The Great Fiberglass Trilogy, Part II- Gelcoat repairs. Note – this article deals only with repairs above the waterline (for water-induced blisters, see Part III). It does NOT cover repair or replacement of non-skid, since this is a separate and more complex subject. Background: Gelcoat is much softer than polyurethane paint, but is present in thicker layers that allow more depth for sanding and compounding. It is much cheaper and easier to apply than polyurethane. However, gelcoat is less durable than polyurethane paint and more easily suffers from nicks, scratches, stress cracks and abrasion. Another, more rare problem is lack of adhesion of gelcoat to the underlying fiberglass, perhaps due to undue delay in applying the original fiberglass laminates to the layer of gelcoat lining the mold. This can result in loss of dime-sized pieces of gelcoat. Another form of damage is wearing through of the gelcoat by abrasion. This can happen with excessive wet-sanding and compounding, in an attempt to remove oxidation (see Part I of this series) or rubbing against a piling during a storm. The final type of gelcoat damage to be discussed is the formation of "alligator-skin" type cracks and/or "crazing" caused by severe and repeated sun exposure. How are such damaged areas repaired? Similarities and differences in procedure are described below. We will start with a description of items needed before you begin repairs. Required Tools etc: For opening up nicks and scratches before repair, you will need a scraper or sharp-edged screwdriver. You will also need sandpaper, ranging from coarse (80 or 100 grit) to 220 - 600 grit "wet or dry" silicone carbide paper. Small amounts of coarse and fine rubbing compound (car supply stores have smaller sizes that boat stores, - we like Turtle Wax brand) and a fine polish. Some wax for final touch up is also required (we like Collinite Fleetwax 885 or our own Superwax coating). Graduated plastic vessels of appropriate sizes are best for mixing. Some wooden or plastic application/mixing sticks (Coffee stirring sticks can be used for small batches of thickened gelcoat). Some Mylar sheet or polyethylene plastic bags are needed for placing over some repairs to aid shape and/or exclude air from the surface while the resin is curing. Plastic squeegee applicators are required for spreading on filler or thickened gelcoat,. If gelcoat is going to be sprayed on, use a propellant-driven disposable spray gun. The one made by Preval is most suitable for small repairs. Before spraying, the gelcoat is filtered to remove lumps and particles that might clog the spray-gun, using paper-cone filters. Masking tape and/or Island Girl's Hawaiian Blue Masking Gel are needed to mask the surrounding area. The masking gel masks non-skid and vinyl upholstery where masking tape cannot. "Fine-line" tape from 3M will be required if the edge of a stripe is involved in the repair. Finally, a paper dust mask is recommended during sanding gelcoat and filler. A charcoal-filtered mask and safety glasses are necessary during gelcoat spraying. Thick-walled rubber kitchen gloves are a necessity as well as old clothing and/coveralls.. Materials: Polyester resin (clear, non-tinted.) is the basis of all gelcoat repairs. When it is tinted with colored pigment or dye it is termed "gelcoat". Regular polyester (laminating) resin is "air inhibited" so it sets with a sticky surface unless the surface is sealed from air. This can be accomplished by pressing plastic film over the repair or spraying with polyvinyl alcohol (PVA) surface sealant. PVA is also a mold release agent, so it can also be used under the plastic film to make it easier to remove. Cured PVA is removed by water, so you will also need a water hose or other source of tap water. Wax/styrene "surfacing agent" can be added to regular resin converting it into "surfacing resin", which can also be purchased in ready-mixed form. We prefer using this type of resin because the wax rises to the surface, sealing it so that no surface coating (plastic film or PVA) is required to prevent surface stickiness, which would otherwise clog sandpaper. Chemical de-waxing solvents cannot remove this wax that is bound into the surface (before painting, for instance), - it must be sanded off. Another precaution with surfacing resin is that set up time must be sufficient (more than 10 minutes) for the wax to rise to the surface evenly. If more than one layer of catalyzed surfacing resin is applied, the surface of the underlying layer must still be tacky. Otherwise sanding between layers is necessary. For manual (rather than spray) application to deep scratches or on vertical surfaces, the gelcoat has to be thickened so that it does not run or sag. Addition of Cab-O-Sil resin powder renders the resin "thixotropic", i.e. it behaves like a liquid when stirred and gelatinous after application. It does not alter resin color and therefore does not interfere with