Callum McCullough

Cork Surfboard

Wooden boards are really heavy. I mean, they look pretty nice, and there’s the whole eco boost from natural materials, but, they’re really fucking heavy. When you actually look into the eco side of it, you really have to ask how beneficial they are. Traditional hardwoods have a loooong turnaround from seed to harvest, making the carbon capture from the trees’ lifecycle pretty small. Sacrificing old growth forest for any purpose (including for just replacing with “new growth” forest) screws your soil biodiversity, creating all sorts of damage that you should read about from a reputable author on the subject (not just some guy on the internet with a surfboard building blog). Cork though, is bloody marvelous. It allows the trees (Cork Oak) to properly establish themselves into the ecosystem, with the exterior bark getting peeled/harvested every few years.

Cork is pretty great for compressive strength, impact resistance, low resin uptake, and the obvious eco credentials. If you tried to use it as an out and out replacement for any wood though, you’d have some challenges. Stiffness and tensile strength aren’t our strongpoints when it comes to playing with our corks. Knowing that, we can’t get away with a hollow board and will have to go for a foam core.

The linked video on this page shows my first crack at a cork-wrapped EPS surfboard, but with a crucial difference from what I’m writing about here. The first one was shaped with a planer (like most hand shaped boards nowadays).

This one was shaped with a hot wire. Hot wires have their share of limitations for this, but, it avoids kicking off a lot of hard to control plastic dust (which is pretty much the worst form of plastic when it comes to damaging the marine environment). When the right guides are used, hot wires also give decent curve control, so the method handles rocker lines, outlines, and even convex bases.

Small hot wire set-ups are pretty cheap (~£20) but larger wire bows are surprisingly expensive. So, I built my own. NiChrome wire is the magic ingredient to make the thing work, and I used an old laptop charger for the power supply. I am not to be trusted for anything electrical, so will give no more advice on that, let alone show photos of my soldering!

The blank itself was shaped out of a 100mm thick block of EPS from the local builder’s yard, using the aforementioned hot wire and mdf guides. The deck chamfer was cut with a smaller hot wire, with a pre-cut wooden guide.

A longboard sanding strip was used for blending the curves, the rails were cut in with a homemade fred tool and regular sandpaper.

EPS foam isn’t closed cell, so can deform under a vacuum. In the interest of making the blank hold it’s shape, I built a simple rocker table to lock it down when laying up the cork skin. Polyurethane expanding wood glue is the stuff to use here, as it seals the eps, and expands to fill any voids in the cork. (Side note – I find it best to apply the glue to the EPS side. Far less glue seeps through the cork, so you get away with less sanding in the next stage!) Some places can end up with gaps, but these are fixed by gluing down strips of cork and sanding back to smooth.

Once the glue has set, the whole board needs going over with sandpaper, particularly where the cork overlaps at the rails. Once this is all done, the board can be glassed in the normal way. Given the EPS core, I really, really, really recommend using epoxy here (so as not to melt the insides). However, I wanted to save cash, and was pretty confident in the PU sealing of the EPS foam. So, I went ahead and glassed this one with polyester resin. Somehow, I got away with it.

I decided to glass on the fins, (to avoid paying for fin boxes) so just laminated a block out of veneer left overs, and shaped it down with an inherited belt sander.

As usual, I gave the whole thing a bit of a sand and polish, results below.
Dimensions are 5’7″ x 21″ x 2.75″ & 34 litres.

3D Print / Cold Mould Hybrid Surfboard

I couldn’t stop thinking about updates that I wanted to make to my Cold-Mould Surfboard method. Being stuck at home due to a global Pandemic felt like the perfect time to have another go.

I’ve been banned from the dining room. Well, not technically *banned*, but my housemates have reached a consensus that it is a dining room and very much not a workshop. To be totally honest I’m amazed its taken them this long.
So, a greenhouse tent from amazon and an extension cord is my new home office.

There are a few pretty good free shaping softwares around. Without exception though, it gets expensive as soon as you want to add complexity, or export fruitier file formats. I use Autodesk Fusion 360 already, so for this project, I created my own parametric surfboard shaping design. CAD software isn’t that interesting, and I could probably write a whole blog post on this alone, so I’ll save the details for another day. In simple terms though, making my own digital tool means that I can chop and adjust the structure, add fancy features, and create a 3D-printable design. It also gives me really reliable measurements that I can reliably refer back to.

I have a fairly budget 3D printer, and it isn’t huge. So I had to chop up the CAD model into 16x 3D printable sections. I purposefully let the printed surfaces have a few gaps and bit of a rough and janky finish, the overall shape was correct, and these rough surfaces would allow for a much better glue bond later on. To join the sections, I used a mix of friction welding with a dremel, and fully welding the seams with a soldering Iron.

