BoatCraft Gel Coat Application Guide

BoatCraft Gel Coat Application Guide

Gel coat is applied onto polyester resin and fiberglass for a UV protective coating, and can be used in mold making processes as a mold release agent and finished surface. Gel Coat is a polyester resin base with a pigment. Some gel coats have pigment added, such as white or black. Neutral gel coat is unpigmented, which is a brown semi-transparent resin base. Neutral gel coat is not “clear” gel coat, it is intended to have liquid pigment added. Marine clear gel coat is completely transparent and used for metallic flake or high gloss coats on top of pigmented gel coat.

IMPORTANT:

·         Gel coat that is too thin is prone to spider cracking and can be damaged by heavy impacts or UV aging and winterization.

·          Do not introduce heat (heat gun, open flame or radiant heat) to a curing gel coat. Adding heat after the gel coat is catalyzed will spike the gel coat exothermic reaction and make very brittle and fragile gel coat. Allow the gel coat to cure at 21 degrees Celsius for its full cure time without intervention for the best strength and durability.

·         Do not use acetone to thin the gel coat, acetone will break the polyester adhesive bonds. Thinning with acetone will decrease the gel coats strength by half. Acetone can be used in small amounts on cured gel coat to remove wax and contamination. Styrene is the proper resin thinner for polyester resin, it is added at 5-8% v/v to gel coat for spray application.

CAUTION: Gel coat contrains styrene. Always wear an active organics cartridge mask, eye protection and gloves. Gel coat requires MEKP (methyl ethyl keytone peroxide) to catalyze and cure, be careful to not ingest. Keep out of eyes, may cause blindness.

NOTE: Working time is approximately 25% of above cure times. Avoid working in extreme temperature or direct sunlight.

Hand Application Techniques:

1.       Heavy grit (40-120 grit) sand the surface, sand down to raw fiberglass for best adhesion. If blending into a surrounding area bevel in the area so that the new gel coat is the same height as the old material.

2.       If gel coating a new surface sand and acetone wipe. Gel coat is not a body filler, make sure the surface is straight and smooth without pin holes, voids, or unstable surfaces.

3.       Acetone or Isopropyl Alcohol or dewaxing solvent to remove wax, sanding debris and contamination.

4.       Shake Gel coat can or mix thoroughly to integrate pigment and resin.

5.       Dispense a small volume of gel coat.

6.       Add MEKP catalyst at 1-10 percent by volume. See catalyst chart for cure time according to catalyzation.

7.       For Unwaxed gel coats, air dry additive must be added to the final layer to make the surface tack free. Unwaxed gel coats remain tacky after fully cured so multiple layers can be applied without sanding and acetone prep. Air dry is added to the gel coat at 2.5 % v/v.

8.       Gel coat must be applied in thin even layers to avoid cracking when curing. For the best result gel coat is applied with a sprayer in 2 coats of 18 mils (.475 mm) per coat to reduce shrinkage.

9.       If Brush applying apply 2 thin coats and sand and polish the surface after fully cured.

10.   Gel coat should be fully cured in 90 minutes, able to be sanded and polished at that point.

Spray Application Techniques:

1.       Sand and acetone the surface. Clean out the HVLP sprayer. Ideal nozzle size is 1.8 -2.4 mm nozzle size. Set the compressor to 60 psi. Set up dust free environment. Set up personal protective equipment.

2.       Shake or stir the gel coat, add pigment. Make sure the colour is fully integrated.

3.       Calculate the 5-8 % v/v styrene (resin thinner) and add it to the gel coat. Add air dry depending on how many layers are being applied.

4.       Calculate the new volume and add MEKP catalyst at 1-5% v/v. Mix and add to the HVLP sprayer.

5.       Set the fan and aperture size on the gun to make an even smooth spray. You are now on the clock as the gel coat cures, you have 12 minutes to use the volume in the gun.

6.       Spray the volume out of the gun onto the surface in smooth even layers. Keep the gun 6-8 inches away from the surface that you are spraying.

7.       After each batch, clean the HVLP sprayer with Acetone. Any gel coat left in the gun will solidify and stop the gun from functioning.

8.       Allow the first coat to cure for 90 minutes, and apply the second or third coat. Follow the cure and tack times.

9.       Apply the final layer of gel coat with MEKP and Air Dry. This will fully cure and make the surface tack free.

10.   Sand and polish the surface. Finish the surface.

IMPORTANT:

1.       Neutral gel coat is not clear gel coat. Neutral gel coat requires liquid pigment added at 5-8 % v/v. Colour matching gel coat is done by adding pigments to a neutral base gel coat.

2.       Unwaxed gel coat remains tacky after it is fully cured. To have a fully cure and tack free gel coat, air dry is added to the gel coat and catalyst to create a skin. This wax skin will cause the gelcoat to be tack free.

3.       Waxed gel coat will cure tack free every time, so every layer must be sanded and acetone wiped before another layer can be added. This includes back-to-back layers since the resin does not stay tacky, each layer must be prepped before more can be applied. If you do not prep every layer you are bonding gel coat to the wax of the previous layer and risk delamination, cracking and soft gel coats.

4.       Gel coat is not a body filler. Gel coat cannot fill low areas in a body fill more than 1/16 inch or less. Thicker applications of gel coat are prone to cracking and are not as strong as fiberglass. Polyester resin and fiberglass, or powder additives can be used to body fill, and gel coat is applied as the top layer finish.

5.       Gel coats must be maintained with wax or polish. Gel coats have limited UV protection, and will begin to pit, oxidize and fade depending on use. Maintenance is required.

6.       Do not use acetone as a resin thinner. It dissolves and breaks down the bonds of the gel coat. Adding acetone as a thinner will half the strength of the gel coat.