Seacocks and backing plates

  • March 27, 2012 12:38 PM
    Message # 869782
    Deleted user
    Any opinions on what adhesive to use when bonding new G10 backing plates to the hull? Obvious choices are 5200, West System with colloidal silica and West Marine Six10. I've read the excellent article on the subject at Compass Marine. Background - I'm replacing my W32 seacocks with new Groco Ball-Valves and flanged bases. I cut new backing plates from a 12"x24" sheet of 3/4" G10. The new flanged bases take 5/16" bolts vs the 3/4" ones for the old seacocks and rather than deal with resizing the countersink and drilling 2 new bolt holes I'm filling them all and have tapped the G10 for 2" 5/16" studs (phosphor bronze screws with the heads cut off). Now it's time to bond them to the hull. 12"x24"x.75" G10: $130 at http://accurateplastics.thomasnet.com/item/epoxyglas-g10-fr4--mil-i-24768-27--nema-fr4/epoxyglas-sup-tm-sup-g10-fr4-panel/geex-7501224n?
  • March 27, 2012 8:46 PM
    Reply # 870270 on 869782

    Ahoy Paul,

    I strongly suggest that you DO NOT use 5200 or any of the polyurethanes.  Also no epoxies.  Just as you have removed the old ones, the new ones will need to be removed someday also.  Stay with something that seals well but does not adhere so tenaciously.  Like a polysulfide.  Boat Life is the big player with polysulfide.  A Buytl rubber compound would also be OK.

    My opinion only of course.

    Good Luck,   Dave

  • March 28, 2012 8:05 AM
    Reply # 870661 on 869782
    Anonymous
    Dave, 

    In the procedure he is mentioning, the seacocks and backing plates are not thrubolted to the hull.  Not sure if that was clear in his post.  

    Surely butyl rubber alone wouldn't be strong enough to hold the plate and seacock in place.  Without a bolt passing through the hull you'd want something much stronger than that. 

    Tate
  • March 28, 2012 2:28 PM
    Reply # 871022 on 869782
    Anonymous
    Tate, are you sure? I think the article says to through-bolt...


    I used polysulphide for mine and no problems

    edit: I see the original poster is not going to do it like the articles says to do.

    Last modified: March 28, 2012 2:36 PM | Anonymous
  • March 28, 2012 3:10 PM
    Reply # 871072 on 869782

    I may have misunderstood what Paul is doing. 

    Sorry for causing any confusion.  Good luck,   Dave

  • March 28, 2012 9:50 PM
    Reply # 871394 on 869782
    Anonymous
    Here is the article I believe the first post refers to: 


  • March 29, 2012 8:37 AM
    Reply # 871703 on 869782
    Deleted user
    Update: Ya, I'd rather not thru bolt them because the bolts are smaller than the originals and downsizing seems like a source of problems later (filling the holes, redrilling them, hoping the material stays adhered to the original hole...) I considered drilling the new bases out from 5/16" to 3/8" but the holes Groco put in them are a little off center and redrilling them would leave one side a little thin. As an experiment I drilled and tapped a scrap of the 3/4" G10, put in a mild steel galvanized carriage bolt and used a SS nut and washer to try to strip the threads out of the G10. The bolt sheared off. I figure that's around the same order of shear strength as the bronze studs I'm using so the G10 threads seem plenty strong. I'll wax the studs, dip them in West System and thread them in. I should still be able to pull them out later if necessary and drill and thru bolt them if there's a reason to. Since I'm not thru bolting them I need an aggressive adhesive like 5200 or thickened epoxy. The 5200 is probably good enough but I'm inclined to use colloidal silica and West System. Note: when tapping G10 start the first 1/4" or so of the threads with a plug tap, they have quite a bit of taper on the tip and you can keep it aligned in the hole pretty easily as your starting the cut. Then switch to a blind tap to cut the rest, they have virtually no taper and so they don't bind in the G10. However, it's possible my impressions here are due more to the plug tap I used being from Ace Hardware while the blind tap I used is a production machining tap that's extremely hard and sharp.
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