I recently painted some Testors 1/4 oz.flat brown enamel, but the paint is not curing after more than 48 hours.

 

I'm not sure if I got a bad bottle or not.

 

The one thing I am doing differently is I thin the paint with Klean Strip odorless mineral spirits. I'm beginning to think that may be the problem. Perhaps I should go back to using good old Testors enamel thinner...

 

Scott

CJC-IPMS

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I'm no paint chemist, but I'd say there's a fair chance you've answered your own question. You added a different chemical to your paint (not what the manufacturer recommends)

and now its properties have changed. It could be a coincidence, but I'd guess it's not.

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10 hours ago, F-16 said:

I thin the paint with Klean Strip odorless mineral spirits. I'm beginning to think that may be the problem. Perhaps I should go back to using good old Testors enamel thinner...

 

Chances are it's the odorless mineral spirits.  Testors enamel thinner rarely fails.  Taking risk with the cheaper stuff is not worth it.  Do a test as mentioned above to be sure.

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Ditto all the above.  I use ONLY Testor's enamel thinners to thin the paint, but use cheapie lacquer thinner or mineral spirits to clean the air (or hand) brush... never had the problem.

 

Ed

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6 hours ago, ElectroSoldier said:

First how old is the paint, enamels do take longer with age, however they should dry in time.
What with the cold weather try and keep it warm to encourage the thinner you used to evaporate. 

 

Well I got some Testors bottles from the mid 1980's that cure in several hours when sprayed in thin layers.  BTW, enamels don't dry, they cure.  Fore more info, read this link:  What can speed up enamel paint dry time?

 

An excerpt from the link above:  

Quote

Technically speaking, enamel doesn't dry, it cures. It's a fundamentally different process.


Paints like nitrocellulose lacquers (like automotive lacquers) and aqueous acrylics truly do dry. The binder of these paints is dissolved into solvent (either lacquer thinner or water), and the paint hardens as the solvent evaporates.

Dehydrators can be very effective in driving off solvents- they're obviously designed to evaporate water out of food, and evaporating solvents is very similar.

Enamels harden due to oxidative crosslinking. When enamel is exposed to oxygen, it starts a chemical process which molecularly hardens the binder- creating a sort of 'shell' as binder molecules link with each other. Heat and convention have a limited effect in speeding this process. I may increase the crosslinking process slightly, but certainly not in the way that it dries solvent.

If you thin enamels with lacquer thinner, you're not changing the curing time. By introducing a volatile solvent, you're creating a mix that needs to cure and dry. But after the solvent has finished evaporating, the enamel binder still must cure- and the binder will still cure at it's own pace.

If you want enamel to cure quickly, the best way is to spray it as thin as possible. This way as much of the paint as possible is exposed to oxygen, and it can all go to work on curing. If you apply enamels thickly, only the outside surface is exposed to oxygen, which can dramatically increase the curing time of the paint deeper in the layer. Spray enamel too thick and it is possible to keep some of the paint from ever completely curing. The outermost portion exposed to air can cure perfectly well- but this cured outer portion becomes a barrier to prevent the paint deeper in the layer from being exposed to oxygen. As a result the paint will always be soft, under a thin cured film.

This is why enamels have such strange application instructions- you must spray everything on at once (within a couple of hours), or you must wait days or weeks to apply another layer. If a layer is applied and it begins (but does not complete) curing, only to be covered by another layer, the first layer will never cure.

 

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Thanks for the info. I wish I had it sooner...

 

The reason I used Oderless Mineral Spirits is because, a few years ago, everyone here told me that OMS and Testors enamel thinner were the same thing.  I guess it is a hard lesson to learn.

 

I am just going to go back to using Testors enamel paint thinner...

 

tes1156.jpg

 

I stopped using it a few years ago thinking OMS was better (Price was also a factor). Not so in this case.

 

Scott

CNJC-IPMS

 

 

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3 hours ago, RichardL said:

 

Well I got some Testors bottles from the mid 1980's that cure in several hours when sprayed in thin layers.  BTW, enamels don't dry, they cure.  Fore more info, read this link:  What can speed up enamel paint dry time?

 

An excerpt from the link above:  

 

Thanks for that. While Im sure it was worth reading. I didnt because I think of it like this.

"Drying: A thin coat of latex paint is dry to the touch after just a few minutes, which means the solvent (or carrier) has evaporated from the coating to form a film that can’t be wiped away with gentle pressure. But if you press a fingernail into the painted surface, a dent may be left behind, and washing, wiping, or exposure to water may damage the paint.

Curing: When you can wipe or wash the paint surface without damage and the paint stands up to minor scratches and bumps, it has fully cured. Curing can take weeks because it is chemical process during which pigments and binders fuse together into a continuous resilient film. Some paints take longer to cure than others."

 

I dont really care about how it works on a technical level, its not all that impressive to know.

Edited by ElectroSoldier
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3 hours ago, F-16 said:

Thanks for the info. I wish I had it sooner...

 

The reason I used Oderless Mineral Spirits is because, a few years ago, everyone here told me that OMS and Testors enamel thinner were the same thing.  I guess it is a hard lesson to learn.

 

I am just going to go back to using Testors enamel paint thinner...

 

tes1156.jpg

 

I stopped using it a few years ago thinking OMS was better (Price was also a factor). Not so in this case.

 

Scott

CNJC-IPMS

 

 

Yeah Ive seen similar before now on here and in other places which is why I always prefer to get advice from somebody who has actually done it rather than somebody who thinks it should be the same.

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1 hour ago, ElectroSoldier said:

I dont really care about how it works on a technical level, its not all that impressive to know.

 

To each his own.  BTW, saying that enamels take longer to dry with age is rubbish since there is no supporting evidence.

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  • 2 months later...

I use Klean Strip  VM&P Naphta I bought at my local ACE hardware store.

 

Perfectly good alternative to Testor's brand.  It actually dries a bit too fast.

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56 minutes ago, pookie said:

I use Klean Strip  VM&P Naphta I bought at my local ACE hardware store.

 

Perfectly good alternative to Testor's brand.  It actually dries a bit too fast.

 

Naptha is extremely volatile. Evaporates very fast. I never found it to be a good thinner for airbrushing. Its great for oil paint washes as the volatility makes it dry faster.

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Is there any difference between these two Testors thinners? I usually use the square bottle to "top off" my bottles of paint, for brush painting, and the can for thinning for airbrushing. It'd probably be cheaper to order the can for every use, since local sources are closed and I need to order online.

 

Testors_8824.jpg

Testors_1156.jpg

Edited by ReccePhreak
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I've NEVER had MM enamel paint not dry, ever ! I thin mine with either enamel reducer or Mr. Color Leveling thinner.

I agree with what David said, the problem would be what you thinned it with, mineral spirits.

 

Steve

Edited by A-10 LOADER
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5 hours ago, A-10 LOADER said:

I've NEVER had MM enamel paint not dry, ever !

 

Same here, unfortunately, it is often in the bottle. I've now got about even good and dried out in the bottle. My MM is rapidly disappearing. The ones that are still good are mostly those that have never been opened. Even those that have only been opened once or twice are drying up. Fortunately I have found other paints that work better. What I liked about MM paint is its ease of brushing. Now I use Valejo for most of my brushing needs.

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Most of my MM stock is from 1997-2000 timeframe, I bought in large quantities, and are as good as the day I purchased them.

 

Steve

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