Tips with Fiberglass and Gelcoat repair methods By John Gabriel
Gelcoat Repair Tips and Methods To Avoid
1.  A key to successful fiberglass repairing is quality materials and patience.
2.  Make sure your boat hull or deck is not a painted surface, search around hidden areas for signs of primer or flaking.
3.  Try to remove minor gelcoat scratches by water sanding using a hard rubber block or hard piece of plastic with grits 220, 320, 600 or 800 then 1000 before a fill or spray.
4.  There is only a couple of after market gelcoat distributors in the United States and most boat manufactures and near all dealerships purchase from these companies. Only few Boat Manufactures will sell you direct, Purchasing gelcoat from after market distributors in most cases are a complete waste of funds as most colors are miles off in color and shade and cannot be fixed especially true colors as Red, Yellow, Orange, Greeen and so on, To save any Aggravation and waste of funds send a quarter size sample or bigger to Michigan Fiberglass Sales for a quality match from the start!
5.  Using gelcoat or polyester resin from any hardware store or boat accessories outlet may get you frustrated and give you a poor boat hull repair, gelcoats may be to transparent even after tinting leaving you the only option to apply too many coats just to cover and polyester resin may be to thick or stale for fiberglass repair.
6.  If using Dixie cups for mixing gelcoat, epoxy or resins be sure to use cups with no wax, any cup with wax coating will leave small shavings from stirring and disrupt your sprayer and your gelcoat mix. On very warm days some wax will melt leaving you with a good amount of food grade wax in your mixture. Wax additive for gelcoat is a combination of hydrocarbon solvents.
Fiberglass repair & laminating
7.  When fiberglass laminating be sure you have laminating resin not finish resin as finish resin has wax additive and must be sanded if top coated. Finish resin is rarely used in boat hull repairs or boat building.
8.  Stress cracks should always be dish ground and fiberglass laminated using 2 or 3 strips of biaxial cloth with matt sewed on the back. Grind deeper wider and apply multiple strips if repairing corner rounds followed by specified filler, the same procedure as repairing a deep gouge as shown in the instructional using at least a 3″ grinding disc. You may just grind the gelcoat off then a fill and fare but most likely the cracks will return quickly. Simply grinding a gelcoat stress crack using a dremel grinder then a fill even with epoxy will crack sooner than later. A professional should check stress cracks below a waterline.
9.  If filling gelcoat chips or voids deeper than 1/8 inch, finely chop fiberglass cloth and add it to activated fiberglass laminating resin for base filler saturating until white air bubbles are gone and then continue with your gelcoat repair.
10.  Repairing a crack thru fiberglass make sure to dish grind 5 to 6 inches each side of the crack, fiberglass laminate and repeat on backside for maximum strength. Be sure when grinding on backside to meet the new fiberglass in along the center removing all fractured glass.
11.  For fiberglass boat repair use 18 oz. cloth or larger up to a very heavy duty 24 oz. woven roving for the major repairs. Biaxial with 3/4 oz. matt sewed on the back is an ideal cloth for all types of laminate work and forms well around corners. If fiberglass laminating a large area, follow the same procedure as shown laminating a deep gouge in the instructional, all size damage is treated equal.
12.  If replacing a rotted deck core: Do not use the old fiberglass skin unless you do not care about voids, waves and surface cracks forming within the first few weeks. When removing the old skin, fractures form in the layers of fiberglass and the gelcoat will fracture throughout the surface that is invisible to the eye when removing, after the skins edges have been fiberglass laminated fared in and top coated, the final finish will only be a bridge over the fractures and all fractures will re-appear sooner than later, also you risk the possibility of voids beneath the skin when attaching to the new wood core. If using the old skin be sure to grind the entire surface to apply at least one heavy sheet of cloth to cover all hidden fiberglass fractures.
13.  When cutting floor sections to replace fuel tanks be sure to set your skill saw at a 45 degree angle for wood to set back in place without falling through avoiding hours of wood work for support.
14.  When repairing snap holes or any small drill holes, simply filling the hole with polyester filler, auto bondo or gelcoat filler paste will definitely crack around the edge sooner than later. Clean the hole using a drill then use a chamfering tool to slightly clean up any broken edge, then chop up fiberglass cloth very fine, saturate with polyester resin and stuff hole, when hardened dremel grind just the thickness of the existing gelcoat then continue with your gelcoat repairs.
