Hand Lay Up Guide

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Some Background on Polyester Resin: with Wax (non-air inhibited), vs. without Wax (air inhibited)

Polyester Resin will not cure in the presence of air. To get around this problem, a very small amount of paraffin wax is mixed in solution with the resin. In the curing process, the wax rises to the surface in a very thin film and excludes the air from coming in contact with the resin, allowing it to cure very hard on the surface. Waxed resin will cure with a satin finish. This means it will not alow for a good bond for the next coat of resin.

Waxed resin is used for one coat glasswork, or for the last coat of resin in a laminating schedule, or for any layer in a laminate that has to be sanded. As long as the waxed surface has been sanded, there will be good bond for the next layer. Waxed resin can be used for multiple layer work as long as each layer is applied on top of a wet layer. Waxed resin is often referred to as Finishing Resin.

Resin without wax cures hard, but remains slightly tacky and gummy on the surface. This surface cannot be sanded but makes for very good adhesion for other coats of resin and glass. This is the type of resin used most in fiberglass construction. For a hard, final finish, a coat of resin or gelcoat with wax can be applied over the no wax layer. No wax resin is often referred to as Laminating Resin.

Pitfalls of using Surfacing Agent (Wax)

  • Surfacing Agent must be clear. Not cloudy or lumpy. It can be warmed in HOT WATER, to clear it up. NO FLAME OR HOT PLATE as fire is possible
  • Resin or Gelcoat must be over 70°F before surfacing agent can be added; this can also be warmed in hot water bath.
  • Surfacing Agent may not work if laminate gelcoat is done in direct sun on hot days.
  • Styrene fumes may accumulate in low areas, such as swimming pools, and can prevent Surfacing Agent (wax) from working.
  • Over catalization may cause the gel to happen so quickly that Surfacing Agent will be unable to work.


Fiberglass Cloth

This is lightweight, woven fiberglass and is available in many different weights, the most common being 6 ounce and 10 ounce (this is the weight of the cloth per square yard). Fiberglass cloth is used mainly as a waterproof covering over small boat hulls, canoes, cabin tops, engine boxes, etc., where great strength, impact, and abrasion resistance is not required. Cloth is also used as a final finishing layer over previous lay ups, such as mat. This is the E-Glass type of fiberglass cloth.

One important fact to remember when using fiberglass cloth is that it does not lend itself to hard angles very well. Whenever possible, break hard angles with a plane sandpaper, or radius inside angles with hull and deck putty or body putty. this, in many cases, is desirable for a good-looking job, anyway. One gallon of resin will saturate or "wet out" approximately 6 square yards of 10-ounce cloth. More resin will, of course, be required to finish the glass job or to fill up the weave of the cloth until it is smooth.

Fiberglass Mat

Mat is the most versatile and widely used form of fiberglass for the hand lay up procedure. Mat is made up of short, individual fiberglass that can be hand laid in place. We stock Mat in tow weights. ¾ oz. and 1 ½oz. per square foot. Mat is used in applications where strength and durability are required, such as, on work decks for commercial and sport fishing boats, cabin tops, all sorts of tanks, washboards, battery boxes, decks and balconies on houses, and auto body repair work.

Mat will conform nicely to hard angles and tuck in close to places where woven fiberglass will not. When layered or combined with woven roving, very strong, rugged glass laminates can be built. Because of the amount of resin it absorbs, Mat is not used in applications where maintaining it extremely lightweight is important. Mat leaves a fairly rough texture, which is an advantage in areas where a non-slip surface is desired. The choice of either ¾ oz. or 1 ½ oz. Mat depends upon the strength required or the complexity of the surface to be glassed. The ¾ oz. will lay down over or into angles and curves with less work than the thicker 1 ½ oz. Two layers of ¾ oz. could be laid to equal the strength and thickness of one layer 1 ½ oz. Mat will not de-laminate or peel off as easily as woven fiberglass. If it were to be removed, Mat would tend to break off in pieces where woven fiberglass would peel off in sheets.

Always use short Nap Roller to apply the resin to the Mat. Never apply the resin with a brush or squeegee. This would mop the fiberglass hairs around into piles and the finished product would have a very lumpy texture, making sanding and finishing a nightmare. Of course, it may be necessary to dab with a brush in hard angles or corners, but never stroke the surface back and forth. Always apply dry Mat to the surface you wish to cover and then apply the resin. In most cases the resin can actually be poured onto the surface from the mixing can and then spread around with the paint roller. One gallon of resin will wet out approximately 3 square yards of 1 ½ oz. Mat. When using Mat, a laminating roller should be used to massage out excess resin and the air that becomes entrapped in the laminate while it is still wet.

Roving Woven

We Stock 24 oz. and 18 oz. (per sq. yd.) Woven Roving. Roving is woven like cloth but is much heavier and thicker. It is used for reinforcement where much strength is required, as in the construction of boat hulls, tanks, swimming pools, etc... Also for smaller jobs such as glassing bulkheads and engine beds into glass hulls.

Roving should always have at least one layer of Mat applied first under it and between any further layers. Never apply Roving directly to Roving. Again, a pint roller is the best tool to use to apply the resin due to the large amounts of resin needed to wet out the Roving. Approximately 3 square yards of 24 oz. Roving can be wet out with a gallon of resin.

