eps/spackle and flex

Headed toward making a flex tail KB w/ eps/epoxy. I know that sealing w/ spackle will conseve resin and likely end up w/ lighter board(?) but weight not big consideration. What is an issue is back end will flex likely 2+ inches under load and return to neutral many times on every wave ridden.

Anyone have thoughts on strength over time on eps/epoxy bond vs spackle/epoxy bond? (I know over time the foam itself will eventually start to fall apart and then of course, game over. Time for a newie. But) which likely to last longer?

And which likely to have “snappier” “twangier” flex (technical terms of course)? Maybe no effect from spackle on the flex characteristics?


I think Greg Loehr would be the best to answer your question, but for now, I would suggest you look at using Resin Research 2040 epoxy for your application. The 2020 might work, but the 2040 has even more flex, depending on how you do your laments, or if you are using a core material other than the EPS foam. All these things could change what the end results will be. I think you should gain good flexibility without compromising the overall strength using the 2040. Adhesion to the spackle should be no problem.


Thanks Airframe! Straight EPS core. No stringer most likely. RR resin for sure. Have heard so much good about it and enough probs w/ others to be totally sold.


I don’t think you will be disappointed…


Biggest concern is durability of 2# eps under constant flexing back and forth thru several inches of arc. Was hoping for 4# but asking around seems only way to get a blank of 4# is buy a whole billet and slice it. Out of my $ league. May end up using Clark “regular” density or even urethane pour foam (8#). Airframe, do you have any ideas on getting just one blank 4# EPS for reasonable price?


I will be making an order with Insulfoam next week, and plan on finding out if 4# is available. If so I plan on purchasing an 8 ft X 22 inch block. At the moment, the highest density foam I have is 3 lb. EPS and some 4 lb density Walker foam.

I’ll let you know if the 4# is available.


If is going to flex that much maybe you should use corecell or divinicell: expensive but it has much better strength.

In my experience corecell is able to withstand severe bending without breaking, divinicell is slightly more brittle

Another thing maybe to check out is last-a-foam polyurethane foam sheets. Not as nearly good as the above options, but the last time I checked it was quite a bit cheaper and less hassle than pour foam. Unlike clark foam the density is uniform so no worries about shaping it too thin. It’s available in various densities - I know they make 8lb.

I think they make up to 30 lb - hey you might not even need glass for that!

You can get it directly from the manufacter at www.generalplastics.com

When me and another guy ordered some a few years ago we were able to get small quantities no problem. I can’t remember if we got one or two sheets.

If is going to flex that much maybe you should use corecell or divinicell: expensive but it has much better strength..

Emailed Dale S asking if he had experience w/ these materials and he said:

"I’ve worked with them during my former vocation in the sign industry. Also some experimentation with various prone/ knee surfcraft.

At least for flexible areas of spoons, I’d invest my money and time in high density PU pour foam: ease of application, use only where needed… tough, excellent bond and shaping, compatible with epoxy and

polyester resins, relatively inexpensive when all considered. In short, PU pour foam simply does what it’s supposed to do."

He suggested using light EPS for shape then after glass bottom dig it all the way out where flex will be. Then seal w/ thin epoxy layer to protect from the PU and pour into the flex areas w/ high density like 10-12 pound…

this is gonna be a flextail???..no stringer is gonna have the whole board flex as opposed to the mandala 18" no-stringer from tail…or is this gonna be like a flashpoint glass tail???..well i have 2 6’2 cs coming my way with 1.5 density eps with no stringer…picken em up next wedsday…theyll end up being a flexspoon and a aussie tri…the guy im picken up from suggested the 1.5 instead of the 2 for the flexspoon…did i give up durability for flex???..hope its worth it…i dont even know what spackle is but im listening for hints…

Spackle is drywall stuff…Greg reccommends Dap Fast and Final Lightweight Spackle, and so do I! Mix it with distilled water until it is nice and creamy, like mayonaise, and spread it on your shaped blank prior to glassing to seal the blanks and keep it from absorbing excess resin during the lam. Anything under 2# density should be sealed, 2.5 and over can be glassed without sealing.

Search for sealing EPS for more info then you can read in a day on sealing!

Welcome to sways!

I won’t pretend to be an expert on spackling EPS, but I would point out the LIGHTWEIGHT part on the label is very important. There are spackles on the market that weigh probably 10 times as much as the lightweight stuff. If you get the wrong type you’ll add a lot of weight to your board.

Hi Keith -

Even some of the “lightweight” labeled spackle is anything but.

Custom brand’s “Patch and Paint” as well as Dap’s “Fast and Final” are two that have microballoon filler. It’s not generally specified on the label, which will probably read something more like “Amorphous Silicate” on all of them. Just picking up the bucket it comes in should tell you - the microballon filler makes a big difference even if the label is unclear.

Mark Spindler and I went round on that and after researching it independently we both came up with the same conclusion…

I promised myself I wouldn’t do this again…

But it’s painful to watch…

Make sure you go real light with the spackle. And consider making your own “spackle” out of microballons and epoxy instead, OK?

And read my sig.

I read over the EPS info on the sticky page. Question though for the EPS experienced on spackle.

-I’m assuming spackling is don’t simply to make the surface smooth and fill in nicks/beads and so forth on the EPS blank?

-Go light on the spackle correct?

-then final sand

any pictures of a finished EPS blank before spackling stage and after spackling stage?

i didnt know i had to seal my 1.5# blanks…good thing im on swaylocks…any epoxy/microbaloon mix-measurments that you recommend…

photos would be great…anyone???


i didnt know i had to seal my 1.5# blanks…

You don’t. The weight saving is also minimal with spackle. IMHO the only good reason for using spackle is to get a good surface for artwork.



For epoxy/microballon mix 50/50 by volume is meant to be the way to go. Still hard to get a nice smooth finish for me though, and being epoxy its pretty hard to sand down afterwards. Might be easier with a power sander, but then if you go through epoxy to the foam underneath you’ll be taking big chunks out of your shape.

You DONT need to use spackle! At all! Like Havard says it’s really something for pure aesthetics and adds no other positive to the board, except minimising resin absorption (and that’s better dealt with using a primer coat of thinned epoxy).

In fact, theres a school of though (of which I am a member) that says it’s very likely to cause delams and reduce durability. Better using epoxy and microballoons (and maybe a bit of pigment) if you need to fill.

The BASIC recipe is supposed to be about 1:1. But I think that varies on what you are using for fill (microballons or whatever) and on your epoxy. I think start with the 50/50 and try it on a scrap. Then thin or thicken to what works for you.

Hey Doug! What happened to You when using spackle? Tried finding Your post about it but gave up, couldn’t find it.

What sort of spackle did You use and what happened? Do You think Your spackle disaster (if there was one) could have been avoided by using another type of spackle?


C’mon…you also DON’T need to use microballons at all. Why the freak about spackle?? Greg has used it for years on production boards…no problems there. I hate excess weight…and you are adding just that with the micro/resin slurry…yah I know its only ounces…but why. The spackle does NOT cause delams…bogus info. Spackle helps keep the board a little lighter, is good for cosmetic work(art) , and there is no problem with the bond between glass and foam. So …use what you want…spackle is quick, easy and effective. Your sig is pretty funny… have fun…

  • any valid examples of your point…real case scenarios???