How to remove stains

Discussion in 'Fiberglass/Wood/Gelcoat Repair' started by Eluther3, May 7, 2022.

  1. Eluther3

    Eluther3 Active Member

    Mar 17, 2019
    1992 Searay 400 EC
    Have the boat out of the water for maintenance and repairs. While I have it out, I'm trying to clean off some of the discoloration on the hull but not having much luck.

    Have hit it repeatedly with Starbrite hull cleaner but no change. Any ideas how to remove?


  2. Windjammer

    Windjammer Well-Known Member SILVER Sponsor

    Nov 10, 2007
    Marietta, GA
    340 Sundancer 2006
    8.1 Mercruiser V-Drives
    FSR (fiberglass stain remover), or On & Off (get the gel and not the liquid). Put on with a paint brush and let it sit a while. Both will also discolor the bottom paint if it gets on it. There's always rubbing compound and a wool pad.
    HP12Sea, FootballFan and Chris-380 like this.
  3. Chris-380

    Chris-380 Well-Known Member

    Jan 20, 2019
    Pontoon Beach IL
    2000 380 Sundancer
    7.4L Horizon w/V drives
    +1 FSR and Mary Kate’s On & Off gel
    Mauler34Rod likes this.
  4. Halfhitch

    Halfhitch Well-Known Member SILVER Sponsor

    Aug 24, 2021
    Venice, Florida
    1988 Laguna 23CC
    1988 Mercury 135 Black Max twins
    Start with 600grit wet/dry. use it wet. When you get the stain pretty well gone, switch to 1000 w/d. When the stains are removed change to 1500 grit w/d and then finsh with a cleaner/polish
    mrsrobinson and Mauler34Rod like this.
  5. KevinC

    KevinC Well-Known Member

    Feb 25, 2011
    Long Island, NY
    2004 340 Sundancer
    Twin 8.1 V-drives
    Try some Barkeeper's Friend.

    Chris-380 likes this.
  6. Captsteve427

    Captsteve427 Well-Known Member GOLD Sponsor

    Sep 8, 2019
    Long Island, NY
    2007 44 Sundancer
    QSC 8.3L 500
    Tape off the bottom paint line, soak a rag with Mary Kate’s on/off and hold it on the stain and let it soak in. Rotate the rag as the on/off dissolves the stain. You’ll probably not get that entire stain out and may want to then wet sand as recommended above. You may want to also consider changing out the fitting with a stainless steel one afterwards, assuming there’s access to the back side of it.
    Once you’re satisfied with the results wax the area then insert a clear rubber hose that stubs out of the thru hull fitting 1/2” to avoid the water from dripping down the hull and causing the stain again. I’ve been minimizing hull stains on my boats for years by using them on all my thru hull fittings that tend to have liquid draining from them regularly.

    Attached Files:

    Nater Potater likes this.
  7. VictorJohn

    VictorJohn New Member

    Mar 8, 2015
    Puget Sound, Washington
    1998 Sea Ray 250 Sundancer
    6.2 Liter 350 hp Mercruiser SeaCore with Bravo III.
    I’d like to share something that I just tried with amazing results. I had filled up the gas tank but didn’t burn off enough gas and the following week we had a heat wave here in the Puget Sound area. Found amber and yellowish streaks down the hull from the gas vent. I smeared some Dawn dishwashing detergent on the streaks and left in on overnight. The next day there was still a blue dawn colored patch stuck to the boat. I simply hosed it off and the stains were gone. Not a trace. I also noticed the hull a bit cleaner and more white than the areas to both sides. I got to thinking what if I smeared The whole boat with Dawn. My wife buys it at Costco in gallon jugs and I doubt it costs much. Do you think there’s any downside to doing this? I’ve become more about cheap and easy. And maybe getting a little lazy. It was just so easy and the results were dramatic relative to the amount of labor involved.
  8. Hoplite808

    Hoplite808 Well-Known Member

    Jan 11, 2022
    Honolulu, HI
    1996 Sea Ray 270 Sundancer
    Mercruiser 7.4 LX MPI EFI (Gen. V)
    SOS scrub pads will sometimes work wonders. I use them all the time to clean and polish stainless steel. I’ve also used them as a first step in removing bad oxidation on gel coat before I polish and wax. They are dirt cheap and give amazing results with minimal elbow grease.
  9. bbwhitejr

    bbwhitejr Well-Known Member SILVER Sponsor

    Apr 14, 2013
    Lake Lanier GA
    2003 420DA, 6CTAs
    Great idea if you are good with removing 100% of the wax. Be ready to buff and wax if you decide to.

    BarryCF, Shaps and Chris-380 like this.
  10. VictorJohn

    VictorJohn New Member

    Mar 8, 2015
    Puget Sound, Washington
    1998 Sea Ray 250 Sundancer
    6.2 Liter 350 hp Mercruiser SeaCore with Bravo III.
    Good point Bennett. Guess I’ll reserve the Dawn approach for stains only. Still not a bad component to add to my boat cleaning arsenal. Thanks!

  11. bbwhitejr

    bbwhitejr Well-Known Member SILVER Sponsor

    Apr 14, 2013
    Lake Lanier GA
    2003 420DA, 6CTAs
    I keep a jug primarily for the bilge....never on a waxed surface.

    brewster16 likes this.
  12. ocgrant

    ocgrant Official Bahamas Boating Ambassador GOLD Sponsor

    Dec 31, 2006
    Miami / Ft Lauderdale
    H2O Therapy
    2006 Sundancer 48
    Novurania 430DL
    Yamaha EX-R
    PADI Divemaster
    Raymarine Electronics
    Cummins QSC 540's
    Dollar store and cheap liquid toilet bowl cleaner. Squirt it on and let it work. The re wax after it is gone. Works like a charm
  13. duckhead69

    duckhead69 Member

    Jun 11, 2010
    michigan lake Erie
    1980 Bertram
    1986 Rinker2100
    2006 Nova
    1989 215 sundowner
    1986 300 weekender lowrance HD-5
    350 chevy inboards velvet drives
    scotch bright soap or a scotch brite pad fine grit then polish it
  14. sbw1

    sbw1 Well-Known Member

    Oct 10, 2006
    West Michigan
    This is listed in my signature
    This is listed in my signature
    This or some good ol' hydrochloric acid from a pool supply store should do the job. I've never seen a fiberglass stain that did not come out with either of these. Soft n' Scrub with Bleach dabbed on the stain after the above could make it even better. Obviously, you need to wear old clothes and use care with these products but they do work. Bottom paint will require touch up at the water line when you use acid.
    mrsrobinson likes this.
  15. dvx216

    dvx216 Well-Known Member SILVER Sponsor

    Feb 1, 2012
    Catawaba Island,Oh.
    2001 340 sundancer 8.1
    8.1s 370 v drv.

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