Clear fillers

See our FAQ and tutorials before posting.
User avatar
Steve_MA
Active Poster
Active Poster
Posts: 423
Joined: Wed Apr 02, 2003 1:00 am

Clear fillers

Post by Steve_MA »

I mixed a little cabosil in with my epoxy when I was covering my rubrail - I wanted it to have a little gap filling properties. I wasn't sure if it would be clear, but it is. I added a couple heaping teaspoons to 3 oz epoxy - it was reasonably thick...thinner than ketchup, but close. I dont need to sand it either.

Are there any other clear fillers? How about milled fibers or cotton fiber? Will they yield a clear finish? Would either have an adv or disadv over cabosil?

Thanks

ks8
* Bateau Builder *
* Bateau Builder *
Posts: 8403
Joined: Mon Nov 24, 2003 1:00 am
Location: NC USA
Location: Now a much longer sail to Tampa Florida! Back to NC, Youngsville FM05tw

Re: Clear fillers

Post by ks8 »

Milled fibers and cotton are not clear. Even cabosil will begin to make the blend white as you thicken it more. Cabosil also makes the blend harder, more brittle with greater thickness, but what you did should be fine. Hopefully someone will correct me if I'm wrong there. :)

User avatar
kiwi
Very Active Poster
Very Active Poster
Posts: 1074
Joined: Thu Jun 03, 2004 12:49 pm
Location: France
Contact:

Re: Clear fillers

Post by kiwi »

All about fillers

http://en.wikipedia.org/wiki/Cabosil as you can see is not a filler but a thickening agent. It will stop epoxy from running but will not add any strength.

Fibres will add strength - cotton (white) and wood dust (reddish brown) add strength and the hardened result becomes like a piece of wood only stronger because of the varying directions of the fibres.

Micro-balloons or glass balls add volume. They don't really add strength because unlike fibres the resulting mix isn't tied together. The hardened mix will be somewhat stronger because of the added volume however.

So the strategy is to mix varying quantities of each with epoxy to obtain the required mechanical properties:
  • fillets - epoxy, micro-balloons for volume and fibres for strength with a little silica to stop them sagging
  • glue - epoxy and fibres
  • fairing compound - epoxy and micro-balloons
The quantities to use in fillets is about as close as we get to rocket science when building stitch and glue boats. You want a mix that is strong, easy to spread, which doesn't sag and yet remains easy to sand. If you are finishing bright you will prefer wood fibre over cotton to keep a nice wood like color and use red micro-balloons rather than white ones.

There are some good formulas in... :doh: the instructions that come with your epoxy.

System Three (and others) also do the hard work by providing premixed products.

Lots of interesting reading in the blue book (GBOBB)

And in answer to the question: thick clearish epoxy can be obtained with transparent (white when dry) micro-balloons and a little silica.

Cheers

Tony
Editor in chief
amateurboatbuilding.com

User avatar
Steve_MA
Active Poster
Active Poster
Posts: 423
Joined: Wed Apr 02, 2003 1:00 am

Re: Clear fillers

Post by Steve_MA »

kiwi wrote:
And in answer to the question: thick clearish epoxy can be obtained with transparent (white when dry) micro-balloons and a little silica.


Thank Tony, thats very helpful. I just used to call everything "filler" although I know some have different properties than other, I wasn't sure why.

I was epoxy coating the rubrail and inwhale and the wood is quite old so there are little seams in places where it has shrunk or worn away and the epoxy just keep sinking into those crevices. Thickening it with a little cabosil helped that and I wasn't sure it the resulting mix would dry cloudy or not - and it was clear.

I didnt even know there where "white microballoons" - I just have the red/purple ones. Good to know. Thanks

User avatar
kiwi
Very Active Poster
Very Active Poster
Posts: 1074
Joined: Thu Jun 03, 2004 12:49 pm
Location: France
Contact:

Re: Clear fillers

Post by kiwi »

Steve_MA wrote: I didnt even know there where "white microballoons" - I just have the red/purple ones. Good to know. Thanks
I didn't say they were easy to find :D The salesman for for a very famous epoxy brand gave us a sample when I was working on the Jolie Môme project back in the early 90s

The white ones become transparent and were to be used for fairing fillets that were a bit rough in bright finished hulls. Ask Joel if he has that stuff on catalogue. It was expensive and of limited use maybe it isn't on the market any more? I have seen it used for fairing carbon fibre weave that was finished bright too (back in the 90s) on a racing car.

My little trick for laminated rub rails is to add graphite to the epoxy cotton glue mix to make the join lines black (very dark grey). Very sexy when finished bright.

Cheers

Tony
Editor in chief
amateurboatbuilding.com

Post Reply

Who is online

Users browsing this forum: No registered users and 12 guests