How to Touch up a Gelcoat Scratch…And have it come out nice – by Patrick of ONNO

For a solid 10 years while developing my paddles and boats I supported myself by repairing high end sailboards, racing yachts and all kinds of paddle craft. Many times my shop looked like a tradeshow except the boats were not all glossed up. I have repaired lots of boats that were thought lost. From the loaded kayak that was bailed out of and womped against a rocky shoreline in 6-8 foot surf to the TWO fiberglass tandems that simultaneously pulled the rip cord, racks and all, off a van at 85 mph.

As most repair guys will tell you, it is most amusing to see the faces of those who sometimes think there’s nothing left but the cryin’. What they will NOT tell you is how easy it is to repair. The mystery behind the curtain is how they make their money. Below are some steps to follow if you decide to work on the boat yourself. Please know this is how many pros do it when time is money and discerning customers are looking to you to ‘ make it go away’.

If you do not make a mess you probably are doing it right.

A lot of this detail work can also be applied when touching up the the newer painted finishes on skis, kayaks and canoes as well … Or even your car.

Be patient, check your work, and use a lot of tape until you get a feel for things.

What you need: Most things can be purchased at Home Depot, a Marine store or an good Automotive parts store..
* Acetone for clean up. Maybe.
* Rubber gloves.
* Dust mask or better yet a respirator for the dust AND fumes.
* 3/4 inch masking tape, generic brand is fine, save your money for more important things …
*… Like sand paper. Imperial Production wet or dry sand paper from 3M is worth the extra cost in time/effort /boat saved.

320grit, 600grit and finally 1200 / 1500grit … 2000 if you can get it. These numbers would most likely be 280, 400, 1000 / 1200 if you can only find the generic brand.

These are the approximate equivalent of the superior 3M. I am already writing a book here but I need to say something about some of these ( non 3M ) sand papers lest other composite guys call me on it. Some of these papers have silicone in them and may cause bonding problems on subsequent repairs should you need to do something over. Just call me if you need a more elaborate explanation.

*POLISHING ! Not rubbing compound. As above please read label and avoid silicones if you can. Label should also say

“For removal of 1200 / 1500 grit scratches.” I use 3M FINESSE IT because it does a great job + washes out of non-skid and clothing,

* Buffer or anything that turns quickly with the aid of electricity and will accept a quality buff pad … People who do this for a living do not have time to waste on one of those wimpy, sloth buffers. Buy a quality buff pad at the same place you get the compound. I prefer the hairy POLISHING pads. Sheep kine ( coarser ) for gelcoat, Mink kine ( finer ) for paint. If you want work on more than your boat you may wish to get a foam pad as these work well and are safer to use on all the contours cars have.

P.S. You really do not NEED a buffer, a little elbow grease will also work with compound and a clean, cotton rag though not nearly as good. Three minutes hand buffing will not bring up the shine 3 seconds with the tool will.

* Utility razor blades … lots of uses.
* Flat file … maybe
* Flat 2″ x 3″ piece of something that bends a little bit. Do not go for the ‘3″x6″ ‘wetsand block ‘ next to the sandpaper on the store shelf … Too big for scratches. My favorite is .250” high density foam. I can even break off a corner for tiny spots. “Bends a little bit” = 1/8″ paneling, rubber truck bedliner, dumptruck mudflap, or a piece of cardboard matching the footprint of a block of hardwood. Or get the above rubber block and cut it down. The speed and control you get with the smaller size far surpass the potential for mistakes for using the full size block.

*Material. If you are lucky you have some of the original gelcoat that matches your boat perfectly. You may contact the manufacturer and request some, have the boat’s serial# at hand. I highly recommend doing this.

If you cannot get it, you can probably just match it up on one of only a couple gelocoat manufacturers charts. Valspar is a good place to start. If you care enough about your boat’s cosmetics to be repairing scratches you will NEVER be satisfied unless the color is at least close. Now that I think about it, a severely scratched boat would look good if the scratches were repaired in a complementary, contrasting color. While I am here I will say this. Most people I have ever talked to are overly worried about scratches. I always try to talk folks out of fixing them.. They really are not harming the boat. Each scratch is it’s own entity and a LOT more work than you think to fix it properly and if not properly, then why do it at all ?

