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Painting Foam Board

Tritium

Amateur Extra Class K5TWM
#3
Another great episode. Another tip is: you just need compressed Air or CO2. A paintball gun bottle and a regulator will run an airbrush just great. Also in my quest for the perfect airbrush I have found a VERY high quality Chinese model. This model works like some $300 models made in the USA.

http://www.pecoglobal.com/Veda_Airbrush_WD180_p/wd180-bulk-package.htm

You might want some paint if you are not near a craft store:

http://www.tcpglobal.com/createx/default.aspx Large selection and FAST shipping.

Thurmond
 
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CrashRecovery

I'm a care bear...Really?
Mentor
#4
Ok question about the min wax..... Shouldn't it be done after we build that way the paper doesn't become too hard not to work with.
 

jhitesma

Some guy in the desert
Mentor
#6
Ok question about the min wax..... Shouldn't it be done after we build that way the paper doesn't become too hard not to work with.
I did a few test pieces a few weeks ago when Chad first mentioned the minwax trick. I haven't tried it on a real plane yet, but the test pieces I did behave pretty much the same as untreated foam board. I've been waiting to see this episode to see if they recommended using it before or after...but from my tests I'd say either should work.

It does make the foam board a little yellowish and a little shiny.

I was a little disappointed to find it doesn't help adhere the paper to the foam any better, at least in my tests on bits of scrap foam it didn't. I was really hoping it would.

I'm going to try a brush like in the video though, I just used a wadded up paper towel and rubbed it on in my tests. Worked fairly well...but living in the desert it was 110 the day I tested and it pretty much dried before I could wipe any excess off, so I'm not sure if I got a good full coat or not.

Going to do a few experiments on full size boards...need to make a new spitfire fuselage anyway :)
 

MrGravey

Senior Member
#7
I have never used Minwax for anything, and there is so little information in this video that it was really just another mention instead of explaining how this works. I looked for the videos on YouTube Chad mentioned but found nothing from which to gain more information. If someone can help me out I have a list of details I would like to have answered to before I take yet another loose recommendation from a YouTube video and ruin my plane trying to get this stuff right.

  1. Speaking of wiping the excess Minwax off the foam.... how? When? I can assume we want this to dry first, I can assume it is very simple to wipe off the excess, but assuming too much tends to ruin airplanes.
  2. Do the pieces need to be cut out first? ( I assume but we know how that works out )
  3. What about the wings? Can they be rolled and bent as we need to on a few of the scratch buids with the Minwax already on the foam board or do I need to make the wing and then cover it in Minwax?
  4. What about the edges of the foam board? Having the better surface to paint on is very nice. Having some resistance to water damage is nice too, but if the edges are all exposed it only helps so much. Chad mentioned it soaked into the paper, this makes me wonder if the exposed foam in the ends will even hold the Minwax.

There are tons of things that could be asked but if we can get more information on these I'll call it a win and move on with this information. As it stands there just wasn't much said about this trick. The Crash Cast had this much information in it a month ago.
 
#9
If someone can help me out I have a list of details I would like to have answered to before I take yet another loose recommendation from a YouTube video and ruin my plane trying to get this stuff right.
I've only done this with one test nutball airframe so far and I did it to the pieces after they were cut and I had my hinges and such.

The idea of the polyurethane is that you are impregnating the paper fibers with the polyurethane by brushing it on. You don't need to 'coat' the paper so much as just allow the polyurethane to penetrate the paper. Any extra layers are just adding weight, that is why you would wipe off excess. And you'd want to do this to both sides of your parts. Once the poly dries it has 'cured' in a way and it has bonded with the fibers of the paper.

So your foam board goes from being a slab of polystyrene foam with dry, porous paper on each side to having sealed paper fibers impregnated with polyurethane on each side.

