blue foam board insulation and spray paint- a bad combination?

Never use any type of oil based paint only use water based paint. Spray paint will ruin foam

Dave 

PS Thanks John for the correction.

Acrylic is water based. If you use that first, then you can spray it. Latex will also work. I think it’s the propellant that’s the problem. 

If you buy a quart of water based primer you can have it tinted to your top coat or final color.  Doesn’t have to be exact. Brush on quick and let it dry(it will dry fast),  finish with spray paint. 

Most of us have a can of water based Oops paint (paint sold cheap where someone didn't like the color) that we test with. That paint can also make a great base coat on foam scenery.

always test first!

I looked this up, but I already knew there were heavy solvents in spray paint. Virtually all spray paints used to use Propellant A. "Since most aerosol chlorofluorocarbons were banned in 1989, CFC propellants in spray paint have been replaced with ether compounds." Ether is a solvent. There will also be a lot of fast drying thinner. That probably means acetone. Acetone and ether will definitely melt foam board. You can use a brush on latex primer as a base and then paint over that with spray paint. You will need to make sure the primer completely covers the foam and has dried for several days. 

George

Plain old water-based latex paint applied after I peeled the polyethlene skim coat from the blue polyurethane extruded construction foam, a skim coating that doesn't favor any paint for long.

Back when I had my previous "O" gauge layout in the '80s, I used foam board to make mountains.  What I did you shouldn't do.  I brushed on lacquer thinner.  It immediately dissolved the foam.  Depending on how much I brushed on, determined how rough the rock faces would be.  Afterward, I brushed on water based paints, added ground cover, bushes and trees.  

I got pretty good at controlling the action of the lacquer thinner.  My layout was in the cellar that has a Bilco door to the outside, so plenty of fresh air was available.  Not sure how much of it got to me however.....LOL

There are water based spray paints on store shelfs now if you look for them.  But a can of brush on latex is a lot cheaper than any spray paint and easier to put on the subject with no over-spray to worry about.  Often for scenery uses you can thin it by as much as 50/50.

     It's not the propellant that attacks plastic it's the solvent.  The propellant does not come out of the can till the paint is gone or you hold the can at such an angle that the end of the plastic tube in the can is uncovered and once out of the can it instantly becomes a gas which diffuses into the air, never reaching the surface you intend to paint. However if you don't need a smooth surface without brush marks use brush on paint.  Whenever I am in a hardware or paint store I always look on their discount table for scenery paint and other materials.          j

I have had success applying light mist coats of spray paint on foam. Each coat has to dry before applying more.

I did the same thing. You can use the effect to your advantage. Cut your foam oversize. Hit it with solvent paint, voila instant coal pile. 

https://www.modeltrainforum.co...c=1&d=1549151148

Pete

Straight out of the bottle acrylic floor wax brushed or sprayed on foam and allowed to dry will make it much more resistant to solvents.   When you don't want that solvent machining. Also works for other forms of plastic that are solvent sensitive.        j

Great insights and suggestions, I probably should have anticipated this (@john in lansing, test first!) but it was a Eureka moment for me. Of course I had to do it twice to be sure I had not missed something obvious.

Definitely starting over in the morning with an acrylic or latex coating.  (Hmmm, do I have black latex buried on the paint storage shelves someplace?)  Until I become expert in estimating shrinkage, I think I will take the rookie route of coating.  Although in favor of the planned shrinkage approach, it certainly smooths the texture!

I use the cheap ooops latex paint as was mentioned above for my layout projects.

I have used spray paint on my foam RC planes.  As mentioned above... it is the propellant, not the paint.  Hold the can 12-14 inches away from the material and spray light coats.   Be careful... too close or too heavy and you will start to see it eat away.

Have Fun!

Ron

hokie71 posted:

I posted under scenery since someone may know if this is common.  I was shaping some blue foam board to use as a foundation for a coal load in a gondola.  All fits well after some shaping and then...... I sprayed it with flat black spray paint to cover the blue before gluing rocks / coal to it.  the blue foam board  "melted away" - it must have shrunk by 10%- it no longer fits the gondola.  Is this common and what is going on?  Any suggestions?  Thanks.

I had the same problem until I went to Hobby Lobby and purchased a spray paint that was "sugar cane" base. Problem resolved. It comes in about 20 colors. Give it a try.

Terry

hokie71 posted:

I posted under scenery since someone may know if this is common.  I was shaping some blue foam board to use as a foundation for a coal load in a gondola.  All fits well after some shaping and then...... I sprayed it with flat black spray paint to cover the blue before gluing rocks / coal to it.  the blue foam board  "melted away" - it must have shrunk by 10%- it no longer fits the gondola.  Is this common and what is going on?  Any suggestions?  Thanks.

I too have shaped pink foam board (exact same stuff as the blue foam) for use as coal load foundations.  Afterwards I painted them with some "Rust-Oleum Painter's Touch Ultra Cover Flat Black Premium Latex Paint".  It won't attack the foam.  One coat of that stuff does the trick (and it better after a mouthful name like that!).  After drying thoroughly, I then glue on my coal load.  Notice we skipped one step - the spray painting part!

Paint brand aside, "latex" or "acrylic" are the key words to look for.  Cheap craft paints work good, too.  If you brush paint or roller paint the foam with the proper color to start with, you won't need to do any spray painting.

Hope this helps. 

@terry, we need a hobby lobby (and a menards) where I live for sure.  Mixed freight, I think I might have that paint, I hope it is not dried out!

Otherwise, i do have the acrylic floor stuff and the OOPs stuff.  I love the options and the ideas.

I first learned of the effects of solvents on foam when I was quite young. My father was in refrigeration, and showed me the affects. Some foams will flame in one direction, and melt in another when introducing a flame. When I worked in construction, one of the contractors I worked for would use 3/4" foam around the perimeter of basement walls. After we poured the floor and the concrete dried, he would pour gas on the foam to melt it away leaving a channel leading to a sump pump.

I routinely use a light dusting of volatile spray paint over acrylic-painted foam in order to simulate "old", weathered concrete.

   Primers are usually meant to seal, adhere well, and provide a better topcoat surface. It isn't just cheaper paint if it's good primer.

  I like water based craft acrylics more than home laytex.  I've had a lot of reactions and adheasion issues with laytex over the years really. (some doozies painting proffesionally when the site bought materials, but wood finishing was my real focus.

  I'm also mildly alergic to laytex and the craft acrylics don't make itchy or sick.

   Just last week while cleaning, I found two (also laytex) halloween masks on a shelf touching the wall had melted to it. I have a 5 or 6" spot of black red blue grey & green laytex mask paint to remove and repaint, IF I can sand the more rubbery part out.

You can use volatile paint thinners to your advantage in shaping foam, too, if you're careful.  For instance, in building an N-scale gravel road on pink foam several years ago, I folded and rolled up a paper towel, lightly soaked it with some lacquer thinner, then rubbed it along either side of the road and thereby chemically "melted" in some ditches.  It worked very well - I was pleased with the way it turned out.  A lot faster, much easier, absolutely no mess, and far more consistent than trying to carve out some ditches with knives, rasps, files, sanders, etc.