WEST SYSTEM TECHNICAL MANUAL & PRODUCT GUIDE

WEST SYSTEM TECHNICAL MANUAL & PRODUCT GUIDE (cont'd)

Published by Gougeon Brothers, Inc., Bay City, MI, USA
Copyright 1994 GBI

Bonding with fillets

A fillet (fil'it) is a cove-shaped application of thickened epoxy that bridges an inside corner joint. It is excellent for bonding parts because it increases the surface area of the bond and serves as a structural brace. All joints that will be covered with fiberglass cloth will require a fillet to support the cloth at the inside corner of the joint.

The procedure for bonding with fillets is the same as normal bonding except that instead of removing the squeezed-out thickened epoxy after the components are clamped in position, you shape it into a fillet. For larger fillets, add thickened mixture to the joint as soon as the bonding operation is complete, before the bonding mixture is fully cured, or any time after the final cure and sanding of exposed epoxy in the fillet area.

Mix the resin/hardener/filler to a non-sagging peanut butter consistency.
Apply the fillet mixture along the joint line with the rounded mixing stick, using enough mixture to create the desired size of fillet. For larger or multiple fillets, empty caulking gun cartridges or disposable cake decorating bags can be used. Cut the plastic tip to lay a bead of thickened epoxy large enough for the desired fillet size. Heavy duty, sealable food storage bags with one corner cut off may also be used.
Shape and smooth the fillet by drawing a rounded filleting tool (mixing stick) along the joint, dragging excess material ahead of the tool and leaving a smooth cove-shaped fillet bordered on each side by a clean margin. Some excess filleting material will remain outside of the margin (Figure 7). Use the excess material to fill any voids. Smooth the fillet until you are satisfied with its appearance. A mixing stick will leave a fillet with about a 3/8" radius. For larger fillets, an 808 Plastic Squeegee, cut to shape or bent to the desired radius, works well.
Clean up the remaining excess material outside of the margin by using a sharpened mixing stick or a putty knife (Figure 8). Fiberglass cloth or tape may be applied over the fillet area before the fillet has cured (or after the fillet is cured and sanded).
Sand smooth with 80-grit sandpaper after the fillet has fully cured. Wipe the surface clean and apply several coats of resin/hardener over the entire fillet area before final finishing.

Bonding Hardware

As the name implies, hardware items are bonded in place with the goal of distributing high, single-point loads over as large an area of substrate as possible, while allowing the epoxy to seal and protect the substrate exposed by the fastener hole. There are two ways to do this. The first is to bond all fasteners (screws, bolts or threaded rod) directly to the surrounding substrate fiber. The second is to both bond the fasteners and the hardware itself to the immediate surface on which it rests. Using proper hardware bonding installation techniques, you can dramatically improve the load-carrying capacity of your hardware over that of standard hardware installation methods.

Fastener bonding

The fastener-to-substrate bond can be done in several ways. The easiest and most common method is simply to wet out a standard-size pilot hole for a given fastener with resin/hardener as follows:

Work the mixture well into the hole with a pipe cleaner or syringe.
Insert the fastener in the hole and allow the epoxy to cure.

This forms a substrate/epoxy matrix around the fastener that is much stronger than the substrate by itself, and distributes the fastener load over more of the substrate area.

Hardware bonding

You can further improve the load-carrying capability of the hardware by increasing the amount of epoxy that surrounds the fastener (taking advantage of the fact that WEST SYSTEM epoxy has much higher density and strength than most substrates) and bonding the hardware base directly to the surface. Bond for increased load transfer as follows:

