Tutorial: Gap Filling Part 1 - Using Styrene Cement on "Flush" Seams

Quick tutorial on how to fill smaller, minor gaps on plastic model kits using only styrene glue!

All styrene kits will have gaps where pieces join. The best are ones that are engineered such that seams are covered due to positioning of pieces, but sometimes, that's just not possible. Sometimes, two pieces have to be joined together in such a way that a small gap, called a seam, is created. What we're left with is an eyesore "line" down the middle of what should be a flat. smooth piece. While a lot of war gamers don't "seam" to mind them, I come from a pure modeling background where these kinds of things are frowned upon in the community, and penalized in contests. So, let's work on abolishing these altogether.

These steps won't work on resin or vinyl. Just a quick disclaimer. I'll delve into those later.

This first part is just going to be how to remove very minor seam lines on styrene kits. In fact, these seams are so small, they can almost seem to disappear when the pieces are fitted together, but will rear their ugly head when paint is applied. What we're doing is using the properties of styrene cement in our favor. Notice I don't call it "glue." What the cement does is forms a chemical reaction with the plastic, softening all styrene it comes in contact with. This softer plastic, when pushed against another piece of plastic, chemically bonds with the other piece. With smaller gaps, we can use this bonding process to our advantage.

For this process I use Tamiya's Extra Thin Styrene Cement, a small glass bottle with a green top and a brush attached to it. I find it easier to control with the fine tip brush, but whatever method or product you prefer is fine. Just remember that you don't want a goopy mess, so finding something with the ability to control the amount of cement you apply is crucial. More cement doesn't necessarily equal a stronger bond...if your cement is too much, it will run excessively (which can ruin details), and take significantly longer to dry, which might make the part fit worse as the parts naturally slide or separate.

OK, enough talk, on with the show.

STEP 1:
First, always, ALWAYS test fit your piece. Find out what kind of gap you'll be dealing with before applying ANY kind of glue, putty, or other chemical. With a lot of newer and more expensive styrene kits, the pieces are made in such a way that gaps are minimal, but sometimes production values are lower, the kit is cheaper, or just standard deviation is in effect. Find out where your problems areas are before doing anything. If you find you have fit issues, usually sanding some pieces down to get a more flush fit is in order.

STEP 2:
If the pieces fit together very well (leaving a minimal seam), its time to whip out the cement. I apply a thin layer near the edges of BOTH pieces I'm gluing together. This ensures my pieces match up and get a good bond.

STEP 3:
Press the pieces together in the best fit you can firmly. If possible, use a clamp (a great investment, get $10 and buy a whole pack of them). This will allow a tiny bit of excess cement to ooze out of the top, but not an excessive amount (the picture below I used just a little too much, but not detrimentally so), if you've done the second step properly. I usually let this sit for a good while. Usually my MO is to glue a piece, clamp it, move on to the next, and repeat until I have a few subassemblies cooking, then leave them for the night. It doesn't take a whole day for the cement to set, but patience in modeling is the best tool in your kit.

STEP 4:
After the pieces have dried, and there is no noticeable gap, I'll take a dulled Xacto knife to it. I usually keep a sharp blade for trimming, and once its dulled, start using it for this process. Basically, I move along the seam, scraping it longways, with my knife tilted just a little bit at and angle so I'm not scraping perpendicular to the piece. I find this "blends" it a good bit better than just scraping perfectly along the line.

STEP 5:
The coloration of the plastic is the key here. You will see darker plastic on top and around the seam. You want the entire section you're working on to be uniform. As you LIGHTLY scrape, you will see the plastic on the part start to become lighter and duller. The places you scrape won't reflect light as well as the places your blade hasn't yet touched. If you continue, and concentrate on the seam line, eventually the plastic around the cement will start to lighten up. You're essentially scraping away the excess on top, to revel the place where the plastic has joined so firmly you can't differentiate one piece from the next.

There you have it! Repeat this process until your piece is solid. In all actuality, if you have no seams now, you have essentially made two (or more) pieces of plastic one solid piece on a molecular level. When the plastic is soft, and pressed together firmly, it joins at the contact points. Once the cement dries, by scraping off the top layer of plastic you are exposing the place where they have fused, creating a truly seamless piece! Congrats, and come back as we worry about seams that aren't quite as flush!