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View Full Version : OK-now how about epoxy fillers?



schifsky
02-01-2005, 07:30 PM
Good discussion about epoxy resins. How about some thoughts about fillers from personal experience.
Mike S

NormMessinger
02-01-2005, 08:04 PM
Well, I'm inclined to use the stuff provided by the brand of epoxy I'm using. However, others, such as Dave Carnell, have success with cheap stuff.

Steve Miller
02-01-2005, 08:05 PM
I'll jump in here.

Wood flour for glue mixes.

Wood flour or Cabosil for fillets. The Cabosil makes for smoother fillets.

Microballons/cabosil blend for fairing and filling nail or screw holes. Sands very easily. The others are hard to sand.

Lots of other choices. The System 3 or West websites give a good discussion on the various fillers though West has special numbers for them.

Frank Wentzel
02-01-2005, 08:25 PM
Mike

As has been suggested previously, go to the System Three website ( http://www.systemthree.com/ )and download their Epoxy Manual. It explains epoxy, fillers, methods etc. They also have a $20 sample kit of their new Silvertip epoxies. I just got one and it is well worth the price.

Then go to the West System website ( http://www.westsystem.com/ ) and click on the Epoxyworks tab. Epoxyworks is a house publication of the Gougeon brother's company that covers a hugh array of epoxy/boat projects and goes into all the technical details of epoxy utilization. There is the current issue on the first page plus an archive of past issues and an invitation to request to be put on their free Epoxyworks magazine mailing list.

Forum members can give you a lot of information but the above is the best way to get it all in one place and logically arranged as well.

/// Frank ///

paul oman
02-01-2005, 08:36 PM
From the 'vendor' point of view, I'll jump in and give some feedback....

Cabosil (tm) is a brand name. The product is fumed silica. Looks like fake snow and weights next to nothing. Fumed silica comes in lots of flavors/sizes etc. Some dissolve in water, other's don't mix with water at all. A real pain to mix into epoxy because it is so light. About 2 parts fumed silica to one part epoxy will produce a 'putty'. Use less and you can get 'body' in the epoxy without thickening it. This 'Body" is the difference between self leveling floor paint and 'regular' paint for walls etc. - ie. less sagging etc. Marine epoxies fall into the self leveling floor paint group.

Wood flour - very fine sawdust. Easy to mix into the epoxy, provides a nice peanut butter color and smells good too!

Microspheres/microballoons - usually hollow glass spheres. Check on the specific gravity generally from 0.2 to 1 (grams per cc). The finer ones (0.2) are more expensive and also float in the air too much for my liking. Best is probably 0.5 or so. One problem is they are so round, it is like filling the epoxy will ball bearings. Generally considered as an 'easy to sand filler'.

fibers - sort of like adding rebar to concrete. Recommended for thick epoxy repairs. Watch out for cotton fibers than can wick water etc into the epoxy. Look for poly or kevlar etc.

cellulose dust - cheap and easy to mix in but about 4 times heavier than fumed silica

'flake' or aluminum, etc. - older commercial epoxies used to offer 'flake' epoxies. These are generally the mineral mica (aluminum based). The little sheets of mica flakes would stack on top of each other and reduce permeability thru the epoxy. This was in the days of solvent thinned epoxies. Probably not needed with today's sovlent free epoxies.

High density - can sometimes be 'rock dust' or ground limestone for the garden store. Forms a cement like epoxy mix.

Graphite or teflon - graphite gives the epoxy a nice midnight gray/black color. Both provide good friction reduction - i.e. inside a centerboard trunk.

copper - some believe it can turn epoxy into bottom paint.

Talcum powder is a 'quick and dirty' filler you can get at the supermarket.

With the exception of the Teflon and (next step down) the copper and the graphite, these fillers are generally very cheap and a real $$ for vendors.

hope this helps

paul oman
progressive epoxy pollymers

Todd Bradshaw
02-01-2005, 09:07 PM
I'd still like to see the test results on epoxy saturated cotton and/or linen wicking moisture. It would be difficult to find a material that wicks epoxy deeper into itself than cotton does, which is why it really sucks-in resin like crazy. If a chunk of cedar will soak up enough resin on it's surface to be effectively "waterproof" and suitable for long term immersion, saturated cotton fiber should soak up far more. I've been using Gougeon microfibers for about 25 years for highly-stressed filling needs and have never seen any evidence of water getting into those fills whatsoever.

Take phenololic mainsheet blocks for example. What kind of fibers do you think that old burgundy stuff contains??? - and there are plenty of forty to fifty year old phenolic blocks still in use with no sign of water wicking into the fibers inside the stuff.

[ 02-01-2005, 10:09 PM: Message edited by: Todd Bradshaw ]

Bruce Hooke
02-01-2005, 09:22 PM
In my experience, unless you are doing a really big job you will not go through enough filler to add up to that much money. So, given that, I generally stick to fillers from the same place as the epoxy I'm using. In my case that means Gougeon Brothers/West System. I figure that the fillers from the epoxy company will have been thoroughly tested with their epoxy.

Tristan
02-02-2005, 07:56 AM
I'm in south Florida, use Fiberglass Coatings (fgci.com) for all my resin products. My experience is to keep it simple. After using wood flour (expensive to buy), microbaloons (seems hard to sand, also the color sucks), talc (OK), and cabosil (fumed silica), I pretty much stick to cabosil. Mix it as thick as I want it, up to really thick, "peanut butter" consistency for fillets, slightly thinner for routine glueing. coat your wood glue or fillet site first with resin and let it start to get a little tacky before applying the "glue" so the wood doesn't wick the resin out of the glue (but don't let the resin coating dry!). You can be snowed by all the choices and specs, but my experience is that cabosil and resin can be used for most everything in the glueing/filling area. Lowell P. Thomas, Naples, FL

Dan McCosh
02-02-2005, 08:22 AM
One that hasn't been mentioned is the "ultralight" filler, which is a thermoplastic powder. It's easy to sand and shape, has the odd characteristic of softening in heat.