15.  Epoxy will adhere to polyester but polyester will not adhere to epoxy.
16.  If repairing fiberglass damage on wave runners make sure to use epoxy resin with fiberglass cloth as polyester resins will not adhere to those types of composites.
17.  Using polyester resin for filler mixed with Cabosil, Aerosil or Cotton for mounting any structure even filling delamination in a deck can get very hot if thick and may warp fiberglass do to extreme heat.
18.  Gunk polyester filler is an ideal product for mounting stringers or anything that requires a thick filler, it only gets slightly warm even when inches thick and is activated by MEK Peroxide (hardener), add 1 or 2% water after activating to make thick, Gunk is an extremely tough product and can be found at Michigan Fiberglass Sales by following the links page on this site, Searay also uses this product on many models. Epoxy with slow hardener mixed with specified milled fibers is another alternative.
Spraying gelcoat
19.  When spraying gelcoat with a preval sprayer, strain your gelcoat after it has been reduced and activated using a paper disposable strainer then disregard the plastic strainer attached to the straw from the preval sprayer, this will give you a heavier and more consistent spray.
20.  For over-all gelcoat refinishing use the same mix and steps as shown in the instructional instead of a preval sprayer, apply using an automotive spray gun, (no special tip needed). Gelcoat has to be thinned the same for a suction feed or gravity feed spray gun although Using a gravity feed spray gun will leave more orange peel than necessary To apply using a suction feed spray gun will give you a smoother surface as gelcoat is more atomized throwing a finer spray yet releasing most solvents when spraying with around 60lb psi with in line water separator, keep your spray gun moving to avoid a wrinkle in the gelcoat over lapping each coat. The heavier the coat is applied the more micro pin holes will exist, using a suction feed spray gun will give you a better quality finish.
21.  Never spray gelcoat in direct sunlight during a hot day, the surface will skin too fast trapping solvents creating pin holes leaving a dull finish at job completion.
22.  Spraying gelcoat on the entire boat deck or hull be sure to prime first to cover all pin holes and repaired areas also to avoid blistering especially near the waterline, apply 4 coats at waterline and below, remember you will be sanding off at least a coat leaving you with 3 coats needed for a water barrier, 2 coats are fine for the rest of the vessel. Use Duratech vinylester primer some recommend polyester primer though it may be too brittle and eventually the primer may chalk beneath the sprayed gelcoat and chip or flake off easily. using auto primers for a gelcoat refinish is a bad idea, spray at least 5 coats of gelcoat when re-surfacing a complete boat deck or hull.
23.  For gelcoat spot repair be sure to sand far past the repaired area to be sprayed to make sure your gelcoat spray does not exceed over the unsanded surface, use the proper grit for sanding during the final prep.
24.  To avoid a wave or warped finish at job completion, never use tape around the area, it may only create a step as overspray build up exceeds onto the tape. Let your polisher remove any fine overspray that traveled onto the unsanded gelcoat if any, if using tape or masking paper stay clear of the area to be sprayed at least a couple feet.
25.  Spraying true colors, red, blue, green etc. and your color is a bit off give a bigger blend line and spray 3 coats of clear gelcoat over the base color and 1 to 2 ft each side of your color blend.
26.  Let your gelcoat cure for at least 48 hours before sanding that will give you a better blend after polishing as the blend line will be much harder and thinner without breaking away leaving a gelcoat repaired area invisible at all angles, using the proper gelcoat additives of course.
Matching gelcoat
27.  Matching gelcoat can be easy! Keeping this trick in mind. Place matching gelcoat in two categories, color value and shade value, blending the different pigments into your gelcoat to reach the same color as the boat. You want the gelcoat your mixing to become a little darker than the boat, this will give you a better visual on where you are with your color match. If the boat is more on the yellow side as your gelcoat looks more on the brown side then add a very small amount of yellow to bring closer to the boat color, once you obtain the colors to be some what in sync then use the shade value. Shade value is the color only lighter or darker , once you feel your color looks roughly close it’s time to make your gelcoat a couple of shades lighter by adding white gelcoat, a very small amount at a time until you obtain the correct shade value. You may use a very small amount of white pigment but using too much white pigment may give you a dingy transparent effect leaving you with a poor match.
