Balsa Pre-Treatment?

Anyone pre-treating their balsa skins prioir to lamming.

Seem like balsa not only sucks alot of epoxy but also releases gas to cause airbubbles/pinhole during hotcoats.

I know there’s cheater techniques to fill the weave during lamming to reduce pinholes during the hotcoat/2nd coat but has anyone experimented with selaing the balsa to reduce resin absorbtion during the lam/vacuum session?

Some have said alcohol or ammonia washes and I see that woodworkers have had for many years a variety lacquer rubs or sprays like

MYLANDS sanding sealer

HUT Crystal Coat

GENERAL Poly/Acrylic Sanding Sealer

SystemThree WR-LPU

some say you can even use CA-based glue to seal the surface to reduce resin absorbtion.

It seems like the dryer you can keep the balsa the better off you are versus having your vacuum permeat the wood grain with epoxy through it’s structure. Strong yes, but also heavy.

So is the routine to ultimate lightness…

Spackle the EPS to seal

Seal the balsa and them lam them seperately under high pressure to build out your skins before applying them to the blank

and use “hardened” rails of Dcell,Corecel or balsa to fasten your skins to without wrapping the rails liek we do…

To stiffen and support use internal “springers” of the denser material used on the rails or other type of wood or petro chemical material…

By the way…

anyone use stainless steel or aluminum stips as an internal “springer” between the skin and the foam?

for the record, i am against pretreat…im building hiperf surfboards not bulletproof tanks…having said that, two thin hotcoats are better than one and preheating your blank/board a bit before lamming and hc’g ensures your board wont outgas during cure…its better to hc in stable or falling room temps

my latest 5 pounder has a super solid deck…it flexes…no fancy preT tricks…just keep it simple dude

I’ve read in other post to do it in a falling temp. as Meecrafty recomends…I can’t say for sure though as I am too looking into it.



How would you pre-heat your board, and are their any negitive effects of doing so beause the heat would cause the board to expand…right?



Prefabing the skins looks like it has solved the problem for me. I did my hotcoat at 3:30 in the afternoon (it gets hotter for another hour in my garage) and I didn’t have a single bubble (and I’m a really bad hotcoater). I did follow Benny’s advice and warmed up the resin slightly. I even tried to make bubbles by slopping it around to fill places where I hit the weave and no bubbles.

Couple of things I’ve noticed about my boards…

  1. They’re heavier than I would expect heavier than my polys… of course there’s two layers of 4oz or 6oz glass on the top and bottom along with the wood and two coats of resin over the exterior glass but the core is light EPS.

  2. After vacuuming on the lam to the blank the resin has been sucked through and actually saturated completed through the wood to the surface which probably isn’t good. Blue tape nightmare cleanup as well…

  3. I still can get dry spots on certain parts of the outside handlam if I scrounge on the resin and the other option is to use and waste alot of epoxy resin to saturate and pull alot off in the end…

  4. No matter what it still starts to harden (fast Hardener) before I am completed done squeeging everything tight…

And no I am not using RR or Additive F.

Am I not sanding enough of the top layers of resin (hotcoat/gloss coat) off?

the board always seems lighter with just the top lam over the wood but we’re squeezing most of the resin out of the weave…

Do I just do a cheater and not a final or gloss coat?

Or do I seal the wood and blank and use less resin to get saturation of the glass cause glassing over a solid sealed surface would require less resin to get the same glass saturation than it would to glass over a porous surface like sanded EPS and balsa especially ones that suck liquid like an overheated dog.

Just a thought

But then maybe it’s just my technique that’s making all my EPS boards heavier than my poly’s…

As far as temperature drops…

here in Ewa Beach I’d have to start glassing at 10PM or 3AM to get a temperature drop during the lam so I don’t think so. I guess I could heat the board up with a gas torch but that would be funny if it caught fire from the flames…

I don’t see how you’re getting 5 pounders with double 6oz/4oz 1/8 balsa skins and rails and two layers of exterior epoxy coats to seal it but of course most of my EPS boards are over 7’.

