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[satch]

Hey everyone!

I'm going to start my first compsand within the next days. Unfortunately I'm not sure about the Rails. I have a rather high-density blank of eps around 2#.  As sandwichmateria I want to use 3mm depron foam which is simliar to xps. glassing will be 6oz on both sides of the sandwich. do you think i should add a wooden parabolic stringer? how would it be to just put a layer of 6oz glass between the core and the rails. As it is my first compsand it would be ok if it s pretty stiff but i want to avoid getting a a super soft board.
Have a nice Weekend,
Sebastian

[Kit Sidwell]

Hard to know for sure, as you're using materials that i've never tried, but I don't think you would end up with a too flexy board - but its just a guess.
The 2# foam stiffens things up a lot, wood rails might be a bit too much.
Not sure how you're going to put the thing together, but just be careful if you are trying to blend the skins into the rail when you are shaping them, as the materials are different hardnesses, and that makes it difficult.
Its much worse trying to blend wood skins into foam rails, but I thought i'd throw that out there just so you know that it might be a concern in your case.
What density is the depron foam?

[satch]

Thanks again Kit!

The Depron foam is a little over 40kg/m². So just not very stiff. Thats why I' going to use 6oz as inner and outer glass lam. As Ican't get my handy on balsa i thougt about using 3mm plywood as parabolic stringer and then the rest of rail made of depron. My other idea was to put one layerof 6oz glass between core and depron rails. that should stiffen it up a little and would prevent the core from sucking water if the rail were damaged.
Perhaps I should just build 2 boards using either technique...

[Kit Sidwell]

Thats the way to go!
Depron rails would be the ticket. I've never had any experience with that foam, but that sounds like a good density.
Gluing the rails on with 6 ounce isn't really necessary, but will give you more stiffness.
Another way would be to just glue them on straight, then asses the flex when the outer glass is on, but before the hotcoat. If it is too flexy for you, just add an extra layer of glass round the rails only.
This will give you a bit more impact resistance for those soft foam rails.
Interested to hear how that depron goes, always keen to hear about different materials.

[lemat]

I use ofen depron in aeromodelisme appication : It's note a good thing for surfboards. Depron is XPS foam like bleu and others. On 2lb foam it's a very complicate building for nothing. Put your plywood  stringer in the center of your blank, shape, hand laminate and go surfing. If you want a sandwich on 2lb foam: shape without stringer, glass lam bottom with lap rails then bag a 1/16 balsa skin with glass on deck, adjust rails and lam.

You can find balsa in modelisme (model) shop.