First off, hello all at swaylocks and I hope this hasn't already been asked. I've used the search function but couldn't find anything specific, so here goes. Making my first board and have access to some free xps sheets. Unfortunately, they are only 600mm long by 100mm thick, so in order to make a board I have to join two sheets together. To do this, I've routed out a 30cm section of each sheet and then glued them together with gorilla glue. I've also put in a stringer and a couple of dowles for strength but I'm worried, what with xps's reputation for delaminating, that it's still gonna be a big weak patch in the middle of the board and it might snap. Anyways, hopefully the pictures will make sense. My question is, is there anything more I can do to strengthen it, and do I need to or will a heavy glassing schedule be enough? Was thinking 3 4s on top and 2 on the bottom, with a tail patch for the fins...
Thanks all.
Gorilla Glue is tough stuff. Just for kicks, glue a couple of scraps together, let cure, and bend at the joint. My own experience with EPS and XPS is that the glue is the last thing to give up. As a security blanket, glass a strip of carbon uni reinforcement fabric down the center on both sides or better yet, on the bottom and in 'love handles' on the deck side.
Here is one type of tape available through our friends down under... https://www.sanded.com.au/products/carbon-innegra-unidirectional-tape-per-50m-roll
Thanks, that sounds like a good idea. Hadn't thought of using carbon tape.
Exactly.
Don´t worry that much about carbon or complex dovetailing. A good PU glue with a tight glue-gap is usually stronger, than the EPS/XPS next to it.
Glue some scraps togehter, break it. It will break next to the glue joint, not in the glue joint.
Dont worry if you use PU Glue like Gorilla it is going to be supertough... I have a couple of fused ones, with and without stringer... No problem, all of them handled portuguese beach break well.
What is the XPS foam density/minimum compressive strength?
Swaylocks Surfboard Design Forum: thoughts & theories ... practical & theoretical
RAIL PROFILE http://bgboard.blogspot.com/2014/03/march-82014-afterr-seeing-recent.html
unfortunately the foam I've got hold of was just some leftover sheets from the building site I work on. The wrapping etc is long gone. I do know, however, that it was intended to be used for floor insulation, as opposed to wall, so should be pretty dense.
Weigh a small, rectangular/square piece of your foam with known dimensions (TxWxL).
Do you know the foam brand/manufacturer?
Swaylocks Surfboard Design Forum: thoughts & theories ... practical & theoretical
RAIL PROFILE http://bgboard.blogspot.com/2014/03/march-82014-afterr-seeing-recent.html
found it, actually took a picture of a wrapper ages ago. It's kingspan, styrozone, n500r apparently. All I can find online about compressive strength is that it exceeds 500kPa at 10% if that means anything? It's used for car parks.
Looks like you have some fairly high density/compressive strength XPS (2.2 pcf/72 psi; page 4 in link below). So it should be less susceptible to pressure dings.
If you want to increase strength, adding a wood veneer to the deck (compsand/timberflex build tech) combined with a stringer should make your board pretty tough -- more of a T-beam structure, helping to resist compressive stresses. With that you shouldn't need a super heavy glassing schedule.
https://www.just-insulation.com/downloads/kingspan/Datasheets/Kingspan-Styrozone-Heavy-Duty-Floor-datasheet.pdf
BTW joining the sheets together something like this should improve joint strength.
Picture1.png
Swaylocks Surfboard Design Forum: thoughts & theories ... practical & theoretical
RAIL PROFILE http://bgboard.blogspot.com/2014/03/march-82014-afterr-seeing-recent.html
Compsand builld tech videos:
https://youtu.be/w9Iy3Y5h7Ww
https://youtu.be/MBMZ6DnATRg
https://youtu.be/xsgBUMUpCi4
Swaylocks Surfboard Design Forum: thoughts & theories ... practical & theoretical
RAIL PROFILE http://bgboard.blogspot.com/2014/03/march-82014-afterr-seeing-recent.html
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