What is stronger for this application? 3M 5200 or epoxy resin and fiberglass cloth?

Discussion in 'Materials' started by magentawave, Jul 16, 2013.

  1. magentawave
    Joined: Jul 2013
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    magentawave Senior Member

    I'm new here and figured that since boatbuilders are always concerned with strength that they would be the best people to ask.

    I need attachment points for hanging upper cabinets to a vertical fiberglass surface made with polyester resin and is only 1/8" to 3/16" thick. The cabinets will be made with 1/2" plywood and will be approximately 12" deep X 12" to 18" tall. I was planning on gluing some horizontal 1" X 2" to 1" X 3" wood stringers (laid flat) to the fiberglass wall and then I would screw the cabinets into those wood stringers.

    Here is my question please...

    Is 3M 5200 strong enough to hold the weight of those cabinets or should I glass the stringers with epoxy resin and fiberglass cloth? One more thing... These cabinets will be subjected to a lot of rocking around and vibration.

    Thank you very much! :)

  2. michael pierzga
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    michael pierzga Senior Member

    5200 is mighty strong stuff. You need clamping pressure and a reasonable fair surface. It will work. 5200 is messy to clean up

    With thickened epoxy clamping pressure is not an issue and thickened epoxy has good gap filling properties.

    Its up to you
  3. magentawave
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    magentawave Senior Member

    Hmmm, thanks for mentioning that because I didn't consider the clamping pressure required for 5200. If I go with epoxy I could probably "clamp" the stringers in place with duct tape or dots of hot glue. Does 5200 require more clamping pressure than that? Also, if you used epoxy, would you use thickened epoxy spread on both surfaces ONLY and be done with it, or would you also add a layer of 8 oz E cloth over the stringers and spreading several inches on to the wall surface above and below the stringers?
  4. upchurchmr
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    upchurchmr Senior Member

    If you think the weight of the cabinet is the heaviest load, I would run the wood stringers vertically, not horizontally since the cabinet is trying to rip the wood off the wall. Horizontally the wood will try to roll off the wall, with only a short distance (vertically) to stop the rolling. Vertical boards will be so long this won't happen.
    That is not a real big cabinet, so I would guess just bonding the wood to the wall would be sufficient. You could always test it by hanging off the bonded wood strip. If it survives it should be good without glass.
  5. gonzo
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    gonzo Senior Member

    1/8" fiberglass may break with a shelving unit of that size attached to it. Also, if that surface is the hull, the shelving will create a hard spot which will concentrate the stresses and may make the structure fail.

  6. PAR
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    PAR Yacht Designer/Builder

    Gonzo has noticed the point I'm about to reinforce. The liner (assumed) you're going to attach these cabinets to, isn't heavy enough to accept a big cantilever load, such as a cabinet, particularly full of can goods. Ideally, these should be mechanically attached to a structural element of some sort.

    3M-5200 is a sealant with especially good adhesive qualities. It shouldn't be used as an adhesive, except in broad area applications under pressure during the cure. It might hold up your cabinets, but it also might just tear out the plywood or glass in the contact areas. This isn't the best thing to live with. You should be able to do chin-ups on a cabinet and stand on a counter-top, without worry. Epoxy will provide this level of security, 3M-5200 not so much.

    Can you provide some pictures of the cabinet locations? It's likely you'll need to install a "cleat" so the cabinets have something stiff and strong enough to hang on. This could be as simple as a length or two of 1x2 epoxied and filleted to the liner, which the cabinets are then screwed to.
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