which eps grade? - Sabs, Bert, Bluejuice

Need some advice from the eps sages.

I’m making a sandwhich eps board using Bert’s recipe. Using 3mm 80 kg m3 core-cell for the skin and rtm styrofoam(xps) for the rails. Which eps grade should I use? the SL (10-12 kg m3) looks like the beads will tear out during shaping. The M grade (at 20 kg m3) looks much better. Is the SL shapable? Using the M grade only translates to an extra 250 gms over the SL in the finished 26 litre blank and an extra 20% in cost.

Appreciate any advice.

For sandwich construction use the lightest stuff you can get. Don’t worry about the shape being real fine, it gets covered anyway and the exterior foam is what shows.

The lightweight stuff shapes just fine. Anything works - I’ve used planer, sander, grinder, surform, screens, and sandpaper. You’ll make up the strength you need in the skin.

As Greg says go for the lightest you can get,hotwire or laminate the rocker on a table

If you hotwire,which is the simplest way,make two templates that are a cross section through the center of the board,stick them each side of the eps block

Cut the bottom rocker first,now turn it over draw your plan shape on it and then shape what ever channels concaves etc

Doing it this way makes it real easy as you are working on a big stable block if you mess up unstick the templates and move them down 10mm rehotwire and start again

For bottom the shapes use only sandpaper on a board 100 grit gentle touch clean off the sand paper every couple of strokes

for concaves make a curved sanding board

Once the bottom is done turn it over use the off cut as a rocker table and then hot wire the top

cut the plan shape,remember to deduct the rails

all you have to do now is the deck roll measure and mark then surform down then 80 grit isanding board finish with 100 grit sanding board Once again use the rocker table left over from hotwiring to work on

That way the board is allways stable

You will find that its just like working a pu blank when you get the hang of it

If you have air blow the surface clean regularly while shaping

You shape the rails after the foam skins are on using a sanding block

I did a board a while ago with 5mm 90 kgm3 skins and 90 kg m3 rails and 3 oz glass each side two layers on the deck It weights just 2.5 kg with fins and is so strong its crazy Im going to do another soon this time i will only put a single 3oz on the deck

How does it ride?

I like it a lot, it maybe has not got quite the spring of the balsa or beech boards but it does have more spring than my pu epoxys

The lightness is the key though for me it feels a lot easier to put it in different places on the wave face


I am lost here. Are we using eps for the main body of the board and extruded for the rails?

what is BERTS Receipe? And what are skins. I have this feeling I’ve missed something good. Can someone please explain to me in beginners terms what we are doing here.

Thanks Keith

Bert made another really helpful thread about vacume forming and construction or something titled like that, and he has a great picture every step process abotu how to make a board thats layered with different foams and stuff to make a flexy, light, strong board. I think the ‘recipie’ is in the recources under memorable posts or somthing.

yea go the light stuff …

you need some movement to make up for the overall stiffness of the sandwiches…

higher density with a sandwich would be hell stiff …

a little movement adds to the durability , under heavy load situations it can absorb a little impact …



how good is superbank???

i wanna live in queensland , hm? with the 50,000 other surfers, ok maybe not


how good is superbank???

Good enough to make Sydneysiders Cry…!

But yeah its too crowded, heck come to think of it so is sydney, I wanna live in west oz…


Thanks for the advice gents - the SL it is.


how good is superbank???

Good enough to make Sydneysiders Cry…!

But yeah its too crowded, heck come to think of it so is sydney, I wanna live in west oz…


head SOUTH, not west, young man…they got it wrong, whoever came up with that expression !

Thanks guys, but what I really don’t understand is,I read somewhere in here that 3oz fabric was used. well the 1 board I made with eps was so soft I kept adding layers till the weight was up to normal and was still soft. Great board though. And what is a diviny cell? I read bert’s vac. forming thread and it was way beyond me,but I did get the idea.


One day I decided no more making surfboards,and that got me thinking about how I would make the next.Guess the resin is addictive,lol.

Thanks Sabs,

Your method might be a bit easier for doing bottom contours on the first board(s). Bert’s contour mat system seems to be a bit labour intensive for a few one off experiments. I’ll be getting the blanks cnc hotwired. So have to be careful not to mess up the bottoms.

What is Divinycell? - Basically a high density sheet foam. Here is a link taken from Fiberglass Supply website.


In excellent post by Bert Burger, he shows it (or something very much like it) being used with epoxy and fiberglass as a composite shell over softer/weaker EPS foam. You might also check Michael Jones excellent essays on his own composite boards using a high density foam composite shell over a laminated dual density core.

PS - If you didn’t get it the first time, try reading again. For a specific problem, you might even try a private message to Bert, Michael or any of the other guys who are dabbling in this exciting technology. I know the concept of a durable custom composite board in the 5 lb range opened my eyes.