Look at the bottom of your boat, which ones do you start with ? There are probably more than you thought. I honestly think a scratched / non-repaired boat looks far more attractive than a cobbed, patched up one. If you are getting ready to sell boat maybe polish it up, but that is really as far as you should go in my opinion.

Still ready to go ?
If you cannot get the proper gelcoat here are some options;
Use any color, try to use those generic pigment kits to match your boat (good luck and over use of these inhibit the complete curing of gelcoat), pay someone to match it, i.e. how much money do you have? … Buy a new paddle with this money instead, or use clear, slightly thickened polyester ( surfboard ) resin. I feel the latter is the easiest to work and live with.

I may raise some dust here but the clear polyester FINISHING resin you can buy at Home Depot or surf shop / possibly model shop but probably not at the marine ( laminating only and not pretty ) store dovetails right into the plan. It’s clear and will only slightly darken original color, no fussing with color and it cures fast and consistently. If you wish you may use straight resin to fill scratches. Gravity may want a say here and your answer to this is to tilt boat or use a bit of filler to thicken the resin. If you are really going for cosmetics, take your time and use straight resin.  Otherwise purchase the smallest amount of any kine filler. West Systems 406 is perfect.


* Soap and water boat. Dry.
* Identify scratches you wish to repair. If you really are going to do this, go for the ones that are through to glass first. Not necessarily because these need it but these are the deepest and will give you a taste of what’s to come and if you want to stop, at least you have solace in knowing you got the big ones done.
* If you have a Dremel tool or die grinder ever so slightly rough up the scratch starting at the middle and working towards the edges on either side of scratch, depending on the bit you are using ( I like the egg shaped ones ) you may be able to do this all on one neat pass. Just clean it up a bit. Use your judgment whether or not to go deeper when cleaning out chipped edges. This whole procedure can also be done using a small round file. I use (and in no way avocate you do the same) a razor blade held perpendicular to scratch in two hands dragged up and down.

P.S. I traded in the noisy, dusty die grinder and dremel for this.

* Contrary to everything you have or may read. DO NOT take this opportunity to wipe the area ‘clean’ with acetone … It is as clean and fresh as it can possibly be and to wipe it with acetone risks smearing surrounding area’s contaminates back into it or glazing ( my word ) the surface over. Blow it out or use a small clean brush.

* Once you have cleaned this up, tape along edge of repair leaving a tiny (1mm) gap next to cleaned out area. This allows for material lifting a bit when tape is pulled but not out of repair and leaves a bit of sacrificial material to aide when fairing things in later. Tape as continuous and flat a line as you can. If you are messy, use paper here to mask surrounding area.

From here on, resin and gelcoat get treated the same way.

* Set boat so resin will run as little as possible if you are using it neat. Use tape to make dams if you want but knowing this is just more sanding later. Mix up resin fairly ‘hot’ and work in small batches. Thicken to slightly thicker than Mayo, thinner than Peanut Butter. MIX IT WELL ! Use a fresh razor blade or cut down plastic applicator to trowel mixture into scratches, pushing a bit and going in two or more directions at first to get a good bond and to be sure the area is ‘wet out’. Hopefully your tape job is good. Do not go too far away from these as you will now use a clean blade set flat on your smooth tape job to drag excess mixture off and thereby cutting your sanding time down to almost nothing.

* Pull tape or not? I will always pull tape straight up unless mixture has started to cure. I do not recommend pulling tape if you are using resin straight. I do it but you have to babysit it and wait for the time where resin will not pull out of repair but edge excess will pull up with tape. You may have to do a second run with the straight resin … do this as soon as first batch of resin kicks in. Do not worry about sealing wax … Just keep going.