28.  Use small strings of tint using a toothpick to add to your gelcoat one string at a time checking color before adding more tint, most off whites start out by using dark yellow or yellow gold followed by dark brown and light brown at times, then add a touch of black for the rich oyster colors. When adding dark tints such as brown, green or black do not use strings of tint as they are too powerful, add eye droplet size or less is best when mixing a pint or 1/2 pint, keep tinted gelcoat in a cool place.
29.  If tinting gelcoat avoid colors in tubes as this may only make you frustrated and could give you a very poor repair also leaving you with colored speckles in your finish. Color tubes have a short shelf life and are not the same pigment as professional tints, unless you just don’t care about the color.
30.  When matching true colors, red, blue, black and so on use Neutral gelcoat for base using clear gelcoat would be too transparent and should only be used for top coating. Clear gelcoat is most used with metal flake repairs.  If using Clear gelcoat for top coating or spraying over a solid color to blend perhaps a yellow apply moderately because clear gives slight yellow/green tint after activating, the thicker you spray the darker it gets, dark color like blue are fine.
31.  If matching with white gelcoat you may want to bring a chip sample to your local fiberglass supplier before purchasing white gelcoat to see if the white gelcoat is darker than the chip sample, if so search for a brighter white. It is very important to start with a high quality bright white, many white gelcoat products appear to be bright white but may have a light grey or pink cast to them making it difficult or impossible to get a good match as many are intended for mold work or tooling.
32.  Michigan Fiberglass Sales has the largest selection of gelcoat tints available and specializes in premium quality marine grade gelcoat unlike most suppliers claim.
Black gelcoat
33.  Black gelcoat is the most difficult to match for many reasons, the tints or gelcoat base used by the manufacturer is different than what you purchase and mixing gelcoat for a repair is different than the application in a boat mold.  Most boat manufacturers that use black geloat have a final result of black porous gelcoat with a hint of grey, very few manufacturers have a jet black finish with a high gloss. For chip or scratch repair filling the gelcoat damage only! is best to avoid gelcoat spraying as this will only create a large noticeable repair. Spraying the entire hull or panel is best for perfect blend and no color changes later down the road.
34.  To achieve a more jet black gelcoat ad 2% 99U Black Imron polyurethane paint to your black gelcoat. Imron is the only alternative product that works excellent for tinting gelcoat when used carefully.
35.  Ebony black from Chaperral purchasing through Spectrum color will do every black gelcoat repair you run across, because
the deep black richness of the pigment in this formula is so great, it's easy to add a little white to get a more grey effect if needed to get the exact match for a black that has a little fade.

Additives and thinning gelcoat
36.  If thinning gelcoat with Acetone, MEK solvent or other optional reducers use the least amount possible start out with 3 or 4% then see if gelcoat sprays without to much orange peel if so thin a little more and keep some distance with the sprayer so solvents get released on the way to the surface. Gelcoat may lose some shine sooner than normal when thinning with acetone. MEK solvent is best when using certain additives and is used for many plastic applications, MEK solvent has a slightly slower evaporation rate than acetone but will give you a better chemical bond to the gelcoat you are covering also a better shine therefore be careful not to over activate the gelcoat and allow a couple minutes between coats for most solvents to release.
37.  If thinning gelcoat with Styrene the following problems may occur: gelcoat to transparent, easy to run or sag even too porous leaving a dull finish. If using styrene wax additive must be added and should not be used for exterior gelcoat repairs unless you just don’t care about the final result.
38.  When using wax additive (surface wax) for gelcoat make sure it is in clear liquid form, if it appears to be crystallized or white in color warm it up with a heat gun and give it a shake and continue.
39.  During boat building gelcoat with wax additive is mostly used for bilges and interior trim panels or spraying the entire cockpit where gloss is not an issue, becoming a very dull finish when dry but looking excellent. Sometimes with addition of adding some patch booster for the extra heat giving a harder finish fast, leaving the top layer less tacky.
40.  Do not use parting fluid over gelcoat that has been mixed with styrene, wax additive or patch booster as the parting fluid would separate, dry and crinkle your gelcoat and leave an uncured layer. Also it would not allow solvents to be released till the end of the gel process leaving you with very porous gelcoat.
41.  f spraying gelcoat for nonskid using wax additive the surface will break down wiping with acetone on any given day and become very sticky until you have wiped off the uncured layer, once cleaned with acetone the nonskid sprayed will have a dull finish at completion.