Out in the tent, the first thing to move forward with this board was to reinforce the fin box. I had left a big oversize slot to fit a 10.5″ fin box. I clamped together a few layers of cork with gap filling polyurethane (PU) glue. This was cut to fit snug in the slot, and glued with the same goop.

The last time I made a board with wood veneer, I had to clamp the strips individually. This was a faff, and slow. This time around, I bought a new vacuum pump.
I cut all of the strips to *just* oversize, arranged them over the printed core, and held them all in place with masking tape. With a strip of fibreglass tape and polyester resin, I joined them a little more permanently.
With PU glue, I put a thin covering over all of the upper surfaces of the 3D printed core. The PU glue expands, and fills the gaps in the printed structure to get a really secure bond.
The first deck layer goes on, and all into a vacuum bag, which pulls it together with really uniform pressure, until the glue is cured.

The second layer of deck goes on much the same way, but with thickened polyester resin as the sticky stuff this time. I clamped the edges on top of the vac bag, just to make sure I wouldn’t have to deal with any warping later on.

The bottom is a little different. For two reasons.
I designed a scoop into the nose, which would need a separately glued panel. I also opted to use a lighter coloured wood, no reason other than for looks, but the Ash veneer made for trickier working than the Sapele that I had gotten used to.
For the scoop, I made a roughly oversized panel of sapele, and used some chalk to mark out a cut line.
The bottom would only have a single wood layer, so after measuring out the rough panels of the veneer, I laminated on a single layer of 6oz fibreglass to give it some stiffness.
After trimming it all to fit, it went in the vacuum bag with some glue for a couple of hours, and was ready for tidying.

Doing this “all-in-one” wood laminating method made for much better alignment than my last attempt, but it did still have some gaps. I carved grooves along all of the join lines with a dremel. The gap filling was done with a wood dust / Polyester resin mix. This could all be sanded to give more of a seamless finish.

After the wood comes the rails. Last time it worked pretty well with the clamped 8mm thick strips, so I did the same again. Spring clamps did most most of the heavy lifting with locking it all in place.
The tail piece had to go round a sharp curve, so I cut some slits to let it bend. This left some gaps, so I just stuffed in some thin cork to fill it up.
Shaping was done with a wood file, which works, but can lead to a degree of lumpiness. I think I would use a big surform if I tried this again.
To fill the gaps, I made a paste out of polyester resin and cork dust. The cork was painted with a layer of resin after the first pass of shaping to give a smoother sanded finish. If I try this again, I think I would use 4mm strips, to let the PU glue expand through the cork better, and leave a more consistent finish.

On to the laminating. Because there is so much strength in the board now, I just put a single layer of 6oz cloth on either side. In the nose scoop I added an extra patch, but that was only because sanding this area left the wood pretty thin.

If you’ve read other posts on this site, you’ve probably realised that I think cork > wax. The deck of this board being dark sapele, with even a glimpse of sunlight the wax melts straight off and goes everywhere. I’m not into that.
I wanted to make sure that the deck patch was really well stuck down, after having some issues with cork pads peeling up in the past. I moved pretty quickly to get this done once the fibreglass had cured. For a good bond with polyester, it really needs to go on within a few days of the initial lamination, as this is when the “surface energy” is highest. I’m not going to go into detail on this as it’s a bit maths-y, and really not that exciting.
I cut the 2mm cork panels to the outline that I thought would look best, and marked on the board the points that they would need to be lined up to. I fully wetted out the cork with polyester resin, and put it under a vacuum bag to get the pressure on it. This also takes away any extra goop.
When it came to hot coating the board, I made sure to go over the cork too, making sure it was sealed against the salt water. This got sanded back to leave the exposed grippy surface, but left covered along the edges to really stop it from peeling up.

It would be a major bummer if this thing got hot and popped, so I figured I should put in a vent plug, for flights or heat waves etc.
I laid up some leftover flax glass fibre and cut a disc out of it with a hole saw. This then just had a little sand, and a coating of glossy resin and it was good.
The thread itself was a brass threaded insert, pressed with a soldering iron into a 3D Printed ABS cylinder. I stuck these together with PU glue, and then did the same into a hole drilled into the board. When I designed the initial 3D printed structure, all of the chambers were connected by putting holes in all of the vertical walls. This means only one plug is needed if the air expands. To make sure it is well sealed when in the sea, I used a button head screw with a greased O-Ring.

