Has anyone heard of venting for extruded foam?
If so, maybe someone can tell me how this is done?
Here’s how NASA does it.
http://www.nasatech.com/Briefs/Sep01/MFS31498.html
It’s very similar to how Epoxy Pro does it. They do it on the deck of the boards only. I wonder why they don’t do it on the bottom too.
this may work on non laminated foam surface. but from my personal experience this technique doesn’t work. tried this through the 80’s. also looks like crap.
Does anyone have pictures showing the deck of an Epoxy Pro board with a vented deck?
Would be interesting to see! Also are the holes all over the deck or only in the spots that tend to get compressed?
Do they put in the vent holes before or after glassing or how do they do it???
/Erik
Try to search the Archives for ‘Goretex’ or ‘Breathable Vents’ There is some really really good info for all that there. Paul Jensen, Bert Burger and some of the other great innovators contributed to that thread. Very, very informative.
My understanding is that as the gas is heated it expands.I was told just to keep it out of prolonged sun light,(sure).
The first board I built from the extruded foam showed some signs of delam after it had been left cooking on the beach.
I am not so sure that the delam accually came from the heat though.
The next board I took a hacksaw blade and cut shallow lines through out the deck and have had no problems so far. But in the back of my mind I worry about gas pressure and if there is a viable solution I’m on it.
rooster … you did the right thing there…
there seems to be 2 different foams being refered to ,extruded polystyrene-xps or xtr…
expanded polystyrene-eps…
lower density eps must be vented,for higher densities its optional depending on climate , even tho a vent will prolong the life of the board…
for extruded foam , no vent is needed coz the foam doesnt hold volumes of air like eps,
the problem with xps is the gas in each cell can diffuse through the cell wall when it gets hot , that can get trapped under your glass job,
a delam in eps results in the core ripping apart internally, but a delam in xps results in the glass lifting off the foam, the main reason is because when they make the foam a small amount of polyethelene is added so the extrusion machine doesnt get gummed up,it acts as non stick and helps the foam slide out of the machine, it gets fed out in a continuous length , like squeesing toothpaste…
but the polyethelene makes it harder for resin and glass to bond, coz its a nonstick formula…
i ended up making a small device , with a stack of razor blades embeded in a resin block with a flat plate , the blades were set to cut at a shallow angle about 8mm deep , i would run the block over the foam leaving fine razor cuts running in a criss cross pattern …
when you glass the board the resin penetrates and bonds the laminate to the foam better , it works well …
but if you want a light board , you will get a print through of the pattern when the board gets hot,that gas is still in the foam cells , it wont lift the whole glass job up , but it will cause enough pressure to create a pattern , or maybe its just plain old expansion and contraction with heat???
but either way the pattern shows through with heat to the point that it creates a contoured surface…
i would say with a heavier glass job this might not happen…but i wasnt interested in creating heavy epoxy boards…
regards
BERT
Bert dispatched:
but the polyethelene makes it harder for resin and glass to bond, coz its a nonstick formula…
i ended up making a small device , with a stack of razor blades embeded in a resin block with a flat plate , the blades were set to cut at a shallow angle about 8mm deep , i would run the block over the foam leaving fine razor cuts running in a criss cross pattern …
ha! I did the same thing with my backyard extruded board…I used little squares of heavy cardstock sprayed with super-77 and exacto blades. gluey mess getting them together, but when done, it pulled 10 or so blades through the foam at a shallow angle, cutting clean little slits in the foam. I chose to just do straight cuts, from nose to tail, as it seemed to hold just as much foam as cross-cutting, and took less resin. Gave it an oxford pin-stripe look, too. !spiffy ! Anyway, I was just feeling all smug and had grooved about half the board, when I got careless and dropped the little block on the table. Arrgh, all the blade tips were bent. more glue…
I’m finding (with heavy abuse) that the foam will compress and tear internally, if the skin is bonded well enough. I’ve got a big delammed area just under my back foot, and the foam has crushed pretty far, and ripped as the epoxy skin popped back into place, with chunks stuck to the skin. I recently repaired the rather large void with some urethane crack-filler, quick and dirty, worked great but is ugly…That board is somewhat of a test platform, I’ve been abusing it, seeing where it falls apart and what remedies that…it’s a regular frankenstick.
wells
yep same thing here . it eventually shears away from it self further in …
you get a bit more life using cuts …but all up i dont rate the foam…at least eps will move and tolerate shear loads without letting go of itself internally…
regards
BERT
Yeah, I’ll not be building another using the blue stuff…next project will be EPS…
thanks Bert and Wells, so you both agree eps is a better way to go. I have enough epoxy for one more board. Do you guys have recomendations on how to treat the formed blank? like I have heard latex paint mixed with plaster.And what about venting,is there a nenting system out there that releases gas without taking in water?
Thanks roostersurf