EPS VS XPS..

Hi there, Last time I mentioned a blue foam, I was confused by the product name since the shop guy did not have the Eng name of it. And I finally got the name of it, its kinda XPS where X stands for Extruded. Its not a new product cos its widely used in roof top insulation. Here in Hong Kong where buildings are made of concret, instead of 2’ x 4’ x 1 inch xps sheet, I can’t get a large block of it. I bought two sheets and tried to build my kiteboard, I can use a electric jig-saw to cut the outline smoothy. When using a 60 grit sandpaper, I can easily to shape without tearing off the beads. This leaves no fault to the blank, you dont have to spackle. Does any epoxy guy try it before? Any sharing is welcome~… Regards, Crabie

I have used it and in fact I was the US distributor for Dow Chemical XPS in the eary 90’s. The foam is fine to use and shapes and laminates well. It will delaminate under certain conditions though. These are heat related but if your just doing boards for yourself and even a few friends, and you know the drawbacks, the foam is fine. I just don’t beleive this product is stable enough to build boards to be sold. In other words don’t start a business using this as your core material. EPS on the other hand is very stable and if produced in modern molds called EDRO. This is our foam of choice.

Thanks Greg, Great info~…I used to hotwire a eps foam block in shape and glued with a wood stringer. It took months to complete a surfboard, never thought of being a pro. That’s another question hope you can help me. I used 2 lbs pcf/32 kg pcm eps foam block to build surfboard. The blank is relative heavier than pu foam. Last time I build the 5’10" blank, it weight about 5.5 lb before glassing. And weight around 9.5 lbs with 2x2 6oz fabric, hotcoating and glossing. So this time, I m ready for the coming summer. Is it possible to build the blank with 1 lb pcf/16 kg pcm eps foam with 2x2 3 oz fabric? Regards, Crabie

What kind of stringer did you put in? A 2# density blank shouldn’t weigh more than two pounds unglassed.

Greg, can you suggest any info sources I might check out to get more familiar with eps materials? I’m not interested in making my own blanks but would like to be more knowledgeable about them (common density references, etc…) if I were to buy them from someone, say from you (if you sell them). I’ve shaped several eps blanks over a few-year period and learned how poor the structural quality can get (cells fall apart into beads when sanding). Last year I bought a Patagonia board, and discovered the eps blank they use has a stiffer, more fibrous quality. Someone I called at Patagonia told me a standard bladed planer drum works well on Point Blanks as long as it’s sharp-- my experience with the “beadier” eps blanks had me using an expensive custom made planer drum to achieve a smoother surace while a bladed drum chopped out chunks. Can you or anyone explain these differences in the foams, and then suggest where I may find a reputable eps blank maker who sells to garage shapers?

EVERYONE should learn to produce their own blanks. It’s one of the easiest steps in building a board, saves a lot of money and offers you a chance to REALLY design the board. I use a standard planer with standard blades. Nothing fancy at all. The foams you want to look for are made in EDRO machines. There are two here in Fl. and four on the West Coast. Where are you located?

I used 1/8" plywood as the wood stringer. This time I 'll try the balsa since it’s lightweight enough. Besides, I did lots of faults in my previous board, the spackling compound and the absorption of resin added weight to the blank. Regards, Crabie

Hi Greg, One more question, how about the 1 lb density of eps together with 1x1 6 oz fabric + 1x1 3 oz fabric? Cos only 6’ in length of 2 lb density eps foam block could be found in here. 8’ or over only available in 1 lb density. Regards, Crabie

Thanks for the reply, Greg. I’m in Houston TX. I’ve seen an operation here in town that sells blanks at a pretty high price; they use a simple hotwire system to slice down billets sandwiched between rocker jigs. Having purchased blanks from them before I’m aware of the intensive work they go through to cut down stringers and glue the pieces together without twisting the final product. I’ve bought crappy product from them before and some decent stuff…I agree about learning the process from total scratch, but the space requirements and time connected to the labor, not to mention initial investments on a decent scroll saw for the stringer, billets, etc… you know, it’s something I want to grow into eventually for sure, like how I slowly learned intial basics with an experienced friend who had tools before aqcuiring my own setup. I’m open to persuasion. I could get the stringers made at work. What could be ballpark startup costs and how many blanks (successes and failures) should that yield? $300 bucks? $400 bucks? Finally, I read briefly info on eps and learned about a more rigid product by similar process-- PE (polyehylene??) or something like that. Can you offer info on what I’d mentioned about the material Patagonia uses or a little insight on your experience with any eps variations? Thanks for the time.

