Author Topic: Sanding  (Read 4672 times)

Offline uthmani

  • Swabbie
  • *
  • Posts: 8
Sanding
« on: July 12, 2009, 01:55:05 PM »
Guys

We've fiberglassed the bottom/outside of the hull recently and now we want to fair the hull. What we want to know is how much to sand back before we apply the fairing compound. How rough do we need to make it for the bond to be strong? When we sand back, basically the string off the fiberglass is coming off but there are still shiny 'valleys' in between. Do we need to get down that much or about half way? I will try and get photos up as well.

Also, what tool is best for this job? If we need to sand some more, doing it by hand is gonna be tough..

Offline walknbob

  • Global Moderator
  • Chief Officer
  • *****
  • Posts: 1298
  • 24'5" Jumbo
    • WalknBob's J24 Tolman
    • Email
Re: Sanding
« Reply #1 on: July 12, 2009, 02:06:29 PM »
We've fiberglassed the bottom/outside of the hull recently and now we want to fair the hull. What we want to know is how much to sand back before we apply the fairing compound.

when I did my hull I sanded only what was necessary to get any high spots.. like glass seams, dribbles etc. Then a light sanding overall. once I got to where you say you have shiney depressions.  I used a marker to circle those areas and lightly sanded the shine off using my orbital sander, making sure the marker lines were still at least visible. After that I began filling with a fairing compund. Smeared it on, let it dry, sand it down, repeat. After satisfied I gave it a last coat of epoxy which was again sanded lightly a last time.

I know some guys made long boards for sanding to prevent creating depressions from the orbital sander but I used  5" and 6" orbitals for 95% of my work. However, I don't have a gel coat quality finish either like some guys do. But I think that is more a resuilt of painting than fairing.
« Last Edit: July 12, 2009, 05:47:07 PM by walknbob »
WalknBob aka Bob Southwick - Depoe Bay OR

Offline jim shula

  • Captain
  • *********
  • Posts: 1721
    • Salt Water Workshop
    • Email
Re: Sanding
« Reply #2 on: July 12, 2009, 03:18:22 PM »
Don't sand into the glass fiber. 

What you do to fair the hull from the stage you're at depends on your personal standards for excellence.  You could prime and paint it just like it is and go fishing sooner.  You could do a couple stages of skimming epoxy thickened with a low density filler and sanding the high spots off.  Or if you're really anal, you could do it the "right" way by skimming 100% of the surface with thickened epoxy applied with a notched trowel.  Then get a long board and sand manually down to the high spots, and fill all the places where the grooves didn't sand off with more thickened epoxy.  Then sand again.  I haven't heard of anyone going to this extent on a Tolman, but you know all the options now.

Remember though, after you flip the hull. no one will see or judge you by how smooth the bottom is as long as its within reason.  If it were a speedboat, the valleys might make a difference, but a Tolman isn't built for speed. 

Offline uthmani

  • Swabbie
  • *
  • Posts: 8
Re: Sanding
« Reply #3 on: July 12, 2009, 05:17:31 PM »
Thanks for the quick replies guys. The thing we were worried about is whether the epoxy would bond well enough with the first layer..

It is only a fishing boat after all, so we won't go overboard with it ...

Offline walknbob

  • Global Moderator
  • Chief Officer
  • *****
  • Posts: 1298
  • 24'5" Jumbo
    • WalknBob's J24 Tolman
    • Email
Re: Sanding
« Reply #4 on: July 12, 2009, 05:49:29 PM »
Thanks for the quick replies guys. The thing we were worried about is whether the epoxy would bond well enough with the first layer..

