Microballoons vs. Wood Flour

Having completed the fiberglassing of the bottom and first panels on my Waterlust's hull, I went on to add the fillet at the panel 1 > panel 2 lap. That went well enough I continued with the other two fillets on both sides.

Now that they've all cured well I'm working them all over with a rat tail file to remove irregularities. What I'm seeing motivates me to ask whetyer I'd be better served using wood flour epoxy mix to add material to those fillets (so they might be more uniformly shaped) or would microballoons be a better choice?

(And is it necessary in either instance to add a pre-coat of unthickend epoxy to those fillets? Or are they prepared to bond to anything I add now after a good rough-up with that file then ScotchBrite?)

They're good now yet in places a little hollow, below the plane of the upper plank's lap edge, where I'd rather see them more evenly concave from that point up to where they fair into the plank below. At most I'm talking maybe 1/32" / 0.5mm so not much to add, but they could be better.

I'm confident the structural element of the filleted laps has been achieved. What I'm after is a more craftsmanlike appearance when it's all done and painted.

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RE: Microballoons vs. Wood Flour

If you'd care to watch how I put those fillets in yesterday, that link will show you a brief clip I've uploaded.

(Sorry I forgot to turn iPhone sideways, I'll try to remember fi I do this kind of thing again!!)  

RE: Microballoons vs. Wood Flour

Since you're going for a cosmetic layer under paint, I highly recommend microballoons. They are very much easier to sand while being strong enough in compression to stand up to the daily trials of a well-used boat. I've used them that way (posted some pics here before), got great results and after 11 years they are still like new.



RE: Microballoons vs. Wood Flour

Thanks Laszlo! I was hoping to get that for an answer.

Do you recommended that this cosmetic layer be placed over still-green unthicked epoxy? Or will it bond securely (even if 100% physically) to the underlying epoxy layer that's not fully cured yet tough enough to have withstood filing / sanding?

I'd like to save the last plain epoxy coat for when all the okoume has been coated at least once. Right now the laps have been coated while most of panels 2-4 are bare save for 1/2"-3/4" adjacent to the panel lap joint along each upper edge.

Does that Youtube video link work for you? Others? Give you a better idea of the state of my project as of this w/e.


RE: Microballoons vs. Wood Flour

I applied mine over a fillet that had been applied over a year ago. Said fillet was sanded with #80 paper to mostly the right shape, then covered with microballoons which were finish sanded to #220 when cured. Absolutely no problem with adhesion, so I think that whatever stage you apply it will be fine.

Yes, the link worked.



RE: Microballoons vs. Wood Flour

Wonderful, thanks so much!

Have a fine evening all.


RE: Microballoons vs. Wood Flour

   Microballoons don't dry in a clear form, so they remain white in color. Their not strong when used in thick areas. Cabosil is much stronger than Microballoons and dries clear. I would use Cabosil under cloth if you want to see your pretty wood when finished. If your painting than the cheaper micro would be best.

RE: Microballoons vs. Wood Flour

HH you must not have read the last sentence in my post.

I'm aware of the differences betwen these three epoxy fillers. Cabosil isn't something I'd use in the application I asked about.

I'm sure it has a place in a boatbuilder's kit; with my current project, it's not in mine.

My goal is to reshape fillets already in place formed from wood flour-thickened epoxy. FIberglass is under fillets there now, what I'm adding is essentially an aesthetic improvment that will be under paint once everything's completed, effectively a variation of fairing lap joint contours as opposed to a stuctural element.

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