42.  Using straight gelcoat or wax additive with gelcoat will not hold a shine very long, also on any giving day long after the repair you would be-able to wipe the repair using rags with acetone, break off the blend line of the sprayed area and bring gelcoat to a dull finish.
43.  Using patch booster in gelcoat will not break down wiping with acetone long after the repair but may heavily oxidize around 2 years.
44.  If using high gloss 15 to 20% is best, up to 50% can be used though exceeding that amount may darken the gelcoat later down the road especially in southern climates. Use up to 10% with clear or neutral gelcoat with dark colors only!. Using High Gloss with Yellow, Orange, Red, Blue, etc will become much darker in just a few weeks. Too much of any additive or reducer can do more harm than good also do not over activate your gelcoat as it will become very brittle
45.  Never add wax additive to clear gelcoat, this will cause your clear to become cloudy.
46.  Clear gelcoat will yellow much faster if reduced with high gloss additive, avoid high gloss when using clear gelcoat unless using for an overall re-finish or very dark colors and thin only 5% to cut down perosity.
47.  If using a filler paste for filling and faring fiberglass do not use auto bondo’s, bondo with fiberglass strands added or tooling aids as they may crack and gelcoat does not stick well to many of them, they just don’t last on boat repair.
48.  Simply by using polyester resin thickened with finely milled fibers (cabosil) to fill in an area may crack sooner than later no matter what the thickness as polyester resin expands with hot and cold weather and more so with cabosil, resin mixed with fillers has no tensile strength. Polyester resin should only be used for fiberglass laminating.
49.  When filling corners and small chips use acetate. Acetate is a clear flexible plastic, specify 30 thousands thick typically used for mold work as shaping filler: 1 yard may give you a hundred small spreaders. Use a straight edge razor blade and cut your pieces using a ruler for the guide, with a sharp clean edge on your spreader you will have a flawless filled area of any shape. Acetate used as a spreader is a very important part of gelcoat repair when using the correct fillers and gelcoat paste. The sharper your spreader is the less it will pull out of the area to be filled as you make your pass.
50.  Gelcoat paste is only good for a quick fill to somewhat hide the scratch that stands out, by just using gelcoat paste in a scratch or chip, the repaired area will be very noticeable unless the damage is small as the diameter of a toothpick. Gelcoat paste will shrink more than liquid gelcoat because the filler to make paste and will eventually crack around the repair due to excess shrinking and may have pin holes that will show up after polishing, also getting your repair 100% flat without a wave or ripple is nearly impossible and in most cases your paste will not match even with new boats. Using liquid gelcoat over paste is a much more effective route for the more professional out come if repairing small chips, voids or tiny scratches as shown in the instructional video.

51.  Paint tools from hardware stores work excellent for spreading filler over your fiberlass repairs (faring large areas) they have a sharp metal edge and very straight, your spreader should be at least a few inches longer on each side of the damage to be filled for fared.
Paint Filler Tool
Boat painting tips
52.  When spot repairing with most industrial paints using a spray gun always polish around the area where the edge of the paint will end up, the compound scratches serve as a light sand for the blend to adhere too and cleans the area to fresher paint giving you a premier spot repair without a dirty blend line, it may take more than one polish to eliminate the course blend line. 3M Super Duty compound 800 grit works best followed by Meguiars Diamond Cut compound in addition a swirl mark remover using a foam waffle pad to finish for the perfectionist.
53.  Spraying base coat clear coat systems with pearl or metallic colors and your repair has a halo or brighter in color at the blend, try a european blend, this works well with most base coats systems, it allows the pearls or metallics to all lay down equally rather than lay on end at the blend line. Also if your color is a bit off it may blend well, many base colors require a shade color first then the base color then the clear of choice (polyurethane or urethane clear), after sanding your primer with 320 then followed by 800 grit, polish around the area with 3M super duty compound to remove any primer over spray and get to good fresh clear and polishing with the 3M super duty compound will give the blend area a scratched surface for the clear to adhere too at the blend.
If spraying a shade value over the primer be sure the blend spray exceeds the sanded primer as this will avoid appearance of sand marks through the base color as base coat is extremely sensitive to sand scratches showing up after clear coated. One dust partical in your shade color prior to spraying base color can be very noticeable especially with lighter colors, if there is dust particles in your shade color let dry for 45 minutes and remove particles by water sand using a hard rubber block with 1000 or 1200 grit paper only, let dry for at least 1/2 to remove all moisture.
