I’m going to build a board using epoxy and 2 lb. EPS (type IX EPS). From reading the archives I know that newer production methods produce a foam that has much lower water absorption than EPS foams in the past. My question is: If the foam meets federal specifications ASTM C-578, (online, most manufacturers claim their foam meets this specification), does this mean the foam is the newer low water absorption type? Or do I still need to make sure the foam is manufactured using EDRO machines with well fused beads?
One of the ASTM C-578 specifications for type IX EPS is, water absorption 2% or less by volume, for one inch thickness and total immersion.
depends on how you glass it as to how water resistant it will be ,if you dont allow the resin to penertrate to far ,then if you get a ding itll be more likely to suck water,on the other hand when you glass it ifs it allowed to suck more resin itll be sealed to a deeper depth in the foam,making it harder to ding to the point of sucking water…but your board will be heavier…
The dealer is R-Factor located in Portland Oregon. The manufacturer/distributor is Northwest Foam Products, Inc. located in Idaho and Oregon. R-Factor is only 20 minutes from my house and said they could have Northwest Foam cut whatever thickness I need from a 4 ft. by 8 ft. block of virgin 2 lb. eps, as long as I could pick it up at Northwest Foam. They are also about 20 minutes from my house, so this would be very convenient for my if the foam is any good.
I’ve make six or seven polyester boards in the past but don’t really know how to judge eps quality. Maybe I should just order a block and and see how it works out.
The above link lists the plants that make EPS. Just find the nearest plant, call, and ask for the nearest distributor. I even had insulfoam send a custom 12’ billet. Price runs about $2.50 per cf.
Make a couple of calls and you should be able to find some.
Good Luck,
Gary
PS Jack, I’m in Portland too. If you need any EPS tips email or message me.
I just posted this on another thread and it seems that it should be posted here as well.
Fusion - We usually kind of run a thumb over the edge to see if it breaks off easy. Some experience helps here. If it does break off easily and you can see that the beads themselves haven’t torn then it’s probably not fused that well. Fusion is the most important aspect. Badly fused foam leaks and breaks easily.
Pack - Well packed foam has very little space between the beads. Looking at the hot wired surface you should see even texture without a lot of holes between the beads. The smoother the texure appears the better the pack is.
Bead size - Beads are graded A, B, C, and T. A is the biggest and generally you don’t see those much anymore. Mostly you see B or C size. Generally the fusion on B will be a little better than on C, but the pack will generally be better on C. A well fused C is the best, if you can get it. Our foamer uses a B/C bead which is an in between grade which gives us a very consistant product. The foam processing machines (generally called a press) that are being used today can also process T bead which is very small. As yet I have not seen this fused well enough. The pack is awesome though.
Density - We use every density but on a daily basis the 2# is best for most boards. It has great strength to weight ratio (much better than any urethane), has the best resistance to leaking, doesn’t have to be glassed that heavy and is best for break and dent strength. 1.5# will make some real light boards with light glassing but those boards tend to be weak and on the disposible side… they do ride awesome though. There are some manufacturers who like using 1.5# and glassing them up. This is a very reasonable product anywhere you have a lot of rocky beaches or crowds. This can also be combined with a more flexible epoxy for excellent impact (ding) strength. 1# is used when coring your laminates, like Bert does. Almost all sailboards and the Surftech boards use 1# for the inner core. I have made boards using 1# with a heavy laminate and they ride awesome and have good ding resistance. They do break easy though.
im actually using about 3/4 lb ,and yes it will break easy if you do a standard laminate ,coz the foam cant support any load and they will fold easy ,but a cored skin can tolerate so much compression that it spreads the load over a greater area …if you double the thickness of a laminate it then spreads the load over an area 4 times bigger …thats where sandwich is so good ,in my case the skin can be up to 16 times the thickness of a normal glass job, allowing it to spread the load over a massive area ,thus you can get away with minimal core strength ,
and if you set your skins up right ,you dont even need a core, coz it can spread load all the way to the rail…
secret, remove shear load and sheer stress from a skin and a whole new world opens up…
That 3/4 lb. foam is nice to absorb impact and localize impact loads though. Hollows haven’t worked yet because any impact goes to the weak point in the structure. Filling the void localizes the impact. Sailboards spent millions on hollow tech and never made it happen. Also you reduce interior structural demands by having that interior foam there. You don’t have to bridge so much unsupported acreage. Bert, your method of supporting the rail is exactly correct. Takes so much load off the skins. Shared load is what I think your talking about and I’m a firm beleiver in that.