Grinding sanding dust further to make wood flower?

[ernie]

I have been using sanding dust as a cheap thickener for epoxy, but it is still rough.
Any ideas how to make even finer powder, other than to start sanding everything with 250 grit paper?
I don’t quite dare do this in any crucial joints, dose anyone have experience or strength test data for this type of filler?

[Toot]

You could just buy microballoons/bubbles or silica or whatever.

I use a lot of microballoons. You can get a pound of them for less than ten bucks and a pound of these things is a LOT. I'd guess it's almost a gallon's worth.

At such a cheap price, why not use them?

[frosh]

Ernie, thickeners for epoxy to make glue or fillets or fairing compound is a lot more scientific than adding wood dust. Also they are the cheapest component in boat building. If you can't afford them then how can you afford the structural materials? I use three types of filler. (1) Microballons
(2) Microfibres (3) Thixotropic Silica. Sometimes they are combined and sometimes not, depending on the exact purpose of use.

[Frosty]

I notice that talcum powder was not mentioned. I know nothing about this kind of stuff but do use talcum for thickening. Is this not the right thing to do then?

[Toot]

I don't know how well talcum powder would work. On the one hand, it's a mineral, right? So it shouldn't absorb epoxy and cause a risk of a dry bond. On the other hand, I don't know enough about its properties to say how well it might work.

Can you really get talc for less money than microballoons or milled glass?

[Frosty]

Talc is all I know of, its what everyone round here uses. I buy it at the fibre- glass shop that sells all the other stuff. My wife tells me it is 1kg per 15baht,-- there is about 40 baht to a US dollar. 2kg is about a gallon. Big gallon 4.4 liters.

Its not the smelly stuff that you put under your arms,-- but I guess you could!!

As far as it being a mineral --not a clue!! Milled glass???? dito.

I can get micro balloon stuff,--but bit expensive? I once filled an old dinghy keel with sago milk pudding powder,, it worked well !! Theres also vanilla flavour custard mix-- , or tapioca flour. I dont suppose the flavour really matters.
I am not joking,-- well, just a bit on the flavours!!!

[gonzo]

Talcum absorbs a lot of humidity which can be a problem. It was used in the early days of fiberglass and found to be of poor performance. You will never see it in quality construction. Fillers have characteristic that are are specific to each use. It is foolish to risk a major failure to save a little money.

[Frosty]

Ok-- but if it were to be used as a skim to fare off a particular shape and then glassed in, it would be ok would'nt it? Such as skimming foam to make a nice smooth surface on which to glass over?

[Toot]

Honestly, I'm trying to approach this with an open mind. I don't want to say don't use it if my only justification for saying so is that "It sounds wrong".

However, don't think I'd use it to skim foam. This is what I was talking about a few weeks ago when I was talking about using slurries. In that application, you want a very strong structural bond between the foam and the glass. This is definitely a structural application. Where I might use it, however, is for non-structural fillets, such as places where you just want a smooth rounded contour and strength doesn't matter... but again, if the fillet is going to flex or carry any weight, then I'd opt for something else.

[Joe6]

In my opinion ideas like this end up in wasted time that would be better spent working. Just buy the stuff and save the hassle.

That said, I'm not criticising you, I've tried everything mentioned on this page and more!

Can't blame a guy for trying to save money, but in this realm I think its better to just spend the $10 and get on with the work.

I once tried 320g linear polyurathane sanding dust harvested from my dust collection system mixed with epoxy, it worked, tough to sand.

Back in the seventies a friend of mine used lime (the stuff used to put lines on football fields) mixed with polyester resin (by the drum)to fair a 90' alden schooner.
It also worked, absolute murder to sand.

Joe

[ernie]

Maybe it’s me, but it just feels wrong to spend money for a filling powder when you can’t feel the weight of it.

But as for as structural integrity goes, the sanding dust is the same stuff as the rest of the boat, so with regards to epoxy adhesion, water absorption and other characteristics, why isn’t this as good as anything else?

I am aware of the special properties of products like colloidal silica and micro balloons, but extra flexibility and super adhesion (more than epoxy alone) are not necessary for every job are they? Especially the large amount of filleting in a stitch and glue project. Obviously scarfing a joint requires something else, as dose the bedding of a mast step or motor mount.


It isn’t a matter of what can be afforded, I just bothers me to pay for a product called wood flower, then go to the shop and dump what seems to be the same stuff from the collection bag of my sander in to a landfill.

But it would be better if I could make the stuff from my sander more consistent.

[bilgeboy]

Ernie, I appreciate your sentiments.

I agree with your views 100%. You should save the dust you collect with 220 grit and up. Why not? Just because you live in the US doesn't mean you should throw out the perfectly good, and replace with the latest and greatest. Hell, you can sell it to boat builders!

Something more interesting to me is that I bought a gallon a few months ago, don't even remember what I paid. I didn't care at the time, I was in a hurry, and bought a big ol' jug of wood flour at Jamestown Distributors.

I never do that. I never walk into the Home Depot and buy "wood". "Could I have some wood, please?" I generally have a clue about the relative weight, rot resistance, grain tightness, etc, etc, etc. But I actually went and happily paid for saw dust of a completely unknown species.

You are creating a composite compound when you mix the flour with epoxy, and there must be good flours for certain applications. To say there is no real difference for this application would be like saying glass and carbon are the same when used with epoxy.

I say go for it, ernie, and let us know which species you like.

Mike

[Frosty]

Thats a good point about the dust being from the boat in the first place. What could be a better thickener than epoxy powder in epoxy to make thickened epoxy?

I am so pleased that i am not the only person to have tries 'custard mix' I am not sure what exactly is 'custard mix' but can it be any worse than foam itself. After all its just meant to fill it out a bit to thicken it?

I used rice once!!! But if its enclosed in epoxy how can any thickening product absorb moisture.

Maybe 'Bisto' thats made to thicken.

Ok joking again, but putting the expense aside I feel sure there must be something in the supermarket that could be a substitute. This modern world of re-packaging makes one very suspicious.

[marshmat]

Not sure how sawdust works in epoxy since I usually work with carbon and such these days.
In my experience with polyester, sawdust proved to be a good thickener but didn't actually extend the volume at all. It made a cup of thin resin into 1.05 cups of gooey resin. The microballoons increase the volume a lot more for the weight.

[fiberglass jack]

one time i was working on a field job a days drive from the shop, we forgot to bring cabosil with us to make paste, couldnt get any where we were up in a mining town in northern canada, so off to the local supermarket and bought flour worked good that was 12 years ago dont know how it would be with epoxy , if your going to make a paste thats going to be sanded and faired go with good stuff the money you save will only be spent on sand paper