Spraying shade color first over primer let dry for at least 20 minutes before applying the european style blend. Using color blender Deltron 2000 DBC 500 mixed with DT reducer a 1 to 1 mix ratio (DT885 reducer works well) PPG products, spray one medium wet coat over the repaired area and outside the shade color then allow 20 minutes to tack up, when you stop with your spray gun after your sweep spraying approximately 12 inches bring your spray gun out and give it lighter coat to mist at the end to give the clear blender a long light blend line at least a couple feet if spraying a large spot repair. A blunt blend line with the clear blender will show as a shade darker beneath your clear coat top coat, therefore it is important to blend far with the clear blender. Spray your final base color, but do not get overspray with the final color outside the Deltron color blender as it may stand on end leaving you back to square one, cris cross your base coat on last sweep light to medium wet coats to avoid dropping the clear blender (sags) wait minimum 20 minutes before top coating with clear of choice. The Deltron color blender eliminates static and lays down the metallics or pearl into it’s sticky coating giving you a very nice blend, be sure to spray your top coat clear way out side the base coat blend line. Excellent for silvers, yellows and other brighter metallic colors.
54.  Spraying stripes, shear stripes, boot stripes or graphics using enamels or awlgrip spray a coat of clear along the fine line tape first prior to spraying color, this will give you very crisp lines as the clear will seep along the fine line tape also covering any flaws that may be in the tape, if using base coat clear coat do not try this with acrylic or urathane clear! use the DBC 500 instead.
55.  For your compressor use quality water traps to collect moisture from the tank and lines, if no dryer is available install one trap at the compressor and another around 10 to 15 ft from the compressor and another filter on your spray gun. The smallest amount of moisture gets mixed with your paint and will give you paint blisters as early as 2 weeks when spraying enamels or awlgrip, keep draining your compressor tank and make sure the surface to be painted has been 

Paint blister problems
56.  Paint Blisters
To avoid paint blisters that appear a week or more after painting make sure the fiberglass is bone dry at least 24 hrs before primer and paint, Cover with plastic sheeting at night to keep the doo off if needed.
Most importanly is your air source. The larger the air tank the more moisture builds inside under pressure, If you are not using a dryer go with a Gas Air Compressor, 11 CFM or more, 5.5 HP 8 or 10 Gallon Twin Tanks, these wheel barrel compressors create very little moisure and keep a steady air flow while industrial painting  for extra protection have a water separator around 15ft. from the compressor, continue your hose from there.
Rolling nonskid
57.  Rolling nonskid with polyurethane enamels – Imron or Alwgrip can be a disaster and I recommend spray only! It is nearly impossible to get a even job because nonskid compounds clump up in your mix and on your roller leaving a heavier grit pattern here and there especially where you start and stop with the roller. Much of the compound will float and when you put your roller into the paint a heavier amount will be stuck to one side of the roller leaving a heavier build up in one spot on the surface, or paint just becomes to heavy over whelming the nonskid. If you do attempt to roll the nonskid using paint follow these simple rules: Do not roll with surface temperatures above 78 degrees and or in direct sunlight. Most nonskid compounds call for 2 to 2 1/2 ounces of nonskid compound per full quart of paint, do not use more than one ounce per quart especially if using Awlgrip 2000 compound, this compound clumps and sticks to it self very fast and will not part no matter how much you continue to roll, the more you roll the more roller marks and clumps you create. Use a small amount of reducer to allow more work time, allow 45 minutes between coats, rolling one final coat without nonskid will resolve some roller marks and show less grit wear later down the road. A flattening compound in your paint may hide many problem areas.
Never attempt to roll gelcoat for any refinishing!
Using the products other than what they are intended for as described on this page will severely decrease the quality and visual appearance of your finish. These tips and methods have been proven by expert using older gelcoat formulas or new with a 100% success rate by Harrison Fiberglass Co. To avoid any complications by using any of the products as described, purchase Gelcoat repairs without a mess and use premier products not mentioned on this site and achieve first class gelcoat repairs to last the life of the vessel. Easy to use with no complications with the best techniques available today.
Fiberglass and Gelcoat repair information by John Gabriel