* Once tape is pulled and resin has started to cure I usually push my luck a bit and trim the high spots down with a razor blade held flat against contours of boat. Beware of pulling repair out or cutting too low and your fingers here.

* Whatever you, do please DO NOT fall for that ” place a piece of wax paper over repair ” thereby smearing your repair all over the boat and having to do it again piece of misinformation. The object is to have your repair be ever so slightly proud to which you blend it in with surrounding area without going too low. This ( wax paper, film negative, mylar, etc. ) procedure guarantees doing things multiple times especially if surface is convex. For small scratches, you really do not have to worry about top layer of gelcoat curing hard ( no need for special waxed gelcoat or additive ) as you most certainly have a fully cured layer just below the top of your repair and will buzz right through that top layer effortlessly. If you want. Purchase some PVA from your marine store/composite supplier with which to seal ( brush on ) top layer right after gelcoat has gotten to a rubbery state … Or spray it on once gelcoat has just started to kick in.

O.K, o.KAY ! : ) For the skeptics of above … Remember part of the title is. Have it come out nice. Guys, you can do, use and believe whatever you want when it comes to wax/paper … But sometime, just for fun, try it as above. I think you will see the savings.

*If I am really feeling lucky I endeavor to use the razor as a scraper and bring filled area down to almost perfect. Then I START wetsanding at my final grit once hardened. Try it and save time precious or ………………….. Walk away for a few hours / over night.

* You should have no more than playing card thickness to sand down … Narrow strips no less. Warning. The gelcoat is very thin on ( most ) kayaks/canoes. Paint can be thinner and less forgiving still. You really do not want to even touch ( too much ) the area surrounding repair until the last few strokes of 600 grit or higher. If you are not confident or just want to play it safe, put tape back down and start wet sanding and changing tape as it peels up. Now I hope you can see why that bigger block would be a hindrance. If you left tape in place (neat resin) keep going until you can peel the tape up. If you really had left a lot, the file or a coarser grit might save a bit of time and chew through the heavy stuff faster. Keep dipping the paper in water to keep a sharp ‘edge’ and check your work often by wiping and inspecting. Wetsand the entire repair a little at a time.

* If your repair was barely sticking up ( fingernail just catches ) you should be starting out with no coarser than 600 grit. 320 or a file if you are a pro and want to get home early. You DO NOT need to run through every grit available. This is a waste of time, energy and money + you end up taking too much original material off. So you can go from 320 to 1000 if you want, or 600 to 2000. Just check to see how your surface is coming. Sometimes it’s ‘safer’ to go to a higher grit right away, other times its faster to not skip the 600. Resist the desire to sand all around the edges of repair … Get the middle down a bit then work towards the edges and finally from the surrounding area into the repair using your smooth, held flat, piece of flotsam ( sanding pad ). If you start to see a dark color from below and feel you are getting thin around the edges,

I would stop, move right to 2000 and call it a day after that. Or switch to a finer grit earlier to be safe. In my experience you will not get as perfect a repair doing this as the finer grits do not take off much material (they tend to simply round things over) even when using a semi stiff pad … But what you have will at least end up shiny.

Speaking of shiny, do you really want to have a bunch of glossy spots on the bottom of your boat? If not, wetsand only to match surrounding area’s sheen and buff. Stopping at 600 or 800 for example. Or remove all the fittings, keep going with the 2000 and buff out the whole boat to have it look better than ever … Then sell it for something new : )

* Wash off all wetsanding sludge / pva. Dry. Install buff pad on machine. I like to put the compound on the boat first … Why load up the pad before you even touch the boat ? Use the chainsaw warm up throttling technique on the buffer trigger / speed so compound does not centrifugally vanish. Gradually increase speed as compound drys. You do not have to get every last bit off with buffer either. To do so or run dry too fast might risk getting the surface too hot ( especially paint )… It will wash off later. Satisfied ? Wax it … or not.

I could ramble on with subtle tricks of the trade. If you come to a point where you do not know what to do please feel free to ask.


Pat is the Owner of ONNO Paddles, click to visit his web site and contact Pat if you have any questions!


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