the effect of added color pigments. Most small "do-it yourself" gelcoat repair kits contain surfacing resin already thickened with Cab-O-Sil. For making up a more "Bondo" type of paste for filling deeper repairs, talc is the cheapest (and heaviest) filling agent for the resin, but plastic micro-balloons are lighter and make a paste that is more easily sanded after curing. Glass beads or other harder to sand fillers are not recommended for gelcoat repairs. You can also use Bondo or other body filler, available in kits, some of which are especially formulated for marine use. The resin becomes "gelcoat" when it is colored by application of pigments (powders of solid color) or dyes (soluble in the resin and seldom used except on surfboards or metalflake finishes). Procedures for color matching to the original gelcoat involve both art and science. Guidance can be provided by use of a color wheel obtained from an art supply store. Pigments are only required in small amounts (1 Oz or less) but you will need at a minimum, the "primary colors" of blue, yellow and red. These can be used to make almost any color in between, although some premixed colors such as brown and dark blue are also available. You will always need white pigment for tinting lighter and black pigment for tinting darker. Of course, these pigments are also needed to make white, gray or black gelcoat. HINTS ON COLOR-MATCHING ARE GIVEN AS AN APPENDIX AT THE END OF THIS ARTICLE. Thinners for spraying gelcoat: For this you can use either regular resin or surfacing resin but the resin must NOT be pre-thickening with Cab-O-Sil. Instead the resin is diluted down with styrene and acetone (no more than 10% acetone) Too much acetone dulls the surface, but styrene is much slower to flash off. Some people like to use a "slow" lacquer thinner with the styrene. Thinning between 15 and 50% may be necessary, depending upon spray gun, operator, ambient temperature etc. Some trial and error is required. De-waxing materials: First scrub the area with strong cleaner such as Ajax or Superclean (a little caustic component aids destruction of silicones from waxes etc). Then use a xylene-based "grease and wax remover" (from an auto paint store). Alternatively, for small jobs, use xylene or xylene-based "Goof Off" followed by acetone or lacquer thinner. DO NOT WIPE ON WITH SHOP RAGS because the silicone used in fabric softener may affect adhesion. Use only cheap, unprinted kitchen paper towel. Catalyst: The polyester gelcoat or filler (if used) is induced to set hard by mixing in the proper amount of catalyst, according to its instructions. For paste filler repairs (not gelcoat) a Bondo- type catalyst can be used which has a dye to assist in thorough mixing. For gelcoat however, colorless catalyst is used, applied with a drop bottle. Again it is important to mix very thoroughly without adding excessive amounts of catalyst that may either interfere with proper pot life or hardness of the cured resin. Usually only the equivalent of 1-4 Oz catalyst PER GALLON is used, depending on temperature (less catalyst on a hot day). Finally do not forget to avoid temperatures below 60 degrees F (resin may not cure properly) or above 90 degrees F (sets up too fast). Also avoid working in direct sunlight except for very small repairs, since UV light accelerates hardening and solvent bubbles may ruin the finish. Repair of Nicks and Scratches: This type of gelcoat damage is caused by collision with a sharp object, or impact with something heavy and sharp. Such damage is fairly easy to repair. Step 1: After de-waxing the local area and light sanding (600 wet or dry) to expose fresh original gelcoat, the scratches or nicks are opened up by the edge of a scraper and rough sanded (80 grit). The opened up area is wiped out with some acetone, to remove debris and then a little styrene to aid chemical bonding of the repair. Step 2: We advise use of a "surfacing" resin for making up the gelcoat repair mix. Color-matched gelcoat (i.e. polyester resin plus pigment), suitably thickened with Cab-O-Sil is then catalyzed and applied with a plastic applicator to the area, filling the entire area proud. On clear (or tinted) gelcoat over metalflake, no pigment or perhaps a little color-matched dye is used. Step 3: The repaired area is sanded smooth with 220, then (stepwise) down to 600 grit wet or dry sandpaper. The area is further smoothed with rubbing compound, then polished and waxed. Note: If the original scratch is so deep that it reaches down to, or into, the underlying fiberglass laminate, some repairmen prefer to use an underlayer of polyester filler and apply the gelcoat by spray as described below for repair of stress cracks. Stress Cracks: The polyester resins of the gelcoat slowly become more brittle with age and are therefore more prone to stress cracks. The latter tend to form around metal fittings due to alternative heat expansion/contraction. They also form (as on my boat) in some areas where the boat has hit the dock and the fiberglass hull flexed. Because the gelcoat is thick and has no fibers for reinforcement, it is less flexible and may form some cracks that go down to the underlying fiberglass laminate, with some localized lack of adhesion between laminate and gelcoat. If cracks are due to underlying structural weakness causing flexure, this weakness should be fixed before the gelcoat is repaired. Stress cracks are best repaired in a different way than for nicks and scratches. Step 1: De-wax, then wet sand (220-400 grit) the area to expose true color of the gelcoat. Prior use of our SEA GLOW Cleanser/Conditioner often assists in brightening up porous gelcoat to the true color. Step 2: Grind out the area (using a Dremel tool) until it is obvious that an area has been reached where there is solid bonding between gelcoat and underlying laminate. Step 3: Wipe out the area with acetone to remove debris, then with some styrene to increase chemical bonding of the repair. Step 4: Fill the area to just above the original (sanded) gelcoat surface level with catalyzed paste filler: the final intention is to cover the area with sprayed on color-matched gelcoat). You can buy a ready prepared Bondo - type body filler, or (better) you can make your own using regular polyester resin mixed with Cab-O-Sil (to prevent runs), and talc or plastic microballoon filler. Pigment may be added to approximate color of gelcoat to aid in "hiding" the color to the filler underneath the sprayed gelcoat layers. Step 5: Sand the area to original contour, using small amounts of additional filler to fill any low spots. The final step is to blend in the repair as much as possible by sanding, ending with 220 grit wet sanding. Step 6: Then wipe over the area with acetone or lacquer thinner, and mask off the surrounding the area with masking tape and/or Island Girl's Masking gel. "Back taping" (peeling back the edge of tape) can be used to provide a "soft edge to the sprayed gelcoat. Another way of making the repair less detectable is to mask to a "factory edge" where minor differences in gelcoat shade will not be noticed. Be especially careful to protect non-skid, upholstery and plastic windows where overspray damage can be serious (our Masking Gel is ideal for this). Uncured overspray or spills on delicate surfaces can be removed by ISLAND GIRL Pink, followed by water-rinsing. DO NOT USE ACETONE OR LACQUER THINNER THAT WILL DAMAGE THE UNDERLYING SURFACE. Step 7: Spray with color-matched, thinned gelcoat using the disposable sprayer, Remember pot life of catalyzed gelcoat is only about 15 min before it becomes a gel (rinse the gun immediately with acetone or lacquer thinner). Apply several coats. Unlike using paint (which would run) one coat of gelcoat can immediately follow the previous coat. Even if runs do occur they are easily sanded out at the end. Step 7A: For a really good undetectable repair, dilute some of the color-matched gelcoat with clear gelcoat and apply a thin coat ending outside the original repair area. This "blending" process can continue to essentially clear gelcoat if you are a perfectionist!. Although not absolutely necessary if surfacing resin was used to make up the gelcoat (it dries tack free), final application of a spray coating of PVA will gives a more shiny surface. If regular resin was used to make the gelcoat this spraying of at least 3 coats of PVA during final cure of the surface is absolutely necessary. Step 8: When the gelcoat has hardened sufficiently, remove the tape by pulling "backwards" on the tape, not straight up. Be especially careful if tape was used at the edge of a stripe. Not less than 24 hours later, lightly wet sand with 600 to 800 grit, then compound, polish and wax the area to make it undetectable. Repairing Abrasion Damage If abrasion damage is widespread, a complete paint job or (cheaper) re-gelcoating will be needed. However, localized abrasion caused by careless use of a buffer or rubbing of the hull against a piling can be repaired in a cost-effective way. The techniques used are similar to those described above for "stress cracks", except that "dremelling" is not necessary. The damaged surface is de-waxed and sanded as appropriate. Filler is only necessary for bringing up the level of the underlying laminate. If abrasion has damaged the laminate, then a laminating repair may have to be done first, using regular resin and mat (beyond the scope of this article). Otherwise follow the steps described above for repair of stress cracks. Repairing gelcoat adhesion damage (loss of pieces of gelcoat). The problem here is ascertaining the extent of the problem. Obviously if most of the gelcoat is not properly bonded to the underlying laminate, the only real cure is to remove all the gelcoat and resurface with new gelcoat or polyurethane. We will assume here that the problem is localized to those areas where gelcoat