How-to Guide – Hand Lay-up on Fiberglass Molds

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1. PREPARING THE MOLD

Remove dust and dirt from mold.

a. If mold is of plaster, wood, or new fiberglass, apply soft wax (Wax #2) and buff with soft towel. Then spray or brush with PVA parting compound and allow to dry.

b. If mold material is glass, metal, ceramic, or well-cured fiberglass, apply three coats of hard wax, carnauba type, buffing between each coat.

2. APPLYING THE GELCOAT

a. If gelcoat is to be brushed on, allow the first coat to cure and then apply second coat to make sure there are no light spots.

b. If gelcoat is to be sprayed on with a gelcoat gun, spray up to a thickness of .015” to .020”. When gelcoat has cured long enough that your fingernail cannot easily scrape it free (test at edge of mold where damage will not show on part) then proceed with next step.

3. LAY-UP SKIN COAT

Cut ¾ or 1 oz. mat to cover your part. Brush catalyzed resin over the cured gelcoat and then apply the mat. Work with the roller, adding more resin where necessary until all white areas in the mat fibers have disappeared and all air bubbles have escaped. A mohair roller is ideal for rolling in the resin, and a ribbed plastic or aluminum roller assists greatly in popping any remaining bubbles. Avoid leaving excess resin standing in puddles. Resin-rich areas weaken the part. Where rollers will not reach, brushes must be used. When this step is complete, clean all your tools in acetone. Allow skin coat to cure before next step.

  1. LAYING FIBERGLASS REINFORCEMENT

For a 12 ft. boat, two layers of 1½ oz. or 2 oz. mat and one layer of roving may be adequate, depending upon design. For a 14 ft. boat, an additional layer of mat and roving will add additional strength. Apply each layer as in step 3, but it will not be necessary to wait for curing between these layers. Be sure to shake all acetone out of brushes and rollers before applying resin. Acetone drips can result in uncured spots in the lay-up.

  1. TRIM

On a small lay-up, the fiberglass laminate which hangs over the edge of the mold can be trimmed off easily with a razor knife if you catch the “trim stage,” of the period after the lay-up has gelled but before it has hardened. On a larger lay-up, it can be trimmed with a saw or diamond blade.

  1. CURE

The cure may take from two hours to overnight, depending upon turnover desired, temperature, catalyzation, and nature of the part. If laid up in a female mold, longer cure will affect shrinkage and easier parting. In the case of the male mold, the part comes off more easily before it shrinks appreciably. If the part is subject to warping, a longer cure may be necessary. In any case, when the part is removed, it should be supported in its desired shape until fully cured.

  1. REMOVE PART FROM MOLD

First, examine the trim edge all the way around the mold and make sure there is no resin bridging the line between the mold and the part. Sand this edge where necessary. Then wooden or plastic wedges can be pushed into the edges to start the separation. Continue separation by pulling and flexing. In some cases, it is necessary to drill a small hole in the mold and apply air or water pressure.

  1. FINISH

Trim edges and back of part may need to be sanded and coated with surfacing resin or interior gelcoat.

  1. GELCOAT PROBLEMS

Alligatoring,” or wrinkling of the gelcoat may be due to the following reasons:

  1. Gelcoat is too thin in spots; consequently it does not completely cure.
  2. Insufficient hardener added, or hardener not mixed well enough. In general, it is best to use about twice as much hardener in gelcoat as in lay-up resin at the same room temperature, since the gelcoat goes on thinner than a mat lay-up.
  3. Gelcoat has not cured long enough before mat lay-up.
  4. Acetone from tools drips onto gelcoat or into skin lay-up.

A Glossary of 122 Industry Terms –

In the world of gelcoat and resin, like every industry, there are terms used that are considered common-place. We have an extensive glossary to help with those terms. Have some others you think we should add? Message us and let us know!

A

Accelerator – An additive to polyester resin that reacts with the catalyst to speed up polymerization. This is required in room temperature cured resins. See Promoter.

Acetone – In an FRP context, acetone is primarily useful as a cleaning solvent for removal of uncured resin from applicator equipment and clothing. Very flammable liquid.

Additive – Substance added to resin mix to impart special performance qualities, such as ultraviolet absorbers, flame retarding materials (antimony trioxide, chlorinated waxes).

Air-drying – To cure at room temperature with the addition of catalyst but without the assistance of heat and pressure.

Alligatoring – Wrinkling of the gelcoat film that resembles alligator hide.

B

Bag molding – A technique for forming and pressure-hardening plastics or plastics laminates by means of air pressure, vacuum and/or heat in a flexible or semi-flexible bag or autoclave, usually in connection with a rigid die or mold.

Barcol hardness – A determination of surface hardness of a polyester using a Barcol Impressor.

Benzoyl Peroxide (BPO) – The catalyst used in conjunction with aniline accelerators or where heat is used as an accelerator.

Bi-directional – An arrangement of the reinforcing fiber strands in which half the strands are laid at right angles to the other half, a directional pattern that gives the maximum product strength to those two directions.

Binder – A resin soluble adhesive that secures the random fibers in chopped strand mat or continuous strand roving.

Blister – A flaw or air pocket between layers of laminant or between the gelcoat film and the first layer of laminant.

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Tech Question: “Can I apply resin to foam?”

foam-blockMany of our customers look to make sculptures out of fiberglass and resin. Foam is a common material as it’s easy to carve and sand to your desired shape. But, can you put Polyester resin on the top of it? It’s a question we get asked constantly.

Your first step needs to be finding out what kind of foam it is. Certain types of foam have different temperature variations. Polyurethane foam, like the kinds we sell in 4’ x 8’ sheets offer different temperature variations from things like Polystyrene. Once you figure out which foam you have, you can figure out what you need to do.

With Polyurethane foam, it will easily withstand Polyester or Epoxy resin applied to the top of it without having to do anything special. We recommend scuffing the surface with some sandpaper to get the best bond, but once the standard surface prep is done, you can apply your gelcoat, resin or epoxy.Polyurethane foam

With Polystyrene or Styrofoam, you can’t directly apply Polyester or Epoxy directly to Styrofoam, as it will melt the foam. Fortunately, we have a couple of products you can use to still make it work. The first product is an FGCI product called Styrocoat that uses a standard epoxy activator and will provide a protective shell over the Styrofoam. The other product is made by Duratec and is called Styro-Shield. Styro-Shield is a Polyester-based product that uses MEK-P and will provide a protective coating once hard.

So, no matter what kind of foam you use, we have a way to make your fiberglass mold or fiberglass-based product. Don’t forget that if you have questions, we are here to help! Give us a call at 1-800-272-7890, or e-mail us or contact us through Facebook or Twitter!

New Product Spotlight: FGCI Mil Gauge

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We talk a lot about gelcoat on this blog. We have stated on multiple occasions that gelcoat has to be applied with a certain thickness, generally 15-20 mils thick. How do you know exactly how thick your gelcoat coverage is? The answer is that you use a mil gauge, also known as a wet laminate gauge.

A mil gauge is a simple piece that you place on to your sprayed surface when the gelcoat is wet. When you pull it up, you look to see which teeth have gelcoat on them. You look at the highest number that has coating on it and it will give you a mil thickness; simple, right?

We have a new batch of mil gauges that are now online through Amazon and Ebay and available on our website, www.FGCI.com or in our showrooms. Pick yours up today.

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