How to Fibreglass a Boat Hull

This was my first yacht building project, and as such I had many how to questions to find answers to. I have
Difficulty: Moderate
Wipe down the surface to be fibreglassed with Acetone or lacquer thinners prior to sanding.
Wipe the surface dry with paper towells before the Acetone or lacquer dries, ensuring that disolved contaminants are removed from the surface.
Special preparation may be necessary for epoxy surfaces as a wax like film being a by-product of the epoxy curing process may form during the curing process. This film can be easily removed with clean water and a abrasive scotch pad. After washing the surface should look dull. Sand any remaining glossy areas with 80 grit sand paper. If release fabric was used then all of the wax would be removed as the fabric is peeled off, leaving a fully prepared surface.
Remove any flaking chalking, blistering or old coatings before final sanding.
Sand hardwoods and non porous surfaces with 80 grit sand paper to obtain a good textured surface for the eppoxy to adhere to.
Remove all dust after sanding. Vacuum cleaning is a good method to remove this dust.
Drape the fibreglass cloth over the hull as per the designers instructions as to the direction the fibres must run, leaving about 50mm over hang on both edges of the hull.
To prevent the cloth moving when applying the epoxy resin, use masking tape, duct tape or staples to hold the cloth in postion temporarily.
Using the West System calibrated dispensing pumps, pump 4 pumps of epoxy resin and 4 pumps of hardener into a mixing container.
I strongly recomend that the mini pumps are bought as they save so much time dispensing equal amounts without the mess of other manual methods.
Do not attempt any more than 4 pumps of each, as you may not have enough pot life left to apply all of the resin before it starts to gel, at least until you are familiar with the curing times of epoxy. Pot life at 22 degrees celsius is about 9 to 12 minutes.
Stir the 2 ingredients together thoroughly with a flat wooden stick for 1 to 2 minutes, ensuring to scrape the sides and bottom as you mix. Use the flat edge of the stick to reach the inside edge of the mixing container.
Mixing the 2 ingredients together begins a chemical reation that gradually changes the combined ingredients from a liquid to a solid.
Careful measuring and thorough mixing are essential for the reaction to occur.
Caution: Heat is generated by the chemical reaction the cures epoxy. I have personally had a plastic container melt when left standing to long as a result of mixing more than I could handle. If this occurs take the container outside where it can cool down safely. do not breath the vapors.
Pour the thoroughly mixed epoxy resin into the painting tray, and with a foam roller fitted to the handle, roll the resin into the roller, ensuring it is saturated.
With the roller saturated with epoxy resin roll the foam roller slowly from the centre of the cloth transferring the resin onto and into the cloth ensuring that the resin has penetrated through to and wetted out the porous hull surface below that the fibreglass is being laminated and bonded to.
During the morning as the day is warming up so were the hull or surfaces that were to be laminated, and as my hull core was made of DuraKore it was a porous surface that expelled gases within the DuraKore as those gases heated and expanded. This produced bubbles underneath my newly curing layup.I recommend that you time any fibre glassing work for curing to happen as the day is beginning to cool down, as the porous timbers or other materials will cool and pull air back into the pores of the material, and therefore the resin resulting in no bubbles. Porous materials breathe.
I learnt this lesson the hard way.
During the resin application process, you may find that you have to cut a pleat or notch in the cloth to enable it to lay flat on a compound curve or corner, make the cut with a sharp pair of scissors and overlap the cloth for now.
When the cloth is completely wet out, wait a few minutes and then look for dry areas that appear white and apply more resin.
Properly wetted out fabric is transparent like window glass when wet, with a smooth cloth texture. Later coats of resin will fill the weave of the cloth if necessary.
Do not force the epoxy into the cloth, as it may trap air bubbles in the fabric.
Before the resin begins to cure, drape release fabric over top of the wet fibre glass, and smooth out with your gloves on. The resin will soak through the fabric as you gently smooth it out.
After the laminate has cured, peel the release fabric off leaving a dull textured finish ready for any other laminating etc to be done without the need for sanding etc.
Release cloth prevented the need to add new layers of resin to fill the weave of the cloth, as it tended to pull down on the cloth bringing the resin to the top, and when the release fabric was peeled off after the resin had cured a smooth surface was almost always the case. I recommend that you spend the extra money for the fabric
If release fabric is not used, then coat the laminate weave with another coat of resin before the resin while it is in its initial cure stage. At this point the resin will feel tack free, and you will be able to dent it with your finger nail. it will be hard enough to be shaped with files or planes but definitely not hard enough to sand.
However, if you miss this initial cure stage then you will need to wait until the laminate has cured completely, and then prepare the surface before adding any further coats.
Here is the finished yacht at speed
Items needed
  • West system 105 Epoxy Resin
  • West system 205 Epoxy Hardener
  • West system 301 or 303 calibrated mini pumps
  • Gloves
  • Protective clothing
  • Disposable mixing containers
  • Roller pan
  • Flat wooden Stirrers with flat end.
  • Paint roller
  • Spare foam roller brushes
  • masking tape
  • Fibreglass cloth
  • Respirator with approved organic vapour cartridge
  • 80 grit aluminium sand paper
  • Acetone or lacquer thinners
  • 3-m scotch-brite pads
Overall tips
  • -- You will need to recognise and get a feel for the pot life of the resin as on warmer days the pot life will be less, and on cooler days the pot life will be longer.
  • Heat can be applied to or removed from epoxy to shorten or extend cure times, by use of a hair dryer for extra warmth or a fan to remove heat from smaller projects.
  • You will gain a natural feel for how much pressure to apply and how fast to roll the brush when applying resin once a couple of lengths of cloth have been wetted out.
Overall warnings
  • By itself West System resin rarely causes skin problems, the hardeners are considered a skin iritant, but is greatly reduced when mixed with the resin, however the manufacturer recomends that certain safety precautions are observed as shown on their product lables.
  • If fibre glassing in closed areas, use a respirator with approved organic vapour cartridge. If not use some means of exhausting the vapors and fumes. other protective clothing to prevent skin iritations.