Back to the grind

Try as hard as I might, I couldn't get all the bodywork done on the Viper.  Every time I got going on it, other people would start making demands on my time.  Now, it's too cold out for fiberglass and bondo to cure properly, so I figured I might as well catch up on my blog.  When we last left the Viper, I'd just finished laying in all the new fiberglass on the bottom side of the hood.  Since the fiberglass is what makes up the structure, we could just leave it as it with some minor trimming.  But, it's the bottom side of a hood in an engine compartment that a whole lot of people ask to see so it has to look pretty too.

Before we can really start grinding, we need to know where to stop.  In a few areas where there was original undamaged fiberglass, I left some spots of the original black paint.  I know that paint is where it should be, so I know that that is where the surface should be when I'm done.  None of it is super critical on the front of the hood, but you still want to make sure the latch hooks are close enough to their original position that it will latch properly(even then, the latch has a lot of adjustability in it).  The round circle is one of the hood scoop nut recesses, the odd shaped black splotch is original paint telling me where the surface should be once we're done.

I started again with my trusty Harbor Freight grinders, first the 7" to knock down and level the big flat areas, then my 4.5" to hit the smaller areas, and finally a 2" pneumatic grinder for the tight spots.  Grinding it down serves two purposes, first to knock down any high spots, and second to roughen up the surface for additional filler work.  Here it is all ground up.  You can see the shape is roughed in pretty well.

You'll notice that three of the four the hood latch hook holes have been completely fiberglassed over.  Before I put any filler on, I want to be sure I know where they are.  Here is where Mineral Spirits works some more of it's magic.  Wiping the ground fiberglass with mineral spirits turns it transparent enough that you can see through it.  here you can see one of the hood latch hook holes under the fiberglass.  It shows up as the dark circle about in the middle of the picture.  All the holes will get drilled out before I add any filler.

Here's the part that I don't generally recommend, but am going to break my own rule and do anyway.  I've mentioned filler a few times.  Standard body fillers work good for a lot of things, but they don't have much strength.  Fiberglass is strong, but is hard to work with(and sands like concrete.).  There is a product that lands directly between the two, fiberglass reinforced body filler(often called Kitty Hair or Tiger Hair).  It's essentially bondo with chopped up fiberglass in it, and has the added benefit of being waterproof like fiberglass(and unlike standard bondo).

I don't generally recommend it for two reasons.  First, because it's fiberglass reinforced and stronger than standard fillers, a lot of people use it instead of doing proper repairs.  This hood had several areas that were just filled with kitty hair instead of being repaired properly with fiberglass.  Far too often I see kitty hair band-aids on things that need actual repair, both on fiberglass and metal cars.  Second is the bubbles...

Because of the fiberglass strands in it, kitty hair doesn't mix or spread as well as bondo(especially the long strand variety).  As a result, you often end up with large bubbles or voids in the filler that might cause problems down the road.  I decided that for the bottom side of the hood, I wanted the extra strength of the reinforced filler and would just deal with the bubbles.  You can see here the kinds of voids and bubbles you typically get in kitty hair:

You can't just fill the voids because filler won't stick to the (relatively) shiny surface of the bubble. The only way to deal with them is to grind them out first, then fill them.  Using a carbide burr in my die grinder, I ground out all the bubbles I could find.  In addition to the big obvious ones, there were also a whole lot of pinholes that needed to be filled.

Once the bubbles were ground out, I filled them with regular body filler and sanded it all smooth:

Unlike the outside of a car, the bottom side of the hood has lots of odd shapes and small contours, so it took a variety of sanding tools to work everything smooth.  For all the filler work, I used 80 grit sandpaper.  I bought a big roll of sticky back 80 grit, it's the most economical way to buy it.  From top to bottom I have my rigid 6" block, a flexible 6" block, a rigid 3" block, half a tongue depressor wrapped in sandpaper, a whole tongue depressor wrapped with sand paper, and my trusty 8" Durablock.  For this kind of work, improvised sanding blocks are often necessary too. Find something that fits where you need it to fit, and wrap it in sandpaper.

Even though most of the surface is covered in filler, it's not very thick.  Just like laying the fiberglass down, I worked a section at a time until I had the shape I wanted.

Once the filler was sanded down, I renewed my love affair with Duratec primer-surfacer.  It's just such a wonderful product, and it's made specifically for fiberglass to boot.  The repaired areas of the hood got a healthy dose, followed by sanding with 220 grit paper.  Normally, you'd want to sand much finer than that for paint or you'll get sand scratches showing through, but I'm going to do something a little bit different and don't need a super fine finish.  For now, just enjoy the Duratec'd goodness...