How much Sikaflex do I need?

Greenheart

Greenheart

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My thwart is embarrassingly bendy. The doctor advised a wood batten to add stiffness. The best glue to hold them together, seems to be Sikaflex.

Here's a pic (taken from below) which I regret doesn't very well indicate the damage or the slenderness of the GRP opposite some previous timber reinforcement...but the unreinforced edge remains seriously flaky and gets worryingly worse under burden:

View attachment 31374

It seems I can pick up Sikaflex in expensive little tubes at most chandleries...but how much will I want? The total area of GRP-wood contact will be about two square feet. I could do less, but I reckon I'd find later that I should have done the whole thing, port and starboard of the centreboard case.

Note to Lakesailor: The seat was more or less destroyed in a dismasting incident some time ago, and the repair was only made to one edge of the thwart. Possibly her previous crew was daintier than SWMBO or self, but I don't trust it to hold when either of us sits on it 'in anger'. So it's not a problem which will disappear in use! :rolleyes:
 
You will be using Sikaflex 292 presumably as that is the one for structural bonding. It comes in 310ml cartridges

You will find some guidance on coverage as well as instructions on the use in the Sikaflex Users Guide and the Sikaflex Marine Handbook both of which you will find on Bluemoment http://www.bluemoment.com/downloads.html

I assume this is a dinghy that can be turned upside down? If so I might personally have considered glassing in a stiffener or two using glass mat and resin over a paper rope former.


You should be able to find the non marine equivalent of Sikaflex 292. If you can it will be much less expensive
 
VicS said:
You should be able to find the non marine equivalent of Sikaflex 292. If you can it will be much less expensive
Click to expand...

Thanks for these thoughts; but as the dinghy may well experience a great deal of briny rough & tumble, isn't a non-marine version a very false economy?
 
prv said:
Not when it's exactly the same stuff but in a cheaper tube because it's being sold to builders rather than Rich Yotties.
Click to expand...

Thanks for that, Pete.

But my original question remains...how much of the stuff d'you think I'll need, to reinforce this cracking and bending, weight-bearing thwart? I daresay I'll find some quarter-inch ply or hardwood for the stiffening.
 
dancrane said:
But my original question remains...how much of the stuff d'you think I'll need, to reinforce this cracking and bending, weight-bearing thwart? I daresay I'll find some quarter-inch ply or hardwood for the stiffening.
Click to expand...

I guess I wouldn't expect to use more than a tube. At the price of the stuff, especially the adhesive variant rather than the sealant, you don't want it to be more than that!

Pete
 
dancrane said:
Thanks for that, Pete.

But my original question remains...how much of the stuff d'you think I'll need, to reinforce this cracking and bending, weight-bearing thwart? I daresay I'll find some quarter-inch ply or hardwood for the stiffening.
Click to expand...

prv said:
I guess I wouldn't expect to use more than a tube. At the price of the stuff, especially the adhesive variant rather than the sealant, you don't want it to be more than that!
Pete
Click to expand...

According to the Users Guide, to which I gave a link in post #2, a 310 ml cartridge is sufficient for a 2mm thick joint 15.5m x 10mm

15.5m x 10mm is 0.155 sq m

0.155 sq m is approx 1.7 sq ft

Therefore you will need a little more than 1 cartridge for 2 sq ft.
However the exact amount will depend upon how uneven the under surface of the thwart is. You might get away with just one cartridge.

Work it out ... see if you agree with the arithmetic.
 
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VicS said:
Therefore you will need a little more than 1 cartridge for 2 sq ft.
Click to expand...

I wasn't expecting to cover every square millimetre of the surface. That 292 is strong stuff, so I expect a decent bead all round the edge (to seal it) and plenty more squiggled into the middle, should do the job.

Pete
 
Thanks chaps, that's a big help.

To be honest, I was disturbed this afternoon by how creaky even the reinforced side of the thwart is...so I'll be doing as thorough a job as I can.
 
Any Sika you have left over, seal the end, packing tape, cling film (or both) put it in the deep freeze, it will last for months, or a year at least. You will need to thaw it before its used next!

Every time I see a Sika thread I give the same advise (its part of my Scots upbringing, waste not, want not). If your wife (or husband) complain - tell them you are saving money (works a treat - as does the deep freeze storage).

Jonathan
 
OK. I will allow this repair. :) However use Sabatack750xl instead. Cheaper and stays alive in the tube for ages so less waste. One guntube should do the trick.


 
Thanks to all.

That Sabatack looks like the business, and I just found it listed on the Robbins timber pfd...

...still sorely tempted to cover my spongey, pitted side-decks with nice 4mm ply...:rolleyes:
 
Double the above:
Allowance to be made for spreading around all that you touch and a fair quantity for hair conditioning!
(Voice of experience, I use the same maths for antifoul!)
 
I actually plumped for a rather petite 100ml tube of Sikaflex, for under a tenner. The chap at the chandlery hadn't heard of Sabatack.

I'll hope to cut a piece of ply to size for the most essential part of the thwart-repair, and make sure it's done thoroughly enough. Then I can gauge how much more, if any, I'll need to finish the job.

I don't know how familiar anyone is with the Mk 2 Osprey's deck? There's a sudden rise of about an inch at the rear end of the side-deck, where it meets the afterdeck. One of mine has a nasty crack which creaks and widens when I press down with perhaps 15 kilos on the area where the helmsman sits...top right in this photo:

View attachment 31457

...and as you may see, that end of the sidedeck is a very long reach from the nearest round black inspection hatch...so it's not obvious to me how I can reach inside the compartment to apply a repair, even assuming Sikaflex will hold a backing-patch to both sides of the crack. Any ideas? Will I have to hack through the internal wall of the buoyancy chamber, from under the afterdeck?
 
I found myself a nice iroko offcut, about an 1" thick by 2.5" and a meter long, for the princely cost of £1.50. Almost a pity to cut it in two, but the thwart is in two 50cm sections, either side of the centreboard case.

Sikaflex 292 was named earlier...my purchase is Sikaflex 291i...have I made a critical error, for GRP-wood bonding purposes?

View attachment 31533
 
For what it's worth, I have and do use 291 to glue stuff. But for structural work I generally use epoxy and woven glass cloth.

Pete
 
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