Hardening EVA and Craft foam.

NOTE: This is a tutorial on two different methods of hardening foam that I use. It will be separated by two posts due to character limits per post. I will attach photos to the first process once I have them in order.

I have been working with EVA and craft foam for a while now, and have a pretty good hang of it. One thing I had a real hard time with in the past was getting the characteristics of plastic and/or metal like surface that foam seems to avoid with every fiber (or perhaps cell) of it's existence. I have experimented with many different approaches to getting that surface while at the same time, "hardening" my foam. But, sometimes that plastic/metal surface is what you want, but hardening is not.

For these two separate applications, I have found two methods that give the high amount of performance required without causing damage to the foam. I will give my knowledge of both.


Hardened, Non-Flexible surface:
The first was by doing some research and finding that a lot of people use PVA glue followed by Plasti-dip or straight to paint (either epoxy or acrylic based). The downside to this style is that the item is not flexible after this process has been done. Basically, the PVA will crack and separate from the foam. For items like weapons or helmets (things that are not meant to articulate or come under stress of bending), this is a perfect solution.

But how do you get that beautifully smooth surface? Up until today, this was my biggest hurdle. Sanding PVA (even the "sand-able" professional grade carpenter's wood glue) is not an easy task and always gave me less than desirable results, as well as the possibility of penetrating the glue and scuffing the surface of the EVA. This, as we all know, is a total pain to rectify. I had previously tried 220 wet/dry sandpaper with little success. Most of what happened was either my sandpaper got all gummed up, the wood glue would "ball" up, or it just straight up took FOREVER to tediously and meticulously take off the slightest amount of glue. I had even gone so far as try to wet sand it. All that happened was the wood glue would reconstitute and become a massively gooey mess. Also, getting into corners, edges, recesses, etc. was next to impossible. Then, it hit me. The answer was right in front of me the whole stinkin' time!

EVA FOAM is the ANSWER! It can be cut to any size or shape you require, and will conform to the shape of just about anything you need it to. Here are the steps I take.

* "Paint" on your EVA glue (nice and heavy, no need to scrimp). DO NOT USE WATERPROOF GLUE if you are going to use these steps! Personally, I go back and forth on diluting it with water depending on the thickness I need or if I know I will need multiple coats. If I do need several coats, I usually start with non-diluted first, then build it up with diluted ones after that. Don't worry about the areas that seem to repel the glue, as we will address that next. (Side note: As soon as I get down to my hobby shop, I am going to pick up a can of spray on Tacky glue to see if "dusting" the item with that first will alleviate that from happening... I will post results after I have done that). To minimalize work down the road, try to only work with level surfaces. This is not mandatory, but it really does help.

* For the areas that repelled the glue, you should have glue surrounding that area. A second or possibly third coat of glue can be pooled into that area.

* Once the glue has dried, you will notice that there will be many imperfections in the surface. This is where spare pieces of EVA come into play. Cut pieces in shapes on an as needed basis. I usually start off with a 2"x3" rectangle for larger flat surfaces, but you may need another size. There is no standard to this part. Grab a shallow container with a bit of water in it. Using the EVA foam as a sort of sanding block, dip it in the water and get a few drops to stick to it, then "sand" the glued surface you wish to level/shape. It should, almost instantly, start to reconstitute the glue. Hint: Less is more. Use very little amounts of water and do small parts at a time. Keep any run-off contained with a no-nap cloth immediately. It will be very slimy to start and should start thickening up fairly quickly. In between this time is your working time. The best part is, if it gets too gummy before you have completed your task, just add a couple of drops of water again! This process has allowed me to level a surface in a couple of minutes that normally would have taken me hours with sanding... and the results were FAR better.

* After you have leveled and shaped your glued surface, and let it completely dry, you are ready for either Plasti-dip or directly to paint. If you do go to a brush-on acrylic based paint, be aware that you mustn't work the paint too much on the surface or you run the risk of reconstituting the glue again!

"Hardened" Flexible surface: This part is a bit more tricky, and I can not guarantee the results. I would HIGHLY recommend using the EXACT products I have found as epoxy can be a tricky beast at best. In fact, this method was discovered COMPLETELY by accident! I was originally attempting to test this mixture on EVA with the hopes that it gave me a nice hard surface without distorting the material due to it's no heat chemical reaction cure process. This was not the case! Since I don't like to re-invent the wheel, I am just going to transfer the information about this directly from my website to here.

* Here, I took an angled piece of foam, and coated it first with Elmer's Carpenter's wood glue, then with woven fiberglass. I made sure that the glue had fully penetrated the fiberglass. (Note: I would skip using the wood glue and use a base coat of this epoxy mixture in its place. The reason for this is described in my Pull Stress Test below.)



