Spray paint & humidity

Model Railroader General Discussion (Model Railroader)
1

I’m in the planning stages of spray painting two plastic kits and one wooden one. I’ve read that humidity levels should “ideally” be in the 40-50% range. However, I don’t have a handy environment to achieve that so I’m wondering what are my options?

The label on one can states not to spray in high humidity. What percentage would constitute “high humidity”? Above 70%? Above 80%?

Also, I’m assuming that primer would require the same sort of painting precautions as enamel or acrylic paint?

Thanks,

Tom

2

Hi Tom,

Yes, up to 60% is acceptable. 70% to 80% is generally considered to be quite humid and muggy.

Although not recommended, I’ll confess that I’ve sprayed in high humidity conditions before, but that was with airbrushes and Scale Coat paint (which is more forgiving due to the ability of applying the paint in very thin, even layers).

If you’re spraying in a shed or garage, an old school trick would be to run one or more house fans (box style) placed in window/door openings, pointed outwards. My Dad used to do this back in the day and, oddly enough, it worked in slightly lowering the humidity level. He often sprayed with rattle cans (Glidden and Rustoleum).

If you really want to paint and the humidity stubbornly clings in the 70%+ range, apply your primer and paint in VERY THIN COATS.

BTW: inexpensive humidity scales are available on the market:

http://www.homedepot.com/p/AcuRite-Digital-Humidity-and-Temperature-Comfort-Monitor-00613/204350179?cm_mmc=Shopping|THD|G|0|G-BASE-PLA-D28I-InsideGardenOther|&gclid=EAIaIQobChMIwpumjq-j1QIVlIl-Ch09oA5OEAYYASABEgKYrvD_BwE&gclsrc=aw.ds

Respecfully where are you spraying at and which brand of paint are you using?

3

Hi Antonio,

Thanks for yet another reply.

I’ll be using a rattle can of Tamiya TS-29 Semi-gloss black lacquer on some “green” truck parts from a Branchline express reefer kit. The can says it’s safe for plastic. I want the details of the trucks to show and I’ve found Tamiya to spray on in VERY thin and sputter-free layers The TS-29 was the only semi-gloss black that was available to me at my LHS.

I’ll probably spray inside my garage when I drive back to OH this weekend. Course, that’s contingent on what the weather and humidity is like.

Tom

4

Hello, Tom

My paint booth is in my basement with an exhaust fan vented outside. Without a doubt, July and August can be very humid in the Great Lakes area!

I keep a small, hand-held hair dryer (blow-dryer) nearby. Sometimes I use it to blow off dust (hi-fan/no heat) and other times I’ll use it on low fan/low heat just after the paint is applied to drive off moisture. You can see the moisture coming to the surface and evaporating.

Even with brass, I’ll hit the model with hi fan/high heat for a minute or so before baking the model in the oven. I primarily use Scalecoat. Some rattle-can paints seem to take a long time to flash and the blow-dryer can help speed things up.

I have an additional air filter taped over the air intake of the blow dryer to reduce the chance of dust although the paint surface is generally not too tacky by the time I use the warm air.

Of course, you have to keep moving and be very careful around thin plastic parts.

This method works well for me— others may have alternative methods.

Good Luck, Ed

5

Solution: Set dehumidifier to 50%.

6

Tom,I do my rattle can painting outside and I found here in Bucyrus early morn is best to rattle can paint since the humidity is around 70.

Why?

During the day the wind picks up along with the humidity at a rapid pace…

7

I have rattle-can sprayed (which I too do outdoors when I can, otherwise in the same vented spray booth used for airbrushing) in fairly high relative humidity without problems. I rely more on “feel” on my skin than knowing the dew point or relative humdity. If it feels damp outside I defer.

Dave Nelson

8

How long do you need to wait for a less humid day in Pennsylvania?

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Believe it or not, here in South Florida I have a painting season. I do no airbrushing from May through October every year. I decal what is painted May-August, and assemble models to paint September-December. The weather controls everything down here.

