EPS sealing

Spackle works fine if you dont care too much about the board.   Downsides are that it has no structural value, and dissolves if it gets wet.  Up side is that it is cheap and easy.  If you want a strong bond between glass and foam, use microballoons.  1 part epoxy, both parts mixed first , to three parts microballoons , by volume, not weight.

Epoxy + Micro-Balloons is the way to go. I like to mix to the consitency of a milkshake and then add couple of drops of white pigment. Apply liberally but pull off all the excess with a squegee. Leaves a smooth, white surface eager to be laminated. If it requires a lot of sanding, it was applied too thick or lumpy. 

Ahhh, the age old “spackle vs. epoxy microballoons debate.”

Both work just fine. As mentioned above, spackle is easier and works great provided you don’t  leave it too thick. It will almost certainly delam if you do.

As for the epoxy microballoons thing, can’t see how it has an enhanced bond unless you glass while the slurry is in early cure stage. Otherwise, it’s just a mechanical bond that needs to be prep sanded just like glassing a spackled blank. 

the way to go…

I apply very very thin and sand back till I hit the EPS.

This one is pre glassing (sanded).

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Have done a couple of test pieces. The adhesion glas to blank is as good as unspackled and as good as with epoxy/microballons slurry.

I´ve stripped one of my early boards recently (4 years old, lot of airplane travelling). When you pull the glass, the break happens down in the eps beads. A layer of EPS beads comes apart with the glas when pulling it.

Exactly. Either work “wet in wet” or prep sand. Working with epoxy for almost 30 years now, mostly non surf related. There is always one rule: Next layer either if it´s still tacky/wet or otherwise wait and prep sand.

Usually I have at least one day between sealing and glassing (sometimes more) and so I always sand. Isn´t a big deal for me.

Both work just fine for me. And I use both ways depending on my mood or whatever. It´s probably 70% spackled boards to 30% microballons slurry sealed boards for me.


After a good amount of boards build and repair those last 25 last years i don’t use spackle anymore. Make and see many spackled with no problems but some with… May be depend of foam and spackle … 

Modern epoxy are far less sensible to blush and so if take care, prep is often reduce to a light keying, cleaning.

Epoxy secret sauce sealer can also be a part of strengh.

no problems with spackle if it’s one make for outside use, diluate so it spread really thin sand to foam and let resin soak in when lam.

Curious if any of the epoxy-microballoon proponents have anything other than opinions and theory on the ifs and whys of it being better than spackle?

Because 2 separate Swaylockers did peel tests years ago and to the surprise of everybody, myself included, spackle with an airbrush did BETTER than epoxy and microballoon. This was confirmed by Stretch to corroborate his findings on his own peel tests.


Anybody done peel tests?

Or is it just opinions and theory?

Hi Chris -

I’ve done a lot of actual testing with a number of different sealers.  One of the best sealers I tried was a purpose specific sealant based on a polyurethane elastic resin.  Of course I also tested basic water based spackle, acrylic based spackles, microballoon/epoxy slurry, etc.

I have tried your basic types of paint sprays as well.  My biggest gripe with water based spackle is what happens when it gets wet… one of the guys who used to be involved with Compsand.com (Doug Irwin) called it “The Creeping Evil.”  Mixing in some acrylic paint helps but it’s always a good idea to keep a dinged EPS board as dry as possible until you can repair it.

Bottom line?  It’s always the beads that were the weakest link in my peel tests.  

My last EPS/Epoxy glass job was a tinted microballoon/epoxy slurry over a rough sanded blank followed quickly with the lamination. Under the carbon was untinted microballoon/epoxy slurry - again, laminated while sealer was still sticky.  I suspect if it ever delams it’ll be the beads that let go.



Good to know John!

The bond between the beads is definitely the weak link.

My understanding is that the goal with spackle is to get a thin layer and let it dry completely. When glassing, the epoxy soaks through the microsphere bubbles and bond everything together.

