How to Fill Gaps in EVA Foam: Easy Methods Anyone Can Use.

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EVA Foam is an awesome crafting material, especially for cosplayers and prop makers. It is easy to work with and you only need a handful of inexpensive tools to be able to create great-looking props and costumes. There is, however, one little problem, that a lot of crafters run into. And that is fixing uneven parts, gaps, and seams in their EVA Foam project. After reading this article you will know exactly how to fix even the biggest gaps and how to smooth the ugliest seams with ease.

So how do you fill gaps in EVA Foam? In short, there are several methods, that you can use to fix ugly seams and gaps in EVA Foam. The two easiest methods are using Kwik Seal to fill in gaps and seams and then smoothing the surface of the Kwik Seal with a little water and your finger. The other method is using Foam Clay to fill the gaps and sanding the clay down to make the surface smooth.

I will explain each method in further detail in the following.

And if you want to learn more about working with EVA foam then consider reading my other EVA foam guides right here.

Filling Gaps in EVA Foam With Foam Clay

Using EVA foam clay is my personal favorite method for smoothing EVA foam. Foam clay functions similarly to traditional clay, with the distinction that it transforms into soft foam once it has cured.

You can buy clay foam right here on Amazon.

This method also requires a glass of water.

  1. Dip your fingers in the water and apply some water to the area around the seam.
  2. Press some foam clay onto the area. Make sure that you spread the foam as evenly as possible. This will ensure that you have an easier time smoothing the clay in the next step.
  3. Moisten your fingers again and then use them to smooth the clay by running over it with your fingers. Dip your fingers in the water again as soon as the clay starts sticking to your fingers.
  4. You can sand the foam clay once it is fully cured.

When foam clay dries, it tends to be relatively soft, this can pose a challenge when sanding if the underlying foam is highly dense. There may be instances where you accidentally reveal the denser underlying foam by removing too much of the softer EVA foam.

The good news is, that you can simply add some more foam clay to the area and repeat the whole process.

Filling Gaps in EVA Foam With Kwik Seal

This is probably the best-known method for filling gaps and fixing seams in EVA Foam and it makes sealing the foam afterward quite easy too.

Kwik Seal can be found in any hardware store. It is a multi-purpose adhesive caulk usually used in the kitchen or bathrooms.

You can also buy Kwik Seal right here on Amazon.

Most crafters and Prop makers, who work with EVA Foam, use Kwik Seal to fix gaps and seams.

  1. To fix seams with Kwik Seal simply apply Kwik Seal to the gap or the seam, that you want to fill.
  2. Then use some water and your finger (I would recommend wearing disposable gloves for this part) and smooth the Kwik seal with your finger and some water.
  3. The result will be very smooth and no seams or gaps will be visible after you are done. Let the Kwik Seal dry for a few hours until it is solid.

If the result is not smooth enough then you can slightly sand Kwik seal with a fine grid sanding paper to give it an even smoother finish.

But most of the time this won´t be necessary if you smoothed Kwik Seal well enough when you applied it.

Fixing Seams by Sanding the Area

Finally, the easiest way to fix seams on EVA foam is by simply sanding the area. This method only works for small gaps, though.

  1. Use some 100 grit sandpaper to remove some material where the two EVA foam pieces meet.
  2. Switch to 150 grit once the gap has become very small. Sand until the gap is completely gone.
  3. Finally, use some 200 grit sandpaper to smooth the area. Once you are done, the gap should be completely gone.
  4. If there are still some holes or a little gap left then either use some foam clay or some filler to fix those.

This whole process is much easier when you have a rotary tool. Simply use a stone bit to sand the entire area and then continue from step 3.

If the sanded area remains slightly rough with 200 grit sandpaper, you can further smooth it by heat sealing the EVA foam in that region.

This process not only smooths the surface but also eliminates any fuzzy foam bits adhering to it. For more details on heat sealing EVA foam, check out my article about sealing EVA foam.

