Sanding vs filling hull stratches

Thread starter #1
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.
 

Merrily

Administrator
#2
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.
 
Thread starter #4
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 ...
 
Thread starter #8
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 ?
 

49208

Tentmaker
#9
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.
 
Thread starter #10
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.
 
#11
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.
 
Thread starter #12
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.
 
#13
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.
 
#14
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)
 
#15
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.
 
Thread starter #16
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.
 

Merrily

Administrator
#18
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).
 

gouvernail

Active Member
#19
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!!!!!
 
#20
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
 
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