How Strong is Epoxy When Used as an Adhesive?

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sailingjupiter

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So how strong is this stuff?
I need to mount an Eberspacher heater to the vertical transom of my boat. I will be using a pad of wooden ply. I don't want to have to bolt it on for cosmetic reasons, so I was wanting to glue it on. Epoxy I am told is the right stuff, but is it strong enough. The heater is fairly heavy without having the pounding forces that a boat is likely to endure.

What are your opinions and experiences??

Thanks
 
Epoxy penetrates the wood fibres, which polyester resins don't. If you use epoxy and it falls off it will be because the wood split, not the resin. If the transom is grp the epoxy will bond to that very well as long as you abrade the surface properly.
 
Sikaflex the pad on - it will never come off.
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"Artificial intelligence is no match for natural stupidity"
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Thus spoke the voice of removal experience! /forums/images/graemlins/grin.gif

Seriously though, my last boat had a fold down pipe cot in the forepeak, attached to the hull by nothing more than epoxied on wooden blocks....

If they could take the strain of a person sleeping in them while boat pitched up and down, then an Eberspacher is pretty safe territory!
 
3m's 5200. The ultimate in "army blanket" stick.

Though it seems that the OP wants to stick the heater to the ply, rather than the ply to the hull.
 
Epoxy softens with heat. I don't know how much heat the Eberspacher will chuck out into the compartment or how hot the ply pad will become but it's something to bear in mind; might be a bit awkward having a hot Eberspacher bouncing around the boat. Otherwise epoxy is a very good adhesive, provided the surfaces are properly prepared and the mixing instructions are carefully followed.
 
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Sikaflex the pad on - it will never come off.


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"Sikaflex 292" I suggest Cliff means. That's the one for structural bonding. but follow Sika's recommendations for preparation and priming for best results.

See www.sika.com/cmi-marine-index.htm
 
Re Also, is it not a tad cold to be using epoxy? You may need to invest in some hot water bottles.
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I thought epoxy was a twin pack and the hardening shouldnt be effected to much due to the catylst effect of the hardener, as long as its not toooooooooo cold.
 
When properly prepared the ultimate shear strength of epoxy can be upwards of 30 N/mm^2. To assume more than 1 N/mm^2 on ply would be foolish, as that is heading towards the interlaminar strength of the ply.
[1 N/mm^2 is also the reliable long term strength of Sikaflex 221.]

If the adhesive is going to be peeled off, then look for a strength of 0.5 N/mm^2 tops. Possibly best to prevent peeling by attaching some small-ish anti-peel screws around the edges of the ply. 6gauge would do. Or use a stiff backing plate such that the minimum thickness on either side of the glue joint is 12mm.

Now, 1 N/mm^2 doesn't sound very strong, but it's 145lb per square inch, so absolutely massive strength builds up very rapidly.

Regards

Richard.
 
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I thought epoxy was a twin pack and the hardening shouldnt be effected to much due to the catylst effect of the hardener, as long as its not toooooooooo cold.

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Caused be grief a couple of years ago when replacing the anode studs. Even now I can mark it with a finger nail. Mind you it was piggin freezin. I could have applied the antifoul with a trowel....
 
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You probably already know this but you need to thicken the epoxy with colloidal silica if you're gluing to a vertical surface.

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Yes, this is critical. (Otherwise most will simply run out, and you may end up with only a very small area bonded.) And although probably not necessary for this application, if you want to maximize the strength, use microfibres for thickening.

As others have said, temperature during curing is another critical factor.

A third critical factor may seem too obvious to mention, but before applying any epoxy, do a dry run to test your clamping system. It is essential that the surfaces are kept together and immobile during curing.

Mark
 
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I thought epoxy was a twin pack and the hardening shouldnt be effected to much due to the catylst effect of the hardener, as long as its not toooooooooo cold.

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The hardener isn't a catylst. The two parts of epoxy form a chemical bond. That is why it's so important to get the ratios right. Otherwise any left over will remain as a liquid. Heat is a catalyst for epoxy as it sets. The reaction is also exothermic, which is why if you make a batch too big, in too small a pot it'll just start smoking and end up as a solid kind of honeycomb.

So, cold weather won't have any adverse reation on the epoxy. It'll just take longer to set. The only thing to look out for is that the surface might be a bit greasy. But thats something you need to worry about if painting.

For fixing something to a bulkhead you'll want to add microfibres to the epoxy mix. Colloidal silica will make the mix non-runny, but thats only an issue if using it as a filler or for filleting. Microfibres give the mix extra strength.

TwisterOwner does have a point though. Too much heat will melt epoxy so you might want to do some research. I find it unlikely that it will get hot enough for the bond to fail but better safe than sorry.
 
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