Finishing Fiberglass Like Glass
Looking for that glossy smooth finish on fiberglass or other custom peices just like on those show cars? Heres to the best of my knowledge how to obtain that look and feel. I won't lie, if you have already made the fiberglass enclosure, you will know already how rough and uneven the surface of your fiberglass will be. It will take lots of work, lots of sanding, and many times filling in the pits and unlevel spots. It is possible for you to obtain that look, or close to it using parts from local home centers, or automotive stores. Some of the materials may not be obtainable easily locally, we will be listing several similar products for you to look for.
Sandpaper: This is easily the most important thing needed to get the surface smooth. You will need a lot, and use a lot. You should have start low with 34 grit, working your way up to 150 grit, 400 grit, 800 grit, and up to 1500 and 2000 grit. (After 150 grit you should be using wetsanding paper). If your surface is large I highly recommend purchaing a palm sander, or belt sander. For tight places, there are sanding sponges that work well.
Filler Putty: This is what will make your surface smooth for the most part, you don't actually sand the whole thing to get it smooth. Once the surface has been sanded a bit, you are to lay this down to give you a better surface to sand. It will fill the gaps and low spots, as well as rough areas. When looking for a filler putty it is very important to find a good quality one. Some will flake off, or crack due to warping or movement. You should look for a filler with re-enforcement fibers, such as Duromax. Here is a list of commonly used materials:
-Bondo Body Filler
Spot Putty: The filler will get things very smooth, but there will still be some small pits and valleys. For that, a spot putty or a thick primer coat will be needed. It is similar to the filler, but you will need to smooth it down, usually with a finger, or flat edge.
Process: As you already know, it is going to take a lot to get this down to a mirror glass like smoothness and shine. The 1st step, and literally every other step from now on is sanding. Start sanding your fiberglass with some low grit 36 or 80 grit sandpaper. Always use a palm sander, or a sanding block, only use sandpaper in your hand when you can use a block. Your fingertips will unevenly supply pressure causing streaking. Sand the whole area until you get a less rough more even area to work with.
Now you can lay down your 1st layer of filler, if your fiberglass is relatively smooth and even, this may be one of the only layers you have to put down. Use a spreader, or a flat edge to smooth the filler out over the surface. For smaller areas, and details, using your finger can work well to control the filler.
We are back to sanding again once the filler is dried, gradually work up to a higher grit sandpaper, and sand down the whole piece. It should begin to be smoother, but still have some uneven spots, or little craters. Go over the piece filling in the spots with more filler, and then sand once again.
Once you have a fairly spot free and smooth area, use your spot putty on the little pits and valleys. It is a really good idea to use your finger or a razor blade to go over and smooth those out. Sand again with a very high grit sand paper (400-800). The whole peice should now be REALLY smooth,
Time to primer! Use only a good quality primer, preferably from the same company as the paint you plan on using. Now while it will be perfectly fine to use spray cans, I recommend using a sprayer, to ensure perfect application. For a primer, I suggest using a thick polyester based primer which will also fill in any spots you may have. Once you have a good coat over the whole area... SAND! Once again using a high grit (800). You should never use a grit lower than around 800 anymore on this. After sanding apply another coat, and sand again. Repeat this 1 or 2 times until the surface is fully prepped, and fully smoothed for paint. Sand using some really high grit sandpaper, (1500 - 2000).
Now you can finally paint. Your surface should be smooth, but most importantly clean and clear of debris. You may prep your area additionally with the use of cleaning agent like rubbing alcohol. Again would be a good idea to use a spray gun rather than spray paints. Paint the surface using smooth even strokes covering the area and continuing off of the surface. Stay an equal distance from the surface as you move across. As the paint begins to loose its shininess, spray on another coat. Continue to add coats as needed until you have good coverage. You can color sand the surface with some really high grit sandpaper (2000), and maybe do another coat.
Once the surface has been painted, and you've obtained a somewhat glossy shine you can now clear coat. You should do this no later than 24 hours after painting, read the manufactuer's directions to make sure when the appropriate time is to apply it. Make sure the surface is once again clean, and smooth, and the paint looks as you would like. You can now add on a clear coat. It is a good idea to use the same clear coat from manufacturer of the primer and paint you used. Spray on a clear coat, and add a few more coats until you have a good layer of protection over the area. Any fine scratches can still be sanded out. hopefully, with some 2000 grit sandpaper. Add more clear over the area you sanded (making sure the surface is clean). Wait a day or two for the surface to fully dry, and then use some buffing compound and a buffer to get a real good shine. When its show time, you can apply some kind of automotive polish, or even wax the surface to keep a good shine.