Sanding a mile of scratches

bjmoose

Member
So in the off season, I'm trying to bring my faded, scratched up 75 laser back to it's firey bright "70's Orange-Red" glory. I pulled off my old vinyl CF numbers and a harbor sticker from 1978 to get a view of the original color. 70's retro is in, right?

Naturally, I started with Gouvernail's "How to make your bottom pretty" article at http://schrothfiberglass.com/LaserMaint.htm#How To Make Your Bottom Pretty

Now, the Gouv talks about "Every scratch that you can feel will need to be filled." Uh, riiiiggggght.

You've gotta understand that I've got a boat that sometime in a former life clearly needed to be dragged over a beach every time it went sailing. My best guess is that if I laid out all the scratches end to end, I'd have somewhere between 1000 and 5000 linear feet of scratches -- and this on a 14' boat. (I'll try and put up some before/after pix)

So I've got a brand new 5" random-orbit sander dedicated for the job. I started in on the 320, just to see how it would go.

Maybe we need some 220.

Maybe we need some 120.

Maybe I should jump to the 80.

OK, so I'm sanding the thing out with the 80 grit, and I'm starting to reduce the number of scratches to something I can possibly imagine maybe trying to fill. I've done maybe half the boat in a couple hours. But I'm burning through lots of 80 grit discs, and lots of fairly superficial scratches remain. And that late-fall sun is heading for the horizon.

Hmmmm. ...still lots of gelcoat depth left.

I've got a couple sheets of 40 grit lying around. Maybe I'll try a small area, just to see.

Maybe it'll work.

Maybe I'll grind straight through to the glass and make even more work for myself.

But I tried it out, and yep, for this particular boat that's gonna be the ticket.

Now, my laser was built in 75, and it's possible the builder was using a thicker gelcoat layup back then than they do now. I can see how thick the gelcoat is by examining a couple of chips that go right down to the glass, and it's clearly a LOT deeper than the gelcoat on the deck.

So starting next weekend, I'm going to flip it over again, and go to town with the 40 grit. I figure I need to take about half the gelcoat down in order to have a prayer of getting a decent looking finish. After I'm done, I'm hoping there will be less than 100 linear feet of real and serious scratches to fill. Maybe a lot less.

Yeah, I know; Fred says fill first, then sand. I figure I need to do my major sanding first just to find the scratches worthy of being filled in. Then I'll touch up the filled scratches.

To be continued...
 
Re: Sanding

Holy jesus.

Post some pics. Sounds horrific. LOL

If a R/O sander and P40 is required, the hull must have looked like a mountain range.

I feel all ill.


(gelcoat weighs a ton. swweep up the stuff you sand off and weigh it.)
 
Re: Sanding

Maybe If I back off a little??
Certainly you should fill and gouges where you can see laminate through teh gelcoat.

If you fill the deeper scratches you reduce the odds of sanding through.

Last week we sanded the sides of a 1972 South Coast 21. We blew through about 25 6 inch 60 grit self stick 3M gold discs.

About the 40 grit...I would try sanding a small area with 80 grit.( 3M Gold, 3M Green Corps or Norton Blue Magnum will stay sharp a lot poonger and actually pay for higher purchase price) Time teh sanding and see if you can stand to take that long. 40 grit is mighty agressive and you may force yourself into a total refinish...which is sooooo much work.

Good luck. The last Laser bottom I refinished is in my yard waiting for me to refinish the deck. I started sanding the bottom sometime in 1993.
 
Re: Sanding

Maybe If I back off a little??
... The last Laser bottom I refinished is in my yard waiting for me to refinish the deck. I started sanding the bottom sometime in 1993.

Guffaw.:D

Anyhow, thanks for leaving that article posted on your website. It's a great help.
 
Re: Sanding

I just got off the phone with McMaster-Carr, my favorite industrial/shop supply house. Plug -- if it's a tool, they DO have it, and you'll be able to find it on their website. Price isn't always the most competitive, however.

Anyhow, the finest 5" hook-loop 8-hole sanding discs available seem to be 60 grit, not 40 grit. So I've stocked up with 25 discs of 60 (plus the full course from there on down to 1500) and I'll take over with that.