NormMessinger
02-02-2005, 09:35 AM
What Bruce and Todd said.

ssor
02-02-2005, 09:44 AM
For very small projects I have used lint from the clothes dryer, wheat flour, the dust off the filter in the shop vac, bandsaw dust. It all works, some are better, some are difficult to get smooth. The choice for me has always been fitting the filler to the job. Cab-o-sil is only a thickener, micro-ballons add substantial volumn, chopped or milled fibers add strength. One will be great for fairing and terrible where you need strength, etc.

Paulyboy
02-02-2005, 10:08 AM
Originally posted by Steve Miller:
I'll jump in here.

Wood flour for glue mixes.

Wood flour or Cabosil for fillets. The Cabosil makes for smoother fillets.

Microballons/cabosil blend for fairing and filling nail or screw holes. Sands very easily. The others are hard to sand.

Lots of other choices. The System 3 or West websites give a good discussion on the various fillers though West has special numbers for them.Is it best to use sanding sawdust for wood flour? And wouldn't you want to use the same dust as wood, or is that unimportant?

westinghouse
02-02-2005, 12:28 PM
I don't think the type of sawdust you use matters, except on the point of aesthetics.

Mahogany dust turns super dark, so a guy might want to experiment with different lighter woods to mitigate that. I don't bother. And I guess teak or other oily woods are not the best choice for flour but I'm only guessing.

And shifsky, when you're mixing up a silica/microspheres filler (yukaflux or smoodgie, whatever you want to call it) it's best to mix the silica in first. It doesn't homogenize well after the low density filler has been added and you end up with lumpy smoodge. Nobody likes lumpy smoodge.

Eli

[ 02-02-2005, 09:31 PM: Message edited by: westinghouse ]

George Roberts
02-02-2005, 05:35 PM
I find wood fiber works well for most of the work I do. I get my wood fiber from cleaning up my machines. My bandsaw makes a nice sized filler for most work.

Cullen T.M. McGough
02-02-2005, 08:57 PM
Originally posted by paul oman:

Wood flour - very fine sawdust. Easy to mix into the epoxy, provides a nice peanut butter color and smells good too!
Good god man, anything you can smell is probably causing cancer. Wear that filter mask!

ssor
02-02-2005, 09:23 PM
Even my wife's perfume????

paul oman
02-03-2005, 09:27 AM
Your wife's perfume hasn't bothered me!

paul oman

JimConlin
02-08-2005, 09:49 PM
I use four or five different fillers .

Quartz microspheres (Q-Cells) or phenolic microballoons (WEST #407) for a light, low-strength, easily sanded fairing material and non-structural fillets. A little bit of cabosil sometimes makes it smoother.
The WEST #410 sands beautifully, but the warnings about its low resistance to temperature scare me off.

Milled cotton fiber (aka 'flox', WEST #403) for
bonding parts together. It makes a slurry/putty thixotropic but will squeeze out of a joint and not present lumps there.

Wood flour for a structural putty and structural fillets. Not for bonding close joints as it doesn't squeeze out uniformly. A little Cabosil makes it smoother.

Colloidal silica (aka Cabosil) makes a fine-textured strong putty. Is very fluffy and messy to mix. Makes other epoxy mixes more thixotropic, smoother and harder to sand.

WEST #404 "high strength" filler for potting fastenings.

Songololo
09-27-2007, 04:29 PM
The next item on my Wee Rob to do list is the laminated stems. The 1/8'' thick Douglas Fir strips will be laminated using West System epoxy and #403 Microfibres.

Ques: How much filler does one generally need to use?

I have seen volume ratios of 2:1 (filler:epoxy) mentioned on aircraft building forums while the West System user manual uses the phrase "Stir in small handfuls of filler until the desired consistancy is reached" ...

Chan
09-27-2007, 05:05 PM
Songololo,
Mix in filler to the desired thickness, but if you measure as you go the next time won't have to be by the handful.

Thorne
09-27-2007, 05:26 PM
My rough understanding is that the filler is being mixed in to give the epoxy enough space in the glue joint so that it doesn't all get squeezed out.

So unlike filler for fairing or fillets where consistency in the mix is very important, you just want some filler in the joint -- "peanut butter-like" seems to be the most common term for the consistency.

John Turpin
09-27-2007, 07:02 PM
Is it best to use sanding sawdust for wood flour? And wouldn't you want to use the same dust as wood, or is that unimportant?

I've used sanding dust as a filler in a pinch, but wouldn't recommend it. The problem is sandpaper grit that will reside within the wood dust. It cannot be sanded and will most likely leave a bumpy fillet surface.

Wood flour costs relatively little, so there's really no cost advantage to using it. (Unless, of course, the stores are closed and you're in a time crunch.) When I did this, I borrowed (Shhhhh) my wife's kitchen flour sifter to sift the sanding dust before using it.

JimConlin
09-27-2007, 08:45 PM
Ques: How much filler does one generally need to use?
...

Fillers can only be reliably measured by weight, which is a PITA. For general bonding and filleting use, i mix the resin first, then add the chosen filler 'til the right consistency is reached. For laminating a stem a little 403/cotton fiber/'flox' to the consistency of mayonnaise is what i try for.