Just some quick tips

Just some quick tips about working with fiberglass for today.  The first tip I have to share is to wear latex gloves when working with it.  When I started the Viper's bodywork, I called it "The long and itchy road." As anyone who's ever actually worked with fiberglass will tell you, it can be a very itchy process.  Fiberglass is called fiberGLASS because the cloth is literally microscopic strands of glass woven together.  Your car or boat is literally made from the same material as the windows in your living room.  While most people tend to thing of glass as solid, it's not.  When you get it thin enough, it becomes very flexible which is why fiberglass cloth doesn't just shatter when you bend it.  When you work with it, particularly when grinding, the air is filled with tiny glass shards that can get embedded in your skin.  It doesn't cause any harm, but can itch like crazy.  Gloves will help cut down on the itching a ton.  Additionally, you don't want to breathe too much of it.  Just like doing the occasional brake job won't give you mesothelioma, occasional fiberglass work and breathing in small quantities won't cause permanent damage, but you still want to avoid breathing it when you can.  For heavy grinding or sanding, a dust mask is a good idea.  It's also a good idea to have some "fiberglass working clothes" that you can take off immediately after you get in the house.  You don't want to track itchy dust all over the place.

Speaking of dust, fiberglass and bodywork work tend to make a lot of it.  Ideally, you want yo do your grinding and sanding outside on a breezy day so you're not working in a cloud of dust.  Outside on a breezy day isn't always an option though.  Either the weather won't cooperate or, like with my current project, I can't physically get the hood out of the garage by myself.  This is where being popular helps.  I always put my biggest fan right next to where I'm working.  It'll blow the dust away from where I'm working, and (mostly) out of the garage.

Next is the matter of Post Curing.  People think of fiberglass as an immovable solid, but it's not.  Fiberglass can, and will, move all over the place, particularly as it's curing.  Left on it's own, fiberglass can take weeks, or even months to fully cure and settle down to it's final shape.  Even "fully cured" fiberglass will move a bit more on it's first day in the hot sun.  This is where post curing comes in.  While it's not so important on the bottom of a hood, on exterior panels, it's critical.  Since we don't have the time to wait, we can speed things along in helping the 'glass take it's final set.  The idea is to raise the temperature of the 'glass to speed up any remaining curing.  Ideally, you want the glass to get up to 140°F, and stay at that temperature for a few hours.  The sun works great, but isn't always available.  Infrared heaters are the next best thing, but most people don't have access to those either.  What a lot of people do have is halogen lights.  Just set up your halogen light shining on the panel.  If the light is too far away, the panel won't heat up enough.  If it's too close, the panel will overheat.  Find the best distance for your light to heat and hold the panel at 140°F.  Since these lights are generally small, and the panel shape is complex, you should move it around every few hours so all the new glass gets baked.

Incidentally, this is the reason so many kit cars have such low quality panels.  Even if the mold is straight, the parts are demolded too soon after laying up, and then are shipped out without post curing.  This leads to very friendly panels that wave at everything.  It's also why so many fiberglass cars with fresh bodywork look great this year, but terrible next year.  When I was building kit cars for a living, we would let new parts sit in the mold for at least a week, usually longer, and then spend another week post curing them.

The last tip I have is of "don't burn your house down" importance.  First off, always test your mixture before actually starting the repair.  Mix up a batch of resin, and make sure it cures.  Liquid fiberglass hardener in particular goes bad quickly after it's been opened, so I ALWAYS use a fresh tube of hardener if mine has been open more than a few days.  Trust me, you don't want to have to peel off and re-do partially set fiberglass because your hardener failed and it won't fully cure.

Second, all compounds where you mix part A with part B to cause curing are exothermic.  That means that they give off heat as they start to cure.  Fiberglass, bondo, JB Weld, 5 min epoxy, etc, all produce heat as they cure.  The amount of heat is determined by how fast they cure, and how thick the mass(thicker means more heat).  If over catalyzed, fiberglass resin and epoxy especially can get tremendously hot as they cure.  I tend to mix my resin a little "hot"(with too much hardener) to make sure it kicks off OK.  I have, a time or two, mixed resin so hot that it's started smoking.  It won't get that hot on the panel because the resin layer is relatively thin, but it will get that hot in the mixing cup.  NEVER NEVER NEVER throw away mixed resin until it's cured and back to room temperature.  It could start your garbage can on fire.  Always set the cup on something non-flammable and non-meltable because that too can cause issues.  Here's an example from this project.  The bottom of this cup was flat when the resin was mixed.  As it cured, it got hot enough to warp and melt the bottom of the cup.