Fixing scratches on fiberglass

Is there some kind of buffing compound to get rid of surface scratches on fiberglass. Failing that, has anyone tried painting out scratches. Suggestions appreciated.


Fiberglass or Gel Coat?
The scratches are likely in the gel coat, not the fiberglass itself.

If this is the case, and depending on the depth of the scratches, you can use a series of dry and wet sand paper to buff out the scratches.

Start in the neighborhood of 150 to 400 grit dry sand paper, then work your way up to 600, 1000, 1500, 2000 and as fine as you want to go.

Beyond that, the surface finish becomes cosmetic and no longer functional. You could move on to buffing compounds, and it will all be for naught the next time you land on a sandy beach.

many people call a fiberglass boat …

– Last Updated: Oct-11-10 11:59 PM EST –

...... "fiberglass" ... when in reality the fiberglass (FG) itself is the woven cloth (or strand fibers) .

This woven fiberglass cloth (or strand fiber) is put in place (called lay-up or laminating) with a resin that is polymerized (chemically reacted) by another agent called the catalyst (commonly refered to as the resin (part A)and hardner (part B) , which are mixed together , applied to the FG cloth (called wetting out) , and the catalyzed resin begins to setup and becomes hard when cured ... the wetted cloth takes on whatever shape it is formed into (like a mold or plug) .

A common resin used w/FG cloth is a "polyester" resin . Others are "vinylester" resins , some are epoxies .

Most common for the exterior coating is a "polyester" resin gelcoat . The gelcoat is a higher grade of polyester resin (and usually color added) than the polyester resin used with the FG cloth lay-up . It is denser (harder) and more durable . Even harder than the general purpose gelcoat , is the tooling gelcoat used to make the forms (but the tooling gelcoat is not flexable enough for boat/canoe/kayak exterior or lay-up purposes .

So I'm assuming what you want to repair or polish out (as possible) are scratches in the polyester gelcoat .

Is it necessary?
I don’t have an answer to your question but just wanted to add to it … At what point are such “repairs” necessary? Is it just a cosmetic thing … like all the scratches on my car caused by my kayak? Or do the need to be repaired?

"Is it necessary " ???
No, but if I had a high end fiberglass or kevlar boat and it got a scratch on the deck or any place above the water line, I sure as heck would want to get it out and would do just what Dressmeister above describes

Why not take pride in what we paddle ?

Jack L

you can listen to this while doing the work…hehe

although gelcoat is cosmetic …

– Last Updated: Oct-12-10 10:53 AM EST –

...... it also is there to help prevent hydrolysis (and even has a structural factor) . Breaches deep enough into the gelcoat can lead to hydrolysis of the underlying laminate materials . (see hydrolysis of "Amide links")

I believe because of the greater density (specific weight) of the gelcoat it in itself is less sucseptable to hydrolysis , and also the reason why the thicker the gelcoat - the greater protection (and durability) .

When one sands down the gelcoat too much (as in tyring to sand out deep scratches) , it becomes a thinner layer (or too thin) , and hydrolysis protection is compromised as well . I would say the gelcoat layer on a canoe or kayak is nessasarily thinner to begin with to conserve weight as oppossed to a power boat . It would most likely be better to not thin it anymore , but rather fill as possibble w/new gelcoat .

It may as well be worthwhile to fill/fix severely scratched and compromised gelcoat hull bottoms , and even add another layer of protection against hydrolysis ... such as a 2k paint or even as some do , an epoxy coat .

The idea in basic is to prevent water from breaching the gelcoat , because it is the water H2O that is the reactor for hydrolysis (the breaking down of the chain link formed during the original polymerization - degradation-weakening-more sucseptable to fracture) .

In my experience/reading gelcoat doesn’t prevent hydrolysis. Hydrolysis and blistering occur because of unreacted solutes that remain in an imperfect laminate, and those create an osmotic gradient that draws water into the laminate. Where I’ve seen this happen, the gelcoat was perfectly intact, and not scratched or damaged.

Besides that, I don’t think hydrolysis and osmotic blistering is much of a concern in hulls that are only in the water a hundred hours a year, as opposed to yacht hulls which live in the water for months or years at a time.

All that is to say, unless you can see bare fiberglass laminate, gelcoat scratches are purely cosmetic. Polish them out according to your personal preferences and how you use your boat.

I occasionally buff out deck scratches, but hull scratches are just part of using a kayak, IMO, so I won’t worry about those. Best treatment for hull scratches is buying a white-hulled boat!

Good advice, but…
…you need to be very careful when sanding gelcoat on a kayak, as on most boats it’s very thin. I would start with 400 grit and only use something coarser if the scratches are really bad and I know the gelcoat is thick in the area to be repaired. That’s almost never the case on the deck of a kayak. I’ve never used more than 320 grit on a kayak deck and have only done that on badly sun-damaged Brit’ boats with thick gelcoat.

OTOH, repairing hulls often requires pretty aggressive sanding, at least of newly-applied gelcoat. Gelcoat is typically very thick along the keel line, but you can’t always count on that.

If you want to see the process, check out my "Gelcoat Repair and Restoration album at:

The deck restoration pics are on the second page.

I think that vinylester is now commoner
than polyester as a canoe or kayak building resin. It is not that much more expensive than a quality polyester, and is likely to be superior both in strength and in resistance to hydrolysis.

As for gelcoat, it is a good UV screen and a good ablation layer for abrasion, but it adds a lot of weight, and structurally it adds nothing.

I had a '73 Mad River fiberglass canoe
properly laid up, with white gelcoat. It used a high quality isopthalmic polyester, for the time.

It eventually developed hydrolysis blisters over most of its surface. The boat was exposed to southern humidity, but was not in the water much at all.

If that canoe had been made with vinylester resin, the hydrolysis would not have occured.

It really is about time to ditch polyester resin for making canoes and kayaks. It is just not good enough.

3M Marine Finesse-It II
My favorite for gel coat scratches is Finesse-it II. Though I pretty much only bother when I’m redoing the rigging on a boat.

I am of Nate’s opinion that the best address to hull scratches is a white hull.

Turtle Wax Color Cure
will fill in small scratches. I just used some on my green OT Katahdin, and it filled in about 80% of the scratches. Needs to go on thick, and it works for the small ones, if it’s available in your color.

Good luck!

Just to keep in mind
The buffing compounds, in fact anything that makes surface scratches in gel coat disappear, work by redistributing the paint in that area. I’ve seen aggressively buffed out boats that have changed to a lighter color over time with that stuff. So - you may want to consider using car protective plastic after doing the buffing to reduce repeat rounds, or just learn to love the scratches. As long as they are only in the gel coat it’s not like they are a risk to the boat.

Actually, deep scratches into my WW
boats’ outer layers of S-glass have had no practical effect whatsoever. But they’re easily filled and leveled if the mood strikes me. These boats have from 3 to 5 layers of S-glass and Kevlar or carbon, max.