Epoxy bonding

[bilbobaggins]

I'm halfway through mounting a pair of winches onto a friend's coachroof either side of the companionway. Also, P&S, some clutches mounted on angled wood pads P&S forward of the winches. Beneath, I've positioned 3mm alloy sheets P&S about 45cm x 20cm, I've drilled all holes and positioned all bolts through, as a 'trial fit', and there's about 25mm accessible gap between plate and GRP deckhead when the nuts are only just 'started' onto the overlong bolts.

The winch bases, wood pads and alloy plates are flat. The coachroof is gently curved, so there are modest gaps to be filled. My friend has already purchased a 1kg pack of Hempel 2-part epoxy filler and, at around £42, I'm expected to make good use of it.

The next step is to ease the winches up, 'blob' on some epoxy putty-stuff, reseat the winches so that they make a flat fit with the bed of e/putty, and clean up the mess. Then let that harden somewhat....

The step after that is to ease the alloy plates down a bit on the overlong bolts, 'ladle' on some more ( lots more ) e/putty, then wind up the nuts to pull the plates hard up close, spreading the putty to fill the gaps, then clean up the mess.

There are two 'uncertainties' I'd like some creative help with, if someone would be so kind......

Firstly, can anyone suggest how I can grease the bolt threads in situ so that their threads will not bond to the e/putty, without wholly removing the winches, clutches and bolts?

Secondly, given the above caveat is achieved, how can I apply thick beads of e/putty onto the upper face of each plate in situ - and what with - so there's enough stuff there to give a sound bond between plate and GRP layup?


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[William_H]

I am not sure I can help much. I would have pressed up the Al plate under the deck with a prop of some sort with the putty on the plate and waited for it to harden before drilling the holes for the bolts. A car jack and a prop of long wood can give a suitable pressure.

The putty can be thickened with a filler. Talc powder or chalk is OK. Put some unthickened epoxy on the surface first then plaster on the thick stuff. Hopefully just thick enough to stop it running out. You can use cling wrap stuck in -place with masking tape to try to hold the putty in.

OK if you want to fit the bolts to hold the bottom plate in place you need to insulate the thread with cling wrap or lots of wax. This hopefully will enbable them to be removed after the epoxy hardens.

I made a new base for the mast step on my boat using polyester resin and chop strand mat. This area was uneven.Needed a wedge shape. So I used pieces of mat not full sized. More small pieces on the low side. I just built it up in roughly the size and shape then shaped and cut it with an angle grinder and file when it was hardened. You could use epoxy putty with some fibreglass cloth (not Chopped strand mat) to hold it in place. ie multiple layers saturated with the putty. The putty will be more runny if warmed up a bit. Again drill when hard.
good luck olewill

 

[oldsaltoz]

Try to minimize the gap under the winch pads and don't pull them down too hard, you need an even spread of at least 3 mm.

Glad wrap or fit drinking straws over the bolts to avoid contact with the resin, again do not tighten the bolts, let the epoxy cure before tightening and make sure you have at least 5 mm of epoxy between plate deck underside.

If you can put the top on and drop some drinking straws through then fit the lower plate secured with tape and small wedges to hold it off the required distance you will get a better job. Drill the holes after curing from both sides using the straws as a guide.

Good luck.

Avagoodweekend......

 

[charles_reed]

I use PTFE tape, not drinking straws (more thrifty but don't always fit) and prefer grp filled polyester to epoxy putty, but can't add much to oldsaltoz's explanation. The secret is a loose assembly to shape it while it hardens (that's where filled polyester is superior IMHO to epoxy putty) and then assemble properly.

 

[lw395]

Not sure that 3mm alloy will be effective in spreading the load from a winch or clutch, as it bend to much. Obviously depends on size of boat etc. I used 8mm alloy, plus hollowing out the balsa cored deck and filling with epoxy/glass mixture. PTFE tape on bolts is good, or cling film over grease. Another trick is to pull the pad into place using a few nylon bolts which can be drilled out easily later. Or even thread an old piece of rope through and pull it tight with a wedge or similar. You can then assemble the fitting with proper sealant etc., after the epoxy is cured.

 

[Cliveshep]

I saw a similar thread a week or so ago, or was that you? Like Lw395 I felt that a sheet 3mm ali was insufficient, and mild steel would spread the loads better, however, up to you.

With regard to bolts, can you not fit them threads uppermost and fit nuts on the top as a temporary measure, reversing them once everything has set?

You can wedge them from below with a batten holding a "mole" or self-grip wrench on the heads if there is only you doing the work and no one to assist. Just thinking outside the box here!

 

[bilbobaggins]

I take the points made re steel vs aluminium plate. Had it been my own boat, I'd have prepared the job much more thoroughly, and probably laid up several extra layers of glasscloth, and perhaps a 12mm ply sheet, bonded in. However, the boat is 70 miles away, the owner is proving to be unwilling to get his own hands dirty, and the job has been discussed endlessly over 4 years. The yard where the boat is kept could have done the job, at a price, any time during those years.....

The owner couldn't ( be bothered when asked to ) find a source of metal - steel, aluminium or gold-plated titanium - anywhere around Cardiff, so I found these pieces of alu road sign in my local scrap metal dealer's yard, as I was passing. At least I can drill holes in that with my cordless drill, on the pontoon. So, in lieu of anything better, that's what he's getting. And in case you're wondering, it's a freebie...

I do have the Gougeon Bros book, and the West System leaflets, but I like the ideas that have emerged here, and will certainly try 'em when next I head down that way. Thanks, guys.

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