I help make one of the products Glen referred to. I just can't not comment
any longer ....
My very limited understanding is that if you want tensile strength ( i.e.
as in gluing) you don't use a hollow filler. Round hollow particles are
exactly NOT what is needed.
If you want to get more volume for your dollar you use a low density filler
which costs less per unit volume than the resin system. So the cost per
volume of filler is reduced ... So lower density is better, provided you
are paying for mass not volume.
If you want to sand it, it needs to be soft. Essentially you are going to
break the sphere when you sand. So it has to be hollow
If you want it very smooth, it needs to be fine. But we are not talking
automotive gloss levels here, so the particle size really does not matter if
there will be other coatings on top of the filler.
The strength of even the weakest grade will be more than enough to withstand
the shear forces in likely mixing processes for rec.boats.building, we are
not talking rapid mixing at very high loadings in ribbon blenders .... And
the pressure we apply to the finished product ( deck, hull etc) is not
likely to break the spheres before it damages the substrate ...we are not
talking stiletto heels here ...

As I often say to people, we are really selling packaged air - in adding
hollow sphere filler to a resin system you are trying to "fill" it with many
small bubbles to reduce it's density and cost in use.

As to using DE - it's hard and porous, so adding it to a resin system (
assuming the resin fills the voids) will not reduce the cost per unit
volume, and will make it if anything harder to sand.

Hope this helps
David



"Glenn Ashmore" wrote in message
news:tX%Xd.60176$SF.48249@lakeread08...
What for? Diatomaceous earth would make it heavy and harder to sand
without
adding any real strength.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Scott" wrote in message
...
How about diatomaceous earth as a filler.
It is the skeletons made of silica of microscopic creatures from long
ago.
Has anyone tried this as a filler? I would think it would be good and
cheap.

"John Cassara" wrote in message
...
I need to fair large deck surfaces in prep for paint. The repair thus
far
has been all polyester, can I use microballons to create a polyester
fairing compound?

John