Drill an oversized pilot hole to increase the amount of exposed substrate area that the epoxy around the fastener will bond to. This may be much larger than the fastener—twice the fastener diameter, for example. Drill the hole 2/3 to 3/4 the depth of the fastener.
Drill a normal sized pilot hole at the bottom of the oversized hole to the full length of the fastener (Figure 9). This allows the bottom threads of the fastener to bite into the substrate material so the fastener will stay in proper position until the epoxy cures.
Prepare the hardware by washing the contact surface of the base with solvent to remove any contamination. Abrade the contact surface with a wire brush or 50-grit sandpaper to allow the epoxy to "key" into the surface.
Fill the holes to the top with epoxy. Allow the epoxy to soak into the exposed end grain of the wood for a few minutes. If the hole remains filled after 5 minutes, remove the epoxy with the syringe.
Coat the bottom contact surface of the hardware with unthickened epoxy. Wire brush or sand the wet epoxy into the surface with 50-grit sandpaper. Sanding the base, coated with epoxy, will expose the epoxy directly to fresh metal with no chance for the metal to oxidize.
Inject a non-sagging epoxy/404 or 406 mixture into the hole. Use enough mixture so there are no voids in the hole after inserting the fastener. Coat the bottom of the hardware and the fastener threads with the thickened mixture.
Place the hardware in position. Insert and tighten fasteners until a small amount of the mixture squeezes out of the joint. Do not over tighten.
Clean the excess epoxy mixture that has squeezed out.
Allow the epoxy to cure at least 24 hours before applying load to the hardware. Allow more time in cool weather.

Bonding the contact surface of a hardware item can contribute a great deal to load distribution over maximum surface area. You can use WEST SYSTEM epoxy to make good bonds with most metals. However, careful preparation of the metal surface is necessary for good adhesion. This includes sanding and acid etching. For example, aluminum requires a two-step surface preparation. The first step involves the use of an acid conditioner that removes corrosion. The second step chemically stabilizes the surface and prevents oxidation, allowing time for coating or bonding. The WEST SYSTEM 860 Aluminum Etch Kit contains complete instructions.

Laminating

The term "laminating" refers to the process of bonding numbers of relatively thin sheets, like plywood, veneers, fabrics or core material. The laminate may be any number of layers of the same material or combinations of different materials. Methods of epoxy application and clamping will differ depending on what you are laminating.

Roller application is the most common method, because of large surface areas and limitations of wet lay-up time. A faster method for large surfaces is to simply pour the resin/hardener mixture onto the middle of the panel and spread the mixture evenly over the surface with a plastic squeegee. Apply thickened mixtures with a notched squeegee.

Staples or screws are good for clamping when you laminate a solid material to a solid substrate. An even distribution of weights will work when you are laminating a solid material to a base that will not hold staples or screws, such as a foam or honeycomb core material.

Vacuum bagging is the ideal clamping method for laminating a wide range of materials. Through the use of a vacuum pump and plastic sheeting, the atmosphere is used to apply perfectly even clamping pressure over all areas of a panel regardless of the size, shape or number of layers.
For more information about vacuum bagging, refer to 002-150 VACUUM BAGGING TECHNIQUES.

Fairing

Fairing refers to the filling and shaping of low areas so they blend with the surrounding surfaces and appear "fair" to the eye and touch. After major structural assembly has been completed, final fairing can be easily accomplished with WEST SYSTEM epoxy and low-density fillers.

Prepare the surface as you would for bonding (See Surface Preparation). Sand smooth any bumps or ridges on the surface and remove all dust from the area to be faired. Wash and sand cured epoxy surfaces.
Wet out porous surfaces with unthickened epoxy (Figure 10).
Mix resin/hardener and 407 Low-Density or 410 Microlight™ filler to a peanut butter consistency.
Trowel on the thickened epoxy mixture with a plastic squeegee, working it into all voids and depressions. Smooth the mixture to the desired shape, leaving the mixture slightly higher than the surrounding area (Figure 11). Remove any excess thickened epoxy before it cures. If the voids you are filling are over 1/2" (12 mm) deep, apply the mixture in several applications or use 206 Slow Hardener or 209 Tropical Hardener, depending on ambient temperature.
Allow the final thickened epoxy application to cure thoroughly.
Sand the fairing material to blend with the surrounding contour (Figure 12). Begin with 50-grit sandpaper if you have a lot of fairing material to remove. Use 80-grit paper on the appropriate sanding block when you are close to the final contour. Remove the sanding dust and fill any remaining voids following the same procedure. CAUTION! Don't forget your dust mask when sanding .
Apply several coats of resin/hardener to the area with a disposable brush or roller after you are satisfied with the fairness. Allow the final coat to cure thoroughly before final sanding and finishing.

