Wood Flour as thickener
frjohn
use cabosil and microballoons, I'd like to make use of the free stuff
where it is appropriate. Here are my questions:
1. In which applications is the use of wood flour appropriate (eg.,
laminating, glueing, etc.)?
2. How should one process sawdust into wood flour? Is a kitchen
flour sifter OK?
Thanks,
John Liebler
New Smyrna Beach, Florida
Glenn Ashmore
fillets that fairly closely match the color of the wood I am using but
wood flour is not that good at thickening. It is more of an extender
than a thickner. It takes a lot more to get a workable stiffness which
means the fillet is a lot more porus and therefore weaker and prone to
absorbing water.
I just don't see how homemade wood flour could possibly less expensive
than fumed silica. To get a smooth fillet it has to be very fine and
clean. (About a 180 sive minimum. A flour sifter is about 70 sive.) You
can't just sweep it up off the floor and sift it. To make enough to
replace $10 worth of silica would take at least $20 worth of sanding
belts/disks.
frjohn wrote:
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Glenn Ashmore
I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
david allen
I've used paper mache mixed with epoxy. when it's mixed well, it can
be smoothed like wood putty. I didn't use it in applications where high
strength was needed, just to fill holes and seal cracks.
da
William R. Watt
sieve, and mixed with plastic resin glue as a filler in areas where there
was more than a 1/8" gap between the pieces being screwed and glued
together. I don't know who waterproof that would be but it has caused no
problems so far. For a finer sawdust I would try chopping it up into a
powder in a kitchen blender.
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Meindert Sprang
news:a4gqe3$p65$1...@freenet9.carleton.ca...
> I've collected sawdust in a bag under a table saw, sifted it in a kitchen
> sieve, and mixed with plastic resin glue as a filler in areas where there
> was more than a 1/8" gap between the pieces being screwed and glued
> together. I don't know who waterproof that would be but it has caused no
> problems so far. For a finer sawdust I would try chopping it up into a
> powder in a kitchen blender.
>
The contents of your belt-sander dustbag makes the best woodflour you can
think of. I collected several jars of mahogany and oak dust.
Meindert
Backyard Renegade
Wood flower is great for fairing and stuff, especially in areas that
will be clearcoated...You can come close to matching colors if you
take the time. Like the previous poster said, it really does not
thicken well, you will see what I mean if you try it. As far as whats
on your floor, well it may be ok for a general filler mix, but to try
to replace wood flower or cabosil with sawdust won't give the best
results...It's like the drywall tape thread of recent, looks like
great stuff, you could really use this stuff, but not necessarily for
boatbuilding...
Scotty, The Backyard Renegade
Brian
wood flour are from people that just have not used it very much. I've built
entire boats with wood flour thickened epoxy, and it is not a problem. And
unlike what someone said, it does not absorb water, and it is not porous.
It thickens epoxy quicker and easier than most other thickeners, silica
excepted maybe, but it's pretty close. And no, it is NOT good for fairing.
It produces a very hard product when cured and does not sand easily enough
to be called a fairing compound, although you can sand it somewhat. It's
just too hard to do serious sanding on. Go to http://www.bateau.com and
check their tutorials ... all those boats at that site are made with wood
flour thickened epoxy. I can provide references of other people who use it
regularly, and the boat building forums at that site are full of people
using it. Soooo, with that said, let's concentrate on your questions:
1. Wood flour thickened epoxy is good for epoxy fillets and space filling
gluing. Mixing it about 20% silica/80% wood flour produces a smoother
mixture. It is thixotropic either way and does not sag. The silica will
reduce the sanding you need to do because it helps produce a smoother
product. I don't recommend wood flour for laminating only because I think
that a silica slurry is best and re-flows better when
clamping/screwing/vacuum bagging laminations. Wood flour does produce a
product that is closer to the color of your wood, but like wet wood, it will
be darker than the surrounding wood (in general.) The mechanical properties
of wood flour thickened epoxy is closer to the native wood and therefore it
makes a good fillet material in the seams of stitch-n-tape boats.
2. How to make/process wood flour? It's difficult to make well by sifting.
The most common homemade way of doing it is to scavenge it out of sanders
which have dust collection systems. Another source is to look in the yellow
pages for cabinet makers. They often have lots of flour-grade wood flour
around. Probably the best of all is to buy it...it's cheap. RAKA Epoxies
in Florida has a pretty smooth product and a good price. System Three
Epoxies in Seattle also sells wood flour, but I think RAKA's is a bit finer.
I've used System Three personally and it is fine. Others I've spoken to
have used the RAKA brand and liked it better than System Three's, and it was
cheaper. Both are on the web. Saw dust is too rough, so don't scavange
from table or band saws.
In any case, the moral of the story is this:
- Wood flour is an inexpensive, easily available, filler that is thixotropic
(nonsagging) and makes a good space filling glue mixture and a good epoxy
filleting mixture. Add up to about 20% silica to make it even smoother.