Hand Lay-up Procedure

Step One: Prepare Surface

Remove paint, or any other foreign material, from the surface to glassed using a disc sander. Do not use paint removers or a torch, as these just drive the oils int o the wood, which will result in a poor bond. Rough up fiberglass surfaces to be glassed with a course disc. Slick, hard, non-porous surfaces do not promote good adhesion of the glass and resin. On bare, dry wood, roll on a catalyzed primer coat of no wax resin and let it cure. This is to seal the surface so the wood does not absorb all the wet resin from the fiberglass. Fill any screw heads, cracks, or gouges with a polyester based putty and let harden, then sand. Use no oil base fillers or putty.

Step Two: Arrange Glass

Precut and fit the fiberglass. Lay the glass out dry on the surface to be covered (there is no wet resin involved at this point). Roughly trim off excess material.

Final trimming will be done with a disc sander and a utility knife. If just one layer of glass is being applied, it's a good idea to overlap slightly where two or more layers are being applied. Just butting pieces together is okay, but make sure the butts are staggered. This will avoid lumps caused by overlapping. Iron out wrinkles by hand and dart corners for neat folds. On vertical surfaces, it may be necessary to hold glass in place with a few staples or tacks (stainless steel won't rust).

Step Three: Mix Resin and Hardener, and Apply

Mix the catalyst with the resin. A common mixture at 70 to 75°F is - two teaspoons per quart of resin. This gives about 15 to 20 minutes workable pot life. In cooler temperatures, up to four teaspoons per quart of resin is okay. Fiberglassing in temperatures under 55°F is not recommended unless some artificial heat is used or the sun is expected to shine on the project the same day.

With resin catalyzed, you are now ready to begin wetting out the fiberglass. In many cases, the resin can be poured directly from the mixing can onto the glass and spread around with the paint roller; otherwise you will have to work from the can or roller pan. The fiberglass will turn transparent when completely saturated. Put on only enough resin to wet out the glass. If the resin begins to gel in the pot, discard it immediately. Do not attempt to continue because in a matter of seconds it will be rock hard. Almost every glass expert loses resin in the pot occasionally. These losses should be budgeted for when the resin amounts needed for a job are being estimated. Now the first wet out is completed. Just let it cure hard before any sanding is done (2 to 5 hours at 70-75°F), unless no wax resin is being used for a continued lay up.

Step Four: Sanding and Polishing

You must decide before you start sanding how good you want the final job to look. Some jobs require little or no sanding at all; others require lots of grinding. Feather edge the overlaps with disc sander using a 36-grit disc. The object is for the job to look like it was covered by one continuous sheet of fiberglass. Sand off any rough spots where a bug or leaf may have gotten caught in the wet resin. When grinding Mat, only concentrate on the overlaps and highest bumps. By the time you have sanded the Mat completely smooth, you have ground most of it away, defeating the purpose.

Instead of excessive grinding, farring putty made from glass beads and wasted resin can be squeezed on the Mat with a wide drywall-taping knife. This fills up the lowest spots in the Mat and, when hard, sands easily. It can then be covered with a finish layer of 6 or 10-ounce cloth, if desired.

Note - If farring putty is going to be used, it adheres best to no wax resin.

Step Five: Apply Top Coat

With all sanding completed, the final catalyzed layers of resin can be brushed or rolled on. When using cloth, only put on enough resin to fill up the weave of the fabric until it is smooth. When these coats have hardened and have been sanded, they are ready for painting.

The best primer is a two part epoxy white, such as Gloucester B370. Oil base gloss enamels go well over this. B370 Primer is also recommended on bare fiberglass below the water line when it is going to be painted with anti-fouling bottom, paint. Oil base primers and enamels will also work on sanded polyester finishes, but are not meant for continuous immersion in water. Pigments can also be added to the resin to obtain a permanent color requiring no paint. However, a smooth, high-gloss finish cannot be attained using pigmented resin. On those surfaces where a beautiful finish is not required (e.g. workboat decks, or fish hold, etc...), pigmented resin is suitable.


The hardener for polyester resin, Methyl Ethyl Ketone Peroxide (MEKP), is a corrosive and flammable liquid, and it should be handled with the greatest caution. Keep from children's reach. Wear protective goggles when mixing resin and hardener together. Shake the resin well before each day's use. The heavier components settle to the bottom of the container and must be recirculated. Drums can be up ended and stirred with a long stick. Do not glass in the direct sunlight on hot days. the surface to be glassed gets too hot and can upset the resin's hardening process. Also, the heat will cause the resin to gel too fast, perhaps before it can be totally worked into the fiberglass.

Rig up some kind of temporary shelter with a tarp to provide shade and cooler temperatures or wait until later in the afternoon when the sun is not baking the surface to be covered. In hot temperatures, lesser amounts of catalyst should be used.

No glasswork should be started without having some Acetone on hand for cleanup. Acetone is the best solvent for polyester and epoxy resins. Paint thinners such as mineral Spirits and Turpentine will not cut resin at all. Do not let uncured resin get rained on or wet.