Hey! I want to make a 9’3"-9’6" longboard, but i only have three pieces of 40"x23"x4" EPS. I was thinking about gluing the short sides together, to get the length needed for the longboard. Will this reduce the strength of the board etc.? Is there anything i can do to reinforce the board, if necessary? (Reinforcement except glassing)
Add a single continuous stringer… or 3.
For a first time shaping project, making a longboard is going to be a challenge. Making it with pieces of foam you need to glue together will be even harder. Glue lines tend to sit proud and getting them “just right” can be frustrating. I try my best to glue up the area I think will be below the surface of the finished board. When you spackle the board, it will fill in any small cracks.
If you glue EPS using Gorilla Glue or a similar product, the glue lines will not break. I make boards up to 8’ long using pieces of EPS foam, and many are stringerless. I glass my stringerless boards with more glass wrapping around the rail. The last 4 have a 1/16" Balsa veneer on the deck for better dent resistance.
A stringer would help, multiple stringers or perimeter stringers would be even stronger.
I’m not too happy with single stringers and EPS. Seems like the foam around the stringer ends up getting pushed down to the point where it can tear along the stringer. I haven’t gotten any that have done it yet, but I have a lot of boards and I use a different board almost every time I surf.
I added a shot of a 7’2" board made from 4 pieces of EPS glued together, no stringer. The glue line across the center is at at angle, but it’s harder to get it right. I glued up the front half and back half then cut the v and glued the 2 halves together. I used this board during a hurricane swell with close to double overhead sets. I thought I had snapped it during a barrel that I didn’t make, but it was and is fine.
I am almost finished with a new board that is only 5-10, I stagger the foam sections to keep the glue lines across the board alternating. I also chose to cut the foam into pieces where I need to glue up 2 peices to get the width I need. The original block was approx 4’ x 4’ x 13". I have 3 pieces on one side and I’m gluing up 2 on the other. The foam was cut with the middle rocker and I added the rest after it was glued up.
I’ve also cut up EPS coolers and glued up small pieces of foam to make boards, but I added stringers in those.
Just glued up a 9´6 Blank the other day… I assume you got your EPS from normal supply with low density? Add a Stringer, for weight and stability purposes…
Dont worry about the PU Glue, its way stronger than the foam. Cheap shaping trick, let it fully cure and mow it down with the handplane when it comes up sanding, like you do on the stringer. Works fine for me.
As Huck suggested, you can add more stringers if you feel like, since its a first one, perimeter rail stringers might be the easiest 3 piece wood option.
I might still do that as well, but my plan is to add high density foam to the rails, like sharkcountry showed to me. It will have the same effect.
You might also want to consider to add high density foam inserts for the fin boxes and leash cup, if the density of your eps is low.
I went like this:
CRUCIAL: Your rocker is going to be around 4" on this kind of board so dont forget to add the board thickness on top. You dont need an extra block, just put a spacer under a block for glueing, see the little trick in the picture below…
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Glue up the 3 or 4 pieces of EPS to 10´ or something
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Use a saw or hotwire and split it in half lengthwise
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Turn the sawed sides out and the manifactured smooth side inside. Glue the stringer to one side and take measurements of its position.
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Glue up the other side to the stringer and press the blank
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Release and hot wire according to your measurements
Have fun 
