Sanding vs filling hull stratches

Levent

Member
This question may be too simple but I don't seem to find a good answer. How can you tell if a scratch should be filled with gel coat or only sanded out. Maybe I could ask the question this way instead: How deep can you sand ? I am working on my boat right now, I use wet #600 paper to remove superficial scratches but I have quite a few that are not deep enough to be filled with gel coat. I also noticed that when I sand a scratch on the top portion of the hull that is turquoise or (blue something) that creates a color mismatch, will that go away after a while ? I would really apreciate your feedbacks on this, my boat is a 2004 and in a couple of days it's going to be damn cold here.
 
I also noticed that when I sand a scratch on the top portion of the hull that is turquoise or (blue something) that creates a color mismatch, will that go away after a while ?

Is it a color mismatch, are a gloss difference? If it is less glossy, it will look different. If that is it, it should be cured with buffing with superfine sandpaper (I hear they make 1200) or buffing compound.
 
You're right, it's a gloss difference, my mistake. Is rubbing compound the next logical step or should I try to sand with a finer sandpaper ? Can I use car rubbing compound ?

Thanks Gouvernail, I red this article before, very interesting but I didn't find the answer there, they are talking about a major hull repair, I only repair the scratches one by one, I don't need to sand all the hull.

I suppose that you try to remove the scratch in sanding first, if not successful you then fix the gel coat, you don't want to sand too much though and that you determine more with common sense than in following some kind of rule ? I'm back to square one ...
 
I know that a lot of people repair their boat every year. The information I find is for major repair, is there any place where I can get info on standard minor repair ?
 
Re: Sanding vs filling hull scratches

You're right, it's a gloss difference, my mistake. Is rubbing compound the next logical step or should I try to sand with a finer sandpaper ? Can I use car rubbing compound ?

Thanks Gouvernail, I red this article before, very interesting but I didn't find the answer there, they are talking about a major hull repair, I only repair the scratches one by one, I don't need to sand all the hull.

I suppose that you try to remove the scratch in sanding first, if not successful you then fix the gel coat, you don't want to sand too much though and that you determine more with common sense than in following some kind of rule ? I'm back to square one ...

I believe the answer is indeed there (and fwiw, Gouv wrote that piece ie he is "they")

Re-read #3. If you can feel the scratch with your fingernail, it should be filled. Otherwise if you try to sand it out, you will end up creating "low spots" or an un-fair bottom.

Take your time filling the scratches - don't glob on the gelcoat as you want to do the least amount of sanding possible. (There are much more easily sanded fillers then gelcoat if you don't mind the filled scratches being more visible) Since you are only sanding the filler back to flush with the rest of the hull, you do not need to sand the complete hull when done -

Also take note of #10 - using the smallest possible sanding block (do not try to do this with just hand/fingers on the sandpaper - again, you will end up with an un-fair bottom). This will keep you from removing larger areas of perfectly good gelcoat around the scratched area.

Assuming the rest of the bottom is in good condition, you will only have to sand/polish your filled scratches and a small amount of area around them.
 
Thanks 49208, it looks like if you can feel it than you CAN NOT sand it because you'll create a low spot in other words it has to be really superficial. The remaining question is what kind of compound should I use, I assume that as long as the stuff is abrasive it will do the job.

I found some useful info in the Tillman as well, he mention to use a fine grain polishing compound.
 
Levent:
On http://schrothfiberglass.com/LaserMaint.htm He mentions using: buffing compound (Dupont 101, Acme 50, 3M Super Heavy Duty, or a similar grit).

I'm about to undertake a major hull job as well. My hull is horrible. It must have been used solely at a beach house and have been drug over the rocks and sand each time it was used. I'm really concerned about using gelcoat and having to sand for days.
 
Levent:
On http://schrothfiberglass.com/LaserMaint.htm He mentions using: buffing compound (Dupont 101, Acme 50, 3M Super Heavy Duty, or a similar grit).

