Cab-O-Sil? We doan need no stingking Cab-O-Sil!

So I pranged the very tip of a borrowed board, offered to fix it and was asked “do you have Cab-O-Sil?”

“No” I replied,“don’t really use it.”

“Okaayyyy” he replied “slide me a few bucks and I’ll take care of it.”

When he didn’t hear Cab-O-Sil he wasn’t really interested in what I do or use and you know what?  That’s okay.

Why don’t I use Cab-O-Sil?  Don’t really need it, I do this instead:

  • Grab the scrap that matches the project

  • Grab the $4 dollar blender (used, thrift store score)

  • Get a couple liters of water

Mix with plenty of water to ease the chopping and keep the dust down.

Keep a pair of scissors handy.

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If the cloth gets wrapped, shut down the blender, use the scissors to free the blades and start it back up.  Typically no more than one binding and none once the blades are really sharp and you figure out the right speed and duration to blend at.

Blend until slurried then let seperate to check chop.
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Filter and drain using a foam mat, coffee filter, vac pump, desiccation jar, microwave, whatever.  I like to spread the filtrate and let dry in the sun.
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Once dry store it off till needed.  When it’s time to use, weigh the chop then mix with resin to the desired ratio, viscosity, flavor, look, I don’t know, however you mix your other filler, same thing but different.

Blend in some carbon, colored glass, tint the resin and use it for casting fins, boxes, fixing pranged noses, creating fillets on bulkheads, reinforcing hard points for drilling and threading.  Might want to go easy on blending kevlar, doesn’t chop easy.

Dat’s it.


and there you have it.


great stuff

That would get you milled fiber.  Used for adding strength. 

Micro Balloons are for adding volumn, while keeping weight down. 

Cabosil is for making the epoxy less runny.  So it will stick where you put it without dripping.  Milled fiber will thicken and strengthen, but you still get the drips.  Add all three for replacing foam, and then glass like normal.

I saw something like what you are doing on the Discovery Channel once, but that was done in the jungles of Columbia for completely different reasons. Either way, pretty clever, and thanks for the idea.

You’ll need one of these

Blend iPhone

Blend iPad

Burt Rutan uses what he calls flox, a mix of cotton fibers in resin, for structural fill.

Mad scientist Herb Spitzer posted a few years back about using disposable diaper stuffing as filler.  No shit!

I get it.....It's a good thing, make your own filler...good stuff for back yard builders....

I have lots of little rules for my life...maybe I should write a book...

I have a thing I call the Hassle Factor....And I have a little rule (unlike the govt..). You can't spend money that you don't have.

Balance the Hassle Factor with how much money you have.....Go from there.....

Right now it's better for me to buy microballons and other fillers because the Hassle factor is too big. But I'm running out of money and I've got lots of 6oz scraps......


I like the Hassle Factor consideration most especially when in production - one reason I’ve plenty of scrap.

You factor your waste, charge accordingly (something my wife will tell you I’ve never mastered), get rolling, get behind, get beat up by life then get left with half finished work and a pile of scrap and pissed off friends and/or customers.  Something that is hard if not impossible to make up but better to suffer the slings and arrows of building than never to have built before.  Who am I kidding?  Failing like that just plain sucks for everyone involved.  There, your daily emo (if you put the you back in emo at least you’ve got a flightless bird).

Been working on trying to turn that around after more than a few failures.

So now while we’re behind broke, I too try not to spend money I don’t have and economize at every opportunity though my wife will pointedly tell you my notion of economy is seriously out of whack with the rest of the world.

However the direction I’m now on with fewer builds at higher cost puts much of the family concern re economics to bed and mitigates the Hassle factor.  Of course when a build fails so to does your margin but then that’s life.

As for the argument concerning the uses of Cab-O-Sil (volume, viscosity) vs. chop (strength):

When you weigh equal volumes of each, Cab-O-Sil is lighter given it is supposed to be micro-balloons.  Runs/drips appear to be managed by the shape of the particles and using a marginal amount of resin to form the paste in conjunction with using treated Cab-O-Sil for better binding.

There is nothing stopping you from similarly mixing a low resin paste with chop to adjust the viscosity.  The run/drip factor is real but mitigated by a finer chop.  Course chop allows to much space for to much resin and longer fibers not jumbled up slip against each other by way of gravity.  Micro chop minimizes both of those effects.  You simply have to play with it till you’re satisfied with your results.  Many people who think there is no art in science have never developed a feel for labwork.  Mechanics can feel when a motor or engine is right.  Chefs can taste when food is right.  People who do casting and lamination can feel when something is right.  Use the force.