Folks talk about spackle failing if it gets wet but they don’t realize that, if you do it right (THIN), the microballoons left behind after the spackle dries get completely soaked during the glassing process. So, you end up with the same basic end product. Microballoons ( which is what the lightweight spackle is made of) soaked with resin. There should be no spackle that is not resin soaked.

personally i have nothing against spackle. i used it a lot and stop when the product i use, interior exterior, change to grayish. Then i do many breacking test on 3 and 4 point bending «  real » mechanical test laboratory machine and not the tumb or the hammer or etc… test. eps epoxy samples breaks from buckling of compress side that creat shear which separate bead of foam. for peel test i use 4 point bending test, same foam same fiber  same resin batch, change only filler. i measure forces to break. I use my epoxy secret sauce «spackle » on « open foam » no paint possible.

That makes sense Chris.  I should mention that the name of that secret sauce I tested as a primer was ‘StyroSpray’ - pretty tough stuff that gets along well with epoxy.

that’s way you need right product and right use, light paint if paint, and a resin that’s able to soak in (not too thick not too fast).

for spackle i used to fine sand blank with minimal bead tear off to let minimal spackle. with epoxy slurry i let coarse sand blank and i had « scarifications » and pinholes, other way to work…

Thanks Lemat and John!

All good info

4th pic in this slideshow is a pretty handy illustration of some things already discussed:


Original board was Marko Envirofoam, spackled and sanded (220 screen), then aerosol painted and glassed w Resin Research. Boxes leaked & owner tends to keep boards in car, so it delammed. Box situation was too iffy to me to repair the delam. 

Next post in the account is the 2nd life of the same blank. This time I did a sealer coat w epoxy/qcel/white pigment mix because the new board will probably get rough treatment, too.

One neato discovery: the watermark from the delam was only a fraction of a mm deep, though the water crept along the surface of the blank to cover a large area.

Great input. Thanks.

A question that is slightly off topic. I want to build up the join between a dense foam stomp pad and eps blank. The step between the two is probably 1/8". Epoxy/beads or spackle?

I’m inclined to qcell, talc, cabosil mix but worry it’s going to set up too hard to sand without damaging the rails and will be a line for delam.


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Epoxy microsphere “dry mix”, = 1 volume resin, 4 to 5 volume micro. A bit tricky to mix, add micro slowly while mix. Better with a long time set and fluid resin. Give a dry paste super light and easy to sand like spackle but stronger. Paint some resin on board before, it help gluing past, with that much micro dry mix isn’t tacky.

How about routing the shaped blank and inserting the stomp pad in order to have it flush with the deck?

also to red_boards: If I’m understanding correctly (that the stomp area is flexible?), how do you get the lam and/or resin over the flexible area to not crack/split/ding up?

Different topic: lemat’s comment on resin type seems timely/crucial. It’s possible (I can’t remember) that I did the original lam on the board in my last post with Kwik Kick, and that that could have had a role in the delam that took place.

One other non-topical but somewhat related discovery (topic: spackle vs other foam fill coats): the bamboo stringer on the Marko blank definitely absorbed (or at least was stubbornly bound to) a small amount of resin. The stringer definitely had a very fine hard surface that was either bound to or impregnated with resin after the lam pulled up cleanly in sheets. Comforting to find out, as far as using bamboo stringers in the future.

Thank you. I have mixed on a resin:micro on a wood plank before with a spatula to get a dry mix, but then someone said I was popping all the microspheres. I try again with better management of the ratios. The pre-wetting with resin is a good tip, thanks.


It’s an idea, but, as you see in the pic, it’s bagged to the board already with a layer of 2oz innegra under.

The foam is Airex, a high density foam, much harder than EPS.

Actually this is a fix. I cut the board too thin, inserted a full height stringer that was 1/4" proud (one day I’ll do a thread on my “backward” blank construction) and “solved” by adding the foam patch.

(edited in Airex name)