I'm about to undertake a major hull job as well. My hull is horrible. It must have been used solely at a beach house and have been drug over the rocks and sand each time it was used. I'm really concerned about using gelcoat and having to sand for days.

Steve, the trick with the gel coat is to put as little as possible to avoid sanding too much, the key is there. The same principle applied to a lot of different jobs too, plastic wood, fiberglass, gyproc joints, etc.
 
I've made that mistake with epoxy before and have doubled my sanding workload.

My hull looks comparable to the writeup on this site, where the guy had the fire red hull that he sanded with 80 grit before using polishing compound. He wanted to sand out the scratches before filling them.

My hull is so scratched, I'm debating whether to sand it down first as well...it sounds like the best way is to gel coat and then sand, but with the current state the hull is in, it sure is tempting to hit it with some 220 grit or less.
 
Hi all... what I have done in the past with various dinks, dings and scratches in the gel-coat that are too deep to sand out (and to be fair I believe the less gel-coat you sand away at all the better it is- the gel-coat depth is there to protect your boat I reckon?) is to mix up my vela grey gel-coat, get a fine brush and paint in the gel-coat along the scratches...

After I have painted in the line (for a scratch) or a splodge (for a dink) of gelcoat (so it stands proud of the scratch/ dink) I then place sellotape (clear adhesive tape to the American Laser sailors here) along the scratch/ over the dink and run it as flat as I can with the back of my thumbnail.

I do this to flatten off the gelcoat fill of the scratch, once the gelcoat has set I then remove the tape and wet and dry the filled scratch line with fine and then very fine wet and dry glasspaper. The tape means you haven't got a big peak/ raised area of gel-coat to take back with the glass paper!

My top tip here (agreeing with a comment above) is use a block/ pad to wrap your glass paper around and sand. My tip is for these small sanding areas/ line of sanding is to wrap the glass-paper around a flat sided pencil eraser, I find this stops you sanding unevenly (deeper in places) and allows only the high spots (the line of higher gel-coat fill) to be sanded back evenly and flushly to the surrounding Gel-coat....

And one once you finished with fine wet and dry, I polish like crazy with 't' cut (cutting compound- says for gel-coat and fiberglass on the tube)
 
I fill them all!!!! But I also am very proficent at gelcoat repairs. To get the gloss back its all about how much you want to sand them. If you sand down to 1200 grit sandpaper you should not be able to distinguish the fill from the hull if you take your time and do a good job.
 
I fill them all!!!! But I also am very proficent at gelcoat repairs. To get the gloss back its all about how much you want to sand them. If you sand down to 1200 grit sandpaper you should not be able to distinguish the fill from the hull if you take your time and do a good job.

I haven't tried to go above 600 grit yet, I used rubbing compound to get the gloss back but I had to work hard. Do you use any compound ?

Also, I'd like to know what you use to apply the gelcoat, metal, plastic, re-usable tools or disposable.

There is a company who makes gelcoat ready to use, no mix, if anyone is interested I can find the link. The company also makes standard gelcoat with catalysis.
 
Isnt there something in the rules about not being allowed to fair the hull?

You can bring it back to its condition created at the factory, but not improve on it. For example, my boat has the slightest indentation in one spot. I can't legally fill that (and haven't).
 
It depends on whether it is a defect common to all Lasers or a defect specific to your boat. If your boat has a unique defect is is not a legal Laser..It doesn't matter whether it came from teh factory with that defect or not. If youir boat is dissilar to a set of ten other lasers, yours is illegal.

So...Merrily...Fix your boat!!!!!
 
I haven't tried to go above 600 grit yet, I used rubbing compound to get the gloss back but I had to work hard. Do you use any compound ?

Also, I'd like to know what you use to apply the gelcoat, metal, plastic, re-usable tools or disposable.

There is a company who makes gelcoat ready to use, no mix, if anyone is interested I can find the link. The company also makes standard gelcoat with catalysis.


I use polybrushes to dab the gelcoat on the scratch, then once it has dried I file it to hull height and then wetsand to a smooth finish. Usually on my race hulls I'll go up to 1000 grit and only to 600 on by bang around boats.

