Summary of Joining Balsa for Deck or Bottom Skins

Could someone summarize the methods of joining balsa sheets to make deck or bottom skins?

Tape or some other method?

Tape on outside or inside?

Type of tape?

Advantages/disadvantages to planks inline =-= or angled >>> ?

Layout methods?


hi dave

5 min epoxy on a flat table

Blue tape.

I tape what will eventually be the outside surface.

Then flip the whole thing.

Cut a piece of cloth just barely bigger than the wood skin.

Fold up the cloth, wet it out with mixed resin & hardener.

Open up the cloth onto the balsa & smooth it out.

Flip the blank down onto the cloth & wood.

Grab the whole works & flip it back over, so the entire thing is now up with the blue tape showing.

Peel off all the tape, the cloth smoothed onto the wood from the underside will hold it together.

Wet out the second piece of glass cloth and unfold it out onto the top of the balsa.

Lay on peel ply & paper towels.

Into the bag.

That’s it…But I keep a reminder on the wall of my shop:


I glue up planks on a table using 5min PU adhesive, using blue tape to keep tension whilst glue dries, quick sand and cut out outline.

Better question…

Anyone building their skins in a vac bag under heat and pressure ahead of time like Bert does?

I haven’t seen the premade (glasses not just glued) skins post link yet… Maybe someone can hook us up…

That’s where I’m going pre-made skins already to glass onwith some exterior glass… Just pick your material option pattern and slap it on to your shape.

Thats how I did it last time! It holds a lot of promise but theres a few bugs to work out. I’m thinking the best way to do it is to do a combination of Ben’s flip and fold technique on the deck with prefab skins on the bottom. It eliminates the pain and cost of taping it. I’m trying it this way next time.

DanB, oneula,

That’s the approach I have been planning to use. Was gonna use a 9.5’ long bit of sheet metal, wet out the glass. Lay it on the sheet metal. Peice the balsa togethor on top toss it into the bag. And bag that onto the EPS with lightest glass I can lay hands on. As the vac is drawing out I can shuffle the bits of balsa around until I am happy with em.

Your thoughts? Anyone else?

This should all be happening in the next month or so - the vac pump is nearly done! Just tracking down an insidious leak. Am I looking forward to this or what :slight_smile:


I think your on to it! If I get to it before you I’ll let you know how it went.

Thanks Dan, I’d appreciate that.


oneula… are you sure that is what bert does? i am not 100% convinced… i have tried preglassing with the bag and some heat (eletric blanket) and have got some really nice pre glassed sheats (dead flat, no bubbles etc) and i have used them on the bottom skin with good success… BUT on the top skin, where i believe they would really help out is a diffrent story, for it is not easy to shape the rail joint when the skin is glassed… ok, now say you did, you now have nice balsa rails that need glass, so do you wrap just the rails giving you top and bottom “laps” that need sanding and fill coating? or do you reglass the whole deck… many problems come up… perhaps just pre treating the skins by just doing patches under the feet area?

on one attemp i waxed up a formica rocker table, used some long pot life epoxy and wet out a sheet of glass, then i took my strips of balsa (i cut and arranged ahead of time) and layed them out on the wetout glass, the idea being no preglueing or taping. then i bagged… the gaps were not so hot.

if i had about 25grand i would do my balsa skins like this… first i’d buys some nice balsa how the places like nationa and lonestar get it, in rough 48" x 4" x 4" or whathaveyou. then i’d run them through my super nice multi drum sander (around 6 grand) and get them all the same dimensions. then i’d square cut the ends. next i’d glue up 8’ x 24" x 4" slabs with the joints all in nice eye pleasing locations. then i would slice the slab into 1/4" sheets on my horzontal band saw (ask the woodcraft owner he has one, around 17grand) finally i’d run the sheets through my thickness sander and sand to thickness… i figure i would spend about the same time trueing up all my sheets from lonestar as it would take to glue up a slab… and i figure it would take less time to rip the sheets and thickness sand then it would to hand lay up and tape etc each skin… i am not saying this is how i think bert does it but i think it would work, but balsa is strange.

Naw J

I think it works best with solid rails so you don’t have to shape the top or bottom skins too much. just but them up against the rails and join or pinch them to the solid rails with glass strips…

Otherwise yup gonna be hard to bend the deck over the rail like CMp and we have bene doing them. Funny that we’ve never got that solid rail thing down…I was thinking of building up layers of 1/2" corecell like Bert did with his divy example in the thread that started all this…

I do it the same way as markyv does, but am thinking of some sort of jig that presses the sheets from the side so you dont need all that tape that is waste.

I need the glue with short potlife put long enough to glue em all up before pressing…

maybe RR with fast hardener and accelerator X-55?

Or maybe the usual pu glue is enough.

Jimmy yoshio shibata.

you gettin all this josh???

at one stage i thought they werre gettin warmer …its amazing how far you can go in the kitchen …



I think the 2 skins are just skins. No lapping of the glass. Then the glass tape to cover the rail & catch both skins.

I did my last one like this, complained about the process and said I wouldn’t do it again (before I’d surfed it)…Bert posted something like, “too bad, I thought you were on to something with this one,”

And then I surfed it.