(organic polymer wrapped fibers | synthetic polymer foam | organic polymer wrapped fibers)

If you were to look at the untreated paper fibers as if they were wood splinters they would swell up with any water based paints, the color would stick to the surface but the water would soak in and swell the fiber. The treated fibers repel the water aspect of the paints so that they evaporate and leave the paint/color coating without swelling the fiber.

Regarding the edges of the parts, since I did this to parts after they were cut and any paper edges were treaded. The foam itself doesn't seem to have a problem holding any non-solvent based paints that I've tried. You definitely want to try this on some scraps of foam board to see how it flexes and feels after.

Hope that was helpful.
 
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MrGravey

Senior Member
#10
Any extra layers are just adding weight, that is why you would wipe off excess.
Yes, wipe off the extra... How? When? With what?

I tried to be clear in the way I asked the first time but I guess I missed the mark. A common thing for me this month so far it would seem.

  1. Do you wait for the Minwax to dry or not?
  2. What do you use to wipe off the excess?
  3. How do you identify "excess" product?
  4. How do you know when you have removed said excess?

As I said before, I have never used Minwax for anything. I don't often find myself having to finish wood so I haven't had a need for this product in the past. I say this so people will assume I know very little about it. I looked for information online but everything I found speaks to the designed use of this product. That does me no good as the differences in foam board and hard wood are well defined and constant.

So, lets say I go home and apply Minwax in the way the video showed (brush on a thin layer, I can gather that much) and then I wait for it to dry some. Will this leave a film of some kind that will be the excess I can just wipe off with a paper towel? Do I need to get to it before it is completely dry? If so will it be tacky and therefor a bad idea to use a paper towel becasue I'll be sticking little fibers all over the plane?

I'm thankful you tried to explain. You did a great job of explaining how this stuff works but I'm looking for more information on practical application.

In short this video really doesn't give much information at all on this subject. The air brush tips were cool enough. I have never tried Windex but I can see why it would work, and more importantly he explained exactly how to apply this advice. Imagine if Chad just said "Buy some paint, air brush it on the foam board, oh and sometimes you can add some Windex to help it dry faster and spray smoother." People with no air brush experience would have no idea at all how to use his advice. Instead Chad explained basic air brush function and not only why but exactly how he mixes his paint. There are tons of videos you can watch to show you how to air brush. The only video I know of with this minwax trick explained really only says "Minwax can help your plane."

I love to air brush my planes. This tip will make that work so much better so forgive me if I'm pushing hard here but I want to understand this clearly because I want to be able to apply it well and improve the quality of my scratch builds.
 
#11
"I was a little disappointed to find it doesn't help adhere the paper to the foam any better, at least in my tests on bits of scrap foam it didn't. I was really hoping it would."

Same here.
 

jhitesma

Some guy in the desert
Mentor
#12
I'm guessing the exact methods of working with the mixwax will vary depending on your climate. I know when I used it (not for this but for wood) back in Ohio it took a lot longer to dry and stayed workable longer than it does for me now here in AZ.

I wouldn't let it sit up and dry very long. The post above goes into more detail but it sounds like a thin coating is all that's needed. You're not looking to build a finish here, just seal the fibers. It doesn't glue the paper to the foam any better - it just kind of plasticizes the paper.

I tried on some scraps from building and confirmed that it didn't warp the foamboard like water based paints and coverings do. I just used a wadded up paper towel to apply it and really didn't even have to wipe it off - it soaked in and dried very quickly (Note: I was working out side on a dry 108 degree day) even on the small 4"x6" or so piece I was testing on the first side was pretty much dry before I got to the second side. I wasn't even sure if I got enough on to be effective. But subsequent tests with thicker layers didn't immediately show much additional benefit, and less is lighter to leave more weight for paint.

The scraps still cut and sanded and bent just like normal with the poly on them.