The last bits were the fin box, and hole drilled through to fit a leash string. I routed a groove to fit the fin box into the aforementioned cork reinforcement. This was then half filled with thickened resin. When it set, I trimmed and sanded it all flush. A hole was drilled through the board from the back of the fin box, which was then sealed and supported with resin and chopped fibre.

All in all, this went together pretty smoothly, it’s lighter than the last attempt at a similar method, and I think it proves the concept pretty well. At the time of writing we’re in the midst of a global pandemic, so it doesn’t look like i’m going to get a chance to ride this board any time soon. I think I’m going to have to find another project to keep occupied through the rest of the social distancing…

Cold Moulded Surfboard

Wooden surfboards are heavy, like, really bloody heavy. The way I went about it here still weighs a ton, but I think it has legs for another attempt at some point.

SO, when you look at the world of boating, the clever sods have figured out a way of making really smooth complex curves out of wood. I’ve heard it said that a lot of people choose this method as it’s stiffer and stronger than GRP, and cheaper than carbon.

The method i’m talking about is known as Could-Moulding. The technique is pretty simple, where you glue layers of wood veneer over a form, at alternating 45 degree angles. What you end up with is a stiff 3D surface structure. The angled wood veneers give strength and stiffness across all axes. Adding a layer of fibreglass cloth and resin to the finished structure locks it all in and weatherproofs the whole thing.

I had a google and a look around, but couldn’t find any instances of anyone trying to make a surfboard like this. (I’m not saying they don’t exist, just that my low-effort search didn’t find anything.) So, I figured that I would have a pop.

I started with some leftover plywood. With a jigsaw, I roughcut a stringer to the rocker line I was looking for, and tidied it up with a hand plane. For the ribs, I used some thinner plywood, with cross-sections spray mounted as cutting guides. I cut these flush with a pull saw. I cut slots into all of these skeleton pieces, a little dab of glue, and it was ready to figure out how to mount the rails.

The outline needed smooth curves. I glued some thin pine strips to the outside corners of the ribs. With string I lashed it down while the glue cured. For now we can ignore the rails, they can be sorted when the deck and base are both in place.

We have the rough shape of the board now, and enough wood locked in to stick the top and bottom too. the first layer goes on pretty easy. With polyurethane (PU) glue along all of the contact areas, I clamped down the veneer strips. They were cut and clamped over length, then trimmed back with a pull saw.

For the next layer, I had planned to vacuum bag the veneer down, again with polyurethane glue. But. When I was vacuuming a test piece, there was a loud bang, and a lot of smoke.
Vacuuming wasn’t an option anymore. Instead, I got a bit creative with my box of spring clamps, and managed to bodge together an arrangement that just about handled it.
I was a little worried about the ribs being a little too thin. (Rightly so, they were flimsy as fuck.) So I filled the skeleton with expanding foam. This took the load off the ribs, and added some more overall stiffness.

The base went on pretty similarly, but with only a single layer of veneer. As the glue I’m using here is gap filling polyurethane, the space between the expanding foam and the veneer is pretty well dealt with. I chose to only use a single layer as it wouldn’t need to deal with a me-sized lump constantly stomping on it.
Once trimmed, there was some inconsistency with the surfaces and edges. Although this can be tickled with a wood file and an orbit sander before moving on to the rails.

Building the rail blanks is really fun.
To build them I used the same gap filling PU glue from before, and clamped together three strips of 8mm thick cork sheet. Where the sheet width didn’t match the overall board length I just staggered the join lines in the layers.
Once I had the rail blanks ready to go, they were stuck to the sides of the board with the same sticky stuff as before. Clamping was done with some left over pine strip and bungee cables.
When the glue had done its thing, the rails were trimmed flush to the deck with a pull saw and a wood file.

There were some gaps left at this point, both at the joins of the rails, and at some points between the pieces of wood veneer. I made some filler by mixing some salvaged cork shavings with the PU glue.
The rail shaping was the natural progression from this point, and was achieved with just a wood file and sand paper.
The tail block used a pretty similar method as the rails, but as its a pretty tricky angle to clamp to, masking tape proved good enough.

It would be a bit of a stretch to do laminating in the dining room. Luckily, where I work has a big composites tent. The timings worked out that I could sneak in after work and laminate the board in the evenings. Glassing and fin box install was done in the traditional way.