As Sabs says, “its all about the resin you don’t use”. You have to go to the lighter weight glassing schedules if your boards are goint to end up super light. I can’t come even close to getting 1:1 by hand glassing without using a wetout table so maybe you’re using extra resin putting the glass down. Going with 2 oz under the wood takes out a lot of weight and for the most part I don’t think the strength will be missed (but I’ll find out since I didn’t even use extra patches on my current board). On my 12lb 9footer I had to do 2 hoatcoats because I sanded through 7 times and each time I could tell a noticable difference in weight between when I started and when I ended sanding. I changed my philosophy to “resin is evil and I must get rid of as much of it as I can”


Ammonia is great for softening the balsa, but the smell as you would expect is overwhelming, I for one will not do it again!!

Last board, which turned out the lightest yet, I sealed the balsa by rolling on a very light coat of epoxy heated in the microwave (warm board first also). Laminated when this had tacked off, definately less pinholes. This 6’2" kneeboard weighs 2.8kg with fins and pads.

When the ammonia dries does the wood retain the characteristics it had befor you used it. Could this be used to preshape the wood?

Hey Oneula,

I’m using the CA glue trick for the glue-up of the balsa; works like a charm; no tape…just glass it up, throw it on your sealed EPS, pop it in the bag and done. Couple spots where the resin leeched through at the seams, but the bag released fine so no problem.

Dan nailed it; gotta use a wet-out table if you wanna get your resin ratios down. At the very least, pre-weigh your glass, only use enough resin to wet out the glass on some plastic and transfer the whole whack. Squeegee with the plastic backing and remove (or not) as you choose before bagging.

You shouldn’t need a full two layers of glass on top of your balsa if the wood is getting saturated. Try putting a patch in if you’re really concerned, but two full layers (especially if it’s with laps) is overkill. You DEFINITELY don’t need two layers on the bottom unless you’re doing darkslides down handrails on your surfboard. Light inner/outer on the bottom, light inner, heavier outer on the top.

I hotcoated really light on my last board, knowing that I was going to apply another layer for gloss. Hotcoat was 270g total mix, then sanded and gloss coat was 170g/side. That’s more than a pound of resin weight, though I did sand alot of the hotcoat off…pretty much right down to the weave…cause I knew the gloss was going on. Were I going ultralight, I would hotcoat heavier to minimize pinholing (which will happen with epoxy, regardless) and sand ultra-carefully to not hit the weave, aiming for a sanded/rubbed finish. And if I wanted an ultralight with gloss, I’d be doing the rattle-can acrylic, not resin. I pigment my glosses, so rattle-can option is out.

“No matter what it still starts to harden (fast Hardener) before I am completed done squeeging everything tight…”

Sounds like living in a warm environment, while pleasant and contributing to easy availability of the tastiest of fruits, is killing you with your epoxy. Slower hardener.

Also…check the density of the foam you’re using in your blanks…I thought those were 2lb density, no?? That’s double the core weight you could be getting away with; especially with your glassing schedule.


yeah it’s 1.8 lb pre molded blanks from Surflight…

Even the 1.4 lb came out a little heavy.

Jeff Johnston’s getting’s getting under 4lb AI 6’2"s for but that’s with a light glassing schedule and no wood.

I’m gonna seal my balsa lam with a light spray of stain spray lacquer or the lacquer sanding sealer and lightly sand the surface down before applying the glass on the inside and out.

I’ll try the wetout table with plastic idea for both the inside and outside glass I like the idea of saturating and squeeging out the excess against the plastic versus the wood. Using this technique would you have to vacuum the outside glass on or would a light brush of epoxy on the sealed wood be good enough to get the glass to stick with out dry spots doing a hand lam.

I’ll also try and use 2oz on the inside of the wood versus 4oz or 6oz to help cut down weight…

Funny thing is we never used glass on the inside until we found out about from Bert’s post.

oneula, i know you make a few boards…you may be over building them…next time push some limits! you have very little to lose…if you dont like it sand and add some glass…its always easier to add glass than to remove it…do it incrementally…there are no rules to adding glass too…use patches and belts rather then carpeting the whole thing…if it doesnt work just build another one…its not like youre gonna quit building them right? experiement…my worst failures have yielded the most insight to what is good…ive learned much more from failures than successes…

if you core the skin with balsa, halve the glass schedule. squee the resin off your glass as mentioned…more ways than one way to do this…

i used 3oz on my latest for everything…the deck is so solid…the bottom is not cored so there’s 3 layers on the bottom…springy soft like poopee but thats exactly the way i want it…the deck is 3 in and 3 out with patches for my lead feet…you could use plain ole 4oz just squeeze it…its only one ounce maybe two max…

i took my five pounder in the water today for a float test…get this, 2 inches thick max, but floats me like a 2 3/8 poopee! when i rode poopee they were 2.5 thick…when you get’m this light theyre like corks…thin’m out accordingly…

did some more flex tests in the water…you know which test im talkin about…its got that boin-in-in-ing thing going…like a fast diving board…im praying for surf…might be a long wait tho


Quote: worst failures have yielded the most insight to what is good...ive learned much more from failures than successes...

