using wood flour (saw dust) in fillets

[Ann and Neville Clement]

We are using wood flour a lot just now in building a little dinghy using ply/epoxy/fibreglass and I think someone here knows the answer I need.  The fillets made from wood flour are a bit rougher than what I was able to get when we built Peace using West System Low Density.  That was lovely stuff to work with, but expensive compared to wood flour and for this dinghy, we need to be economical but still get strength.  I am thinking of mixing in a little bit of left over  microlite from West  along with the wood flour to see if it will make smoother fillets.  Can anybody give me a better idea?  We look forward to when this darn economy picks up again...   Ann and Nev

[paul anderson]

hello there guys what about talc powder? ithink i heard someone use it before but it may be heavy and not too cheap.

cheers paul.

[clif high]

you can 'sweat' the  fillet with a layer of  thick plastic over the fillet as it cures. This is most effective when reasonable temps can be had. The plastic is put on the fillet, and then worked with flexible bit of rubber (like a thin spatula) over the fillet causing both bubbles of air to emerge, and a layer of resin at the top, smoothing the product. Try a lump between plastic (like thick contractor trash sack  3 mil or higher) on one side and news paper on the other.  The newsprint will compete with the fillet for resin, drawing some up. But with it, the material absorbs and bonds. But it is thin, and easily sanded off. Try a bit to see which effect you are after, shiny or matte.

 

[Ann and Neville Clement]

Sounds like I would make the fillet, then put a strip of the plastic on top, then use the filleting tool to get the bubbles out and the epoxy to make that film.  Worth a try, for sure.  I make fillets quick and super tidy with low dense mix and they are where I want them, but the wood flour leaves it looking pebbley.  I hate to leave them looking pebbley because that makes so much sanding for Nev.  Thanks for your help.  Ann

[Ralf]

I mix wood flour with silica for strong filletes and bonding. . I never use saw dust (to big particles) but only sanding dust caught up in the little bag of the sander. Different woods allow for color variations of fillets. Even though the sawdust looks and feels very smooth when it comes out of the sander`s bag I always sieve it through a rather fine household sieve before I use the sanding dust. It is surprising how many large particles and longish pieces one finds in the sieve.  Avoiding 'large' pieces in the wood flour make for smoother fillets, I find.

Ralf

[Ann and Neville Clement]

In truth, I am using some quite nice and very fine dust consistency wood that a friend gave me to "play with".  He gets it by the big drum for boat building but he likes to put fiberglass tape on all of his fillets and I cannot afford to do that to each one if it is not structurally required.  Putting fiberglass tape on a fillet is easy and has excellent results, but we are just building the dinghies for fun in the family (lots of grand children) and so economy must be considered.  I will try the silica, Ralph, and it does sound comfortingly strong and there is still a lot of leftover silica from building Peace.  Ann and Nev

[Russell and Janet Puryear]

I've used commercially purchased wood flour that I mixed with 20% silica by volume. Good results if applied as a very firm soft peak mixture, ie a 1/16" peak will colapse, a 1/8" peak will not, but not so good when applied as a chunky peanut butter mixture.  Now I've got to try sweating the fillets as above!

[Geminidawn]

Another option would be to omit the fillets altogether, take a step back in boat building tradition and use solid wood chines instead.

The pros : you'll use a lot less resin, no need for additives, you can use a cheaper marine adhesive like Balcotan or Resorcinol, no need for glass tape, all in all it's a lot cheaper.

The cons: it will test your wood working skills and it is a lot more time consuming, with Resorcinol, gaps can't be any greater than 1mm, Balcotan is more forgiving. you'll need fasteners like screws or ring-nails for reinforcing in the absence of glass tape.

[Russell and Janet Puryear]

For a substitute for the PITA of Resorcinol, if you go the more traditional route of actually cutting the wood to fit :-), you might use Tightbond III.  I've been boiling and drying and baking a joint for a while and haven't had any problems either.

[Ann and Neville Clement]

Nev did build boats using Resorcinol and lots of solid wood - about seven, so I have heard.  But the epoxy is  forgiving of oopsie moments down in the boat building basement, and we can feel secure about the bond using epoxy too.  Wharrams talk about the fillet actually "welding" the wood and it seems to do exactly that if  one follows the correct methods.  The ply/epoxy/fibreglass method with fillets is so darn easy, it is hard to beat.  I will try the mixes that have been suggested and see how it goes.  We are nearly finished with this dinghy, but there are a few more fillets to go.  And lots more grand children to build dinghys for in the years ahead.

[Jeff Kittle]

Hi Ann,

 

On the little dinghy I made last summer I made fillets out of wood flour and then when it got partially cured I followed Boatsmiths recommendation of smoothing them with denatured alcohol. It worked quickly and gave amazingly smooth fillets that required no or minimal sanding.  

Perfect considering Nevs allergies.

 

Sue

[Ann and Neville Clement]

So did you brush on the denatured alcohol?  That sounds super easy and the alcohol is not expensive either.  I guess it would change the color of the fillet, but that is not a problem if we paint and we will surely paint this boat which will be used by kids and likely not treated the way you would want a varnished boat to be treated.  Hopefully it will  just be sailed and loved so we can get the kids "hooked on sailing" and truly ruin their lives.  Can't have them all scholastic and work oriented now, can we!

[Jeff Kittle]

I just put on a pair of gloves, poured a little bit of alcohol in a cup and rubbed it on with my finger. That way they got really smooth. This works even if they get  stiff - just rub harder... It did not change the color of the fillets at all. 

 

I left my dinghy wood colored on the inside - lots of varnish which quickly disappeared as Jeff treated her like the work horse she was supposed to be. Drat. Wanted a work of art that was not to be. 

 

Right now she's sitting in the garage of our rental house in Florida awaiting refinishing.  And all 5 of us are sitting in a car driving north to Michigan for son #3's wedding.  Time just seems to be whizzing by faster than I would like!