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-Kevin

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9

I was able to get outside today after work and spray paint the truck parts for one of my kits. The sun was out and the humidity dropped to ~51% so I went for it.

Using Tamiya lacquer paint meant that the light 1st coat dried quickly. 2 hours later I applied a 2nd light coat and will let that dry for 24 hours. I’ve had really good success with Tamiya rattle cans in the past. Because the nozzle emits such a fine and sputter-free mist, it gives the surface you are painting a beautiful even coat.

Once I trim the parts from the sprue I’ll need to touch-up the small bare “green” spots where it was attached to the sprue with a quick final coat. I’ll try and post pics when I have all the truck parts painted and assembled.

Tom

10

Here’s a quick pic of what the Tamiya semi-gloss lacquer black looks like next to one of the unpainted green sprues:

The Tamiya paints are wonderfully thin so they are less likely to cover up and obscure small detailing like the truck springs. Sorry the lighting in the photo doesn’t show the detailing better.

Tom

11

I’ve been hesitant to spray anything this summer because of humidity. I live in Minnesota, and any painting will be my first attempt at doing so. My plan was to set up an area in my garage with the door open. My dad painted several motorcycles during the summer months and offered a few recommendations. Once day with spraying, I was going to move the painted parts into the basement to dry. Not sure if this is recommended, though.

12

I live in Minnesota also. Yesterday was quite humid, but I sprayed some Tamiya flat finish on a building I’m working on, turned out fine. I think the issue with paint and humidity is that the more humid it is, the longer it will take for the paint to dry. Generally, it doesn’t affect the success of the painting being done. Acrylic paint dries pretty quickly anyway, so even if it takes twice as long to dry, it’s still like two hours instead of one.

It can happen when spraying a clear coat that if it’s real humid, it may turn out a little cloudy…but in many years of spray painting, I’ve only seen that happen once or twice.

The problem with painting outside is a lot of the paint can get blown away and never reach the model. What I generally do is paint in the garage, with the large garage door and the small door on the opposite side both open. I usually have what I’m going to paint on a paint handle; if it’s very still out, I’ll go out on the driveway to spray and then take the model back in the garage to dry.

BTW dew point is probably a better indication of how moist the air is rather than the humidity. Dew points around 50-60 or lower are dry/comfortable, 70+ is getting to be ‘tropical’.

13

Stix,

I agree. IIRC, the temp was around 72 and the dew point <60. It was quite comfortable and their was no wind. The only thing I had to do was to pick out a few minute pieces of dust between coats.

Tom

14

Hello all,

Just another thing to throw into the mix…

I was just now detailing some generators that came with the American Model Builders Generator Flat Car Load.

After rattle-can painting them John Deere Green, a few days ago, I was using a silver paint pen to detail the ends of the shafts when the pen burped!

With my hands-of-ham and fingers-of-sausage I managed to make the spill worse.

After several expletives I decided the best course was to repaint the entire unit.

On other units, that the silver paint had strayed, I used a cotton swab with turpentine to remove the errors. This mistake was more detrimental!

As fate would have it was raining with a temperature of 45ºƒ, with an ambient humidity level of 75%.

Not the ideal conditions to spray paint.

Using the water-bath method of warming the rattle can, I adhered the generator to a block of foam. All this was done at an internal room temperature of 75ºƒ.

I quickly went outside, under the porch overhang, and quickly re-painted the unit.

After a few minutes, to allow the most volatile fumes to dissipate, I brought it into the train room.

“She who must be obeyed” is used to strange smells coming from the train room. I opened the windows, to create a cross-breeze, and am now waiting for the paint to fully dry.

For small applications this method worked well in high humidity and relatively low temperature conditions.

Hope this helps.

Post Script: “She who must be obeyed” noticed the smell, crinkled her nose and walked out of the train room with no immediate objections.

HTH!

15

I always warm my rattlecans no matter how warm it is or how cold it is.As soon as the can start to feel cold I rewarm the can.

Using this method I have recieved good results no matter what the temps are.One other thing is that the first (and possbly the second) coat of paint will do nothing more than put a slight tint on the primer.