I don’t know if that’s exactly how Bert does his, but its how I’ll keep doing mine, that’s for dang sure.

Bottom skin goes on with both inner & outer glass. Then template, add & shape balsa rails. Then top skin goes on, again with inner & outer glass, lapping onto the top of the rail balsa but not around the rail. Then 4" glass tape covers the rail & laps the skins. I’m sure you’ve noticed that Bert’s boards show a clearly defined balsa rail joint on the bottom, but the top looks like the deck balsa lapped over & was sanded…the process is actually pretty easy, once you’ve been through it. And the ride is amazing.

I am pretty sure Bert will agree with me on this one, but don’t be dissuaded from trying new techniques. The object is not just to figure out exactly how Bert is doing things. Besides, I pretty sure he is using an epoxy infusion system. It will be a while before anyone catches up with him.

One idea floating around for my first burger will be to knock off my existing “go to” board, my 6’1" flyer. My first step using Benny’s method will be to tape and flip balsa with 2oz in/out on top of my flyer with a sheet of plastic in between so that the skin will come back off. Repeat for the bottom. Then I will shape some #1 eps and attempt to clone the flyer, but a touch thinner. then vacuum the preshaped skins onto the foam. Maybe some pre-wet 1-1/2 epoxy mat as a binder? Anyone know the flex characteristics of that stuff?

Here is the fun part… I’ll chop off the rails, check the bond out. build back up with strips of balsa PU glue and maybe a layer some other springier wood. Plane/sand down the rails to shape, and vac another layer of 2oz on the deck and around the rails w/ maybe some extra tape around the rails.

I might be making some extra work for myself, but I would rather be working towards a shape that I am already familiar with.

I’ve experienced many of the same problems jjp has experienced. The problem comes with blending the balsa into the rails (on the deck). I found to get it smooth I had to sand it way to far up the rails. What I ended up with was my best performing board, but my worst looking. I’m hoping the hybrid approach will give me the best of both worlds (pretty rails with lite glass). I’m starting a new one on the new year so I’ll keep people up to date.


do you need to lap the rail or just butt joint flush against it?

and wouldn’t you want to finish shaping the rails after the top sheet has been put on so you can flush things out on the rail?

I think this is the formula for us garage banders.

This smooths the whole process out though I still prefer having the top and bottom sheets premade and preglassed and just lam them on with 2oz that way I can stack all my skins in a pile until I need them… But I can envision doing the bottoms your way cause I can go from a completely flat sheet of EPS with the bottom shaped in to a rockered blank minus the outline then cut out the outline as needed… I can even see a bunch of 2’x8’ flat 1lb EPS sheets preshaped with reverse vee/spiral vee from a single to double concave right down the middle for later use to be “rockered” using a table of a board you like… Be interesting to “fasten” your premade top sheet with some form of flexible urethane glue so that it transfers it’s load directly to the rail instead of being bound to the foam. gluing a thin sheet of that white Polyethelyne packing foam from your bag supplier might be an idea as a “buffer” between the top sheet and the EPS. I can see using thicker glass on the deck with the balsa or 1/8"-1/4" thin PVC like Divy or Corecell as the deck sandwich core…

If I use 4’x8’x1/2" corecell or last-a-foam instead of balsa strips for the rails I can cut out my entire rail band and glue them on two per side once the outline has been defined using the offcuts and some 2"x4"x8’ clamped boards in my racks like you showed… If I prebuilt out my balsa into 4’x8’x1/8" sheets I could do the same cutting out the entire rail band our of a single sheet of balsa…

I glad to hear the concept is working out…

All in all Bert must be laughing at our struggles

kind of like walking around blindfolded in a room of cacti… or keawe bushes

I shape the rail down to just a little thinner than I want it to end up, pinching it from the top side. Then the deck skin goes all the way down to about the apex of the rail, just doesn’t turn the corner or tuck under anywhere. Once out of the bag, I hit it with the surform, cutting top glass & balsa. The balsa’s only 1/16 so it comes out nice & smooth & flat.

You can see the bottom skin & balsa rails meet at a plain butt joint (don’t know why the board looks so twisted in this photo):

While the deck skin laps the rails & then gets surformed & sanded smooth, obscuring the joint:

That’s one reason I’ve gone away from decorative dark wood in the nose & tail blocks…

While the deck skin laps the rails & then gets surformed & sanded smooth, obscuring the joint:

so you deck goes on last and wraps to about the apex?

That's one reason I've gone away from decorative dark wood in the nose & tail blocks...

because your deck skin would cover it?

are you contouring your bottoms? or just going flat?

concave nose, belly, vee?

I haven’t tried it on balsa but it should work fine:

Use spray contact adhesive to stick the glass to the wood prior to wetting it out with epoxy. On glass and solvent-resistant foams I know this works very well.

Use a repositional adhesive spray so you can take your time and ensure that the blasa joints are tight. It doesn’t take much at all so I very much doubt it will affect the strength.

This is a common method for laying up dry laminates when doing vacuum infusion. It works well for wet layup too if you are trying to get the reinforcement around tight corners.