Airbrush in between coats

[Dougboy]

Ok, this might seem like a silly question:

For those who paint with an airbrush, what do you do between coats? Dump any remaining paint and clean it out? Leave it and hope it doesnt dry in the brush?  Now I'm not talking about color change, I mean when waiting in between coats of the same spray. 

I mainly use solvent-based paints like Tamiya TS or Mr. Color and wait 15-30min in between coats. Its tedious to empty/clean/reload an airbrush just to lay down another coat of the same paint 20min later..... yet I feel like the paint will dry and clog within 20min if I just leave it. 

Any tips and pointers would be appreciated. 

Edited January 16, 2019 by Dougboy

[peteski]

You would probably have a reason to worry is you used water-based paints. But with organic-solvent-based paints (the stinky type), you worry about nothing.  This is not a 2-part paint which will harden (by chemical reaction) inside your airbrush.  You should be fine leaving it in the airbrush.

I use a siphon-fed airbrush with a glass paint bottle on the bottom.  When done with one coat I close the needle to stop the paint flow, but blow the air through it (to blow the paint off of the tip).  When getting ready for the next coat, I gently swirl the airbrush around for a while to mix the pigment which might have settled down to the bottom of the bottle (not need to do that with clear lacquer). Then I open the needle and spray onto some unwanted surface (like a paper bag), to make sure the paint flows smoothly again, then spray the next coat onto the model.

[StevenGuthmiller]

I dump the paint out of the cup if it's a gravity feed, and remove the jar if it's siphon feed, and then run some lacquer thinner through the brush.

It only takes a few seconds and it will assure a clean brush when you're ready to paint again.

If nothing else, I do this just to be sure that my paint gets a good shake again before the next coat.

Metallic particles will settle to the bottom in a matter of minutes.

After 15 to 30 minutes, the majority of those particles will be sitting in the bottom of your paint jar, or in the throat of the air brush.

Giving the paint a swirl as Peter stated may work with a siphon jar, but it will not get all of that metallic out of the throat in a gravity feed.

You can shoot the heavy metallics out before you begin again, but now your paint has lost a lot of the particles and will not be uniform with the previous coat.

 

 

Steve

Edited January 16, 2019 by StevenGuthmiller

[Miatatom]

I agree with Steve on the metallics. The small metallic particles will sink to the bottom of a gravity feed. They'll also sink to the bottom of a syphon feed bottle. Either way, you wind up with too much metallic on some places and not enough on others. If you're lucky, it won't be too noticeable. Solid colors aren't as much of a problem and you can wait a little longer between coats. Maybe 10-15 minutes. If you have to wait longer than that, let it dry completely before you do anything to it.

[peteski]

2 hours ago, Miatatom said:

I agree with Steve on the metallics. The small metallic particles will sink to the bottom of a gravity feed. They'll also sink to the bottom of a syphon feed bottle. Either way, you wind up with too much metallic on some places and not enough on others. If you're lucky, it won't be too noticeable. Solid colors aren't as much of a problem and you can wait a little longer between coats. Maybe 10-15 minutes. If you have to wait longer than that, let it dry completely before you do anything to it.

I have no problems when I swirl the bottle for a while. The airbrushed paint is thin, so it is easy to re-mix the metallic particles back into the liquid.  Then, like I mentioned, I blow the "stale" paint out until it comes out properly mixed.

But I agree, this would not work with a gravity-fed airbrush and a paint cup.

[Pete J.]

I agree with the metallic comments.  You really don't need to do a complete strip and clean of the paint brush though.  If you have a top feed, empty the cup and blow a little thinner through the brush.  Since you are using solvent based paints, acetone is cheap on works.

  With solid colors, don't worry about it.  Put the brush in the holder and walk away.  I know some are going to call me nuts, but I have left paint in the brush overnight with no issues on solid colors or clear.

  If you use a siphon feed, have a second bottle with thinner only.  Pull the color bottle and cap it, and blow the thinner through and you are good between coats. 

Pulling the needle and nozzle and cleaning all the passages is only necessary if you change color or are done for the session.  A good clean and lube of the needle and seals keeps it running well and freely. 

One other maintenance tip.  Pull your needle gently across a piece of tissue or paper towel while you rotate the needle between your fingers.  It is snags any fibers, then you have a damaged tip.  A light polishing on some very fine grit abrasive paper can fix that and keep your pattern even.  

[Michael jones]

Just wondering, but why wait so long between coats? I usually would only wait max of about 5 mins. Sometimes I don't even bother waiting if it is hot. Especially with Tamiya lacquer paints as they dry quite quick. I guess spraying a lot of paint in one go, would require a long wait time for it to dry. When spraying matt colours you can see the paint dry, so get a good idea of how long to wait before adding another coat. 

