Deep cuts into urethane blank then glassed with epoxy

General Discussion
1

Deep cuts weaken a urethane blank.

Will a urethane blank that is missing most of its crust still be stronger than a styrene blank? Let’s say a lightweight urethane vs 2lb styrene with similar stringers and same glass schedule with epoxy.

 

 

2

Depends on the blank density, but from what you described, probably not.

3

Thanks.

I’ll keep working through my block of EPS

4

EPS strengh as foam surfboard blank mostly come from cohésion between bead. Comp strengh of EPS is mostly density dépendant, and because it’s visco elastic bead pak EPS have a great comp strengh/memory by weight. Cohesion strengh depend of bead fusion, it dépend of how foam was made, some are better than other. Search some trick to improve cohésion after…

5

Thanks lemat

We worked our way through a lot of the EPS manufacturers here (Melbourne, Australia) and the quality varied a bit.

Bubbles of foam in eps vs bubbles of CO2 in urethane. In both cases it seems that small bubbles is better.

6

Bigger beads can reduce space between bead and allow better fusion, so reduce macroscopic porosity and increase cohésion between beads. But bigger bead have bigger cells and lower cells wall wich reduce their strengh. When you break small beads foam it break between beads whereas with big beads it’s beads wich break.
You want small bead strengh with big bead fusion…