This is a Tutorial on basic Expanding Foam knowledge and how to incorporate it correctly into your Pepakura Weapons, Grenades, and Equipment. I've gotten many PMs asking the same question on "How to use Expanding Foam without turning my rifle into a balloon". So I thought I'd finally share my knowledge on the subject with the rest of the community. Everything in this tutorial is step-by-step.
<span style="color:#FF0000">***Pictures will come at a later time!***</span>
NOTE: If you've never used expanding foam before you might want to take everything i'm about to say to heart. Also, this method works with all the weapons (including grenades, and equipment).
First thing to know, there are 2 main ways of goin about strengthening your weapon. There are some other ways to get this done that I DO NOT RECOMMEND.
<span style="font-size:14pt;line-height:100%">Method 1:</span>
1. Resin the outside of your COMPLETED pep piece about 6 times in light/thin coats to make it semi-sturdy
2. Get a saw or dremel (with a diamond wheel cutting bit) and cut your weapon in half (if you are filling a grenade you dont need to do this step)
3. Fiberglass the 2 halves on the inside about 3-4 layers, you may or may not use expanding foam at this point to fill in the cavity, there really isnt a need to since you just glassed it a few times.
4. To put it back together just line up the pieces and epoxy them back together. I recomend an epoxy putty with a work time of 20 minutes (ex: AquaMend)
Method 1 notes: I personally dont like to do it this way, because when you cut it in half your gonna lose some of the body and you'll have to just hope you line everythign up correctly when you put it back together... you may even have to improvise and build a "filler" in the gap between the pieces with Epoxy putty or Body Filler. It can get complicated...
<span style="font-size:14pt;line-height:100%">Method 2:</span>
1. Resin the outside of your pep weapon, grenade, or equipment about 4-5 times in light/thin layers.
2. Drill a hole, using a 1/4 inch drill bit, every 10 inches on one side of the weapon (for grenades, you only need 1 hole, for equipment, depending on which one, you will need up to 2 holes, max)
3. Using the expanding foam straw, place it into the first hole.
Fill ONLY one section at a time!!!!!!!
3.2. When that first section is about 1/2 full (remember this is EXPANDING foam, it is reallllllllllllly important that you dont over fill) stop and pull out the straw and let that section cure before moving onto the next one.
And for the love of Halo, DON'T fill the whole weapon with foam in one go.... you do that and you might as well kiss it goodbye.
<span style="font-size:14pt;line-height:100%">Expanding Foam Important Information:</span> This is the most important part of Method 2
Expanding foam cures over a 10 hour period (it says 8 hours on the can but it LIES).... therefore you need to keep your eye on your weapon, grenade, or equipment for 10 hours . About once every 30 minutes, during those 10 hours, you need to check on your weapon (grenade, or equipment). You NEED to "gas-out" the foam in all your 30 minute check ups. To "gas-out" all you need to do is unbend a paper clip or get a metal BBQ skewer and poke at the curing foam, Poke it so the metal goes all the way into the foam and gently hits the other side of the weapon (grenade or equipment). When you do this you will usually hear a pop and then an escape of air. That is what "gasing-out" is.
If you DON'T "gas-out" your weapon (grenade or equipment) it's shell (resined pep)will usually first balloon outward and eventually (when the air escapes, uncontrolled) it will be vaccuumed inward and it will litterally suck itself into itself (trust me it happend with my SR and I had to repair that damage with an ungodly amount of bondo, and in the end still turned out to be an epic FAIL). After 10 hours and 30 minute increments of poking your foam, you'r pretty safe to do another section of the weapon (grenade or equipment). Once your weapon (blahblahblah) if full and completely cured all you have to do is fill the holes during the next step (Bondoing). Doing it this way will be much more time consuming but the end result will be perfect.
And just as a side note, depending on which weapon you build, you might want to make an internal skeleton using PVC pipe. For example: my SR's barrel is also my rifle's "spine", it runs the entire length of the body internally to help with structure.
That's it for my tutorial right now, I will continue to add/edit this as time goes along, I will be updating it with step-by-step pictures soon.