At the end, I'm going to have to assess just how much was spent just on sandpaper. :eek:
 
Hi Steven,

I'd fill first. Bondo with some red/yellow coloring comes out pinkish, but it helps. Fred may suggest other fillers, even gelcoat. Then do all that sanding. I use a steel taping knife to push/scrape the bondo, so little extra is left on. It helps when there are too many to count. The bondo(polyester) will shrink, so two coats are better. And it's not waterproof so dry sailed only. I gelcoat scratches when they are countable, thus cleanable.

The time you save can go into bomb=proofing that mast step, thru-hull fitting, Hull/deck joint, etc. etc.

Al
 
Hey, who changed my topic tagline?

Well, Mr. Moose, there aren't a lot of choices on that one. ;) I did it. There's a standing Bradley directive to make unique titles to the threads, in order to make it easy to find them with the Search feature.

A mile of scratches is an exaggeration, of course, but if you've got a possible 5000 linear feet of scratches, you are not far off.
 
I have a question. A friend of mine has a blue hull (blue sides - grey bottom and deck) boat mid-1980s vintage. Lots of scratches - same situation as you. However, it appears that most have gone into the gelcoat such that they are light blue. I assume that this means that each scratch must be filled individually with a matched color. Is this correct? Would it be better to just repaint the whole hull with gelcoat? Is that possible?
 
My internet connection has been completely hosed for about two weeks now; I've taken 30 or so photos I want to post, showing differences between scratches I filled and scratches I'm just sanding out.

To answer the last question, it sounds as if you're saying there are two layers of gelcoat, with different colors placed one over the other. I find that hard to believe and suspect that the scratches are just oxidized differently, and that is what's causing the color difference you see. But I've been wrong before, and I plan to be wrong again in the near future. ;)

I found that filling the scratches was pretty much a pain.

After sanding the entire boat with 60 grit, there were three classes of scratches:

1. Those that were already gone
2. Those that were deep enough that they needed to be filled
3. Those that were still there, but shallow enough that a little more sanding will take them out completely.

Sometimes, deciding the difference between 2 and 3 takes a judgement call. I made multiple passes around the boat with a pencil, marking the ones I decided to fill, and filled scratches in two separate passes.

Scratches need to be deepened and roughened for filling. I tried using a nail, two different kinds of X-acto knives, a dremel, and an old pair of scissors.

The dremel removed more stuff than I wanted, and I had trouble keeping it IN the scratch. The fatter X-acto knife worked better than the thin one. The tool I liked best was the old pair of scissors. Thick, sturdy, easy to hold onto, dug in to about the right depth, and stayed in the scratch I was following.
 
Finished!

From 10 feet away, it looks great.

One of these days I'll post the photos. But there are a couple key lessons:

1. 60 grit is too coarse. By the end of the job, I was visibly thinning the gelcoat and had worn through a couple of small "high spots" (such as at the mast step.) There wasn't enough gelcoat left for me to sand out all the sanding marks left from the 60 grit. So my "finished" hull still has thousands of tiny 60 grit sanding swirls. Waxing hid the more superficial ones. You MIGHT be able to successfully use 80, as there's a fair difference between 80 and 60. But I'd consider going coarser than 100 only with great reluctance. But that WILL make the job take longer -- and it already took the better part of three days.

2. Most of the improvement in appearance came from simply using rubbing compound. I'd say I got 80% of the improvement from the last 20% of the work -- which was the change from the heavily faded and oxidized hull back to a bright color. Obviously rubbing compound won't remove any but the most superficial of scratches, though.

For someone considering refinishing a hull I'd suggest rubbing out the hull FIRST. If you're happy with the result, great! If not, you're now in a position to contemplate -- are you willing to spend 5x more work than you've already invested, getting to the next phase?
 
Photos, as promised. Before:
 

Attachments

  • 02_PreSand (Small).jpg
    02_PreSand (Small).jpg
    43 KB · Views: 81
  • 01_PreSand (Small).jpg
    01_PreSand (Small).jpg
    41.9 KB · Views: 98
After attacking sanding with 80 grit, and the right tool for the job:
 

Attachments

  • 03_PostSand80 (Small).jpg
    03_PostSand80 (Small).jpg
    32 KB · Views: 76
  • 04_PostSand80 (Small).jpg
    04_PostSand80 (Small).jpg
    28.5 KB · Views: 72
  • 05_TheToolForTheJob (Small).jpg
    05_TheToolForTheJob (Small).jpg
    61 KB · Views: 62
After pre-sanding with 60 grit:
 

Attachments

  • 06_PostSand60-1 (Small).jpg
    06_PostSand60-1 (Small).jpg
    37 KB · Views: 73
  • 07_PostSandBowScratches (Small).jpg
    07_PostSandBowScratches (Small).jpg
    42.6 KB · Views: 69
  • 07_PostSandMastStep (Small).jpg
    07_PostSandMastStep (Small).jpg
    46.8 KB · Views: 72
Techniques for scratch and ding prep -- xacto, dremel, scissors. The scissors worked best.
 