I don't quite have the guts to try it on one of my finished planes. Most of them have some edges fraying already and since this doesn't seem to help bond the paper to the foam any better I don't see much point in upgrading those planes at this point. But I'm going to coat a few pieces of fresh foam later today and use them in my next builds. I may try post-treating the wing for my spitfire since it's still in almost new condition despite several hard crashes...but I think this is going to be something I do to the board before cutting - or at least after cutting but before assembly.

My one concern is how it affects the bonding of hot glue. I may do some tests on that before I start coating boards.
 
#14
Hi Guys.
Ive a few questions. I want to get away from the spray cans, Ive been using Tamiya PS paint. It is very nice but expensive for a tiny can. The spray cans also seem to spray the air more than the plane, my garage & everything in it is starting to turn orange (I paint all my RC Cars & planes fluro orange.)
What is the brand of paint that was recommended if the vid??
Any brands that do a nice fluro orange.
Are the HobbyKing dual action airbrushes OK, I wont be doing anything fancy.

A vid on how to clean the airbrushes would be great.
Cheers
 

Tritium

Amateur Extra Class K5TWM
#15
The paint is Createx as I linked to in the 3rd post of this thread. Also the airbrush I linked is a very good Chinese and ships very quickly. It is very easy to clean since the cup is permanent on top of the airbrush. You run some cleaner through it then some water till the output spray is perfectly clear on a piece of white paper.

Thurmond
 
#16
Minwax Polyurethane treatment of foam board tests

I took a scrap wing and treated half with the Minwax (OIL BASED) polyurethane and left the other half untreated. I then take both sides under the microscope so we can get a closer look at what both sides look like.

I then test both premium and cheap spray paint, brush on acrylic (as a demonstration of what not to do) and test the water repentant aspects of both treated and untreated sides. I don't have an airbrush but chad already did an amazing job documenting that aspect of painting. When you try this do it on a scrap to get a feel for it.

Hopefully this will answer any outstanding questions around the Dollar Store Foam Core + Polyurethane topic.


You can see more of the details in the following stills.
You can see the Poly changes the color cast of the white
IMG_1093.JPG

This is the treated side under the microscope
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This is the boundary, treated on the left untreated on the right under the microscope
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What not to do or How NOT to paint your foam core.
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Water applications
IMG_1105.JPG
IMG_1106.JPG

The water beads on the treated side while the untreated soaks the water up
IMG_1109.JPG

IMG_1111.JPG

Notice that even though this is NOT how to paint you can see that the treated side takes the paint just fine.
IMG_1114.JPG

The paint right from the tube soaks into the untreated surface and the maskting tape pulls the whole surface up.
IMG_1115.JPG

Here you can see the surface sheen of the spray paints on the treated, background section, and the untreated, foreground.
IMG_1116.JPG

The rest of these are closeups of the boundary with the treated on the left and untreated on the right.
IMG_1118.JPG
IMG_1119.JPG
IMG_1120.JPG
IMG_1121.JPG
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#18
Wow. Thanks Jason! Very through!

I take it the treatment was wipe on, wait 30s, wipe off excess?

Also, how well did the acrylic adhere to the treated side?
 
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#20
Jason - This is extremely article worthy! Make this an article, please.

Great job!!!
Will do. I'll get it edited up later today, thanks!


I take it the treatment was wipe on, wait 30s, wipe off excess?
More like 15 seconds if that. Basically once I've verified that I haven't missed any spots, you look for dull spots that may still be 'dry' when brushing it on, I then almost immediately wipe off the excess. The thing to remember is that you're basically varnishing a single sheet of paper so it doesn't take long to permeate the paper.

Also, how well did the acrylic adhere to the treated side?
Pretty well. I just took my thumbnail and ran it back and forth across the whole treated acrylic painted area to see if I could get it to chip or rub off. Not one bit came up and I was really being rough. (Picture using a big pink eraser to erase a whole sheet of writing, that's what I was doing across the entire red/treated area, edges and all.) Again, it was applied right from the tube. I would feel comfortable using the acrylic for lettering, details, or nose art on a treated foam core model.
 
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