How to fiberglass  

Here are a few general things you need to know. We don't pretend to be experts but we do offer these tips to help someone who's just getting started and would like to skip some of the really hard learning challenges most of us have had to endure. 

One thing I want to say from the start is that fiberglassing is not easy.  One important thing to know is that resin goes from a liquid to a solid and stays pretty much where it is after it's no longer in the liquid state. I know this sounds trivial but if you get it on your clothes it won't wash out. If you get it in your hair you can wash it out somewhat with shampoo before it cures but it will be with you for a while if it cures before you get it out. Don't breath the vapors.  Epoxy and Polyester are both pretty bad - Polyester is more of an obvious smell.  What you smell with polyester resin is the styrene monomer.  With epoxy the hardeners are more vicious than the resins.  That applies to the skin also.  For hands I use Ply #9 or other barrier creams.  I've done a lot of layups with just ply #9 on.  I have used a lot of latex, vinyl, and nitrile gloves.  Be careful and be protected.  Wear respirators when the resin vapors are heavy and particle masks when grinding or cutting cured fiberglass.       

Before getting started:  

• Be sure to prepare the surface you're going to fiberglass.  If you sand or grind be sure to clean the debris off with a shop vac or blow off the area well.  Make sure there's no water of any kind. If there's moisture dry with a hair dryer or let it dry.  High humidity will keep polyester from curing.  Epoxy parts will not be as strong. 
• Make sure the working temperature is adequate - 75 deg Fahrenheit. 
• Wet out the area with resin then lay cloth on. Have the cloth precut and ready to put in place before mixing the resin.  It's a good idea to try the cloth to be sure it's going to lay down where you want it before you mix any resin also.  If it won't stay down while it's dry don't expect it to when you put resin on it.  Radius any sharp corners - if you're going to layup around a 2 x 4 board, file the corner off to a smooth curve.  If you're doing something with a lot of curves use some cloth like 7781, 7725, 7533, 1522 or some easily pliable material.  I like to put a layer of peel ply on at the last.  You can squeegie the peel ply and get a much better final shape.  Unless your layup is really wet you'll want to add a little resin to be sure not to dry the cloth out underneath.  Don't leave the peel ply too wet though.  If there's extra resin on top of the peel ply it'll hinder the peel ply removal later.  If there are wrinkles this will keep the peel ply from coming off later also.  Be sure to leave some extra unwetted peel ply around the outside of the layup to give you something to grab later to remove it.  Be sure to remove all peel ply after it cures.  If any gets left in the laminate any secondary laminates over it will delaminate later. Using peel ply will greatly decrease but may not eliminate the need for sanding after cure.

Hints and Notes:

• The styrene in Polyester resins will dissolve Styrofoam - Most epoxies work okay on Styrofoam but you should avoid polyester resin when using styrofoam.
• If you want to make a straight cut across the cloth pull a fill yarn thread out - this will give you a straight line to go by.
• If you're cutting Kevlar make one pass on the cutting part of each blade on a bench grinder.  Done with skill this will work excellent.  Keep a pair of scissors dedicated to just cutting Kevlar and other materials besides carbon and fiberglass. Always squeegie the resin from the middle of the material outwards. 
• Mix small batches of resin at a time - even on large layups.  The thicker the resin the more exothermic it will build and the faster it will cure.  Mix too much and the resin will cure before you get it all used up. If it starts gelling throw it out - don't try to use it. 
• You can hot wire polystyrene foams but no others.  PVC and polyurethane give off some nasty gases when they burn.  If you're doing layups over foam you can save weight by mixing a slurry of hollow glass microspheres to the resin in about a 1/1 by volume ratio.  This will help fill the voids and be lighter than having pure resin in the low spots.  Don't use micro between the layers of the cloth though - this will cause delaminations.   Lay the cloth on before the micro cures or you'll have to sand the whole thing.  If you use Kevlar in your surface layers and later sand it will fuzz up.  

How to Cut:

• Fiberglass cloth can be easily cut into shapes with a steel rule die as well as many other types of tooling. In order to make the cut well, with no hanging threads, a sacrificial belt system or an operator with great experience, or both, will have to be involved. The problem comes after the cut in the unraveling of the edges that have been freed during the cut. Like in a slapstick cartoon, a single thread can lead to the entire part falling apart, leaving you exposed to all sorts of problems. If you need just a basic, jagged cut, they can work well. If you need to retain the shape perfectly to pass on to the next operation (usually some type of gluing), you need to make a change to the material.
  
  Add material to the fiberglass to give all the fibers a pre-bond. Either a permeable laminate or a specialty additive work well to give the parts some bond before you make the cut. Your fiberglass supplier should be able to do this for you. Besides adding something to the material to keep it together we have heard of no other way to cut this product and keep it from falling apart. Even a heat sealing type cut is hard to make work because fiberglass is heat resistant. Great question in a very specialty field.

 Steve Thayer