When to fill and when to sand

R

rogerbum

New member
Today I decided that I'd start working on taking out 5 or so years of scratches and scuffs and try to get the boat back in to new looking condition. So I have a few questions of the experts out there.

1) How thick is the gel coat? I have some scratches in the color stripe and I am wondering how much sanding I can do before I go through it.
2) In general, when should I fill a scratch and when should I just sand it out? This is somewhat related to question number 1.
3) I assume that it's OK to start out with some wet and dry of say 400-600 grit, move to 800 and then 1000 and finish with a rubbing compound and wax. Any other advice?
 
Roger,

Hurry up and get those brats to respond. I've got some sheer strake scratches courtesy of a tire bumper in the Broughtons (Lagoon Bay) where we spend a rough night on the side of a fish pen waiting for the wind to die down. I look forward to the advice as well.

Steve
 
IN the Hunkydory's travels it as aquired its fair share of scratches, nicks and scuffs too. Am also interested in the answers to Roger's questions.

Jay
 
I'll rush in where wiser souls fear to tread. My reply is based on what I know from major and minor repairs on plenty of fiberglass cars.

1)I don't know how thick the C-Dory gel coat is, pretty dern thick where I repaired a major blemish low in the bow, but it doesn't matter because...
2)If the scratch is through the gel coat to the underlying layer(s), sanding it out would require sanding the surrounding area down to that layer, so filling would be necessary anyway. The warning, usually even before you start, is a color change (sometimes slight) in the depth of the scratch. Start experimenting in an inconspicuous area for those that might be deep. Indeed if it's a really inconspicuous place, maybe just slap on something waterproof, not OK on a car.
3)For "surface" scratches, your sanding regimen sounds good, and paper of 2000 grit (sometimes finer) can be had at auto paint supply stores and some quickie parts places, saving some buffing.

Incidentally, mine came with a good-sized can of each color gel coat and I've seen in these pages where they are also available from the factory, assuring a very close match. Good luck. Enjoy your newly slick C-Dory.
 
Where's Dr. Bob when you need him?

Well, here is my 2 cents worth based upon other boats:

The depth of the gel coat varies between boats and often between different areas on the same boat.

As mentioned, color change is a good clue, say from a bright white to a cream white on some of my old boats, or from the cream colored gelcoat on a C-Dory to a more stark white internal layer.

Also, the roughness of the surface varies, somewhat like what you run into when sanding thru the fine outside plaster of a lath and plaster wall into the more coarse underlying support coat.

As mentioned, you need to bevel/feather the sanding whether trying to polish the blemish out or repair it properly with gelcoat. If you do happen to sand too deep, there is an underlayment base fiberglass you need to put in. i.e., if you sand into roving or support fiber areas, you cannot just put gelcoat directly in that.

West Marine Epoxy and other manufacturers have detailed instructions online for most fiberglass repair projects, as do some marine product sales companies.

I guess you'd have to decide whether you are repairing a "scratch" or a "gouge". Several fingernail thicknesses in some boats and you'll be thru the gelcoat, but that is not a problem if you have the repair gel coat.

Think of an auto paint job and the scratch/gouge determination there. I figure a scratch as deep as a healthy man's thumbnail is about as deep as you can hope to polish out safely. But, it is not difficult to place the proper gelcoat repair on a properly sanded out and primed "gouge".

John
 
I know this is an old thread but I have a scratch in the colored stripe of my Tomcat and I'm curious how it should be repaired.

I left the boat at a boat yard to get an estimate on some minor work. When I arrived the rear portion of my hull was without a fender and I immediately noticed a 2" scratch. It's not super deep but it does appear white.

Thanks for the suggestions.
 
Dr Bob was off enjoyng his boat in the PNW--like I would like to be doing all of the time!. 20 to 30 mills would be a very healthy Gel coat. Probably the average C Dory would be 15 to 20 mils and a bit more in some corners.

If I can remove the scratch with heavy duty rubbing compound, that is what is done. If it would require sanding, then I fill it. If you sand the gel coat it will always be thin in that area. The problem is matching the gel coat. All gel coats fade with time. You want to do a good compound job before doing a gel coat match-- The old gelcoat will be already faded, and new gel coat will fade some more.

After applying the "patch" of new gelcoat, you will probably sand it with very fine wet and dry on a block to bring it back to level. I prefer to start at 600 and work up to 1200--then to Finesse it by 3 M.
 
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