For all you ding repair experts out there…Ive done plenty of repairs myself but one thing that always eats me up are the holes left after filling a repair with Cab-O-Sil...Ive tried different ratios of resin to cabosil but still manage to end up with the surface of the moon after it sets up…pinholes are fine as they fill almost invisibly with the subsequent layers of glass and resin. The holes that get me are the ones that require a second coat of fill…the size of these generally go from the head of a pencil to about a BB…any thoughts?

…let the paste settle…


stir again, check, then apply

For ding repair forget about Cab-o-sil.  Use Q-cell for any ding that you need to fill.  Cab-o-sil has it's place, but not as a filler for ding repair.  Ground fiber and white pigment for fin box stuff, Cabosil for clear stuff (like beads, tips on the nose or tail) Q-cell for any other ding that needs to be filled.  I did ding repair for years on Maui(sailboards and surfboards) and almost never used Cab-o-sil.  There were two or three ding repair Maestros other than myself on Maui over the years (way better than me) and none of them used Cab-o-sil for filler.

Cabosil is generally used for clear fills, and mainly to make the resin into a heavy paste.  The holes you have are from undissolved clumps in your mix, the more you use to thicken, the more holes you’ll have.  Normally, you’ll get pinholes (from air in the mix) after sanding and the subsequent lam and hotcoats usually fill these.  To avoid excessive and large holes, add the cabosil to the resin, mix very well with a big stick, and let sit couple of hours or more before you catalyze.  Stir the hell out of it again after adding the catalyst.  It should be an even paste, no lumps.  You can color match the filler using pigments, but first add some Q-cell to opaque it; about 1/2 tsp for 3 oz. mixed filler. 

I really appreciate all the replies and maybe I have the components confused?. I have two different “fillers” from FH…Aerosil fills clear but much harder to mix…the other I assumed was Cabosil but maybe its QCell? Its a very fine white powder and the final paste is opaque white…the Aerosil does not mix well but I was told to use this for tint repairs and I have with good results…the other fill for opaque work… I airbrush most opaque repairs than glass over so the white makes a nice base…just not the holes :slight_smile: Thanks again for the help…

…Aerosil or Cabosil are the same fumed silica made by 2 different companies.

qcell is colloidal quartz


Use cabosil for things under 1/8th deep. Its nice bc its clear but it will crack if its a deep fill bc it is not flexable. Q cell is great for filling deep holes it is more flexable. 

To get the least amount of bubbles: take a small amount on your stick and whipe the entire wall inside the ding. them pour in to the top. poke and twist your mixing stick till the bubble stop coming up then overfill the ding. Most of the bubbles will be at the very top if there are any. Thats why all ding shops use a grinder. Overfill so you only have to fill once since resin shrinks. Then kill with grinder.

mix just a little resin w/ a lot of cab.


I really appreciate all your help! The knowledge floating around this place is priceless :slight_smile: Thanks again!

     Howzit Herb,Don't you just love how Qsel expands and gets lighter the more you use. Aloha,Kokua

yup mike,that's the difference between qcell and airocell.

most beginners stick just a little qcell in alot of resin and it just clumps up,leaving you with lumpy resin.

but the experienced person will mix it correctly and it blends into a nice paste.

here's how i do it.

i grab a container and fill it up 1/2 or so with cab.then i put just a spoonful of resin in that.

while mixing it ..........the resin will wetout the cab evenly.............later you can add more resin to it ...........if you want it thinner.

airocell on the other hand will mix easily and doesnot require these steps.

airocell is a space filler........not a also displaces heat.


…hey Herb, I never heard about this Airocell…

I talked about Aerosil, that is a name brand exactly as Cabosil, that is other brand…both silica

Ok, expanding on this for a noob in need of some filler, for filling a (not too deep) crack putting a nose back on a board, I was going to use qcell, but would airocell work better or perhaps give a more consistent fill? Also for those of us that haven’t yet worked with the stuff, I see a lot of mentions of microballoons, but where I see them for purchase, they are described as a reddish/marron color. Does this coloring disappear when used? I’ve been scouring the archives and pages and pages of threads looking for the definitive information and most of it get’s me about 97% there but just not completely.

what i mean by "air-o-cell" is a type of microballon filler.

it looks simular to p.e.g.

white,round, hollow,micro balls.

if you are filling very light cracks .........thinnned out resin w/o fillers works best.

then you can cap that if needed.

otherwise just cab is best.


ya rev,

i thought that's what you were talking about.

the stuff i get is called several things,but air-o-cell is what i was told back in the days when dinosaurs roamed the

microballons is the more common term now days.

i'm not sure it's the same product as i use ,because i've only seen it in white...........i mean like opague stark white.

if you use micro-b like takes a sh#tload to make thick and then it's extremely weak.

i use air-o-cell mainly as a coloring agent/cooling agent.



As Pete said;  Cabosil is clear and works as a resin thickner.  I've used it for the tips at the nose or on swallow tails, around fin bases etc.  Q-cell is white and is best used for deep gashs etc.  Q-cell is the most commonly used filler around a ding repair shop.   Ground fiber is a good filler also.  I've used it mostly in the repair and reset of finboxes and plugs.

i also use exofiller(the contents used in disposable diapers as an absorbant).

mill/chop... it up great !


qcell ding,

that's what i call air-o-cell.



      Howzit Herb,Actually I think air-o-cell and Qsel are 2 different animals and I have seen air-o-cell used in boat building. Aloha,Kokua