Not immediately.
Typically, the discoloration (brown foam) happens when light, probably UV light hits foam. You see that in older boards, t’suntan’ look, especially those of highway surfers who ride around with their boards on the racks 24/7, that are exposed to bright sunlight all the time. The foam breaks down, shrinks in serious cases and when the foam is kinda crap to begin with, say old popouts. But it takes a while.Polyurethane isn’t the weakest molecule.
However, water is interesting stuff, salt water even more so. Oxygen, in a polar molecule, and salts making it even more so. that breaks the foam down faster. If your glassing is flawed, well, when the board gets warm in the air and light the foam outgasses a little, the gas that makes it a foam rather than a solid resin expands, that escapes through pinholes. If your glassing is light, it may permeate through.
Okay, neat, but what happens when you go in the water? Well, that’s cooler. The board cools and the gases in the foam cool and by the Ideal Gas Laws, they take up less volume, creating a vaccum. And if your board has pinhoes, well, it sucks in water. Repeat it, plus sun exposure to turn it brown, you eventually get ‘freckles’ in the foam. Though it’s too late by then to do anything about it.
This is pretty much cosmetic, no biggie. But it can, in my experience, lead to delamination over time, which is a biggie. Again, the foam is breaking down right where the glass bonds to it.
Now, surfboards are ephemeral things. They don’t last forever unless they don’t get used. They bang into things, doorways, parking lots, rocks, you. You can build them to last, I rented out boards that were made as rentals, multiple layers of 10 oz cloth top and bottom. Surprising number of them are still around, But they’re heavy. Now, the premium is on light weight, which means light construction. And shorter lifespan. Including light glass, hotcoats and glosses thinner than they were.
And yes, those are more permeable. They break more easily. And they ding more easily. The manufacturers like that fine, a board that’s cheaper to make with a more limited lifespan, well, that is something you use up and replace more often.
Caveat emptor
doc…