Applying woven cloth & tape

Fiberglass cloth may be applied to surfaces by either of two methods to provide reinforcement and/or abrasion resistance. It is usually applied after fairing and shaping are completed, and before the final coating operation. The "dry" method refers to applying the cloth over a dry surface, either before the surface has been wet out or after the wet-out coat has reached its initial cure (or final cure and sanding). The "wet" method refers to applying the cloth to an epoxy-coated surface before the coat reaches its initial cure. Often the cloth is applied after the wet-out coat becomes tacky, which helps it cling to vertical or overhead surfaces. Since this method makes it more difficult to position the cloth, the dry method is the preferred method whenever possible.

Dry method

By working with small quantities of mixed epoxy it's possible to work at a comfortable pace with no limit to the size of the glassing job.

Prepare the surface as you would for bonding (See Surface Preparation).
Position the cloth over the surface and cut it several inches larger on all sides. If the surface area you are covering is larger than the cloth size, allow multiple pieces to overlap by approximately two inches. On sloped or vertical surfaces, it may be necessary to hold the cloth in place with several pieces of masking or duct tape, or with staples.
Mix a small quantity of epoxy (three or four pumps each of resin and hardener).
Pour a small pool of resin/hardener near the center of the cloth.
Spread the epoxy over the cloth surface with an 808 Plastic Squeegee, working the epoxy gently from the pool into the dry areas (Figure 13). As the fabric is wet out it will become transparent, indicating the cloth has absorbed enough epoxy. If you are applying the cloth over a porous surface, be sure to leave enough epoxy to be absorbed by both the cloth and the surface below it. Dry areas will show up whiter and less transparent than a properly wet-out area. Try to limit the amount of squeegeeing you do. The more you "work" the wet surface, the more minute air bubbles are placed in suspension in the epoxy. This is especially important if you plan to use a clear finish. You may use a roller or brush to apply the epoxy to a horizontal surface, and they are essential for applying cloth to vertical surfaces.
Continue pouring and spreading (or rolling) small batches of epoxy away from the center of the cloth toward the outside edges, smoothing wrinkles and positioning the cloth as you go. Check for dry areas (especially over porous surfaces) and re-wet them as necessary before proceeding to the next step. If you have to cut a pleat or notch in the cloth to lay it flat on a compound curve or corner, make the cut with a pair of sharp scissors and overlap the edges for now.

Note: For clear wood finishes (stripper canoes, etc.), an alliterative wet out method is to lay the epoxy onto the fabric with a short-bristled brush. Dip the brush in the epoxy and lay the epoxy on the surface in a light even stroke. Don't force the epoxy into the cloth, which may trap air in the fabric and show through the clear finish. Apply enough epoxy to saturate the fabric and the wood below. After several minutes, lay on additional epoxy to areas that dry out and appear white. Use 207 Hardener for clear fabric application and coating.

Squeegee away excess epoxy before the first batch begins to gel. Drag the squeegee over the fabric, using even-pressured, overlapping strokes. The object is to remove excess epoxy that would allow the cloth to float off the surface. Avoid squeegeeing too hard, which will create dry spots. Excess epoxy appears as a shiny area, while a properly wet-out surface appears evenly transparent, with a smooth, cloth texture. Later coats of epoxy will fill the weave of the cloth.
Trim the excess and overlapped cloth after the epoxy has reached its initial cure. The cloth will cut easily with a sharp utility knife (Figure 14). Trim overlapped cloth as follows:

a. Place a metal straightedge on top of and midway between the two overlapped edges.
b. Cut through both layers of cloth with a sharp utility knife.
c. Remove the top-most trimming and then lift the opposite cut edge to remove the overlapped trimming (Figure 15).
d. Re-wet the underside of the raised edge with epoxy and smooth into place.

The result should be a near perfect butt joint, eliminating double cloth thickness. A lapped joint is stronger than a butt joint, so if appearance is not important, you may want to leave the overlap and fair in the unevenness after coating.

Coat the surface to fill the weave before the wet-out reaches its final cure phase (Figure 16). Follow the procedures under Final epoxy coating. It will take two or three coats to completely fill the weave of the cloth and to allow for a final sanding that will not affect the cloth.