[Tommy124]

7 hours ago, StevenGuthmiller said:

I dump the paint out of the cup if it's a gravity feed, and remove the jar if it's siphon feed, and then run some lacquer thinner through the brush.

It only takes a few seconds and it will assure a clean brush when you're ready to paint again.

If nothing else, I do this just to be sure that my paint gets a good shake again before the next coat.

Metallic particles will settle to the bottom in a matter of minutes.

After 15 to 30 minutes, the majority of those particles will be sitting in the bottom of your paint jar, or in the throat of the air brush.

Giving the paint a swirl as Peter stated may work with a siphon jar, but it will not get all of that metallic out of the throat in a gravity feed.

You can shoot the heavy metallics out before you begin again, but now your paint has lost a lot of the particles and will not be uniform with the previous coat.

 

 

Steve

I fully agree here. Regardless of the type of paint used, I would never let the color set inside the airbrush for such a period. I use a gravity-feed (Harder & Steenbeck Evolution) airbrush, so I empty the cup into the paint container. After that I fill in a small amount of the stuff that I found to be the most effective for cleaning the AB just aswell as stripping paint off a model. It's called Methoxypropanol (https://www.kremer-pigmente.com/de/methoxypropanol-pm-70920.html). I also found it useful to close the nozzle with a plastic cap (https://www.everythingairbrush.com/plastic-nozzle-cover.html) before spraying with a bit of of that stuff inside the cup. With the nozzle being closed, the pressure is reversed, so the cleaner goes back the other way and makes sure for a good (intermediate) cleaning inside the AB.

Edited January 16, 2019 by Tommy124

[Snake45]

I'm with Steve G on this. I wouldn't think of leaving paint in my airbrush for 15-30 minutes. 

[DON-T2]

I put 3 or 4 bb's in the jar when using metallic's pearls and alclad just a quick swirl and everything stays mixed.

[Dougboy]

Thank you gentlemen for the replies and suggestions. It appears that dump/clean/backwash/reload is still the preferred method. Yes I do use a gravity fed airbrush, and I simply give the cup a stir with a little paintbrush or toothpick before spraying if I'm concerned about metallic particles settling to the bottom. 

As for wait time between coats, I guess I dont necessarily have to wait 20-30min. My go-to thinner is Mr. Hobby Self Levelling Thinner and it does give a really smooth finish, but at the expense of slower dry time because of the paint retarder. With thicker coats, I'd rather leave it for at least 15+min before I lay down another coat. 

[Pete J.]

Just one point.  Paints don't actually "dry" per se.  They cure.  Part of that process is "off gassing" which means the solvent departs the paint as part of the chemical process.  The issue with the thinkness of the paint is how long that process takes.  Lacquers and other "fast drying" paints actual flash.  That is they create a skin on the top that appears dry but the paint underneath is still soft and partially cured. Once the paint flashes, surface contamination like bugs or dust won't settle into the paint and mess up you finish.   What is actually happening is that below the surface the solvents continue to migrate to the surface and have to pass through that flash for the paint to fully cure.  During that time, surface contaminants may not get through but you can still get fingerprints in the paint because the substrate is still soft. Also at that time the solvent can be working on the plastic underneath and crazing it.  The thicker the coat the longer it takes for the solvent to leave and the paint to be fully cured.  An rule of thumb that an old painter told me was that double the thickness quadruple the cure time.  Cured paint can be handled, sanded and polished.  Uncured just makes a mess.  

[StevenGuthmiller]

17 hours ago, Michael jones said:

Just wondering, but why wait so long between coats? I usually would only wait max of about 5 mins. Sometimes I don't even bother waiting if it is hot. Especially with Tamiya lacquer paints as they dry quite quick. I guess spraying a lot of paint in one go, would require a long wait time for it to dry. When spraying matt colours you can see the paint dry, so get a good idea of how long to wait before adding another coat. 

I usually wait at least several hours between coats of paint, sometimes overnight.

This is mainly because as Pete stated, if you spray another coat before the previous coat is at least mostly cured, you bare the risk of the solvents penetrating the first coat into the plastic causing crazing, especially with a hot automotive lacquer.

I have had this happen when I "rush it".

I find that each cured layer of paint acts as an additional barrier to subsequent coats of a hot paint.

I have never had any sort of paint adhesion problems with waiting longer to re-coat, but have had crazing issues with re-coating too soon, so as with most processes, you're better off taking your time.

 

Steve

[Michael jones]

Gidday Steve, 

Automotive lacquers are pretty hot, so yeah possibly a problem especially depending on the primer used. But I have not encountered any problems with Tamiya/ Gaianotes/ Mr Color paint,  as they seem to work very well with Tamiya primers providing a great barrier. For sure worth the extra money for the Tamiya primers.