You can also use "micro balloons" used for thickening epoxy resin into a paste.

ballotini are glass beads, micro balloons are hollow phenolic resin balls

Microballoons is a fairly broad term and not exclusively phenolic resin. Most of the ones you encounter used for balsa aircraft (because of their inherent lightness) are usually white. https://www.christinedemerchant.com/filler-micro-balloons.html

All very interesting.

Am I right in thinking that these fillers are also accelerators? I thought bicarb was and that this was its main use (apart from domestic uses).

Bicarb seems to be used as an accelerator in the absence of the real McKoy, but all superglues start the cure process in the presence of water ( or rather, Hydroxil Ions). So any moisture sets them off. The control of the cure when using bicarb is a bit of a hit and miss affair, depending on its moisture content. There are spray accelerators that work very well and the rate of cure can be controlled to some extent by the amount you spray. Micro balloons and Cab-O-Sil are not accelerators, but if they have absorbed any moisture they will set the glue off.

Bicarb tends to work as an accelerator since commercial Bicarb has a starch ( normally corn or potato starch) added which absorbs moisture to prolong the efficacy of the powder in storage. It is the moisture in the starch that triggers the cure.

As I said before, any of the fillers that are powder based as opposed to fibre based have little strength in shear, and any flexing will crack the filler. Most superglues also cure to a glass hard bond, which cracks if flexed. Loctite Ultra-Gel is a flexible superglue that is rubber infused and remains very flexible, but is a thick gel prior to curing and does not flow well. There is also a 'Gorilla glue' that claims to be more flexible than normal superglues – I disagree…

Since you have not explained the intended application ( other than filling a gap..) I cannot comment on the suitability or otherwise of any of the aforementioned products..

Joe

It was many years ago but I’m pretty sure the hollow glass spheres were sold to me as micro balloons.

I seem to remember they used to make something called Syntactic foam with glass microballoons years ago to form a very tough but lightweight filler. I’ve probably still got a small pot of them somewhere.

Small hollow glass microbeads used to be recovered from the flyash of coal-fired powerstations. They were known and markerted under the name Armospheres. In the match industry they were used as a way to control the density of the match composition applied to the end of the match stick. I guess with the demise of coal fired power stations they are less available than they used to be.

Mike