Same. Many more failures than successes - and I’ve only made about 9 epoxy boards! I’d say 3.5 were good…or 3 were good & one’s halfway good :slight_smile:


…my worst failures have yielded the most insight to what is good…ive learned much more from failures than successes…

Same. Many more failures than successes - and I’ve only made about 9 epoxy boards! I’d say 3.5 were good…or 3 were good & one’s halfway good :slight_smile:

But all things being equal I would just as soon learn from others failures :wink: (its much cheaper!)


I think so!!! I treated the deck on this board, to get the balsa (diagonal planking) into the concave deck. Wet out, the balsa and it goes soft almost immediately, vacuum over the blank (with polythene under so foam doesnt get wet) and left overnight. Let it dry in sun before vaccing onto blank and it appears to harden back up again. Although it changes colour when wet, it retains normal colour when laminated. Please do it outside though, unless you want to poison your workshop!!!

I only used it because the veneer softeners do not seem to be available in the UK. I contacted joe woodworker, but would need 3 gallons to make up the min order and the shipping costs would be prohibitive. their stuff is water based so I imagine no bad smells.

Companies like Baltek have a balsa treatment that they claim is for minimizing resin absorption during processes like VARTM which tend to force more resin into the balsa than other processes. They say it also helps minimize water absorption too. But it is proprietary and they won’t tell what it is exactly.

There was recently a good article in Professional Boatbuilder on balsa water absorption, and they now have the full magazine digitally online for anyone to view at ( Here is a link to the magazine that had the article on wet balsa:

I know that surfboards don’t sit in the water full time like boats do, but there is some great info about balsa in this article.


I’ve read in other post to do it in a falling temp. as Meecrafty recomends…I can’t say for sure though as I am too looking into it.



Grasshopper- I believe that would be dropping humidity, not temp. exhaling, not inhaling

wax on / wax off

In dropping temp wood inhales. In rising temp it exhales.

If it exhales we get bubbles and pinholes. If it inhales we get resin absorbtion.

Best to aim for a stable a compromise as possible… Erring towards a dropping temp.

Once timber is coated in a viscous solution humidity doesn’t matter.

But I am glad that someone is thinking about average local humidity. We want it as stable as practical (with respect to local humidity) with temp falling before we coat timber with any kind of sealing solution.


Hi Guys

A very simple solution for sealing is to mix your epoxy then thin it with acetone,this does reduce the strength of the epoxy but this is not a problem in this context.

Thin to the consistancy of water and apply a quick thin coat, try not to go over the same spot when brushing it on as the balsa will absorb as much as you put on it

Do not bother sanding before laminating over it as long as you are within the time frame it will bond ok

I do not seal my eps or the balsa for the inside glass lay up,just prewet the glass as disscussed here use the same amount of resin as the glass cloth weighs

Apply the glass to the balsa not to the eps if you do this the other way round you will get delams on the balsa

Other products such as ever dure work just as well

A thin seal coat like this and you will eliminate most out gasing problems

For this seal coat on a 6’8" board 20" wide use 30 gms resin per side max thats all it needs to work

Using this system I now only glass the outside with 3oz single layer deck and bottom

If you are worried about high load areas like were knees go etc when duck diving just put slightly more sealing resin on this area that will increase the balsa density which means that the sandwich core is now stronger in vertical compression which inturn will make the whole sandwich area stronger with out increasing laminate schedule

Remember all you are doing is changing the sandwich core density



okay mike i want some figures if ya got them

density relation to core thickness equals skin strength?

can your decks be pressure dented with finger pressure(mine cant with double 4 oz)

i wanna try just 4 oz glass job this time

ps are you using balsa or paulownia

i guess the epoxy would need to thinned with solvent to get better penetration to increase core density.(make sure it doesnt get on your eps guys)

Presealing the inside of the skin would be just as important if this is the case.also ensureing better lam as well as the resin wouldnt soak in to much to the balsa.

mike what density eps are you using by the way and are you venting?