Fiberglass Armor Construction: Trim and Rough Sand the Piece
Trimming and Sanding
Now that you have a final piece the rest of the work is to finish it so it looks good.
Similar to the safety guidelines above you will want to make sure you are working in a well ventilated area (preferably outside because of all the dust you will generate) have eye protection, a breathing mask so you are not breathing in the resin dust and preferably some gloves to protect your hands.
The first thing to do is trim the edges so you can easily grab the piece without hurting yourself. To do this I used a Dremel with a flexi shaft and a cutting disc. The flexishaft is not necessary, but it sure is nice. The Dremel is pretty necessary if you want this done well and quickly. You will want to have a handful of the cutting discs around. I found I went through them pretty quickly. They can break in a variety of ways from being snapped to overheating and crumbling.
Take the cutting disc and cut off the rough edges where you laid the fiberglass past the end of the mold. Do not cut directly on this line but instead cut just outside it.
When you are done cutting off those bits you will want to sand the edges the rest of the way down to the line where the mold actually ended. You can use a Dremel sanding disc (my favorite option) some hand sand paper or if the piece has long flat edges you can use a power sander. If you use the Dremel option you will have choices of usually an 80 or 120 grit paper (the higher the number the finer the grit). For the other options you can use any grit you want. For the Dremel I like 120 grit the best. It seems to be a good balance between speed to sand stuff down and control of not sanding off too much too quickly. Be sure to stop often to look at how things are progressing. You don’t want to sand too far down and then have to either remake the piece or try and build it back up.
Now move your attention to the front of the piece. How does it look? Are there lots of little imperfections from the original model that got transferred here? Or does it look almost perfect and just ready for the paint? If there are areas that need to be sanded down now is the time to do that. If the areas have only slight imperfections then you can use something like a 220 grit paper. If there are a lot of big imperfections you may want to start at 120 grit and then move up to 220 grit. If the piece has a lot of big flat areas you can use a palm sander to do the work more quickly. If there is a lot of detail and angles and curves you will need to sand it by hand.
All around I have found a wet/dry 220 grit sandpaper with a bucket of water to be the best. The water helps keep the dust from getting everywhere, helps keep the andpaper from getting clogged and it helps in finding imperfections that still need to be sanded out of the piece.
Whether you are going to gel coat the piece or paint it you will want to sand everything smooth to a 220 grit level. Even if you are going to paint the piece you will want to at least give it a quick once over with the 220 grit as the roughness it will make on the piece will help the paint stick better.
If you are going to paint the piece you are almost done. Once everything is sanded give it a good rinse under the tap or with a garden hose and let it dry. Once dry you can paint it however you want.