Attachments

  • 08_ScratchPrepWithNail (Small).jpg
    08_ScratchPrepWithNail (Small).jpg
    34 KB · Views: 55
  • 09_DingPrepWithDremel (Small).jpg
    09_DingPrepWithDremel (Small).jpg
    44.3 KB · Views: 55
  • 10_ScratchPrepWithXacto (Small).jpg
    10_ScratchPrepWithXacto (Small).jpg
    37.3 KB · Views: 61
  • 11.1_ScratchPrepWithScissors (Small).jpg
    11.1_ScratchPrepWithScissors (Small).jpg
    46.4 KB · Views: 70
Ready for ding fill:
 

Attachments

  • 14_ScratchGroundOutWithDremel (Small).jpg
    14_ScratchGroundOutWithDremel (Small).jpg
    50.4 KB · Views: 52
  • 13_GroundOutMoreCracks (Small).jpg
    13_GroundOutMoreCracks (Small).jpg
    54.9 KB · Views: 57
  • 12_GroundOutGelcoatCracks (Small).jpg
    12_GroundOutGelcoatCracks (Small).jpg
    54.1 KB · Views: 56
  • 11_GroundOutOld5200Repair (Small).jpg
    11_GroundOutOld5200Repair (Small).jpg
    56.9 KB · Views: 66
The boat used to be transported on the world's worst trailer. Two dents were created in the hull from the small contact points, which were probably rollers for an aluminum row boat or something. Here, I've made a shallow fill for the dents with bondo, and filled the holes around the trunk with bondo as well.
 

Attachments

  • 15_TrailerDentsBondoFill (Small).jpg
    15_TrailerDentsBondoFill (Small).jpg
    43.8 KB · Views: 63
  • 16.0_TrunkHolesBondoFill (Small).jpg
    16.0_TrunkHolesBondoFill (Small).jpg
    35.9 KB · Views: 59
Time for gelcoat color match, add color, try it out, repeat.
 

Attachments

  • 16.1_MixingGelcoat1 (Small).jpg
    16.1_MixingGelcoat1 (Small).jpg
    41.7 KB · Views: 60
  • 16.2_MixingGelcoat2 (Small).jpg
    16.2_MixingGelcoat2 (Small).jpg
    46.7 KB · Views: 57
  • 16.3_TestingColorMatch (Small).jpg
    16.3_TestingColorMatch (Small).jpg
    50.9 KB · Views: 64
  • 16.4_AddingMoreYellow (Small).jpg
    16.4_AddingMoreYellow (Small).jpg
    39 KB · Views: 45
Before sanding out, the color match looks good...
 

Attachments

  • 17_GelCoatOverBondo (Small).jpg
    17_GelCoatOverBondo (Small).jpg
    48.2 KB · Views: 60
  • 19_CenterboardTrunkGelcoat (Small).jpg
    19_CenterboardTrunkGelcoat (Small).jpg
    36.7 KB · Views: 60
  • 20_MastStepGelcoat (Small).jpg
    20_MastStepGelcoat (Small).jpg
    37.2 KB · Views: 65
Gelcoat doesn't cure in air. You must cover it. At first I tried spraying on mold release agent.

But it was a lot easier and came out a lot better to cover the gelcoat repairs with wax paper held in place with painter's tape.
 

