Do It Yourself EPS Blank Making

I figured I would do my part in adding to the archives for all those wanting to try the EPS garage build.

I’m sure there are some out there who will want to add to it. I’m sure there might be some who are tired of hearing the same things. :slight_smile:

But maybe there are some who will get some use as well.

Step 1 is aquire some EPS. This can be done from many sources, you can do the Home Depot route (read Benny1’s 14$ blank thread) or you can find an EPS manufacturer near you. (do your google searches) I discovered one in my area that makes blocks for geo-fill.

The block I purchased from them was a 12"x48"x96" of 2#/ft3 foam. The reason I bought one this size was that with 2 pieces of 12" wide foam I could simply glue a stringer in between them without the trouble of then cutting the blank in half. (thanks to one of the Europeans for this insight. Can’t remember who though… sorry)

Make yourself some templates. You will need outline as well as profile/rocker templates. I use the APS3000 software to do my designs and then print out the outlines full size. A little work with Adobe Illustrator and I put both templates for a board on one big page and send it to a local print shop to have them printed. Cut them out, trace them on masonite and then jigsaw followed by a belt sander to true up/smooth out the curves. Drill holes in the rocker templates so you can screw them to the block of foam.

You will also want to make a hotwire. There are plenty of ideas, schematics and pics in the archives. Just search ‘hotwire’. My own I made using an old train set transformer, a bow I made out of maple (16" wide and 8-9" deep) some electrical wire and alligator clips and finally for cutting I am using a fishing leader. I also found some NiChrome wire after some hunting, but haven’t used it yet, it is supposed to be the best for the job. Go and check out your local Hobbyshop for replacement wire for there small hotwires.

You want to put the block on edge and then get it Level, so all your marks will come out even from one side to the other.

Screw the first template to the block of foam and then use a level and square to make a straight line from that side to the other at the tail and nose. Take measurements from the end of the block and down from the top to get an accurate point to place the second template on the other side of the block. Putting the second one on is tricky by yourself, an assistant would make it a lot easier especially for longer boards, but I have made do so far.

With the templates you can get ready to fire up the hotwire. Have a fan blowing air on you while you work and the door open. This keeps the wire from getting too hot and it will vent the fumes to the outside. When you are doing the cutting I found that the advice of another swaylocker works best. Push then Pull. Do the top rocker first, pushing the wire down the nose curve and then pull the wire towards you, again from the nose to the tail.


When your first piece is cut out you simply repeat the proceedure and cut out the second half.

When you have 2 rockered pieces you can then glue them together. This question seems to get asked about twice a week, but a good glue recomended for gluing foam is PU glue. It is sold as Gorrilla glue, or cheaper as Elmer’s Polyurethane glue.

The one problem that I have with PU glue is that it seems to penetrate the foam to quite a distance sometimes. As much as an inch and a half. While the stuff is easy to sand it is still harder than foam and I have found that it can make it tricky when it comes to the buttcrack of a fish, and cosmetically it will show somewhat through a glass job.

It is not a huge hassle; and it might be a case of applying a thinner coat of it or it might be the quality of foam, but I am going to try it with some epoxy resin the next batch of blanks I make, just to test out the difference.

The PU glue is simple to apply. Just put a thin coat on the edge of each piece that will go against the stringer, run a damp cloth on the stringer (the PU glue needs moisture to work) and then put the pieces together and clamp with bar clamps. I only have 4 bar clamps, but it works allright, I just use tape to tape the nose and tail together.

I found that it is best to lightly clamp the pices together on my table, then tranfer them to the floor (on edge) and then I can make adjustments to the blank, before clamping totally (not too tight, is foam after all). My stringers come out 1/16" larger all around due to router jigs, so I have to make sure that the foam is equal all around. If your stringer is got a good curve, then jujst line up the foam on one side of it.

So now you have (4 hours later at any rate) a blank that is ready to shape.

Usually it will be a large rectangular thing with some PU foam glue drips here and there, some but not too many hotwire wobbles and hopefully no big difference between one side and the other.

At this point you will want to take down the stringer with your small block plane until you hit the foam. I will then take my big sanding block (24"x4" with a 50 grit sanding belt cut and glued to it) and use it to smooth out and true up the blank a little. You have to be carfefull doing this, so as to not make the thickness uneven from one side to the other.

The next step is to cut out the outline.