You should be able to get a block of foam that will yeild 10 blanks for under $150. You can buy smaller blocks if you’d like. These companies are in the Phone book under insulation materials, yellow pages. The variac (voltage regulator) sells for about $125 and can be bought at Wicks at www.wicks.com. I think the rest is in the article I wrote below. The making of urethane foam is very toxic, expensive and difficult to do. It takes a large capital outlay for molds, chemicals, safety gear, etc. Conversely it is quite easy to make a polystyrene blank. You can generally get blocks of foam locally from insulation foam suppliers. The rocker templates are made from 1/8 inch masonite. They are attached to the block with nails and you then slice the foam with a harp, strung with a piece of nicrome wire, that is powered by a variac. A variac is a voltage regulator. For the foam, look in the yellow pages under insulation and look for a supplier of foam. Almost every major city has at least one. For the variac, they are available from Wicks aircraft. They have a nice voltage regulator for hot wiring for about $100. I think they also have wire. They have an online catalogue at www.wicks.com. The harp is just a piece of plywood cut in a U with the wire strung across the open end. It has to be wide enough to fit across the foam your cutting and deep enough to cut the thickness of the blank. Give yourself lots of room on that one. You attach the voltage regulator to each side of your harp (we use alligator clips), turn the regulator up to about 25 volts and your ready to cut. Set the wire on the templates that are attached on either side of the foam block and push the wire slowly through the foam. When you finish the deck, hook the wire under the templates and pull it through the bottom. It helps to have a fan blowing down the block of foam to cool the exposed wire that’s outside the block otherwise that portion of wire super heats and you break a lot of wires. After you’ve cut your blank, set it on a shaping rack bottom up. Get a piece of hot wire long enough to reach the length of the blank and about 2 feet extra. Attach a piece of wood (these are handles) to each end of this wire. Now attach the voltage regulator to each end of the wire. Now you need to find the middle of the blank and mark it on each end. You need a friend to hold one end of the wire while you hold the other. Set the voltage at about 70. Stretch the wire from end to end on the marked center of the bottom of the blank and turn on the variac and slowly pull the wire from the bottom of the blank to the deck. You now have the blank cut for the stringer. You need five bar clamps to glue up with. For a stringer you can use 1/8 or 1/4 inch Luan plywood which is available at Home Depot. This stuff doesn’t shape great but its easy to find and works. You can also use 3 mil PVC which comes in 4x8 sheets and is available from sign supply companies. Comes in colors and looks great. For gluing Luan you can use good old Elmer’s glue. For PVC there is a glue called Roo Glue that works well. You can probably find that on the web. When you glue up, you wet both sides of the stringer and both sides of the blank line up the parts and then bar clamp it together. And that’s about it. Any questions?

Crabbie, When using one pound density we always glass with at least 2 layers of 6 oz on the bottom and 3 layers 6 oz on the deck. For 2 lb density, usually 2 layers of 4 oz bottom and 2 layers of 6 oz or 3 layers or 4 oz deck.

Greg, Thanks for you info. Would it make much weight to the board? I did a 4’10" mini short board for my friend’s 8 years old son. Its a 3x3 6 oz fabric, 2 lb eps foam, weight around 8 pounds, this one is stringerless. Regards, Crabie

Very valuable, time-saving information, Greg. Thanks for sharing. It seems far less intimidating when explained, and will be fun to persue with my next round of efforts.

Wilbur, I don’t think anything we do as hard. It’s just knowing the techniques. Crabbie, I’m not sure your scale is correct. 8 lbs. for a 4’10" seems a bit heavy to me.