Alright, so I just finished shaping my first board. Before I glass, I want to paint the blank, but I'm worried about a few things. Keep in mind I'm a total rookie at this and not too keen on industry lingo:
First - I'm recycling this from a broken old board, what's the best way to tell what kind of foam I'm working with (pretty sure its plolystyrene but not sure what other options there are other than epoxy)?
Second - related to the first question: what kind of paint is safe to use on what kind of blank?? I know certain paints will actually melt and eat through certain types of foam, and I don't want to ruin my first board over a paint job.
Also, what is the best way to prep the blank for painting, and are there any special precautions I should take after to prep it for glassing (like sanding, using low volumes of paint, clear-coating over the paint but under the glass, or allowing a specific ammount of curing time before laminating)?
Sorry if this has already been covered. I tried the search function but there's just so much info on here it's a bit overwhelming sifting through what is and isnt relavent.
In response to your first question, I’d say if the foam looks like it’s composed of lots of little beads, it’s EPS, but if it appears that it is more of a solid foam, it would be PU. You could also take a scrap piece and put some acetone on it. I think the EPS will melt and the PU will not. I’m sure others on here have better ways to identify.
In response to your second question, here are two threads on the topic of spraying blanks that I have found extremely useful in the past:
Thanks guys, the threads are a big help… How long does it take for the reaction to take place and the foam to melt? Pretty sure from the description of the foam I’m working with PU but I just want to be sure.
The acetone test is the best way to tell the difference. Extruded polystyrene foam can look very simlar to polyurethane foam but the XPS will melt just like EPS if you hit it with acetone. The melting effect is immediate.
When painting, use water based paints (I like tempera/poster paints) and spray light, allowing complete drying between coats and before glassing. Depending on temperature and humidity, I'd say 24 hours before glassing is pretty safe. Less if you can put it out in the sun on a hot day.
Shootz John - Absolutely working with PU here both from description and the acetone test. The one thing I’m worried about is colors running - I’m gonna be using rattlecans and markers just cause it’s my first job. Do you reccomend hitting it with clear enamal before glassing, or should a thurough dry do the trick?
There are so many different rattle can and marker formulations it's impossible to say. Best thing to do is test whatever you have and stick with what works. In California, where I live, they're constantly changing formulas so what works one year might not work the next. A light coat of acrylic floor finish is what I have used over tempera but you should still check. I use a spray gun.
For PU blanks & PE resin, I have used Krylon H2O Latex in rattle cans with great results and no bleeding or compatibility issues. The stuff is hard to find in stores, but some Wal-Marts carry it, or you can order it on line from tcpglobal.com. I’m pretty sure you will have issues with acrylic or enamel spraypaints if using PE resin. As for the markers, use Posca paint pens or Sharpie paint pens on the sanded hotcoat, then go over with 4 light coats of Krylon Crystal Clear Flat acrylic, then sand with 320 grit to match the texture of the sanded hotcoat. The H20 latex is low VOC and odor, but wear a respirator with the Crystal Clear. Make sure everything is completely dry before going on to the next step. Good luck & post up some pics…
Thanks for the info, I’m gettin’ some. The Krylon H2o works pretty good with no kind of compatibility issues, but some cans have spray nozzle issues and the paint globs out & fucks your paint job.