Michigan Fiberglass
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Tips and repair 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 . 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.

5 . 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 and Laminating

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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 unvisible 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.

7. When repairing snap holes or any small drill holes, simply filling the hole with polyester filler, auto bondo or gelcoat filler paste will definatly 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.

8. Epoxy will adhere to polyester but polyester will not adhere to epoxy.

9. 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.

10. 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.

11. 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

1. 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.

2. 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.

3. 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.

4. 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 bearier, 2 coats are fine for the rest of the vessel. Use Duratech vinylester primer some reccomend 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.

5. 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.

6. 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.

7. 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.

8. 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.

Preval Sprayer
Matching Gelcoat

1. Matching gelcoat can be easy! Keeping this trick in mind. Place matching gelcoat in two catagories, 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 dingie transparent effect leaving you with a poor match.

2. 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.

3. 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.

4. 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.

5. 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.
Michigan Fiberglass can match any color Gelcoat.

Send us a chip sample of the desired color and are lab will come up with the exact match.

Additives and thinning gelcoat

1. If thinning gelcoat with Acetone, MEK solvent or other optional reducers use the least amont 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 therefore becarful not to over activate the gelcoat and allow a couple minutes between coats for most solvents to release.

2. 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.

3. 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.

4. 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.

5. Do not use parting fluid over gelcoat that has been mixed with styrene, wax additive or patch booster as the parting fluid would seperate, 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.

6. If 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.

7. Using straight gelcoat or wax additive with gelcoat will not hold a shine very long, also on any givin 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.

8. Using patch booster in gelcoat will not break down wiping with acetone long after the repair but may heavily oxidize around 2 years.

1. 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.

2. 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.

3. 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.

4. 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 noticable 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.

5. 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.
Material cost-Estimate per job type

Fiberglass and gelcoat repair can be very costly, charging between $75 and $110 per hour. A gouge or chip may take several hours to repair.

For fiberglass repair using the tool and material list inside the manual you can pickup everything you need with just a couple stops; your local Marine store and local fiberglass suppliers should carry all you need. Fiberglass suppliers on links page carries all the products you will need and ship fast to your door at a fraction of the cost compared to paying a professional.

Repair all types of damage
Hours of repairs from start to finish by a professional
keeping in mind a markup on material cost
Labor 15 to 17 hours
Material cost $110 to $130
Labor 9 to 10 hours
Materal cost $70
Labor 3 hours
Material cost $25
Labor 5 hours
Material cost $35

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