* Next, I waited patiently for the glue (or epoxy) to dry completely.



* Here is the magical mix. I really don't believe these two items were ever meant to be used together, but I took a chance anyways. They are designed to be used on cement floors, and if I understand the labeling correctly, would normally create a hard coating. This was not the case here!

I used equal parts of each, and it starts out like normal latex based paint. I used a standard paintbrush to apply it to the surface. I did notice that the more I messed with it, the more it created micro-bubbles, so try to limit the brush strokes you make.

In case you can't quite make it out in the picture, here are the details of these products.

PART A: Pratt and Lambert Palgard Epoxy (Base 2) #S3492 (Polyamide) This is the one you add your tint to.
PART B: Columbia Polyamide Epoxy #07-910-PTB Gloss



This is the piece just after I applied the epoxy mix. It took about 6 hours for it to become tacky, and 12 hours before I could handle it. It seems to have cured after 18 hours at approximately 50 degrees and 65% humidity (our power went out this morning, so no heat or dehumidifier).



At first, I was very disappointed with the results, as I really wanted the hard surface. The more I looked at the properties of this surface, I realized it would have some great uses. But of course, I could not leave it there! I mean, heck, I had a test piece... I gotta test it!!!

Here is what I found out about the material. It is about 1/32" thick, and has a very shiny and waterproof surface. It accepts indelible ink very well, and the transition from the glue/fiberglass to the foam was completely seamless.

I decided to test the material in six different ways. As you can see in the picture, I was a bit cramped for space. In the end though, everything worked out fine.

Here are the tests, and their results:

BEFORE:


AFTER:


Heat Test: I applied heat directly to the surface, making sure I got both the treated and untreated areas. I performed this test with a heat gun on low for about 45 seconds, no movement, and about 2-3 inches from the surface. I also used direct flame from a lighter, touching the surface, for about 15 seconds in another area at a later time.

Result: Upon introduction to either source of heat, the material starts to bubble, but oddly enough, the bubbles disappear and leave no trace they were there. The surface was initially too hot to touch, but cooled quickly. It did not seem to damage the foam below. Where the heat was exposed directly to the unprotected foam, it was discolored (normal). All in all, this stuff seems extremely resistant to heat.

Puncture Test: In the square test area, I took a ball point pen and stabbed the material so hard that I was shaking things off my table.

Result: While the pen tip did penetrate the material, when it was removed, it nearly self sealed. Due to the fact that there is fiberglass embedded, it did not create a weak spot in the material. Out of four attempts, two actually breached the material, while the remaining two left dimples.

Pull Stress Test: This was performed to check the elasticity, recovery, and durability. I took one portion and my wife the other. We pulled in opposite directions so hard that the reinforced glue seam actually gave.

Result: Well, the seam broke. Other than that, no signs that any stress had been applied was evident. To include, the material was still fully connected to the foam. After REALLY pulling up the material, I noticed that it was easy to remove where only the wood glue was (thus the reason for me recommending not using the wood glue as the base coat). It was only where the epoxy had seeped through the wood glue's cracks that were practically impossible to peel from the foam.

Crease Stress Test: This was to test the ability to bend the material completely over itself on a compound angle, and whether this would alter it from it's original state.

Result: This was performed many times simply because at this point, I was just trying to find a flaw. I even twisted the material in a wringing motion. After numerous attempts, I was unsuccessful in altering anything. At first, the compound angle was a bit deformed, but after a few seconds of "massaging" it, it was back to original.

Peel-ability Test: This was to test the ability to peel the material. Starting from where there was no fiberglass, to the point where the fiberglass had a full weave.

Result: It was a pain to start the peel, as it really adheres to the foam. After a while I was able to get it started. It would only come off in tiny pieces, and even then, only to the point where the fiberglass was at full weave. Past that point was impossible for me to peel.

Sandpaper Test: Let's try and scratch this stuff! Using both 60 and 150 grit sandpaper, attempt to damage the surface.

Result: Okay, this stuff has it's limits. The 150 grit made it not shiny, and the 60 grit scuffed it up a bit. That was it!

Remember, if you do go this route, the surface is not meant to be painted. The material is meant to be dyed with a epoxy colorant. As I have not needed to yet, I can not attest to how well a flexible type paint would perform.

I hope this information has helped anyone in need of it

very nice info. I do wonder how a flexable paint woud hold up on the second method. that would make a wider spectrum of colors easily available. great job .

Interesting research. Thanks for sharing. In the past I have sealed my foam with coats of PVA glue, then used a polyeurethane resin to harden it. It leaves a nice, sandable surface that paints really nice. Have you tried anything similar?