Using Filler to Fix Gaps

You can use regular wall filler from a tube to fill in gaps and fix seams. While there is also filler available that requires mixing, using filler from a tube is significantly more convenient and faster.

Filler is a good alternative to Kwik Seal.

You will also need a glass of water to smoothly apply the filler to your foam.

  1. Apply the filler to the area. Make sure that you fill in the gaps completely.
  2. Moisten your fingers with water and spread the filler across the entire area using your finger. Re-dip your fingers in water as needed to prevent the filler from sticking to them.
  3. Finally, move your wet fingers over the filler to further smooth it.
  4. Once the filler is dried it can be sanded with regular sandpaper to smoothen it even more.

The only drawback of using filler to fix seams is its lack of flexibility. Therefore, only use this method for props that do not require flexibility, such as weapons, breastplates, helmets, and similar items.

This is the finished project. All of the gaps and seams were fixed with the methods shown in this article. You can´t see any of the gaps and seams anymore.

Can You Use Bondo on EVA Foam?

Bondo is a body filler that is mainly used in the automotive industry. It is a two-part mixture, that you can shape any way you like. It is quite cheap and easy to come by.

So can you use Bondo on EVA Foam? In short, yes you can. You only have to lightly sand the area of the EVA Foam where you want to apply Bondo so that the Bondo has something to grip onto. Then Mix your hardener with the right amount of Bondo and simply apply it to the surface of your EVA foam. Once the Bondo has dried you can sand it to give it a smooth finish.

Bondo is available in almost all hardware stores or car repair stores. It is quite cheap and easy to use.

You have to mix the hardener with the right amount of Bondo before you can apply any Bondo to your Project.

Make sure, that the surface, that you want to apply Bondo to is rough enough for the Bondo to stick to. So if you want to apply Bondo to EVA Foam, then lightly sand the area, where you want to apply it to.

Mix the hardener and the Bondo well and then apply it to the EVA Foam. You can use Bondo to fill in seams, cracks, or gaps.

Roughly apply the Bondo to fill in the gap or seam, that you want to fix. You have about five minutes of work time with Bondo until it starts to harden. It depends on how much hardener you mix in.

Once the Bondo becomes kind of Crumbly the work time is over and you should stop moving or shaping it. Wait for a couple of hours until it is completely dry.

Then use rough grit sandpaper to roughly shape the Bondo and to get rid of blobs or other uneven parts. Then move on to finer grit sandpaper like an 800 grit to smooth the surface of the Bondo. If you want a very smooth surface, then you can even use a 100 grit and wet sand it. But most of the time, I find, that Bondo is smooth enough once I sanded it with an 800 grit.

Bondo can be sealed with Plasti Dip or White Crafts Glue and it can be painted without any problems. So it is an awesome medium to use for Prop making and Foam crafting.

I personally prefer using Foam Clay or Kwik Seal over Bondo for fixing seams and gaps because it is faster and easier to use these methods compared to Bondo but there are a lot of other projects, where Bondo is better. For example, if I have to fix a big surface, then Bondo is better because it is so much cheaper and it is easier to mix a big batch of Bondo than using a lot of Foam Clay or Kwik Seal.

I also use Bondo if I want the surface of my Foam to be rigid. So for crafting armor, I like to put a small layer of Bondo on top of the armor to make it rigid. This gives an extra layer of detail when people touch the armor.

But that is entirely up to you.

Disclaimer: This article has been written with the assistance of artificial intelligence (AI) to enhance its readability and grammatical accuracy. The content and information presented in this article are entirely original and originated from the author. The AI was used solely to rewrite certain sections of the article for the purpose of improving clarity and coherence, without altering the substance or meaning of the content.

Hi, I am a passionate maker and professional prop maker for the entertainment industry. I use my woodworking, programming, electronics, and illustration know-how to create interactive props and puzzles for Escape Games and marketing agencies. And I share my knowledge and my experience on this blog with you so that you can become a maker yourself.

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