Prepping the bottom for Graphite

I read Laszlo's post on coating his WD12 with the graphite on bottom.  He stated that he filled the weave with Epoxy and the microballons to help save weight.  Is this still a good suggestion? In order to do this do I lay the glass and wet it down with plain epoxy then use the microballons for the additional coats till ready for the grahpite?  Is the weight savings on a shearwater sport enough to justify it?  Will there be a problem with Durability by using the microballons?

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RE: Prepping the bottom for Graphite


Yes, yes, depends and no :-)

I still think it's a good enough idea that I did it for every boat I've built since then.

You've got the procedure down, it's really that simple. If I was painting I'd sand inbetween layers and prime afterwards, but a thick graphite mix always has a bit of orange peel. I never sand graphite mix bottoms smooth (it's too messy and only the fish see it) so a smooth substrate is not needed.

How much do you care about weight? That'll tell you if it's worth it. Depending on your exact technique, you can probably save 4 to 8 ounces per square yard using microballoons.

Weight's also not the main reason I use them, though. There's also cost but mostly reduced labor. A couple of thick coats is faster to apply than lots of thin coats and microballoons are so much easier to sand than unthickened epoxy.

I launched my WD12 at Okoumefest 2018 and as soon as I finish typing this I'm heading to the river with it for a morning paddle. 8 years old and no signs of quitting. The outer graphite layer's been touched up every year, but the microballoon layer is still original.

Microballoons are very strong in compression. The wood underneath will dent before they do. They're soft in abrasion, and weak in tension, torsion and shear. That's why you never use microballons as a glue thickener or other structural application. But they're ideally suited for filling the weave.

In fact, the question of justification is sort of backwards. Unthickened epoxy is the plain wrong choice for filling the weave, not microballoons. The only justification for using unthickened epoxy is a bright finish. Being able to see the grain justifies the deadweight, the extra labor and expense. Since the standard finish for most of the boats here is bright, unthickened epoxy is the most popular filler/fairing compound.

Have fun,


RE: Prepping the bottom for Graphite

   Most of you don't know this but Laszlo also has a time machine :-)

RE: Prepping the bottom for Graphite

Thank you for for the advice.  I am always impressed by the response I get on here as far as advice and such.  How much of the microballons do you recommend using and would the 1 quart be enough or will it take a significant quanity?  I plan to fiberglass the hull in one step, then run a tape line for the section to be done with graphite fill the weave with the microballon slurry then apply the graphite.  Then I plan to go and finish the remainder of the hull and deck for brightwork as normal. 

RE: Prepping the bottom for Graphite

I quart should be plenty. If you mix it runny it'll be easier to apply, mix it thick and it'll be easier to sand. Be sure to clean up any drips ASAP.

Your procedure is fine, as long as you don't forget to sand between microballoons and graphite. Up top I was talking about not sanding between microballoon coats. It's still good to sand after the last coat.



RE: Prepping the bottom for Graphite

Hi guys,

Ive tried the S3 Black WR-LPU on small areas of the deck over the the Varnish.

My results came out OK, except for the part (mentioned in another post) where the tape peeled up the varnish.  I don't like the way the LPU applies. Using foam brushes the first stroke goes on fine, the second adjacent stroke picks up the first.

So before I try a larger area for a graphic on the hull (to cover my ugly scarf joints, not the entire hull),  what more can you tell me about this graphite stuff?

Would it be a better choice on a Hull Stripe about a foot wide going across from sheer to sheer?,...

I want to save most of the wood tone look and just have a Coast Guard style stripe.


RE: Prepping the bottom for Graphite

Paint is best for painting.

Graphite/epoxy is for a slippery, scratch-resistant surface. It will leave an orange-peel finish unless you sand it. Sanding it is a horrible mess and the surface turns pencil lead gray.

Stick with a black paint for your stripe.

Alternatively, a black vinyl decal might work, too, and you wouldn't have paint issues.

Good luck,



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