Sticky question

[Michael Rogers]

Dear Experts-on-these-matters

Is there a contact adhesive which can be regarded as 'suitable for marine use"? Is, for example, Evostik up to it?

I want to glue down some pieces of structural veneer (two thicknesses of 2.5 mm) on curved surfaces (convex) to form a capping along the edge formed by a cambered deck and a curved, slightly raked transom. For me anyway, that's rather complicated 3D geometry. I can build up a capping with veneer, but I can't think of a way of holding the wood in position on curved surfaces while epoxy cures. I'd rather not drill holes for holding screws because the finished capping is to be varnished (well, Seacoated actually). Am I missing an obvious solution?

Experienced advice very gratefully received!

Michael

[Port-Na-Storm]

Hi Michael,
I suppose it depends which particular Evostik you mean. The original sticky gloop that used to come in a screw top can or the more modern Grip Fast type which comes in a tube. Either way I'm not sure I'd want to try.

One of Epoxy's less endearing habits is that it tends to lubricate the two surfaces you want to glue and they slither around all over the place.

There are lots of ways people have used to keep it all in place. Epoxy doesn't need strong clamping pressure so it should be possible to hold things in place;

try weights, i.e. anything lying around the workshop.



Sticks wedged down from the roof.  



Try Gaffer tape, ratchet straps around the hull/building frame, staples, or just get the wife to stand there for a few hours I'm sure she won't mind.

[Jeremy]

There are a couple of potential problems with using contact adhesive, it isn't very tolerant of exposure to heat (it tends to soften) and it's also susceptible to quite a wide range of solvents, probably including the oils etc in wood finishes.

I think I'd be inclined to try 5 minute PU glue.  I've used this recently to glue the foam sheets together on the Duck Punt, and it's pretty good.  You still need to hold things in place, but unlike epoxy it doesn't tend to make the bits slide around and unlike the slower PU glues it doesn't seem to foam quite so much.  Once you've squeezed two bits together they tend to stay there, even when being clamped.  You'd still need some form of clamping, but as well as weights there is also the neat technique that Anders used to clamp the stem on to his dinghy, using a cat's cradle of Spanish windlasses (see here: http://uk-hbbr-forum.967333.n3.nabble.com/file/n2850786/5642368673_9ce4be580f_b.jpg).

One technique I've used when gluing thin rib caps (often just 1/16th ply) to the edges of aircraft ribs has been to staple them in place, but with a short length of plastic strapping (the tough stuff that's used to bind big crates etc together) under the staple.  The strapping allows the staples to be removed easily and if you then run a damp cloth over the surface the staple holes usually virtually disappear, as the wood fibres resume their original positions.  The same technique was used to build cold moulded hulls using veneers of around 2 to 3 mm thick, so should work OK for your task.

[Paul H (admin)]

I quickly drive in 3.5 x 25mm screws - next day remove them and they leave a tiny hole that is easily filled, sanded and painted.  

You can be sure the glue gap is thin which is important for PU and all air gaps in epoxy have been expelled which seals out any water. For bigger stuff I use more screws or bigger screws - you only need to clamp for an oiled/varnished finish or stuff you have to fight with like in/outwhales.

-Paul

[Paul H (admin)]

I forgot to add that epoxy thickended with wood fibre is medium brown and when used to fill screw holes blends in well with varnished ply.

Not the purists approach, but I bet nobody has found where I did that on MilliBee - there's a challenge for you!

-Paul

[Michael Rogers]

Thanks, everyone. I didn't think contact adhesive was a goer, but wanted to check.

I should perhaps have mentioned that the surfaces to which I want to glue (wood) have been glassed followed by wet-on-wet epoxy resin x3. The sanded down result is, though I says it meself, a lovely surface for painting in due course. I wonder though, Jeremy, whether staples would penetrate well enough, at least from my modest staple gun. I expect everyone faced with my problem claims that their particular circumstances are especially difficult, but mine are (he whined), and - not being a craftsman guitar maker for whom cats' cradles of spanish windlasses may be an everyday routine (?) - several long spells of gazing fixedly at The Problem waiting for inspiration to dawn have been fruitless. My dear wife is too busy fettling her recently acquired horse (a far more voracious consumer of personal resources than boat-building, by the way), and cooking (which I can't), to spare me the necessary hours as a human clamp. (Oh, and she also still works job-wise, to help keep me in epoxy and bronze fastenings.)  

So it'll have to be epoxy (which I much prefer anyway) and holding screws. To fill the holes, my past attempts at colour matching with fine sawdust of varying hues mixed into the resin have not been brilliant, but if at first you don't succeed... I could try plugs, having just invested in a plug cutter (for a different purpose), although I've only got 5 mm depth to play with. It won't be plywood, by the way, but two layers of structural veneer (mahogany).

Michael

[Jeremy]

Staples will work just fine, Michael.  They build veneered boat hulls this way and it works very well indeed.  See here for some idea as to how this technique is used for cold moulded hulls: http://smalltridesign.com/Trimaran-Articles/Construction-Methods/Cold-Molded-Construction.html

A good hand staple gun will usually push through 6 mm or so, enough to hold 3 to 4 mm veneers in place.  The strapping tape is needed not only to allow the staples to be pulled out, but also to prevent them burying themselves too deeply in the veneer.  I have a reasonably cheap B&Q staple gun that I've used on 1/16th birch ply, which is almost certainly a lot harder than something like mahogany.

[Michael Rogers]

OK, Jeremy, I'll give it a try (I too have that B&Q gun!); and I'll report back. Won't be for a couple of weeks, I'm awaiting delivery of the veneer.

Michael

[Michael Rogers]

Jeremy, your stapling wheeze is an absolute winner! Works wonderfully well for what I am doing. For anyone who's interested, just follow Jeremy's comments/instructions on this thread. I used a double layer of the tape - ie a short length folded back on itself. The staples fired through the tape and 2mm veneer and into glassed ply as if I was building in balsa. Potentially dangerous bit of kit, my innocuous looking little staple gun!

My wife would be (I didn't actually ask for her help) very grateful not to have had to wrap herself in cling-film and sit on the stern of my boat build until the epoxy cured (= quite a long time with the temperatures we've been having).

Thanks, Jeremy.

Michael

[Jeremy]

Glad you found it helpful, Michael.  My experience with the temporary stapling technique was mainly holding thin birch ply strips and gussets to thin spruce aircraft wooden aircraft parts, where it works a treat.