Painting Foam Board

Tritium

Amateur Extra Class K5TWM
Since you are now painting a fiber reinforced plastic after coating with Polyurethane and since the surface is still a bit rough from the texture of the now coated paper fibers, you really have an IDEAL surface to paint.

Thurmond
 

jhitesma

Some guy in the desert
Mentor
Great overview! Just gave your article 5 stars.

I did my first two full boards last night after seeing your post. I used a foam brush (I got a big bag of them at the dollar store so no messing with mineral spirits to cleanup, just toss them after a use) and was really nervous...I've warped foam board before with paint when I thought I was adding it slow enough and dry enough not to cause problems. But sure enough the oil based poly didn't cause any warping (the boards weren't exactly flat to begin with but then again none of the DT foam board I get is ever as flat as I'd like it to be...even out of a brand new box.)

After brushing it on I used a wadded up paper towel to wipe off the excess...At first glance I didn't think this step was going to be necessary as it looked like a nice thin coat just from the foam brush - but I was surprised to find a LOT came off on the paper towel while still leaving behind enough to seal the paper.

The second one I tried to let it "soak" a little longer before wiping. I also wasn't as careful applying it and just slopped it on since I knew I'd be doing the wiping.

After letting them dry over night this morning I was kind of surprised to see that the first one that I didn't let soak was a little rougher than the second one. So I'm guessing when I let the second one soak it took up a bit more poly and that's why it has a slightly smoother surface.

But both looks great, Can't wait to cut some parts and do some painting on them now!
 

MrGravey

Senior Member
I can't seem to get registered for the main site or I would certainly be rating that article very very highly. I'll work on this when I get home from the office. Maybe it is just the office computer because it wont let me log in with Facebook either...

Thanks a ton for this information. This is much more than even I was asking for and I was asking a ton of specific questions. I love the idea to use brushed on paints for finishing touches! I'll be doing that with the next scratch build for sure.
 

JasonEricAnderson

Senior Member
A followup to my tests. This is treating and painting an assembled FT Nutball.


2013-06-25-sma.jpg
2013-06-25 sma.jpg
 
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I've got the right type of minwax (the non water based) in a can and some foam brushes. I also have a spray can of the same stuff.

I've got a half dozen sheets of black dollar tree foam and a jones to make several Bloody Wonders. My white untreated BW is looking a little furry from handling and flying in the edge of a fog bank. I want to make some planes for friends.

Which application method would be more effective at sealing with minimal weight gain?

I also plan to strip the paper from the inside of the wing once I have made the indentations that steer the wing creases properly. Once the wing is ready to close I'll take that paper out to save weight. Does it peel properly even if treated if you're trying to peel it?

Any feedback or tips?
 

xuzme720

Dedicated foam bender
Mentor
I've got the right type of minwax (the non water based) in a can and some foam brushes. I also have a spray can of the same stuff.

I've got a half dozen sheets of black dollar tree foam and a jones to make several Bloody Wonders. My white untreated BW is looking a little furry from handling and flying in the edge of a fog bank. I want to make some planes for friends.

Which application method would be more effective at sealing with minimal weight gain?

I also plan to strip the paper from the inside of the wing once I have made the indentations that steer the wing creases properly. Once the wing is ready to close I'll take that paper out to save weight. Does it peel properly even if treated if you're trying to peel it?

Any feedback or tips?
Spray with very light coats for minimum weight gain, but will also be giving you the minimum protection. I have seen it recommended to treat after the airframe is built for sealing the edges better, but treating after the foamboard is kitted should work also. That being said, maybe just don't treat the inside of the wing to be sure it peels properly as the minwax might prevent an easy peel.
 

JasonEricAnderson

Senior Member
BTW, what's the magnet on the can for?
Honestly, it's what I use to open the can. It's one of many hard drive magnets I have all over the place. I was about to go to the garage for my paint key and saw this sticking to something. "That'llWork". And it stays with the can nicely so I don't forget it. ;)

For the record this Nutball is no more. I had issues with my rudder linkage slipping while trying to maiden it. After 4 attempts at fixing and a lot of tape it looked like a Kaiju had chewed on the front of it. Total write off.

So now I get to make another and do a new paint job! :applause:
 
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Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
Thakns Jason, that's a good Idea.

Shame to hear that about the NB, but you get a chance to top yourself! (next time, you might want to set the bar lower the first time through ;) )
 
Did some treatments. Had the front side of two sheets coated by brush and excess wiped off before I realized it was the wrong minwax. I have both water based and traditional because the water based is good for glassing stuff with coffee filters and the like. Oh well. Sprayed the back side with the traditional, then hit it with the water based again to see if it would balance out any warping.

Two other sheets sprayed with the traditional minwax from a spray can, easier to not dollop so much onto it. Trying to toughen it a bit without turning it into the weight of a plastic plane, the brushed on stuff adds up fast.

