Paint Curing

jhande wrote:

As previously stated, there are many variables regarding curing and speeding up the process. Also to what level of curing do you need for the next step in the project. I've sprayed a second coat while the first was just tacky. I also sprayed a second coat after waiting 3 weeks and color sanding the first. In the 1:1 auto refinishing field, we always told customers that got an enamel paint job to wait at least 4 weeks before washing and/or waxing their car. * Never apply lacquer over enamel paints. *

There speaks another Voice of Experience.  There is the science and technology side of paint, and then there's the practical craft—ignore either at your project's peril.

As previously stated, there are many variables regarding curing and speeding up the process. Also to what level of curing do you need for the next step in the project.

I've sprayed a second coat while the first was just tacky. I also sprayed a second coat after waiting 3 weeks and color sanding the first.

In the 1:1 auto refinishing field, we always told customers that got an enamel paint job to wait at least 4 weeks before washing and/or waxing their car.

* Never apply lacquer over enamel paints. *

Ron, I've never heard of a paint that oxidized as it cured. In fact, that would be extremely dangerous. Do you mean air circulation?

Actually, the "sniff test" is very conservative—but who wants to chance ruining a nearly finished model.

Concur with Ron. I used to commercially paint model railroad equipment (brass locomotives, etc.), and still use the test I used then: the sniff test. If you can still smell the paint, chances are that it hasn't cured completely.

Cheers,

John Snyder, White Ensign Models, http://WhiteEnsignModels.com

Very close, curing also requires oxygen for enamel based paints, low temperature merely retards the reaction while high temperature speeds it up. Most hobby enamels (including some gloss acrylics like Gunze or Tamiya) actually take a minimum of one week to cure to about 80%, full cure can take two or three weeks.

The best way to speed it up is plave the model in a warm box with a fan and 25 or 40 watt light bulb. Every day open the box and sniff, if you smell anything like paint it isn't cured yet.

When is itdry enough to work on again? When you can handle it gently and not disturb the paint. Personally I hate the slow dry and cure times for enamel and switched to acrylics years ago.

Triarius wrote:

This sounds like a simple question, but it isn't. Paint curing is a chemical reaction, and temperature dependent. Drying (loss of solvent) is usually mostly complete within an hour or two at room temperature, but curing even to a tack-free state may take much longer, and varies not only with the brand of paint, but even between paints in the same product line. Solvent continues to escape throughout this time, at a decreasing rate. Polymerization of the binder is occuring at an ever increasing rate, making the escape of solvent more difficult. Humidity plays a role in both solvent evaporation (even with enamels) and speed of polymerization. The simple answer is: It's cured when it's cured. If you want to know when it's safe to handle or recoat, spray a piece of scrap right after you spray the model. When the paint on the scrap is ready, so is that on the model. You can speed curing by warming the model and providing air circulation AFTER THE PAINT HAS REACHED A TACK-FREE STATE! Doing that sooner invites disaster, up to and including a fire.

I used to paint and finish with T/MM enamels exclusively..still do for small projects when I'm lazy.  The gloss enamels completely cure in approx. between 48-72 hours.  Flats are cured in approx. 30 min. to 1 hour.  Like another member has mentioned above, drying time can be reduced by providing heat and air-flow, such as a hair-drier.  I use a home-made drying oven that provides heat via a household 60 to 100 watt light bulb.  The airflow is provided by a small diameter low-speed fan installed to circulate air.  Always be on the look-out for dust, however!  As a result, I've reduced the drying time of a freshly gloss painted model, figure, etc..down to approx. 6 hours.  

PS: *Source: Testors/ Model Master "Modelers Technical Guide."

Wilbur - good luck with that kit... I built it about 18 yrs ago and it was a blast.. I do remember it took me about about 4 months of steady modeling to get it done...  I used to work rotating 12 hour shifts, 2 days on - 3 days off, 3 on - 2 off so there were plenty of days off during the week for modeling.  (Wow I just realized every other week I only worked 2 days!  I need to find a job like that again!!)

I really want to tackle this one again but I don't know if I have it in me...    I was young and didn't know any better back then haha

Wilbur Wright wrote:

I think this plane is a long term project, which needs to be slowed down, to get right. I'm going to build some armor, and go back to the big plane from time to time when I have the enormous patience needed to do it justice. Thanks.

I kept telling my kids—and anyone else, for that matter:

"If you're in a hurry, you're in the wrong hobby."

Of course that doesn't apply to the editors of a certain scale modeling magazine, or those who do kit reviews…

Spraying a piece of scrap is a good idea, although in the case of this plane with many coats,  it would be a pia to replicate each sequence.

The question was to get opinions of other experienced model builders, and I thank anyone for that.

I am painting a 1/72 scale B-36. By far the most complicated paint job in my 30 years of modeling. All aluminum and magnesium colors and variations with a ton of masking. I'm going to use testors flat laquer, on some sections and I want the gloss paint to cure enough. I don't usually paint with gloss or in fact bare metal surface replication. Only other time was a 1/48 B-29.

I think this plane is a long term project, which needs to be slowed down, to get right.

I'm going to build some armor, and go back to the big plane from time to time when I have the enormous patience needed to do it justice.

Thanks.

This sounds like a simple question, but it isn't. Paint curing is a chemical reaction, and temperature dependent. Drying (loss of solvent) is usually mostly complete within an hour or two at room temperature, but curing even to a tack-free state may take much longer, and varies not only with the brand of paint, but even between paints in the same product line. Solvent continues to escape throughout this time, at a decreasing rate. Polymerization of the binder is occuring at an ever increasing rate, making the escape of solvent more difficult. Humidity plays a role in both solvent evaporation (even with enamels) and speed of polymerization.

The simple answer is: It's cured when it's cured. If you want to know when it's safe to handle or recoat, spray a piece of scrap right after you spray the model. When the paint on the scrap is ready, so is that on the model.

You can speed curing by warming the model and providing air circulation AFTER THE PAINT HAS REACHED A TACK-FREE STATE! Doing that sooner invites disaster, up to and including a fire.

I do know their gloss colors seem to dry slower than the flat... which would lend to a slightly longer curing time... is this a hypothetical question or real?  If real I would give it at least 2 or 3 days if you are unsure, I know it's a long time but I have had one or two bottles of paint do that to me... take forever to cure... I immediately replaced them because they shouldn't take that long...

I'd hate to throw caution to the wind and get a big fat sticky fingerprint on the paint.. (voice of experience, 28 hours after painting I said to myself "it HAS to be dry!!")

It does depend on how you define "cured" and your local  temperature and humidity, but 3 days sounds a little excessive.  I use MM enamels extenstively, and I've masked over paint that has been drying at most a few hours.  If masking is not required, I've carefully handled models that have been drying for under an hour.

A couple years ago during a one-day group build, I applied a three-color camo, acrylic gloss overcoat, decals, another gloss overcoat, and several flat coats all in the span of a few hours without any problems.

Andy