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Old 04-08-2013, 23:08   #1
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Bedding Compound That Dries Hard

I'm putting in the backing plates for my Hydrovane, so it's a pretty beefy install.

The interior of the hull isn't smooth. It's a 1975 boat and the fiberglass is a little.. bumpy. Whatever I use for a backing plate (probably going with teak, maybe stainless if I can find something that will fit) won't fit flush against the hull.

I'd like to bed the wood against the bumpy service with something that will fill in the voids well.

Additionally, it will be under a lot of compression so I don't want anything that will move around (silicone, polysulfide, etc).

Any ideas?
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Old 04-08-2013, 23:12   #2
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Re: Bedding Compound That Dries Hard

i have been using sikaflex,, is a yellow tube, available in home depot.
we rebedded everything on topsides for rain season--stuff works great and is hard when dry.
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Old 04-08-2013, 23:15   #3
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Re: Bedding Compound That Dries Hard

From the Hydrovane website:

Quote:
BACKING PLATES – NUTS MUST BE FLUSH TO PLATES – EPOXY or FIBREGLASS RESIN FOR SPACER - The bolt nuts must be flush against whatever surface. To fill any gaps between the backing plates and the hull: mix a suitable quantity of epoxy or fiberglass resin and put it into a Saran Wrap or plastic pouch – fitted between the bracket flange and hull – tighten bolts – before the epoxy or resin hardens you must cut or mould the material to the desired shape – carving away any surplus – must be nimble – once hardened that stuff is brutal to work with.
I don't really get how you do that.
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Old 04-08-2013, 23:23   #4
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Re: Bedding Compound That Dries Hard

Eric, essentially you are grouting a cavity between the backing plate and hull. The Saran Wrap or plastic bag is a easy, convenient way to prevent the epoxy from running. The epoxy filled bag is sandwiched between plate and hull.

My question is about torqueing the nuts. It seems you would start with some lower torque value (finger tight?) then increase torque as the epoxy cures and eventually arrive to the recommended torque. I wouldn't go to full torque until AFTER the epoxy has fully cured. By then, you should be very close to the recommended value.
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Old 04-08-2013, 23:28   #5
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Re: Bedding Compound That Dries Hard

Not sure what the confusion is?

Why not just sand the hull then put very thick epoxy on the backing plates and press into position. You can easily clean up any that squishes out or runs but thick epoxy mish mash usually doesn't run much.
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Old 04-08-2013, 23:29   #6
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Re: Bedding Compound That Dries Hard

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Eric, essentially you are grouting a cavity between the backing plate and hull. The Saran Wrap or plastic bag is a easy, convenient way to prevent the epoxy from running. The epoxy filled bag is sandwiched between plate and hull.

My question is about torqueing the nuts. It seems you would start with some lower torque value (finger tight?) then increase torque as the epoxy cures and eventually arrive to the recommended torque.
Yeah but how do you push a fastener through a plastic bag and not epoxy the nut at the same time?

If there's a 2"x5" board, and I put a ziplock of epoxy behind it and put it against the hull, how can I tighten it down enough against the hull to make it conform to the shape? That's the part I'm missing.
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Old 04-08-2013, 23:33   #7
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Re: Bedding Compound That Dries Hard

Another method would involve the same epoxy filled bag sandwiched 'tween hull and plate. In this method you secure the plate in place but not with the bolts. The plate would leave a flat base on the cured epoxy. Then, after the epoxy, has cured you drill the bolt holes using the bolt pattern from the plate.

If this is doable I would prefer this method since I don't know how the constant increasing torque would work while the epoxy cures.
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Old 04-08-2013, 23:35   #8
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Re: Bedding Compound That Dries Hard

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Not sure what the confusion is?

Why not just sand the hull then put very thick epoxy on the backing plates and press into position. You can easily clean up any that squishes out or runs but thick epoxy mish mash usually doesn't run much.
It's probably the hardest spot to reach on the boat, and I really don't want to be in a confined space sanding fiberglass if I can avoid it.
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Old 04-08-2013, 23:38   #9
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Re: Bedding Compound That Dries Hard

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Another method would involve the same epoxy filled bag sandwiched 'tween hull and plate. In this method you secure the plate in place but not with the bolts. The plate would leave a flat base on the cured epoxy. Then, after the epoxy, has cured you drill the bolt holes using the bolt pattern from the plate.

If this is doable I would prefer this method since I don't know how the constant increasing torque would work while the epoxy cures.
Yeah that's a decent idea too. There are also the various epoxy "putties" that can be used, or west mixed with a filler. Clean the area, goop the putty on, push the backing plate onto the goop, let dry, drill through the goop and plate.

I was really hoping for something more like a 5200 but less permanent and that dries hard. Ho hum.
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Old 04-08-2013, 23:40   #10
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Re: Bedding Compound That Dries Hard

Admittingly I'm in the dark about what it looks like. Pictures are worth a thousand words. I reckon you could use a spacer to stand the nut above the uncured epoxy. Tape the threads or liberally grease the threads to keep them clean of epoxy.
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Old 04-08-2013, 23:47   #11
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Re: Bedding Compound That Dries Hard

Just say no to 5200...lol

If you did use 5200 or whatever and you didn't want it to be permanent, place a layer of plastic, wax paper, or whatever that won't soak through with the goop.

When temporarily joining wood or FG, I use a layer of paper at the glue joint. I have a weak joint but strong enough to even turn a large bowl on the lathe. This works with aliphatic resins (wood glue), Gorilla Glue, and CYA (super glue). You could use this method for epoxy but don't use regular paper because that will soak up the goop. All you want is a bedding plate that conforms to the interior of your hull and presents a flat base for your vane plate.
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Old 04-08-2013, 23:56   #12
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Re: Bedding Compound That Dries Hard

Okay what about something like this then:

Marine Tex Epoxy

I:

- tape some saran wrap to the bulkhead
- jam some putty on, getting it into the grooves (against the saran wrap)
- use one of my backing plates with saran wrap to form a flat surface
- let it cure
= I have a hardened piece of goo that should be able to sit between the plate and the hull

It has a 30 minute pot life at 72 and it never gets below 95 during the day here so even if I have to hold the plate against it with my hand it won't take too long.
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Old 05-08-2013, 00:02   #13
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Re: Bedding Compound That Dries Hard

That sounds like what I was thinking. Hull/saran wrap/goop/saran wrap/plate = sandwich. Now how to ensure plate is in alignment with the rest of the vane hardware?

I've used the Marine Tex. I like it. But in your case with high ambient temps you may have to work fast in a confined space.

You could mix the stuff under water in an ice chest to lengthen cure time. Even mix it inside a plastic bag. Saran Wrap gets problematic because it clings to itself and it's too flexible.
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Old 05-08-2013, 00:13   #14
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Re: Bedding Compound That Dries Hard

This thread title potentially sounds sexual.
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Old 05-08-2013, 00:24   #15
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Re: Bedding Compound That Dries Hard

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This thread title potentially sounds sexual.
What type of repressed sexless existence do you live in that talking about bedding compound choices sounds sexual to you?
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