Wet method

An alternative is to apply the fabric or tape to a surface coated with wet epoxy. As mentioned, this is not the preferred method, especially with large pieces of cloth, because of the difficulty of removing wrinkles or adjusting the position of the cloth as it is being wet out. However, you may come across situations when this method may be useful or necessary.

Prepare the surface (See Surface Preparation).
Pre-fit and trim the cloth to size. Roll the cloth neatly so that it may be conveniently rolled back into position later.
Roll a heavy coat of epoxy on the surface.
Unroll the glass cloth over the wet epoxy and position it. Surface tension will hold most cloth in position. If you are applying the cloth vertically or overhead, you may want to wait until the epoxy becomes tacky. Work out wrinkles by lifting the edge of the cloth and smoothing from the center with your gloved hand or a squeegee.
Apply a second coat of epoxy with a foam roller. Apply enough epoxy to thoroughly wet out the cloth.
Remove the excess epoxy with a squeegee, using long overlapping strokes. The cloth should appear consistently transparent with a smooth cloth texture.
Follow steps 7, 8 and 9 under the dry method to finish the procedure.

Any remaining irregularities or transitions between cloth and substrate can be faired by using an epoxy/filler fairing compound if the surface is to be painted. Any fairing done after the final coating should receive several additional coats over the faired area.

Final epoxy coating

The object of final coating is to build up an epoxy coating that provides an effective moisture barrier and a smooth base for final finishing.

Apply a minimum of two coats of WEST SYSTEM epoxy for an effective moisture barrier. Apply three coats if sanding is to be done. Moisture protection will increase with additional coats, up to six coats or about a 20 mil thickness. Additives or pigments should not be added to the first coat. Mixing thinners with WEST SYSTEM epoxy is not recommended.

While coating, remember that the thinner the film thickness, the easier it is to control the evenness of the film and avoid runs or sags in each coat. Thin urethane foam roller covers, such as WEST SYSTEM 800 Roller Covers, are essential for good results. They give you greater control over film thickness, they leave less stipple than thicker roller covers, and the smaller volume of epoxy in the cover is less likely to exotherm. Cut the covers into narrower widths to reach difficult areas or for long narrow surfaces like stringers.

Complete all fairing and cloth application before beginning the final coating. Allow the temperature of porous surfaces to stabilize before coating. Otherwise, as the material warms up, air within the porous material may expand and pass from the material (out-gassing) through the coating and leave bubbles in the cured coating.

Prepare the surface as necessary (See Surface Preparation).
Mix only enough resin/hardener as you can apply during the open time of the mixture. Pour the mixture into a roller pan as soon as it is mixed thoroughly.
Load the roller with a moderate amount of the epoxy mixture. Roll the excess out on the ramp part of the roller pan to get a uniform coating on the roller.
Roll lightly and randomly over an area approximately 2 ft x 2 ft to transfer the epoxy evenly over the area (Figure 17).
As the roller dries out, increase pressure enough to spread the epoxy into a thin even film. Increase the coverage area if necessary to spread the film more thinly and evenly.
Finish the area with long, light, even strokes to reduce roller marks. Overlap the previously coated area to blend both areas together.
Coat as many of these small working areas as you can with each batch. If a batch begins to thicken before it can be applied, discard it and mix a fresh, smaller batch.
Drag a foam brush (see illustration above) lightly over the fresh epoxy in long, even, overlapping strokes after each full batch is applied. Use enough pressure to smooth the stipple, but not enough to remove any of the coating (Figure 18).

Recoating

Apply second and subsequent coats of epoxy following the same procedures. Make sure the previous coat has cured firmly enough to support the weight of the next coat. To avoid sanding between coats, apply all of the coats in the same day. See Removing Amine Blush. After the final coat has cured overnight, wash and sand it to prepare for the final finish.

Finishing

Proper finishing techniques will not only add beauty to your efforts, but will also protect your work from ultraviolet light which will break down the epoxy over time. The most common methods of finishing are painting or varnishing. These coating systems protect the epoxy from ultraviolet light and require proper preparation of the surface before application.

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