If your glass is less than 48 hrs (depending on temp) all you would have to do is wash it down with an ammonia and water mix, dry it off and epoxy again. For the most part I sanded only what was necessary to take the shine off. Additional epoxy stuck to it fine.
WalknBob aka Bob Southwick - Depoe Bay OR

Offline funhouse

  • Boson
  • ****
  • Posts: 380
  • real Tolmans don't have windshields
    • Email
Re: Sanding
« Reply #5 on: July 12, 2009, 11:13:13 PM »
You only get one chance to do this so do it to your intended/desired finish with the hull upside down ..... I used long boards for a couple weeks with primer in between and am glad I did.....with the store-bought two part paint, I've got a mold-hull finish.....Aaron's Jumbo is just as nice but he was much more careful during construction, had fewer problems to sand out and didn't finish his skiff in as shinny a paint as did I......Done again, I'd be much more careful during the construction phase and forget some of the fancy bits.....Bruce

Offline dinghyman

  • Able Seaman
  • ***
  • Posts: 140
    • WoodenBoatBlog.com
Re: Sanding
« Reply #6 on: July 13, 2009, 04:25:58 AM »
Don't sand the glass off. Just bust the sheen with 80 grit on a 6" orbital DA. See my tool of choice for this:

After you take the sheen off, you can fill low spots as needed, especially areas where you may have air bubbles or holes in the glass coating. If you see spots you missed sanding, use a scotchbrite pad for scuffing. Mix up a paste with microspheres or any of the epoxy based fairing compounds for filling holes and low spots. Use a wide (6"-8" putty blade). Go at this again with your DA and 80 grit and you'll have a good surface for primer and a finish that will look good. The long boarding step is only required if you want to eliminate every little dip and wow that comes from taping and building a wooden boat. I think the only place needed for this would be along the taping edges. That's a good compromise as opposed to boarding the whole boat.

One more step in getting the nice finish comes with your primer. I sprayed one layer of gray system III and then another of white. Then when sanding I could tell where the high and low spots where. I used Interlux Brightsides enamel http://www.yachtpaint.com/usa//product_guide/finishes_undercoats/US_brightside.asp as the final finish coat. I've heard of folks having problems with the System III being too hard for a good bond. I personally think that's because they didn't sand it well enough. Good tooth = good bond. I do know for sure that 100 acrylic latex primer sticks well to everything and that everything sticks well to it so I sprayed on one coat of latex primer over my now gray and white splotchy (but smooth) System III primer. I'm VERY happy with these results. Millions of dollars a year go into making great latex paints. They can be great on boats too. My topsides are all latex deck paint and we're still happy in our 5th season.

BTW, we'll be Jumbo heavy tomorrow with 6 adults, 1 dog and tons of food and camping gear heading downriver for a few days. It's a party cruise with the newly installed sound system ready to scare away any salmon.

;-) Paul
Make things better.

Offline tolman_paul

  • Chief Officer
  • ********
  • Posts: 1322
    • Ukverun Consulting LLC
Re: Sanding
« Reply #7 on: July 13, 2009, 05:38:31 PM »
It's much easier to fill in the low spots than to knock off the high spots.  You need to scuff up and clean the epoxy to get a good bond, but asside from that, let your filler do the work. 

Offline kiwi les

  • Boson
  • ****
  • Posts: 404
    • Email
Re: Sanding
« Reply #8 on: July 14, 2009, 01:26:40 AM »
I did as Bruce did, but used when I could, an inline sander about 400mm long and 100mm wide. Dam good tool. The rest was done with a cheep orbital of which I went through 3, They really were cheap!. Paint is Altex, a 4 paint system the final coat being a re-coat able urethane. Filling was done with a 10" wide plastering trowel, using micro spheres. Despite a little dust landing in the paint in the last moments, I am very pleased with the finish! The more time spent in this process, the more the boat will be worth if ever I decide to sell!

les

Offline uthmani

  • Swabbie
  • *
  • Posts: 8
Re: Sanding
« Reply #9 on: July 14, 2009, 03:39:23 PM »
Thanks for all your tips and advice guys.. it gives us a bit more confidence knowing what methods other Tolman builders have used.