Fillers in Epoxy

[jfblouin]

Thanks for these information

My boat will be a moderate speed planing boat, so I'm affraid about solidity. I'm interresting to use more than just silica for structural bonding. For my strip planking bonding, I want to use harder Epoxy. Maybe I'm wrong but I try some test of resistance on Epoxy strip and I find that Wood fiber+silica is stronger than only silica. Microballoun with Epoxy is the brittlest one.

In my area, I find Microballoun (Silcel) for $5 / Kg and Colloidal silica (Aerosil200) for $15 / Kg. Both in large quantity. I can't find more than 120 gr box of wood fiber at $ 15 each. So it is for what I try to make my one.

Today, I go to a shipyard near me. They dont use Epoxy but with their chopper gun, they will cut me some Kg of 3/8" chopped strand. It is the only way I can find chopped stand.

Thanks and sorry for my bad english

[PAR]

Frankly, you'll not get very much harder then colloidal silica. Microballons don't belong in the same sentence when talking about hardening up epoxy, compared to milled fibers or colloidal silica. Microballoons are mostly air and used as a soft filler to make sanding very easy and it will impart very little strength to the epoxy. You may save some money, but I wouldn't make a structural gap filler out of it, and then trust it to get me back to shore, when I'm farther away than I care to swim.

You need to brush up on the methods, techniques, tools and materials necessary to perform the tasks of building this stripper. It's generally not wise to second guess the engineer who designed the craft, without a very complete understanding of the concepts, principles, materials, methods and techniques used in it's creation.

Wood fiber or dust will be the very weak sister in filler, when compared to West 404 (no, it isn't aluminum, that's 420), colloidal silica, or even milled glass fibers. Again, if you build your boat to plan (always a good idea) and work with care, you'll not need but a few cans of light weight filler. If you do a hack job and have lots of structural filling you need to do, then a mixture (almost always the case with fillers) of silica, 404 and/or fibers will get you through. 404, colloidal silica and milled fibers (in that order) are the strength building reinforcements recommended by the epoxy manufacture (and industry leader) microballons are literally air balls to thin out the 100% solid content of epoxy, which makes it easy to sand (fairing purposes)

If you want to add some additional reinforcement to the silica fillets then slap on some tape set in more epoxy. I suspect, the designer has a more then reasonable margin within the design of the joints, fillets, etc. to address the strength a "moderate speed planning hull" will ask of them. It's likely you'll just be adding additional weight, effort and materials in you attempt to stiffen her up. Inside the strip seams you'll not need anything more then a creamy mixture of silica and epoxy. The resulting bond between the strips is well over the abilities of the wood strips themselves, so the point is moot.

[sham]

hi,
you can use microballons to enhance quality in respect of rigidity, toughness in resin. it will also make it lighter in weight.GFor additional info you may send details to envirotech_pune@yahoo.com
sham

[sham]

microballons in epoxy resin will impart impact strength to the structure of boat along with added buoyancy.It will also save on resin requirement and hence reduced cost.
fibre strands or glas mat added definitely give reinforcement to composite structure.
Microballons to be added in certain properation to get best results.

[flame]

@jfblouin

Hi,

when talking about strip-planking, you mayby need not concentrate on "hardness" so much (where colloidal silica should be your choice), but on getting maximum adhesion between your planks to form a good hull.

this adhesion is determined by large by the depth the resin makes it into the wood, so ideally a very thin epoxy mixture should be used. As this is not so convenient to work with, you need to make some trade-off's and add fillers

You also can pre-preg your strips with pure epoxy, and then, within 0.2 to 1 hours, when the resin still can react to form long chains (gelly-phase), finally glue using some fillers.

Why fillers at all?
to raise the viscosity of the epoxy while working with it
to ease closing of gaps
to assist bonding to the surfaces you are glueing
to modify the properties of the cured epoxy (brittleness, color, heat resistance, UV resistance etc)

so more of the times you use fillers to modify epoxy properties while it is still uncured (!)

glueing wooden strips I am using micro-fabric (cotton) on one side, having pre-impregnated both sides with pure epoxy. micro-fabrics can take up a lot of resin and facilitate bonding towards the wooden surface. They are soft enough to fill the very small holes in the wooden surface to deliver resin everywhere.

I definitely do not recommend wood particles from your sanding machine, they are uneven in grain size and widen your gaps unnecessarily. with just one particle in the 1-2mm range you can spoil an area of 2-3 cm2 by introducing a gap.

hope this helps
cheers

[jfblouin]

Very interresting

Thanks a lot

[nero]

"pre-impregnated ... with pure epoxy"

Often thought this could be an advantage. What cures the resin? Anyone else got an opinion or info on this?

Thanks flame for the input.

[flame]

@nero

Hi again

and sorry I may have used the wrong wording (I am not an English native speaker)

"pure epoxy" in the above context of course ment a mixture of resin & hardener without any additives

the resin-hardener mixture cures by itself; resin and hardener react with each other without any other components (like water or oxygen taken from the air) in stoechometric quantities. In very simple terms it's like a set of scale model railway rails that find together to form long chains, connecting to each other by their ends which make "click"

Therefore you need to obeye the mixing ratio and have no advantage of resin or hardener in excess. And therefore normally there are no solvents in the epoxy componets that evaporate.

However the epoxy reaction is exothermic (i.e. generating heath), which you notice when you mix resin/hardner and let it stay in a beaker with small diameter. It gets quite hot, which accellerates the curing process. Therefore I always pour the mixed epoxy out into a tray.

Cheers