Shortly after finishing it, I took this plank with me on a Christmas trip to Morocco. For the most part, it worked pretty well. But, there were some issues.
Firstly, it’s heavy. That’s not such an issue on the water, but you get sick of carrying it. Secondly, it needs a vent plug. I was concerned about it popping on the plane, luckily that didn’t happen, but I could definitely feel it inflate under the midday sun!
Finally, I didn’t really gel with the shape. Using this method does carry some risks, and cutting the internal structure by hand can lead to errors that can’t be fixed later on. For this project, the main drawback was how thin I ended up making the tail. The board paddled really well, and providing the wave is steep, takes off well. The skinny tail though had a habit of bogging down when the waves were small. I’m going to try again with an evolution of this construction at some point. It works, but there are definitely improvements to be made!

NB. I was rushing to get this thing finished and ready for the trip, but the whole project took around three weeks of working on it most evenings and weekends.

Longboard and Cork Deck Pad

Hands up, I didn’t shape this. But when one of the best shapers in Cornwall is trying to clear out his factory, it would be silly not to get hold of a pre-shaped blank or four. Obviously these aren’t all for me. This project was shared with a couple of friends. As all three of us were all lacking in the longboard department, this stack of foam logs was the answer to our collective prayers.

After explaining to work the severity of my need to be two hours late on a Wednesday morning, I bundled the blanks into my van, and then into a neighbour’s garage kindly donated as he was skiing for the week.

Now I couldn’t very well sand and glass a whole longboard by just balancing it on the dining room table, we needed some real shaping stands. Unfortunately, there was a lesson to be learned here: when agreeing on a design for something, do it sober. These things were gopping, but they were what we had, so we made do. It’s only three boards anyway…

Rudi posing with our second-rate shaping stands…

There’s plenty of literature across the internet on what to use and how to sand down polyurethane foam, and we found that 80 Grit “Mirka Abranet” is the rough stuff of choice.

Polyurethane blank means I need to use polyester resin. Decision made on that front. But we need to have a think about how much glass we slap on, these are big logs. They are meant to be heavy, and they aren’t meant to snap. So with that in mind, I’ll do two full layers of 8oz all round, with an extra 6oz patch on the deck for good measure. The tricky thing with laminating in Devon in January, is that it’s cold. To battle this, you sometimes have to get creative with space heaters.

Grinding down the laps can be done kackhandedly, and slowly (but easily) with a hand file. Or carefully (and quickly!) with an orbit sander. Time was pressing, so I chose the orbit sander. Somehow, I didn’t go through all the glass, and I moved on to fin boxes, leash plugs, and a deck pad.

This stick is lucky enough to have double stringers down the middle, and sure you can talk about responsiveness, flex, overall strength, or whatever. Right now it’s just going to make it so easy to route out the hole for the fin box. This is a log, so it only needs one. I used a standard 10” box.

Instead of a separate leash plug, (which can pull out) I just drilled a 12mm hole all the way through the board, from the back end of the box. A bit of tape over the hole stops resin pissing all over the floor. Drilling a hole through here, and following through with bit of leash string makes a sturdy little point for strapping a leg to.

The deck pad is the last bit to go on. I had a load of cork sheet left over from other projects, so I figured it would be good to try it here. After marking out the area it had to cover, and cutting out the sheet, the next step was to lay down a thick layer of resin. It needs a little extra viscosity to keep it in place, so a scoop of glass microbubbles is enough to get that working. The resin is going off at this point, so you have to work quickly here. Ideally you should plan ahead and cut peel ply, breather cloth, and vacuum bag in advance. I don’t always remember to do that, but I did here. Tack it all in place, and plug in the vacuum.

Once it’s all cured, it’s well worth giving the top a little once over with the sander. This will stop your chest or wetsuit from being ripped to shreds.

Dining room Kite Board version 2

From the fact that there’s a version two of this, you might infer something didn’t work too well with the first one. You would be right. In essence, I learned that you shouldn’t make kite boards out of underfloor insulation. Because they snap.

On the plus side, we have a nicely reviewed design. But to add to the challenge, a couple of weeks before making this, I goosed my ankle falling off a climbing wall. So, while we’ve got some design improvements, I have to make the whole thing balancing on one leg.

This time round, I decided to get sturdier with the composite layup. This meant I needed a core material that is better at letting the resin seep through, to join the two skins of the sandwich more effectively. I’ve been playing around with vacuum pressing cork-resin matrixes recently, and it works real nice as a substrate that’s not too spongy, but still absorbs the goop well.

The other design flaw that needed a tickle was with the threaded inserts. My old method (3D printed bosses, with a standard hex nut) kinda sucked. One of the nuts holding down the handle pulled out. Not a major drama but irksome nonetheless. This time round I got hold of some flanged, barbed, push fit brass inserts. And oh mama, these are an upgrade for sure! They are a tad spenny in comparison, but I chatted to some fellas working for tappex at a trade show, and was given a bag for free! I still used 3D printed blocks, but this time round they were given a bigger footprint and a tighter tolerance at the hole. To secure them properly, I used a soldering iron to melt everything in place.

