Wood flour vs cotton flocks

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Stachu
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Wood flour vs cotton flocks

Post by Stachu » Mon Apr 15, 2019 6:21 pm

Hello again,
I have hard time getting good wood flour. All the producers I found in Poland sell it only in tonnes :doh: I found only one guy that sells "wood flour" for ordinary people. He says it's fine pinewood dust from a dust collector in his wood pellets factory. Is it good enough?

Alternatively, my epoxy supplier have cotton flocks as an organic filler. Is there any contraindications for using it instead of the wood flour?

Thanks,
-St.


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fallguy1000
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Re: Wood flour vs cotton flocks

Post by fallguy1000 » Mon Apr 15, 2019 9:03 pm

Both materials are hygroscopic.

This often upsets the bateau builder crowd, but the fact is wood flour and cotton both take on water, if it gets to it.

I used cotton in one of my glue joints; sort of as a test and it is awful to work with.

The only fillers you truly need are cabosil or fumed silica and microballoons. Cabosil is exceptional fillet material and not hygroscopic. However, it is toxic and you MUST wear a dust mask or you will cough badly, not to mention exposure can cause silicosis; a deadly disease.

Microballoons used in fairing. You can skip these if you buy costlier fairing compounds.
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Chenier
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Re: Wood flour vs cotton flocks

Post by Chenier » Mon Apr 15, 2019 9:19 pm

The first build I did 20-ish years ago we simply used sawdust. That worked but the surface was a bit coarse and lumpy. You're looking for a substance that, when mixed with epoxy, makes a thick paste that can be more or less smoothed out. The smoother it is the less epoxy it takes to fair the surface in later steps. I'd think you could make the pinewood dust work. The wood flour we get in the states is pretty dust-like. Run it through a sieve if it has lots of bigger lumps in it.

Cotton flocks sound a lot like one of the thickeners we use to make thickened epoxy for glue, expanded cellulose. Works great as a thickener, but takes a lot to make a paste that won't sag when you apply it. I'd start with the pine dust.

Ideally, see if you can get small samples of each from the vendors and give them a try.

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pee wee
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Re: Wood flour vs cotton flocks

Post by pee wee » Tue Apr 16, 2019 9:42 am

fallguy1000 wrote:
Mon Apr 15, 2019 9:03 pm
Both materials are hygroscopic.

This often upsets the bateau builder crowd, but the fact is wood flour and cotton both take on water, if it gets to it.
I'm not upset that you say that, I just think you're wrong! :lol:

Consider this- builders say don't use marine fir for many reasons, one being that it soaks up a lot of resin. If a layer of plywood, where the resin has little access to end grain, soaks up a lot of resin, how much more would a tiny particle of wood accept the epoxy? Once saturated in epoxy, I don't think either cotton or wood will take on water in any meaningful measure.

So to your comment - I would agree that dry wood flour and cotton will take on water if it gets to either, but I don't agree that it will once used as directed. So, I'd say you're right on a technicality, and I'm right in a practical sense!
Hank

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Re: Wood flour vs cotton flocks

Post by fallguy1000 » Tue Apr 16, 2019 11:18 am

by the way, cotton is clumpy in a fillet and when you pull a tongue depresser across it; the thicker clumps catch and the fillets are not very smooth

Perhaps I undermixed it, but not likely.
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Netpackrat
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Re: Wood flour vs cotton flocks

Post by Netpackrat » Tue Apr 16, 2019 1:31 pm

Sounds like it would be worth it for somebody to make a hockey puck of wood flour putty, weigh it, soak it in water for a period of time, and weigh it again to see if it took on any water. Put the thing to rest once and for all.

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Re: Wood flour vs cotton flocks

Post by TomW1 » Tue Apr 16, 2019 2:31 pm

The cotton is hard to sand after being encased in epoxy. Wood flour is easier. Both once encased have no problem with water. I would go with the wood dust and try it. If you need to sift it so be it as long as it is cheap enough. Maybe ask to get a sample first.

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BarraMan
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Re: Wood flour vs cotton flocks

Post by BarraMan » Tue Apr 16, 2019 8:03 pm

fallguy1000 wrote:
Mon Apr 15, 2019 9:03 pm
Both materials are hygroscopic.
This often upsets the bateau builder crowd, but the fact is wood flour and cotton both take on water, if it gets to it.
I have to disagree with this statement re wood flour!

I used wood flour to build my 22' boat. I only used a bit of carbosil in the mix where I needed to make a vertical fillet.

The wood flour we can buy here is high quality and cheap. I think it cost me about US$50 for the whole build.

I don know if you mean that wood flour takes on water before or after mixing with epoxy or both, but I live in a very high humidity area and the wood flour that I keep in a small plastic bin remains dry and fine. I sieve it before use.

Once mixed with epoxy I don't believe that wood flour can absorb water - sorry, I just don't buy it! You are then dealing with plasticized wood!

Epoxy/wood flour fillets are very easy to make and work with.

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Re: Wood flour vs cotton flocks

Post by fallguy1000 » Tue Apr 16, 2019 8:22 pm

BarraMan wrote:
Tue Apr 16, 2019 8:03 pm
fallguy1000 wrote:
Mon Apr 15, 2019 9:03 pm
Both materials are hygroscopic.
This often upsets the bateau builder crowd, but the fact is wood flour and cotton both take on water, if it gets to it.
I have to disagree with this statement re wood flour!

I used wood flour to build my 22' boat. I only used a bit of carbosil in the mix where I needed to make a vertical fillet.

The wood flour we can buy here is high quality and cheap. I think it cost me about US$50 for the whole build.

I don know if you mean that wood flour takes on water before or after mixing with epoxy or both, but I live in a very high humidity area and the wood flour that I keep in a small plastic bin remains dry and fine. I sieve it before use.

Once mixed with epoxy I don't believe that wood flour can absorb water - sorry, I just don't buy it! You are then dealing with plasticized wood!

Epoxy/wood flour fillets are very easy to make and work with.
I think a lot of people miss the point.

If he can't source wood flour and wood flour is not the premier solution then he ought to use fumed silica versus cotton which is hygroscopic, clumpy, and hard to sand.

It wasn't a choice between the three when first presented unless I have lost my marbles, which is possible, I suppose.

He presented cotton and I said no. He did not present an excellent solution of fumed silica.
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BarraMan
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Re: Wood flour vs cotton flocks

Post by BarraMan » Tue Apr 16, 2019 8:42 pm

fallguy1000 wrote:
Mon Apr 15, 2019 9:03 pm
Both materials are hygroscopic.
This often upsets the bateau builder crowd, but the fact is wood flour and cotton both take on water, if it gets to it.
Seems pretty clear to me !!! :doh:

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