Standard Yellow-Grey 2-Part Self Hardening Putty

I've been using this epoxy for about 8 years now. Use it for just about every model I've built in that time. Great for filling gaps but I use it mainly for sculpting and modding figures. Make sure to mix parts as evenly as possible so it dries and cures well. Also keep your hands clean in order to make it easier to sculpt. It cures in about a day or overnight and can be filed, sanded, and polished until as smooth as styrene/plastic. You definitely need this in your tool box.

With some of my Revell kits of older vintage. (real old molds like the 1/426 Arizona) i've used this quite a bit to fill gaps. It's real easy to use, doesn't shrink unlike Tamiya putty (although Tamiya is better for some tasks) and is real easy to use to make custom pieces and fill large gaps. Be sure to mix both parts REALLY well though so that you don't get soft spots.

If you're building a big kit, and I mean a BIG kit like a 1/200 Missouri, then you NEED this. In my case Trumpeter's Missouri kit actually needed almost the entire two bars to fill in weak areas and mold errors. If you do use this keep in mind that once it cures, it's like a rock. It's very hard to sand, so if you're one of those people who leaves a bunch of putty sticking out... good luck. It also works well for making hollow areas of your model heavier. A heftier model just feels higher quality, so I use this often as just dead-weight.