Concern of yellowing spot

I recently I left my board out in direct sun for about 10 minutes to remove wax form the bottom as a result of stacking my boards. I left the board out for 10 minutes before I noticed a yellowing spot! It was only 77 out and oddly that specific spot was extremely hot compared to the rest of the board. Thankfully the spot isn’t mushy or delamed but I’m pretty lost as why that spot got hot and started to yellow! Any ideas to how it happened? Should I be concerned since there will be many days I will be leaving this board out in above 77 degrees weather in SoCal?

Huh. Interesting - 

I figure there’s four possibilities. 

First, foam is never perfectly homogeneous. There’s variations everywhere in a blank which is why you’ll see ‘freckles’ on an older board that’s been in the sun a fair amount and the glass is still perfectly watertight. 

But this is more of an area, not a spot, shading a bit as far as I can see, and there’s the localised hot spot you felt - so it leads me to the …

Second possibility, far more likely: you happened to put the board somewhere that a reflection or refraction of the sunlight heated up that particular area. No idea what, window, curved shiny surface, any number of things could do it.You might see a bright spot, you might not.  If, say, tomorrow at the same time of day, car parked in the same place and everything else set as identical as you can make it, you set some bars of wax where the board was including right where the brown spot on the board was, see if that bar melts or softens and the others don’t. I’ll note that that would confirm my little theory but if it doesn’t it’s still a possibility; there’s a lot of other variables involved. 

Third, a person or persons unknown put something hot on the board right there when you weren’t looking, then took it away. Stranger things have happened. I had this girlfriend once …

Then there’s the fourth possibility- I’m completely wrong and it’s something very different indeed. I’m just guessing from incomplete information. And sometimes I’m not that bright

In any event, sunlight and UV light break down foam over time, shown by how many older boards turn brown. They don’t do the resin any favors either. It’s a polymer, after all, UV is pretty energetic and breaks chemical bonds quite well… Those relatively inexpensive reflective day bags ain’t a bad idea and they also help with the many little knocks and bumps you accumulate without one.Which increases the lifespan of the board considerably.

And they keep wax from transferring from the deck of one board to the bottom of another. So you wouldn’t have had this problem.

hope that’s of use


Solid info there from Doc.

The most common cause of yellow spots on a board is water entering via pinholes in the resin. The salt water causes the UV protection to fail and the foam turns yellow where water has entered.  I had a board that developed many spots over time and when I looked at them with a magnifier I could see pinholes. I dabbed small bits of catalyzed resin where each one was to stop the water entry.

 A photo or two of the problem area would help to ID the issue.


pindots came from the t&c and takayama clark foam fallout 

they called it blow through… you guys brought up all tthe things

I thought of except one,… evil spirits…


plant some ti arround the yard


When was that? The example I gave was a board made in 2001.

Poor hotcoat and oversanding on a sanded finish board is da $#!ts.  And is exactly what a board will eventually look like.  Shit brown spots here and there.  Sometimes the the whole board.  The oversanded hotcoat allows water to penetrate the weave.  Brown spots here and there around the rail are usually a result of over grinding or sanding done on the laps before the hotcoat. Lots of high speed friction turns resin impregnated cloth brown as it overheats.  Most of the time the amature doing the oversanding doesn’t even notice it until the board is finished.