- Wood flour can be used for laminations (I've done it), but silica is
better. If the lamination is going to show on a bright finished boat, try a
blend of wood flour and silica to make a nice flowing slurry that matches
the color of the wood.
- Use microballoon thickened (usually plus a bit of silica to help reduce
sagging issues) for fairing work. Put one or more seal coats of epoxy over
any sanded microballoon surfaces.
Download the free Epoxy Book at http://www.systemthree.com.
Brian
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"frjohn" <frj...@stpetersnet.net> wrote in message
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Frank Hagan
I'm not as much of an expert, having built just one boat (and assorted
furniture repairs) using wood flour and epoxy. I bought maple wood
flour from RAKA for use with mahogany (it dries to a dark brown color)
and pine wood flour for use with fir and oak (color comes very close
with it too). Works very well for making fillets and making a "paste"
to glue small things together (like my cockpit coamings.)
Sam Devlin uses wood flour extensively in his boats; see his "Devlin
Boat Building" book for more info on that.
Frank
http://www.messing-about.com
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http://www.messing-about.com
Resources for the Boat Builder, Renovator and Small Boat Skipper
Brian
have reason to justify something else. Here's some examples:
- Scarfing plywood. Similar to laminating, except the gluing surface is
narrower. Use 8:1 angle on the scarf and silica thickened epoxy, or a
wood/silica blend on bright boats. For applications that need extra high
strength, do the same thing but use a lower angle, 12:1. For the highest
strength, use the 12:1 angle and glass fiber filler instead. Airplanes go
even higher on the angle, say 24:1 ... not necessary for boats. 99.99% of
scarfs use 7:1 or 8:1 and silica thickened or wood & silica thickened epoxy.
- Laminations. You can laminate with plain unthickened epoxy, but it tends
to run out. It's better to use a nice flowing slurry that has just barely
enough filler in it to reduce run out. Silica works best for this, but keep
it as thin as possible unless you want thick lamination glue layers. Note:
You can laminate in this way over 90% of the lamination, leaving edge areas
that would show on a bright finished boat 'open', then later fill with a
wood flour thickened epoxy (fill the cracks) to make it match for color
(silica makes a white line). Or, you can blend wood flour and silica in
your slurry in the first place (my preference), being very careful not to
make it too thick.
Brian
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"Frank Hagan" <fsh...@ev1.net> wrote in message
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kf4sign
I'm actually going the other way in my boatbuilding. My first boat was built
with woodflour thickener. No problems with it, however, wood is not water
resistant and the epoxy does allow the transmission of water and water vapor.
I have heard others say that workshop sawdust is too coarse and variable to
make a good filler. High quality extremely fine stuff is available rather
cheaply in larger (10lb.?) quantities.
Best regards,
Warren
line lepage
how filler work
like
silca is for ??
wood flour is for ??
limestone
ect ect
regards
stef
Backyard Renegade
> I forgot to say that I recommend wood flour for all your needs unless you
> have reason to justify something else. Here's some examples:
>
Let me be clear here...I use woodflower all the time, have pine and
maple right here next to my aerosil...What I meant to say is sawdust
is not wood flower and wood flower does not smooth as well as
aerosil...That's all
Scotty
Brian
Tutorials at http://www.bateau.com (free)
The book "The Gougeon Brothers on Boat Construction" (see
http://www.amazon.com, $29.95)
The book "The Epoxy Book", downloadable for free from
http://www.systemthree.com
The book "Devlin's Boatbuilding" (see http://www.amazon.com, $16.06)
There are many other books too, so my apologies to all those other authors
out there who produce great material for us boat-addicted types.
In a nutshell:
- Wood flour and silica, blended or separate, will be used for most space
filling gluing and filleting. If the designer says it's ok, you can use
microspheres and microballoons for the same applications.
- Microspheres is generally not used a lot, but produces a lighter weight
space filling epoxy that some people like to use when the highest strength
is not required.
- For a putty that can be sanded (faired), microballoons (plus a little
silica to reduce sagging) is the best choice
- High strength applications such as spar and mast scarf joints, the glass
fiber filler is stronger. But it's rougher, harder to finish nicely, and is
best avoided unless the designer said to use it or you can justify the need
for greater strength.
- The smoothest, but hardest, fillets and glues are made with pure silica
(fluffy glass powder, non-sharp), also known as Cab-o-Sil, fumed silica,
colloidal silica etc.
Note also that most of the above is pretty forgiving. You can mistakenly
use the wrong thickener in most cases and still be ok. But those are
general guidelines, and it is ALWAYS a good idea to check with the designer
of your boat before making final decisions if there is any question about
it. He/she will be an expert on epoxies and will tell you the best
thickener to use, or what selection of thickeners you can use (in that case,
pick the easiest to use/cheapest to use/etc. from that selection.)
Brian
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"line lepage" <line....@sympatico.ca> wrote in message
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Ron Magen
Take a look at one of my past columns in Duckworksmagazine.com; will 'answer
all'
Regards,
Ron Magen
Backyard Boatshop
"line lepage" <line....@sympatico.ca> wrote in message
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