A series of links about Fiberglass, Polyester, Gel Coat, prepared for West Marine's Presentation March 15th, 2008.Please use the "BACK" feature of your borwser to return to the Belwoodny site.

The additional information following was pulled of the LBI site

General Technical Information

WHICH RESIN ??
EPOXY vs. POLYESTER vs. VINYLESTER

Beware of the "one size fits all" approach.

More than 95% of all boats, truck & car bodies made of fiberglass are made primarily of E-glass,
orthothalic polyester resin and isothalic polyester gelcoat.  Items constructed with these materials
should be repaired with the same or compatible material.  LBI's 301 Orthothalic Polyester Resin is a
good choice for most repairs.  It provides a chemical bond to the existing laminate with similar
strength & flexural characteristics.

Orthothalic polyester, isothalic polyester an dvinylester resins are compatible, they all have styrene
(commonly known as the "fiberglass smell") and and chemically bond to one another.

If higher strength, bond and water resistance are required (such as keel, rudder repair, or outboard
transcom replacement) use LBI's 302 Isothalic Polyester Resin.

For the highest bond strength, bond strength and water resistance use LBI's 901 Vinylester Resin. 

Vinylester is essentially a styrene modified epoxy resin.  It gives excellent strength, rigidity, adhesion,
water and chemical resistance.

Keep in mind...

* Epoxy adheres to wood much better than polyester does.  To cover wood, a laminate using
  epoxy resin and 10 oz., cloth will yield a much better job than 10 oz. cloth and polyester resin.
  The epoxy / cloth laminate is comparable to using polyester resin with 3/4 oz. mat and 10 oz. cloth.
  However, the epoxy laminate requires much less labor to fair.

* A polyester laminate job is somewhat less expensive in material costs than an epoxy laminate
  project of the same size.

Remember...

* Fiberglass mat cannot be used with epoxy because the binding material in the mat will NOT
  dissolve in epoxy resin.

* Either mat, cloth or woven roving may be used with polyester resin.

* Since mat sticks much better to wood than cloth does, always make mat your first layer against the
  wood to be covered in a polyester laminate project.  

* We recommend using a layer of mat between layers of cloth for maximum adhesion between layers.

PREPARATION FOR COVERING WOOD WITH FIBERGLASS AND POLYESTER OR EPOXY

NOTE:  If working with old wood, remove all paint and foreign material from surface.

Step 1:  Sand surface with 60 or 80 grit samdpaper to rough-up surface.

Step 2:  Brush or roll on a primer / saturation coat of catalyzed polyester resin thinned 25% with
                acetone or styrene.  Epoxy resin should be thinned 25% with 1271 Epoxy Solvent.
               
                (Use either polyester or epoxy for a job.  Never mix the two together).

Step 3:  Sand lightly with 60 or 80 grit sandpaper to de-burr the surface.  Be very careful not to sand
                through the primer / saturation coat.

Step 4:  You are now ready to proceed with the lay-up method you've chosen.

OTHER HELPFUL HINTS

* No laminating project should be started without having a solvent handy for clean up.  Use acetone
  with polyester resin and 1271 Epoxy Solvent with epoxy resin.

* Keeping mixed resins, particularly epoxies in a wide, shallow pan, such as a roller pan, will
  increase the pot life.  This allows the mixture to shed heat and prevents an accelerated reaction.

* Use caution when laying-up glass in direct sunlight because it can greatly decrease working time.

* Remove air bubbles and wrinkles from uncured laminate by using an aluminum or nylon air bubble
  roller.  The air is driven from the uncured laminate into the fins of the roller thus yielding an even,
  bubble free surface.

* Our epoxies, as with most all epoxies, require 5 to 7 days at 70° F to achieve full cure.

SAFETY AND HANDLING

* Keep all resins, hardware and solvents out of the reach of children.

* Always work in well-ventilated areas.

* Safety goggles, gloves and respirators should always be worn when handling resins, hardeners
  and solvents.

* Harmful if swallowed - consult a physician immediately.

* If polyester or epoxy resins or hardeners should splash in your eyes, rinse eyes repeatedly water
  and call a physician immediately.

* Never use or store resins, solvents or hardeners near open flame.  Do not smoke when working with
  these materials.

* We strongly recommend that an organic vapor respirator be worn when using polyester or epoxy
  resin.  However, it is mandatory to wear a respirator when working inside a mold or in confined
  areas, even though good general ventilation is provided.

* Dust masks and safety goggles should always be worn when grinding or sanding cured fiberglass
  laminate.

* Uncured resin spills should be absorbed material.  The surface can then be cleaned immediately with
  hot water and detergent.

* A clean, neat, well-organized work area is generally a safe work area.


FIGURING HOW MUCH RESIN AND GLASS YOU NEED

Use the following Resin Chart as a rule of thumb guideline to determine resin coverage.
Resin to glass usage for polyester and epoxy are very similar.

Gelcoat Application Guide For a Mold

 * 304, 206,307, 308 GELCOATS ARE DESIGNED FOR USE IN A MOLD AND WILL
   NOT CURE "TACK FREE."

 * In a mold that has been prepared with mold release, apply 15-20 mils (check
   with wet film thickness gauge) of gelcoat with a brush, roller, or spray gun.

 * Gelcoat is quite thick so take care to apply as even a coat as possible, taking
   more care with a brush or roller.  Too thick may distort and pull away from the
   mold as it cures, too thin, it will be attacked by the resin/glass build-up
   laminate causing it to crinkle up or "alligator."

 * Ventilate or fan the gelcoat while it is curing to remove the styrene vapor which 
   can cause the gelcoat to cure unevenly and pull away from the mold creating
   unwanted waves in the finished part.

 * As soon as the gelcoat is cured (so that is doesn't come off on your fingers) it's 
   time to back up the gelcoat with a laminate.

 * Apply a layer of .75 or 1.5 oz mat with polyester or vinylester resin.  Once
   stabilized with the cured "backup" layer, proceed with the rest of the laminate.

309 Gelcoat Plus (Air Dry Application)

 * 309 GELCOAT PLUS is an "air dry" gelcoat used for regelcoating, refinishing or 
   as a finish coating over a polyester or vinylester fiberglass laminate.

 * Can be sprayed, brushed, or rolled onto a sanded gelcoat or a sanded primed
    surface (use Fourseal Primer).

 * When a smooth gloss finish is required, spraying is the best application method.
   Use a siphon spray or HVLP spray gun with a larger tip, suitable for primer.

 * To spray, catalyze and thin 15-30% with acetone and strain before loading the 
    spray gun.

 * Spray thin coats (2-3 mils) and allow acetone to evaporate for 1-2 min. before
   applying the next wet coat to that area.

 * Continue to apply wet coats until a wet film thickness of approximately 20 mils is
   achieved.  Then let cure to a mat finish that usually has a orange peel texture.

 * The gelcoat then can be wet sanded and buffed to a gloss finish.  Start with 400
   or 600 grit on a rubber sanding block and progress to finer grits.  Finish with a
   wool buffing pad and a buffing compound.

As a Rule of Thumb:  For One Quart (32 oz) of Resin:

MEKP %      Approx. cc      Approx. Teaspoon      Approx. Liquid oz
   1.00                    10                                2                                     1/3
   1.50                    15                                3                                     1/2
   2.00                    20                                4                                     3/4