Attachments

  • 22_FirstTryWithWaxPaper (Small).jpg
    22_FirstTryWithWaxPaper (Small).jpg
    56.1 KB · Views: 59
  • 23_WaxPaperCloseup (Small).jpg
    23_WaxPaperCloseup (Small).jpg
    43.7 KB · Views: 58
Filling a scratch:
 

Attachments

  • 28_DenseScratchRepair (Small).jpg
    28_DenseScratchRepair (Small).jpg
    46.2 KB · Views: 70
  • 29_DenseScratchRepair (Small).jpg
    29_DenseScratchRepair (Small).jpg
    41.1 KB · Views: 58
Here's what the first round of fills looked like after removing the wax paper:
 

Attachments

  • 33_TransomCorner (Small).jpg
    33_TransomCorner (Small).jpg
    36.2 KB · Views: 50
  • 34_DingRepairCover (Small).jpg
    34_DingRepairCover (Small).jpg
    42 KB · Views: 52
  • 31_ThisFillsALittleRough (Small).jpg
    31_ThisFillsALittleRough (Small).jpg
    39.3 KB · Views: 63
  • 32_IncompleteRepair (Small).jpg
    32_IncompleteRepair (Small).jpg
    43.3 KB · Views: 59
  • 30_RemoveFirstCoverPaper (Small).jpg
    30_RemoveFirstCoverPaper (Small).jpg
    47 KB · Views: 52
Here's the technique for covering a scratch or filled area with paper.

The first covers of the trailer dents with the mold release agent came out very poorly -- by the time they were sanded flush/flat/smooth the gelcoat was pretty much gone. So I reapplied those areas, as well as many more scratches in the second pass
 

Attachments

  • 35_SqueegingAirOutofWaxPaperCover (Small).jpg
    35_SqueegingAirOutofWaxPaperCover (Small).jpg
    43.8 KB · Views: 51
  • 36_SqueegingAir2 (Small).jpg
    36_SqueegingAir2 (Small).jpg
    43.1 KB · Views: 50
Here's the result of sanding out a gelcoat scratch fill. In the second pic, I've wiped away the dust with acetone. It looks pretty good though you can see the color match isn't perfect. At this point I'm pretty happy with my work...
 

Attachments

  • 37_ScratchRepairSanded60grit (Small).jpg
    37_ScratchRepairSanded60grit (Small).jpg
    31.1 KB · Views: 62
  • 38_RoughScratchRepairRubbedOutForColor (Small).jpg
    38_RoughScratchRepairRubbedOutForColor (Small).jpg
    35.3 KB · Views: 67
Wax papering the boat after the second round of scratch filling. You can see I had to do a lot of work in the bow area.
 

Attachments

  • 39_SecondRoundOfRepairsCoveredUp (Small).jpg
    39_SecondRoundOfRepairsCoveredUp (Small).jpg
    45.1 KB · Views: 45
  • 40_BowScratchCoverUpCloseup (Small).jpg
    40_BowScratchCoverUpCloseup (Small).jpg
    34.3 KB · Views: 48
Now I've sanded down the whole boat again with 60 grit, to smooth all the gelcoat repairs and sand out all the scratches that I didn't fill. That made the work go reasonably fast (still took hours) but using 60 grit for this second sanding will turn out to have been a mistake...
 

Attachments

  • 42_After2nd60GritSanding (Small).jpg
    42_After2nd60GritSanding (Small).jpg
    36.1 KB · Views: 33
  • 44_After2nd60GritSanding (Small).jpg
    44_After2nd60GritSanding (Small).jpg
    34.7 KB · Views: 37
  • 43_After2nd60GritSanding (Small).jpg
    43_After2nd60GritSanding (Small).jpg
    40.1 KB · Views: 42
  • 41_After2nd60GritSanding (Small).jpg
    41_After2nd60GritSanding (Small).jpg
    40.4 KB · Views: 47
Now I've wiped down the boat with acetone. You can see in some areas the gelgoat's gone thin on me. Actually, at the mast step I've sanded right through it.
 

Attachments

  • 45_WipedDown (Small).jpg
    45_WipedDown (Small).jpg
    29.4 KB · Views: 55
  • 46_WipedDown (Small).jpg
    46_WipedDown (Small).jpg
    28.9 KB · Views: 51
In this pic, I've started the next finer course of sandpaper, 100, etc... But I now can't afford to remove enough gelcoat to take out the sanding swirls left by the 60 grit sandpaper:
 

Attachments

  • 47_UhOh (Small).jpg
    47_UhOh (Small).jpg
    30.2 KB · Views: 37
  • 48_UhOh (Small).jpg
    48_UhOh (Small).jpg
    27.9 KB · Views: 54
Cutting my losses, I resumed sanding with either 240 or 320, then sanded through 800 and stopped. No point ing going on to 1200 as we can't get to perfect anyway.
 