The 3D printed rails worked well before, so well that I used it again! This time though, I mixed up some ABS offcuts and acetone into a slurry, this was then used to create a fully penetrating join between the ABS rail segments.

Remember that this is being done on a dining room table. I live in a shared house, so I’ll avoid pumping the building full of polyester resin styrene fumes where possible. This implies that I’ll be using epoxy again. But an extra layer of glass on both sides for a little more stiffness.

Last time around, my henry hoover had to do a lot of heavy lifting when it came to pulling a vacuum. As an early Christmas present to myself, I got a dodgy Chinese Vacuum pump from eBay. This project gets to be it’s first big outing.

This thing cracked off the mould real easy, but right now it ain’t a sight for sore eyes. A spray of paint helps it along*.

*I showed a colleague a photo, to which he asked if it “was supposed to look like that”.

Dining Room Twintip Kite Board

Let’s start from the fundamentals. A twintip kiteboard is essentially a fibreglass tea tray. Sure, you can add all sorts of contours or fancy grooves. You can finely tune the flex characteristics to give just the right amount of “pop”. You can even run computational simulations to calculate the optimised layup, orientation, and thickness of fibres. Or not.

Instead let’s strip back the complexity and acknowledge that it’s just a fucking tea tray.
Problem is, it’s a bendy tea tray. We’re going to need to implement some sort of curved table as a mould, for what is then a relatively straightforward GRP Panel.

Barebones, this rocker table is a simple construction. A thin sheet of plywood bent over some MDF stringers. The stringers have two options, lateral or longitudinal. Now longitudinal would be nice. Very nice. You get complete control over the rate of curve of the table, and you can contour by keeping some curves flatter than others. Sounds great, but there’s a risk: I’m marking out and cutting these cats by hand, and I don’t trust myself to keep the accuracy.

I’ll stick with the lateral option. This is done pretty simply, with easy to measure rectangles. Resin wash and polish the mould surface. Screw and glue some pine battens for overall stiffness. And SHAZAM, rocker table ready to use.

Now we have a mould, we can push forward with the board itself. Sticking roughly to convention, these tend to go together with five main ingredients. Fibreglass for the top and bottom, a core in the middle for stiffness, fastening inserts, rails, and resin to stick it all together. To figure out the best way to do each component, we need to consider what it’s likely to go through.

The fibreglass is going to take load in a few ways, but the overriding factor is going to be torsion. So we’ll use a couple of layers of nice heavy biaxial glass to account for this. But it also is going to have to laminate well, so I’ll sandwich that with some 6oz plain weave.

For the resin we have two options. Polyester or Epoxy. Polyester isn’t as strong, Epoxy isn’t as cheap. Epoxy smells like cat piss, Polyester smells worse. Seeing as I have tubs of both and therefore don’t have to buy any, we’ll stick with Epoxy as it’s just better. It sucks with UV damage, but a coat of paint can help with that.

The core is the next thing. Around half an inch thick is about normal so I’ll just copy the experts. I have some extruded polystyrene sheet left from insulating the floor of the van, it’s compatible with epoxy, so I might as well see if it works!

The Industry standard for fastening down the pads, straps, handles, and fins is with M6 thread. I’ll use 316 Stainless steel as it’s going in the sea. For now I’ll just use normal nuts, and I’ll 3D print some recessed blocks to hold them in place.

The rails are a tricky one. They have to define the outline of the board, be tough enough to take knocks and be compatible with my choice of resin. Luckily, I have a 3D printer which will give better dimensional control than anything I can cut by hand, and I can use ABS filament to work with the Epoxy, so that’s what I’ll do. To join the rail segments, they can be friction welded with a Dremel. This way, no extra chemicals are thrown into the mix.

To get a decent, strong lamination, we only need a fairly simple wet layup, followed by vacuum bagging for consolidation. Currently, I don’t have a vacuum pump so a henry hoover will have to do. The hose is a bit big, so a pasta pot made a good enough chamber to step down the diameter to go into the vacuum bag.

After the lamination is done, the outline of the board can be trimmed to the rails. The trimming is easy, start with a rough cut using a jigsaw, and finish with a surform. Also, don’t breath the dust. Really, really, please. do. not. breath. the. dust.

Most of the way there now, it just needs a can of spray paint, and all the peripherals to be screwed in place.