Bondo - or more accurately polyester resin, is one of the most important tools for a modder. It’s fast setting, sandable/cutable, and relatively cheap. You can sculpt with it, fill with it, and resurface with it. Nothing is perfect though and Bondo has its issues. First, the vapors from it are toxic. Then of course, the particles abraded off during sanding can be toxic as well. The resin likes to stick to anything and prolonged exposure can cause burns. Of course, all of that can be mitigated using proper ventilation, gloves (latex or nitrile) and a respirator (I recommend a half face P100 Type with an organic/VOC filter - check your local hardware store). What can’t be changed is the fact that Bondo typically has to be mixed in large batches.
As a quick review, Bondo type resins are two part systems. The resin will only harden when mixed ~25:1 with a hardener. Too little hardener and the stuff will never fully set. The result is a nasty mess that’s hard to clean up. Too much hardener (actually preferable if you are gonna make a mistake) and the stuff sets before you are done even mixing it. The hardener comes in a little tube with a ¼” opening. With an opening that big and a 25:1 mixing ration, experienced Bondo mixers know it’s almost impossible to mix small batches of the resin and get the mixture right. This is an issue as a modder typically doesn’t need half pound batches to fix a hole or fill a gap. Making matters worse, the processes is a bit temperature sensitive and even more so in small batches (it sets very fast in higher temps). I have a small pile of hard Bondo pieces in the shop that never made it to the project because of hot rooms and bad ratios.
Solution? Yes - Disposable spoons and syringes.
The plastic spoons are to dole out the resin in small reproducible quantities. Like little disposable measuring cups. The syringe (if you haven’t guessed) is for controlling the amount of hardener in a precise fashion. Simply pull the plunger and squeeze a tube of hardener into it. Replace the plunger and you are ready. You may have to tap some air out.
It will take some practice and you’ll likely waste a few small batches in the process, but once you get the mix right, you’ll be saving material, money, and mess (start with a 1“ line of hardener to a spoonful of resin). The graduations on the syringe will help you out as well. Oh, and the temperature? Bondo and similar products don’t typically stick to wax paper, so get a roll and move the operation into a cooler (but well ventilated) space. You want to try and stay under 85 F if possible. Yeah, your friends will scratch their heads when they walk in on you in the bathroom with a gloppy plastic spoon in one hand, a syringe in the other, wearing a respirator and donning surgical gloves. But ya know, a little mystery in life is a good thing.
...Ok fine, I just googled him.