has fallen off in small pieces. The repair is done basically as described for stress cracks. Repair of alligatoring and crazing. Short of removing all the gelcoat and repainting or regelcoating, the easiest way to fix such damage is to de-wax and sand down to a reasonable level of smoothness. After masking, apply one to three coats of two-part (catalyzed) epoxy primer paint, with wet-sanding (220 grit) between coats. To further ensure adhesion, add some "fish eye eliminator" (ironically, a low viscosity silicone) to the paint. The excellent bonding and flexibility characteristics of the primer will fill in the cracks. After wet-sanding the final coat to suitable smoothness (400 grit), apply one to three coats of two part polyurethane such as Interlux by brush, roller or spray with sanding between coats, unless the finish is already smooth (but still soft) when a final coat can be applied without prior sanding. ADDENDUM: A BRIEF INTRODUCTION TO COLOR MATCHING OF GELCOAT About Colors As a guide to color mixing, you could use a sheet of paint chips from a hardware store for the nearest color to that of the area to be repaired. Then ask the store assistant to give you the tinting formula (if they will!). You can also buy a color wheel from an art shop. These range from about $3.00 for a simple one to as much as $15.00 with a detailed book and charts on color theory made by Grumbacher Inc (www.Grumbacher.com). In synopsis: there are three primary colors: red, blue and yellow and these can be used to make secondary colors (e.g. green= blue plus yellow; orange= red plus yellow; purple= blue plus red etc.). These secondary colors can then be mixed with each other and/or tinted with white or black to make tertiary colors. White and Black pigments are used to control shade (darker, add black; lighter, add white). Obvious examples are: black plus orange = brown; black plus red=maroon. Obviously white and black can also be used as stand-alone colors. A cold "arctic" or "snow" white is white with a tint of blue, off white or creams are white with a tint of yellow, orange or brown. Grey = black plus white; for bluish gray add a tint of blue You can buy ready made darkened or mixed colors, brown for instance. However, be aware that as the gelcoat is diluted its color may change since the relative contribution of the primary components may change (e.g.diluted brown may become pinkish because red is a stronger or more "intense" color). For some popular boats, you can buy gelcoat premixed to the original factory color but this may no longer be original due to fading of the gelcoat or even changes in materials used to make the gelcoat since an older boat was manufactured. Never the less, factory colors can be a useful starting point that is easily modified by small additions of other colored pigment. You may look at www.tapplastics.com for examples of the color pigments and dyes that they sell. How to do the actual color matching Color-matching is best done in daylight, preferably not in direct sunlight. An area of gelcoat adjacent to that being repaired is de-waxed, lightly wet sanded (600 grit, compounded and wiped with acetone or lacquer thinner to expose fresh gelcoat. Step 1: A reasonable amount of gelcoat (enough for total repair, plus some spare for future use) is made up to the approximate shade of the color to be matched. It should be a little lighter for light-colored hull gelcoat and a little darker for dark-colored hull gelcoat. As an initial guide on solid colors, no more than 6-8% pigment is added. For a Cream color, for instance, make up (or buy) white gelcoat. No catalyst is added at this stage. Thinned gelcoat is easier to match, since the pigments will mix more evenly and (as described for brown) a change in color may occur if thinned significantly after addition of the pigment. For this reason, if color-matched gelcoat paste is being custom prepared by the user add the Cab-O-Sil later, after color matching. This is not possible with the beginner's kits found at West Marine. Step 2 (example with light-colored gelcoat): You then dab a little of the gelcoat on the area of boat to be color-matched, using a cleaned (with acetone), thick rubber glove-protected finger. The color should be too light. Then dab on a tiny spot of colored pigment, smearing in such a way that a gradation in darkness of color intensity is produced. If you guessed correctly, at least one section of this gradation should approximate the underlying gelcoat color Step3: Transfer what you have learned to the larger batch of thinned gelcoat in the pot, adding the new pigment a tiny bit at a time with plenty of stirring. Repeat this process with the next tint that seems to be needed until the color is matched as closely as possible. AS A GENERAL RULE OF THUMB - ERR ON THE SIDE OF "LIGHTER" ON LIGHT COLORS AND PASTELS; "DARKER" ON DARK COLORS. THE HUMAN EYE SEEMS TO NOTICE THIS LESS THAN THE OTHER WAY AROUND!