Help filling seams on foam

[NK4U]

Hi all I’m new to cosplay and decided to learn the foam workflow by making shoulder pads. After a few attempts I finally have 2 shoulders that are good enough to paint but I’m going to learn to paint on the old ones before I ruin these good ones.

Im using Kwik Seal caulk for the seams on a reject shoulder pad and I really liked how much I could smooth it out. I tried foam clay but as shown in the photo below but it didn’t turn out too well for this application.
After using the Kwik Seal the seams practically vanished and it added some nice rigidity to the foam.
I got some plasti-dip and started applying layers over a few hours. Immediately i noticed that the foam had a noticeably rougher texture than the caulk and the smoothness of the caulk stands out like a sore thumb. (The foam clay stood out so much that using it was out of the question.)
Adding more p-d layers didn’t work so I painted over it with some gloss paint I had lying around to see if it would even out. It didnt…

So last night I made some swatches from my foam and smoothed some caulk on it as much as possible. It was invisible on the foam. Before this I ran one swatch under a heat gun to see if that is what the foam needed to match the smoothness of the caulk.
I applied a few layers of p-d to all 3 swatches and some automotive primer to two (including the heat-gunned one) and took a photo of the results to better show what I’m dealing with.
Primed-but-not-heated ended up looking the best but it’s still a little bit visible in different lighting angles. The primer did, however, make the texture much more uniform for painting.

Am I not adding enough layers of something? Between these swatches and the shoulder I’ve used like half the can of p-d and I see a lot of people not using primer at all. I cant just cover the entire thing in Kwik Seal so I guess I should stick with matte? But then again the p-d dried to a matte black and i could see the seam coverup clearly, too.
Does anyone else even use primer or do you just layer the plasti-dip as many times as it takes until it's smooth?

 

[Dirtdives2424]

Hey NK4U. You could also try 50/50 to get a better top coat on the foam......50% water mixed with 50% glue. I use wood glue because it dries faster and has a bit more adherence to the foam. A few layers of that either painted on or sprayed on (yes that works also), keep in mind that this stuff will form drip marks so you have to wipe those up, and then a light sanding and the outer layer will have a nice coating to it.....Aslo it will act like a paint undercoat......Your finished product will look much better.

 

[PlanetAlexander]

I've recently started using foam clay to fill in seams. At first I didn't like it because it would stand out after sealing and priming, but I learnt that after taking a palm sander to seams with foam clay, it works so well for hiding them. Some tips are to overfill the seams and smooth the clay out with water (so it really sticks to the foam), wait for it to dry at least 24 hours, and use a high grit sandpaper.
TillXValhalla has done really well at using foam clay on seams, perhaps he can add some insight?

 

[TillXValhalla]

I've recently started using foam clay to fill in seams. At first I didn't like it because it would stand out after sealing and priming, but I learnt that after taking a palm sander to seams with foam clay, it works so well for hiding them. Some tips are to overfill the seams and smooth the clay out with water (so it really sticks to the foam), wait for it to dry at least 24 hours, and use a high grit sandpaper.
TillXValhalla has done really well at using foam clay on seams, perhaps he can add some insight?

Absolutely, Foam clay is a godsend for seams. Like PlanetAlexander said, use more than you need to with water to smear it in nice and deep. let it dry and sand it beautifully smooth. It should be noticeable only in color but not in touch. Then you can take it a step farther and seal it using leak seal because you can then sand the leak seal with very fine grit too to blend any micro discrepancies. Also leak seal will let you layer it if you need to fill a gap. If there is still a seam after leak seal you can hit it with some filler primer to help fill the gap like you would for a 3d print. Re seal it in leak seal give it one last touch of sanding and boom should be as smooth as Porcelain.

 

[Rock Lobbster]

Hey NK4U. You could also try 50/50 to get a better top coat on the foam......50% water mixed with 50% glue. I use wood glue because it dries faster and has a bit more adherence to the foam. A few layers of that either painted on or sprayed on (yes that works also), keep in mind that this stuff will form drip marks so you have to wipe those up, and then a light sanding and the outer layer will have a nice coating to it.....Aslo it will act like a paint undercoat......Your finished product will look much better.

does your 50/50 crack? When I did that for my ODST I noticed that the coating got spiderweb cracking on the topcoat when bent.

 

[Dirtdives2424]

I followed mawrTRON foam sealing guide (Step #2) which I did several coats, and even when I knelled down on my knee armor, not a single crack!! And I had to do that several times over the last 2 years since I finished my Centurion armor......Still looks good.