how to harden eva foam

2024-04-08

Solution For Eva Foam:How To Harden Eva Foam

Hardened, Inflexible Surface:

How to harden the surface of EVA foam sheets is a problem that many people encounter, and we find that many people will use PVA glue first, and then use Plasti-dip or directly paint (epoxy or acrylic based). The disadvantage of this method is that after this process, the item is not flexible. Basically, the PVA will crack and separate from the foam. For items such as weapons or helmets (items that are not intended to be hinged or subject to bending stress), this would be a perfect solution.

But how to get a smooth surface? To this day, this is the biggest obstacle that many people encounter when processing EVA foam. Trying to sand PVA, even with "sandable" professional grade wood glue, is not an easy task and always gives me unsatisfactory results, and there is a risk of penetrating the glue and wearing away the surface of the EVA. As we all know, this is a very troublesome thing to do. We at hyheva team have tried 220 wet/dry sandpaper before, but with little success. Most of the time, either the sandpaper stuck, the wood glue "balled up", or it took a long time to carefully and tediously remove a little bit of glue. We even tried wet sanding it. But the result was that the wood glue re-set and became sticky. Also, it was almost impossible to get into the gaps, edges, grooves, etc. The answer to the solution to this problem was actually right in front of us!

how to cut eva foam?

EVA foam is the answer! It can be cut EVA foamto any size or shape you need and can adapt to any shape you need. Here are the steps I took.

"Paint" on your EVA glue (nice and thick, no need to skimp)

If you're going to try this, don't use waterproof glue! For our team, we dilute it back and forth with water depending on how thick it needs to be or if we judge we need multiple layers. If we do need multiple layers, we usually start with undiluted first and then work with the diluted. Don't worry about areas that seem to repel the glue, as we'll fix that next. To minimize the amount of work later, try to work only on horizontal surfaces. This isn't mandatory, but it does help.

For areas that repel glue, you should apply glue around the area. A second or third layer of glue can be gathered around the area.
After the glue dries, there may be some surface imperfections, depending on the quality of the EVA foam sheet. This is where the spare EVA sheet comes into play. The sheet can be cut into various shapes as needed. For larger flat surfaces, we usually start with a 2"x3" rectangle, but you may need other sizes. There is no standard for this part. Get a shallow container with a little water in it. Use the EVA foam as a sanding block, dip it in the water, let a few drops of glue stick to it, and then "sand" the glued surface you want to flatten/shape. It should immediately begin to restructure the glue. Tip: Use a very small amount of water and work on a small section at a time. Immediately wrap the glue that runs off with a lint-free cloth. It will be very sticky at first and will soon begin to thicken. This period of time is your working time. If it becomes too sticky before you are done, just add a few drops of water again! This process allows us to level the surface in minutes, whereas sanding would normally take hours…and the results are much better.

Once you have levelled and shaped the bonding surface and allowed it to dry completely, you can then either Plasti-dip or paint directly in. If you do use a brush-on acrylic paint, be aware that you cannot get too much paint on the surface or you risk having to re-formulate the glue again!

Tips for Painting EVA Foam?

“Hardening” the Flexible Surface

This part is a little tricky, and our team recommends using the exact product we found because epoxy is notoriously tricky. In fact, this method was discovered completely by accident! We initially tried to test this mixture on EVA, hoping that it would give me a nice hard surface without warping the material due to the lack of a hot chemical reaction curing process. It did not!

Here we took an angled piece of foam and coated it first with wood glue and then with woven fiberglass. Make sure the glue completely penetrates the fiberglass. (Note: We will skip using wood glue and instead use a primer with this epoxy mixture. The reason is described in the tensile stress test below.)

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

This is the magic mixture:

We didn't really believe these two were meant to be used together, but took a chance anyway. They are designed to be used on cement floors and usually result in a hard coating if the label is correct. That was not the case here!

We used equal amounts of both materials and started out like regular latex paint. I applied it to the surface with a standard paintbrush. I did notice that the more I worked it in, the more micro bubbles it created, so try to limit your movements.

This is the piece right after the epoxy mixture was applied. It took about 6 hours before it became tacky and 12 hours before I could handle it. At about 50 degrees and 65% humidity it seemed to cure after 18 hours.

Here are the tests, and their results:

BEFORE:

AFTER:

Heat Test: We applied heat directly to the surface, making sure both treated and untreated areas were heated. This test was performed with a heat gun on low for about 45 seconds, without movement, and about 2-3 inches from the surface. Later, a direct flame from a lighter was also touched to the surface for about 15 seconds, in another area.

Result: Upon contact with either heat source, bubbling began, but oddly, the bubbles disappeared without leaving any trace. The surface was initially too hot to touch, but quickly cooled down. It did not appear to damage the foam underneath. EVA foam changes color when heat is directly exposed to unprotected EVA foam (normal). All in all, this material seems to be very heat resistant.

Puncture Test: In a square test area, we pierced the material with a ballpoint pen so hard that I shook things off my desk.

Result: While the tip did pierce the material, it almost sealed itself when the tip was pulled out. No weak points appeared in the material due to the embedded fiberglass. Out of four attempts, two actually broke the material, while the remaining two left dents.

Pull Test: This test is done to check elasticity, recovery, and durability. One person holds one part, and another person holds the other part. We pull so hard in opposite directions that the reinforced glue seam actually breaks.

Results: The seams broke. Other than that, there were no obvious signs of any stress being applied. Including the material was still completely attached to the EVA foam. After really pulling up the material, I noticed that the places where there was only wood glue were easy to remove (hence I recommend not using wood glue as a primer). Only the places where the epoxy had penetrated through the cracks of the wood glue were almost impossible to peel off the EVA foam.

Crease Stress Test: This is to test the ability to bend the material completely to a compound angle and whether this would change its original state.

Results: This test was performed multiple times, just because at this point, we were just trying to find a flaw. We even twisted the material in a wringing motion. After multiple attempts, it still didn't succeed in changing anything. At first, the compound angle was a little deformed, but after a few seconds of "massaging", it returned to its original state.

Stripping Test: This is to test the ability to strip the material. Start from where there is no fiberglass, to where the fiberglass is fully woven.

Result: It was a pain to strip at first, because it really adheres to the EVA foam. After a while, you can start to strip it. It will only come off in small pieces, and even then, only to the point where the fiberglass is fully woven. Beyond that, it is impossible to strip.

Sandpaper Test: We tried to scratch this thing, using 60 and 150 grit sandpaper, to try to damage the surface.

Result: Well, this thing has its limits. 150 grit left it not shiny, and 60 grit left it a bit worn. That's it!

Keep in mind that the surface is not suitable for painting if you choose to go this route. The material should be stained with an epoxy stain. Since we haven't tried this yet, we can't attest to how well the flexible paint will perform.

Conclusion

HuiYiHao GROUP is an export-oriented entity group company. Focus on the production and sales of the industry's best EVA sheet, EVA packaging products, EVA craft products, EVA toys, furniture products and other types of EVA foam, EPE, sponge products.

The predecessor Shenzhen Huiyihao Packaging Materials Co., Ltd. was founded in 2003 in Shenzhen, Guangdong Province, mainly for domestic first-line brands and world-renowned enterprise customers;

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