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Heat Damage

kind 'a cute, actually

and provoked all manner of hilarity as it reposed on my racks

but the owner of this almost new custom extruded EPS board was not amused

Most everything in our daily lives is heat sensitive. We know better than to leave the dog locked in the car on a warm summer day. We know better than to leave a cake of wax on the dash, or a can of pop. But for some reason, people continue to be surprised when their boards blow up after having been exposed to that same sort of heat. Most materials change their molecular structure when heated dramatically. So does the EPS foam in Epoxy boards. As it changes, it releases prodigious amounts of gas. That gas has to go somewhere. It will make itself room. It will blow a bubble. Or two - see above.

So keep it cool! If you are comfortable, so is your board. If you feel sick from heat, so does your board. If you leave your board in a dark car, windows up, and the outside temperature is 95 degrees, the inside of your car may well go above 130 degrees. EPS foam outgasses at 130 degrees, Divinycell shrinks markedly at 130 degrees, room-temperature-cure Epoxy resins turn brittle at 130 degrees. The result at minimum is a reduced lifespan of your board. You may get away with a printing through of the reinforcements and inserts. But you may well end up with a bubble.

So - how come these problems are just localized? Localized bubbles are usually the result of concentrated heat. I have seen boards transported on top of hatches on motorhomes, where the glazing reflected the sun's heat onto a square patch of board, producing a square bubble. Also, if a board is fatigued, a general heating up can cause a locally fatigued spot to blow. Or it can be a combination, such as when my Olde Trusty blew an aneurysm while waiting for wind under a blue tarp. Mid-bottom had already delam'd in a few places, and it gave way this time where the tarp touched the bottom, creating a patch too hot to touch.

Keep it cool!!


not quite as picturesque a bubble as the purple one above

all ingredients were properly processed, adhesion was good between layers, there was no contamination, no cavities

the cause was unequivocally heat, as evident by the altered structure of the EPS foam: the "fluff" surrounding the foam beads shrunk, leaving the beads standing proud. Instead of a satin-y feel, the surface feels scratchy, i.e. the material turned brittle.

These changes require at least 130 degrees of heat. At 130 degrees, EPS out-gasses strongly, blowing the "lids" off things, distorting boards, and generally wreaking havoc.


smooth, healthy EPS at top of cut-out; shrunk, heat-damaged EPS bottom 3/4s

The fix: bevel-grind the edges, vacuum-bag new inner glass & PVC foam
glass over, fair, prime, coat w/ LP, rub out, and send home with a stern lecture about keeping the board away from extreme heat.

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