Epoxy with Colloidal Silica?

I’ve been working with this stuff making a plywood boat. Is thickened West Systems 105/206 similar to JB Weld? Can I use it to fix metal bits?


you would be better off
you would be better off with mixing microfibre (epoxy glue) to the resin than silica as it seems to have more strength.

epoxy thickeners
Coloidal Silica is meant to keep weight down plus it won’t sag as it cures. It will make a rock hard epoxy. However, my guess is if you want to sacrifice weight for hardness, use a ceramic dust like marble dust.

If you need a small amount, hardware stores sell those syringes of 2 part epoxies with metal particles made for metal work.

It should work
But West Systems seems to recommend G Flex over 105/206 for bonding of metals.

As for colloidal silica weakening the bond, if West Systems info is to be believed addition of colloidal silica to epoxy is deemed desirable for a bonding agent.

A table on this link:


shows the tensile adhesion data for bonding of G Flex to a variety of metals (copper, bronze, 1018 steel, galvanized steel, 2024 T3 aluminum) for both unthickened G Flex (G Flex 650) and for G Flex that has been thickened with colloidal silica powder to a mayonnaise consistency ( G Flex 655).

In each case, for the same metal pretreated in the same way the tensile adhesion is somewhat better for the colloidal silica thickened G Flex than it is for the unthickened epoxy.

I haven’t used JB Weld so I can’t say how it compares.

what metal “bits”?

Nothing particular
I actually don’t need anything specific fixed at the moment, but while working with it I got to thinking this stuff (which I have plenty of) might be useful for all sorts of repairs. I thought about using it to glue some arrowheads on to arrows, which is a high impact sort of application. I also might eventually fix my car antenna which was mounted where my canoe goes, and broke off. When I have used JB, it’s been because it is much easier to work with as a putty than liquid resins.

just don’t breath the silica …
… hope you have been using resperator protection , but I’m pretty sure you have and understand about the silica .

JB Weld fillers
The fillers in JB Weld seem to be iron dust and calcium carbonate.

Yes and no
I used the respirator for the first couple of batches - then I got quick enough that I could hold my breath until it was mixed. I understand that this particular stuff doesn’t cause silicosis, but shouldn’t be inhaled just like any dust shouldn’t go into your lungs.

I have no difficulty mixing small
batches of West Epoxy and colloidal silica, without a mask. Just don’t mix all the silica in at one time, and go easy.

it’s not a high level precaution …

– Last Updated: Apr-24-12 9:15 AM EST –

...... when handling the powder silica (MSDS is a #1) , but it should be thought of as more than just dust . As I understand it will be much more of a respiratory irritant should you breath it in than just dust .

A dust mask or respirator is the advised thing to wear when handling .

I believe collidial silica is considered the liquid form , the powder form is fumed amorphous silica .

Colloidal silica such as the 406 adhesive filler sold by West System (also known as Cab-o-Sil) is a powder but it does not easily become airborne so the danger of inhaling it is relatively minimal.

Maybe my supply is old. It is light,
feathery, and can get to wafting around in air currents. But in the still air in my basement, it’s no problem as long as one doesn’t mix it like whipping biscuit dough.

You can get it suspended in the air if you work at it a bit, but if you mix it into the epoxy in a sheltered area I have no trouble picking up a gram or two at a time with a little plastic spatula or tongue depressor without it flying about.

west systems
hi-Ive been researching west systems myself-and they say yes, given adequate surface prep. Their web site has numerous links to experts with techniques on that subject-such as sinking nuts or internally threaded objects. It has excellent adhesion-except to polyesters.

when doing boat work …

– Last Updated: Apr-24-12 1:14 PM EST –

....... like transom replacements , under deck work (remove boat's intire inner shell) , major structural repairs , etc. ... the silica is scooped out in quart size containers and dumped into the resin/catalyst mix which is being stirred in with a power drill and paddle spade .

I know that smaller jobs don't handle as much of the silica at one time , but the stuff is easily airborn , there are much smaller particles that you don't see that get into the air around where you are using the stuff . Same situation when sanding glass work , it's the tiny , tiny small particals that get to you .

We just consider it poison so there's no need to think about how dangerous the stuff can be ... although it's not very dangerous it's always a good idea to use the respirator when handling it , that's all .


Silica fume is an even smaller particulate and more easily airborn , like in a bag of concrete (cement) .

Fumed silica is flat , silica fume is round , colloidal silica is liquid form .