Two things to consider when using this jump out:

  • Weight; chop, even micro chop which is what you’ll end up as opposed to what most people think of as glass chop, is heavier but then you shouldn’t use much filler anyway.

  • Strength.  When cured, chop is, or should (gaurded comment there based on subjective testing) be stronger.

Prep time?  Takes less time to make a good Margarita and the savings pay for a better quality Tequila.

It seems to me that we are talking about three different materials here. One is chopped fiberglass (what you’re doing with your mixer) which can be found in a variety of appearances, from relatively long fibers to very short ones to (ultimately) fine powder. Mixed with resin, it will look greenish because of the density of glass in it. Microballoon is a different beast that looks like a white powder but is really made of very tiny glass or PVC hollow balls. It’s very light and appears white when mixed with resin, hence its use for filling up holes in foam because it is both light and white. But it has no real strength. Then we have silica mixed with resin: this will prevent resin from dripping (the more silica you add, the less dripping occurs). What’s great with this is that if you don’t over-stuff resin with it, the mix will remain reasonably clear, almost like pure resin and at the same time will be easy to conform to any shape with a squeegee or some other tool and will stay like you shaped it untill fully cured. Is that what you call “Cabosil”? Here in France, it’s called “colloïd silica”.


Is that what you call "Cabosil"? Here in France, it's called "colloïd silica".


That's the stuff Balsa!

Before?  or   After?


Before?  or   After?


Ha! I'm hoping before!!! :D

Although, if it's a brown or dark green board, baby poop might make a good filler.

Hi Brian...

it's wife's asleep...I just went through the kitchen cabinets....I found a blender...It hasn't been used in years!
...Score....So...tell me why you use water when you grind up the cloth.... It would be nice to do it dry.

You know all about the Hassle Factor... I bet there's a good reason for the water.....

... Cab-O-Sil... If you go into a Surf Shop in So Cal and ask for Cabisil you will walk out with a little baggie full of white stuff. Looks like sugar or flour or cocaine. Works great for dings. If you go into a supply shop that sells to board builders and ask for Cabisil you will get this light fluffy stuff that is nothing like the the White stuff the Surf shop sold you.

And that's how it works.....mis-information at every I tried to out smart the industry...I went into a Surf Industry supply store and told the guy I wanted some Resin filler....The guy said "Cabisil"?.  I said No........I want the white stuff they sell in little baggies at the surf shops....Big blank face from sales guy. This has happend at two different shops.

No worries....



Balance the Hassle Factor with how much money you have..... 



Ah the story of my life nailed it.


Hmmmm - I wonder if I can dump some the ever-growing pile of Divynicell offcuts in the Blender?


since there is another thread on foam waste, I was wondering - could you mix foam dust with resin for a lightweight filler?

Balsa brought up a great point that I’d not paid much attention to, yes, the chop does appear to have a green glass tint to it as against the Cab-O-Sil.  Why?  Doan know for sure but a SWAG - difference between the spectra of quartz~silica (primarily silicon and oxygen) and fiber glass (silicon, oxygen, aluminum, calcium, boron, magnesium, ?).

The composition of fumed amorphous silica appears to be doped with less if any other shtuff so the spectra doesn’t come off green like glass.

Aside from the doping, the primary difference between Cab-O-Sil (fumed amorphous silica) and glass is that the former is micro lumps with voids whereas glass is actual strand.  Once chopped, glass becomes tiny strands with no voids which is why it’s heavier.

Now, there are strand filler products which may be what the surf shop is selling Stingray.  By doing a quick search for silica strand filler, fumed silica strand filler, silica filler, the following popped up:

which just happpens to be …

Tah-Dah!   Micro chop, more or less.

As for why the water, the reason was hidden in the write-up, sorry, my bad.  It should be prominent.

Safety and ease of blending.  The dust is nasty chit so the water keeps that down.  The water also acts as a lubricant when blending otherwise the fiberglass binds up around the blades then waps the entire rig unmercifully all the while throwing off breathable micro spears that can get lodged in places you really don’t want them.

Well, maybe you want them but I don’t.

Anyway, most everything you probably didn’t want to know about filler lectured on by a dullard.

It’s a fantastic sunrise out over the ocean as I sit and type this.

Going to rain like hell today. 

Time to make the coffee.

For sure Huck - many a time I've shovelled up PU off the shaping room floor for bogging big holes. Its ugly though.


Planer-powdered EPS is no good - it melts. Whole separated beads are OK.






       Howzit brian, Just buy some Q-sel and do it the right way unless you have diapers,then do what Herb does plus you'll have plenty left over for the next ding.Aloha,Kokua

Can the ageing Surfer use Depends instead of Diapers?