As far as compound is concerned, I use 3M marine compound. It does a nice job and is relatively inexpensive. It's important not to use a compound with wax because the wax residue left on the hull will cause small turbulance as water runs over it. You never know... that 1/10,000 of a second could be a big deal!!!!:D:D:D
 
Polybrushes are great because they're less expensive. Should dab the gelcoat over the scratches and always make sure that there is a little more than you need. This way when the filing is done there is a smaller percentage of having to re-apply gelcoat and repeat the process over again.

The more heavy duty the compound the more stuff it will take out and the better shine it will give. Super heavy duty is great for taking out the black scuff marks when you get too close to a dock with rubber bumpers in pre-start maneuvering. Gel gloss? I dont know much about that. I've never used it and it has always come out fine. The stuff you found online should do the job very well. I use a different one.... http://multimedia.3m.com/mws/mediawebserver?66666UuZjcFSLXTtOxfVOXz6EV76EbHSHVs6EVs6E666666-- I think any of them will work well.
 
I have poly brushes at home I never use so there is no reason not to give it a try. The link you posted doesn't seem to work, can you check ? thanks again for the useful information.
 
No prob. Hope it works out well for you. I'll see what i can do about getting that link to work.
 
I started applying gelcoat to my hull today. I have a ton of scratches...my hull 21XXX, must have lived on a rocky beach for a few years.

Real Quick: I tried the clear tape on top of the gelcoat and I also tried putting masking tape around the scratch to avoid overspill (less gelcoat to sand afterward). And against all reason, I tried just smearing the gelcoat on the very scratched hull, which actually appeared to work well, however tomorrow I may be hating life.

I'll post my progress and I'm taking pictures along the way. Expect a full write up in a day or two.
 
I start by 'scraping' a very thin coat of gel-coat over all scratches, using a plastic putty knife. Try to leave only gel coat in the scratches, and as little as possible on the surrounding areas. It takes a little bit to get the feel so that you don't drag it our of the cavities, but eventually you will get it to work. To get a nice finish, stop by an auto-body supplies shop; they have up to 2500 grit sandpaper.
 
There are a slew of high speed cutters that work ( http://www.hobbyplace.com/tools/drebits.php/0 ) - from the ball shaped, to the tapered head ones. I have used the ball shaped metal ones, only because that's all that's usually left after my son has been working on a project - a good old can opener will also do the trick.
 
Thanks, I have ball cutters already but I'm wondering if the round shape is appropriate since they always mention to V shape the groove.
 
You don't need to over-think this. I tried a bunch of techniques for scraping out scratches. It comes down to what works well for you.

I couldn't keep the dremel within the scratch and ended up making extra gouges with it.

What ended up working best for me was using one of the points of an old pair of steel scissors.

The more material you remove, the more you have to fill, and the more you have to sand.
 
Bjmoose I think your'e right ! I rarely use my Dremel, I prefer manual tools. I often use an Exacto knife I keep dull on purpose for that kind of job (an a lot of others as well that demand any type of scraping)
 
I use a bottle opener for widening plaster cracks, the kind that my family has always called a 'church key'... it's the kind that has the triangular end and the oval end... you know, the one you use to put the triangular holes in a big can of hi-C (back in the day).
 
A church key ? that's funny

I found that it has to be very sharp to work well.
 

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A church key ? that's funny

Yup, we called it a church key, too.

Seems like the corner of any scraper would do the job of making a V-shaped groove on the cracks. I've used an old slotted screwdriver on an angle to widen drywall cracks. Ought to work on gelcoat too.
 
Dredies - Yes, I did just that. I scraped the gelcoat over the scratches and kept it very thin...it worked pretty well.

A couple things I noticed were how the gelcoat shrinks as it dries. Deeper scratches may require more than one coat of gelcoat.

Also, it's important to test your gelcoat mix, so that it hardens appropriately. I didn't do this and todays application didn't harden completely, so now I'm entering day 3 of my bottom job and I haven't started sanding yet...haha...
 

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