We'll see how it works when it comes time to assemble the black bloody wonder. Going to use Foam Tac to save glue weight too I think.
 

jhitesma

Some guy in the desert
Mentor
This week I finally got around to using the two sheets I coated back at the end of June. The boards have been stored inside in my back room. Even with the AC going it usually gets a bit over 80 back there this time of year so that probably plays a big roll in this but....

I found that the coated board had turned considerably yellower than it was immediately after coating/drying. Doesn't really bother me since I plan on painting but I was still a but surprised at just how yellow the board got.

The other thing I discovered is that after sitting for a month and a half the boards warped somewhat away from the coated side. (so the coated side was convex and the uncoated side was concave.) Again not enough to make the boards unusable but considerably more warped than uncoated boards from the same batch and they were not warped when I initially coated them. I'm guessing the heat in the back room is a big culprit here.

I just picked up another half dozen sheets today and after making sure to pick the flattest ones in the store when I got home I had to ask myself why I bothered as the ride home in my truck in our AZ heat left the boards as warped as the worst of the ones at the store :rolleyes: Still usable but don't think I'll waste so much time trying to pick the flattest ones this time of year :)

Going to try and coat these both sides to see if that helps keep the flatter. The ones I did in June I only coated one side since I was still experimenting.

Coating right now is kind of tricky...gotta do it outside since even outside this minwax gives me a nasty headache. But it's over 100 in the shade still and even after dark it's over 90. So by the time I get a whole board coated the minwax on the first bits is already dry enough that I can't wipe off any excess :)
 

jhitesma

Some guy in the desert
Mentor
Finished coating some boards and took a few snaps to try and catch the color difference between bare board, freshly coated board and 2 month old coated board:

foam.jpg

That would be freshly coated a few hours ago on the left

Uncoated in the middle

Coated about 2 months ago and stored inside but at about 80F on the right.
 
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JasonEricAnderson

Senior Member
I've noticed similar yellowing in mine. If I make an airframe that I really want to look white I my try spraying it with white spray paint after poly coating.
 

proctous

Junior Member
so just build my FT Spitfire, and i just bought a airbrush, question is what type of paint should I use? Complete noob here. I heard othe rmembers using minwax first, do you have to do that step or can you skip.
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
Proctous,

Think of the oil based minwax as a waterproofing primer. Some people have had limited success with long distance sprapainting from the can, but most of the airbrushing I've seen will warp the paper and board. An even brush-on-wipe-off coat of the minwax will prevent that.
 

jhitesma

Some guy in the desert
Mentor
It is possible to airbrush without the minwax...but it's not easy. You need to do really really light coats - if you get just a bit too heavy - the paper will shrink and warp the foam.

I've painted DT foamboard with both spray cans and airbrush successfully without using minwax...but really can't recommend it. FAR too easy to end up with warped foam and a destroyed airframe.

With the minwax just about any paint will work and the only problems with heavy coats are you add extra weight and don't get as good of finish.

I've been using the cheap <$1 acrylics from walmart diluted with windex in my airbrush on my last few builds and have had good luck. Others have said they didn't have such good luck and suffered clogging using those paints...and I did get some mild clogging with one of the paints. But for the price it's tough to beat if you're just looking for a bit of color.
 

TripleChime

Junior Member
Alright. I need some advice. Bought the FT3D (great kit Josh, Chad and Co.) Min-waxed before the build, followed the build video and made a beautiful plane. Happy so far. I then masked off with low tack frog tape and newspaper, grabbed my dual-action AB and some of the "Apple Barrel" acrylic paint from Wal-mart, thinned with Windex as I've learned here. I dusted my first coat of blue on the tops of both the horizontal stab/elevator, and the wings. When I came back for another pass, the foam had warped more than I am happy with. I have this problem every time I paint foam board. I know it is something that I'm doing wrong since I see the phenomenal pictures here and on the FT videos (my kids want me to paint up Dusty from Planes!). Hate to tell them no, but I cannot seem to get a descent result AND not warp the board.

IMG_1933.JPG
 

JasonEricAnderson

Senior Member
I've never done the Windex thing but then I don't own an airbrush. I'm wondering if it's the ammonia in Windex that helps it thin? Maybe test with some scrap and just ammonia.

When I do masking I'll use office paper and tape so that there is only about 4mm of tape actually clinging to the model and most of it on the paper but then it looks like you're doing some pretty thin stripes so I don't know if my way of masking would work for you. I've never had warping like that with a rattle can so I'm thinking it's the Windex.

OH, and how long did you let the Minwax cure once you applied and wiped it back off? I am really light with my minwax as I only leave it on for about 15 seconds before I take it back off. After waiting at least an hour (in summer so I'd wait two now) I didn't have any problems masking and hitting it with the spray can.
 
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TripleChime

Junior Member
I let the Minwax on less than a minute before wiping. The OAT was about 70F when applied. About 3 weeks passed before I had time to build the model and absolutely no warping occurred in that time. I was thinking that maybe I didn't get good penetration in the paper with the poly but I find that hard to believe. Looks like its time to run a few tests. Thanks Jason

Dave