Put your outline template on the blank and trace it out. A handsaw doesn’t work very well to cut EPS, so I found a long blade for my jigsaw(5") and use it. True up your outline with a small sandingblock (8"x4" with 50 grit) and now you have a basic shape that just has to have bottom and deck contours put in and then rails turned.

For now I have been using my sanding blocks to do the deck and rail bands, but other are using electric planers and some others here at swaylocks have built adjustable angle hotwires to do the banding. Seeing as my budget is limited right now, I will be trying to build the hotwire before I buy a planer.

After rough shaping I take a scrap piece of EPS with some 100 grit and gently knock out any edges left by banding and rough spots, then I finish it up with 80 and 120 grit sanding screen with a couple of pieces of soft foam as backing. After that spackle, consistancy of melted ice cream, and then screen again when dry then you are ready to glass.

Anybody want to add to this? Give there methods?

What ever you do; have fun!

Edit: Oh yeah, I bought my block here in Canada for 240$, and I was able to get 7 blanks out of it. Comes out to very cheap blanks, especially for me who would otherwise have to pay hefty shipping fees.


About glueing the 2 halves to the stringer using epoxy resin. Good idea but…

If I’d do that, I’d “shoot 2 birds at a time”: why not lay a band of 4oz. fibreglass on each side of the wood stringer just before clamping??? When resin is set, just use an exacto knife to cut the excess of fibreglass.

This would be a trully “sandwich stringer” which would add a lot of stiffness to the resulting board. You know: 2 vertical fibreglass layer all the way long.

I guess the “sandwich stringer” would be a little tricky to shape, but since the EPS is already hotwired to the final dimms, I guess you don’t need to touch the stringer very much. Am I wrong??

BTW: I did something similar to you sometime ago, but going the hardway (no hotwire).


Hey Neira!

That thread is what inspired me to use 12" thick pieces after hotwiring a 24" wide blank. Muchos gracias muchacho!

As for the laminating stringer idea… yes ideally I only have to plane the stringer when doing bottom contours (concaves) or as finishing when I have done sanding the board. Have you tried it before? I am wondering how hard it would be to plane through fiberglass at the stringer.

Nice board you made to! Like the cloth inlay idea. Will have to try it sometime.

Hi Johan! One more try…

I tried gluing up my stringer on my first board with epoxy, it works ok but it’s a pain in the xss to sand and plane so no good in the end.

When I sanded and planed down the stringer it took a lot of effort and time beacause You end up with a ridge that is hard to get even with the foam.

Now I’ve tried with pu- glue and it works out a lot better.

I find gluing up the stringer the most difficult part in making the blank, still working on a better way…

Thanks for the pics.


Thanks for the tip Erik.

Good to know before I go and mix up resin…


Just a hint: we clamp both of the 12" blocks together and hotwire at once, eliminating the need to hotwire twice as you described, and possibly getting two “truer” halves while still ending up with the factory edge in the middle for glueing…

Good idea drew!


You can use your hotwire guides as clamp pads too - then your clamps won’t dent the foam.

Hey Jonah,

There is one advantage to doing each side one at a time. Assuming you don’t want a flat deck, if you match and level your bottom rocker templates, but make your outside template thinner (a little thicker than what your final rail thickness will be) you can “pre-dome” the deck. It actually comes out like a panel vee on the deck side, but will save a lot of planer passes later. You have to do a couple of planer passes down the stringer after you glue up to flatten the vee some. You can get fancy and make the nose and tail part of the outside template even thinner than the middle to accomodate for the fact that the outline will take the cut closer to the stringer.

Hope this makes sense.


Even another way no build a blank. Still not put on practice by me, but it’s passing through my head from time to time.


or, you can use a hotwire, hand held (with appropriate insulation, and avoiding standing in water), about 2 feet longer than your blank and hotwire the stinger cut. That way you can accurately do double stringers and A-frame stringers. Loehr used to have a rack out of 2X4’s and hinged on one end and just laid it down on the blank to cut. Very cool.

Now that is an idea Greg.

I have been wondering about that… I have templates for an 8’mini-mal and was wondering how I could do a triple stringer.

Had thought of making curved templates for my little hotwire and doing 2 curved ones on either side of the center.

And a double center stringer has advantages for putting in a fin box without weakening the board…

I guess by hand held you mean a piece of wire that 2 guys hold at each end? (with gloves of course) :slight_smile:

Easy enough to set up.

Loehr’s rack sounds perfect for a production shop.