The Silica powder is used to help with bonding, filling voids and strengthen the epoxy.

When your "glassing" use only epoxy.

Silica powder is just that, a powder.  You add it to epoxy to thicken it and change its properites.  It will increase the viscosity of epoxy and bonding (as hammar said)... it also turns the epoxy to a milky white colour hence when you are glassing, use unthickened (straight) epoxy.  When you mix in enough silica powder (AKA cabosil) it will have the consistency of toothpaste and is great for creating filleted joints.  It is very strong and very hard to sand.

Okay,  I get that part and thanks for the help. 

Now there is no place that tells me how much epoxy is needed for this procedure.    I plan to join just the hull pieces this week and the deck later, so how much do I mix up with the silica and how much without silica? 

Thanks, Coach C

Mix only a little bit at a time - 8 ounces total is good to start with.  I would go for less until you find out how easy it is to work with and how fast it takes to set up.  I found out the hard way what "hot in the cup" means with epoxy.  If you mix up too much, it gets really, really HOT all of a sudden - to the point it burns your hand and it is totally useless.  It is better to mix a small batche, use it up, then mix another batch.

 Thank you Penny. 

What Penny said, except that if you're a total beginner, you might want to go with 3 ounces until you get used to how it behaves.

Also, if you want to make your sanding go easier, woodflour works just as well for making fillets & glues as cabosil, but it's a lot easier to shape and smooth.

Have fun,

Laszlo

Thanks for everyones help.  I plan to get started today. 

Merry Christmas to all.  

Coach C

Okay,  it went pretty well. Remember I am a rank beginner. Be kind to me.

NEXT Question?  instructions said to saturate  the tape.  I think I did, however some of the weave is still visible and in places it is not . Do I need another coat.  or leave it be.

Coach Clay. 

Clay,

It sounds like you saturated the tape, just got a little more in areas where you don't see the weave.  Key to saturation is that the weave become clear (vs white).  Best to squeegee off excess so that a clear weave is visible; that gets covered in subsequent layers of epoxy (on the hull, deck, not on the taped seams... isn't necessary).

Sounds like you're rollin!

Larry

Laslo

You mentioned that wood-flour did the job of cabosil, but was easier to smooth and sand.  I haven't got anywhere near the assembly stages yet but, in preparation have collected quite a bit of spruce wood-flour over the past few weeks.

What I am a little concerned about is the exact definition of "flour".  If the spruce flour that I have needs to be like baking flour (i.e. very very fine) then what I've got will not work.  It's almost there and certainly finer than table salt but not what one would call a powder.

What say you ?

Dave