Attachments

  • 52_Transom (Small).jpg
    52_Transom (Small).jpg
    44.7 KB · Views: 39
  • 50_FinerPaper (Small).jpg
    50_FinerPaper (Small).jpg
    37.7 KB · Views: 38
  • 49_WipedDown (Small).jpg
    49_WipedDown (Small).jpg
    44.4 KB · Views: 44
  • 51_TrailerDentRepair (Small).jpg
    51_TrailerDentRepair (Small).jpg
    40.9 KB · Views: 46
Time to go the rubbing compound. These photos show various repairs after they've been rubbed out. In two photos you can really see the swirls.
 

Attachments

  • 59_PortTrailerFill (Small).jpg
    59_PortTrailerFill (Small).jpg
    22.4 KB · Views: 35
  • 58_StbTrailerFill (Small).jpg
    58_StbTrailerFill (Small).jpg
    29.1 KB · Views: 36
  • 57_DamnSwirls (Small).jpg
    57_DamnSwirls (Small).jpg
    32.2 KB · Views: 40
  • 56_AFilledScratch (Small).jpg
    56_AFilledScratch (Small).jpg
    28.7 KB · Views: 44
  • 55_RubbedOut (Small).jpg
    55_RubbedOut (Small).jpg
    49.3 KB · Views: 52
  • 54_RubbedOut (Small).jpg
    54_RubbedOut (Small).jpg
    45.9 KB · Views: 51
  • 53_SandingsDone (Small).jpg
    53_SandingsDone (Small).jpg
    75.1 KB · Views: 44
The trunk, and more fill details. Damn swirls.
 

Attachments

  • 60_Trunk (Small).jpg
    60_Trunk (Small).jpg
    30.4 KB · Views: 49
  • 61_DeepFilledScratches (Small).jpg
    61_DeepFilledScratches (Small).jpg
    30.4 KB · Views: 46
  • 62_MoreFilledScratches (Small).jpg
    62_MoreFilledScratches (Small).jpg
    29.7 KB · Views: 38
  • 63_DamnSwirls (Small).jpg
    63_DamnSwirls (Small).jpg
    24.4 KB · Views: 40
Nice and shiney after two coats of wax. Yes I used a good auto wax. Let's save the whole "slow-surface-tension-inducing-wax vs. high-speed-non-beading-teflon-boat-speed-polish" for another thread, OK?
 

Attachments

  • 64_Waxed (Small).jpg
    64_Waxed (Small).jpg
    57.5 KB · Views: 91
A couple pix of deck repairs. When going for an "off white" repair, take care not to add too much color, as it's hard to "go back." I ended up with a little too much yellow.

My deck sequence was:

1. Clean. I used marykate on-and-off which is slightly too caustic to be used as a drain-clog-remover ;-)

http://www.westmarine.com/webapp/wcs/stores/servlet/producte/10001/-1/10001/264455/377%20710/0/marykate/Primary%20Search/mode%20matchallpartial/0/0?N=377%20710&Ne=0&Ntt=marykate&Ntk=Primary%20Search&Ntx=mode%20matchallpartial&Nao=0&Ns=0&keyword=marykate&isLTokenURL=true&storeNum=33&subdeptNum=299&classNum=299

2. Remove tree-sap polka-dots. Drops of tree sap fell at some point and resisted all forms of chemical removal. I finally removed them with a tiny wire brush mounted in a dremel. I could do this on smooth gelcoat without marring it, but on the non-skid a few tiny scratches remained -- still not as bad as the original tree-sap-nodules.

3. Fill. I had lots of fair size nicks and gouges, especially at the "tie down" points; for a while the boat was tied to the trailer with a fairly thin line. This ended up being a place where chips formed. Also, the docks at shoreline lake have pads that are too high to strike the laser gunwales. It turns out to be a LOT easier to use gel-coat PASTE, as it will stay in place on a vertical surface.

4. Sand. Only enough to smooth the gelcoat patch repairs.

5. Rubbing compound. I did the whole deck, including non-skid.

6. Wax. Again two coats. Whole deck, including non-skid. Yes, it's more slippery than it was before. I think that's going to be OK. I've actually found that my wetsuit doesn't slide on the deck as easily as I'd like it to.
 

Attachments

  • 65_BowDeckFill (Small).jpg
    65_BowDeckFill (Small).jpg
    39.1 KB · Views: 70
  • 66_DeckFillsBeforeSanding (Small).jpg
    66_DeckFillsBeforeSanding (Small).jpg
    42.3 KB · Views: 70

Back
Top