Bamboo build, advice on finishing.
The frame is built and it was a fun but long and slightly stressful experience!
I would do it again though, lots of learning along the way.
My question is about the finishing of the bamboo surface and the joints.
Should I prep the bamboo lightly with 200 grit and paint epoxy over the whole lot or do something different with the tubes and the joints?
Sanding and total epoxy coating followed by more sanding and a UV resistant varnish coating is the way to go if you want it to last forever.
You have to get the gloss off the bamboo if you want anything to stick to it. You don't have to take it right down to the power fibers although it looks more finished if you do.
I have a frame sitting in my yard that's under the weather full time and it still looks like it was finished yesterday.
Here is a pic of a coated frame;
Last edited by Canaboo; 07-29-14 at 02:02 PM.
the best builders of custom bamboo fly rods use spar varnish. Man O War in the red can (unless you are in California where it has been gutted) is popular. It is very tough. Bamboo rods are probably exposed to UV as much as bikes and certainly flex more. In addition to that they are exposed to water all the time. Over a period of years the varnish will darken from the UV exposure. As mentioned above, breaking the shine on the surface is a good idea since it give "tooth".
In this case the UV resistance of the varnish is solely to protect the epoxy, not the bamboo.
There are UV resistant epoxies, and there are some cheap epoxies that are pretty UV resistant like clarkcraft. I would have no concern about just using epoxy, if it starts to show any signs of problems then you can varnish at that point. But simpler is that if the bike spends all its time in the dark except an hour or two, and a week or two, here and there, you don't need varnish. But if it sees a lot of outdoor light, you can gloss varnish it, and it will protect the epoxy and the wood. Some theory holds that while the epoxy yellows the wood is affected by UV in such a way as to reduce the bond to the varnish.
A Canaboo notes, you need to get the waxy cuticle off the surface before doing anything.
I disagree with MassiveD above: UV stabilised epoxies don't stay that way for long and by the time any damage becomes evident they're basically ruined, the UV radiation undoes the crosslinking which was the reason for using epoxy in the first place.
On my wooden bikes I use a five layer protection system. The first three layers are epoxy: one layer of a high temperature low viscosity laminating resin* (excellent penetration), then two layers of West System 105 / 207 (UV stable). Fine sand (320 or 400 grit) between layers of course.
I then top coat with two layers of 2k marine polyurethane*, again sanding to 400 grit between coats, to protect the epoxy. Attempts to use the 2k by itself have failed, it has lousy penetration.
IMO normal spar varnish is pretty close to useless, the yachties are used to applying multiple coats and replenishing them every couple of years.
* The products I'm using are Australian so there's not much point in naming them for you.
i have taken back the sharp raised edges left from the tape wrapping process but basically not cut into the hemp wrapping much to avoid weakening the structure and I don't mind the organic look (look at the wobbly bamboo I picked!)
I flatted the surface back with 120 grit an painted a layer of 2 PAC epoxy resin on the BB joint to see how it looks, it seemed to penetrate well and took the light spots back to the brown hemp color.
i haven't finished the joints yet, once I do if they are too my liking I will likely go
with the advice above and lightly key the tubes and use the epoxy as the first coat.
Last edited by alex jb; 07-31-14 at 04:38 PM.
Bit of automotive polish to the layer of epoxy and it is looking a lot better.
tried the new BB in also.
There is no reason why you shouldn't smooth the lugs completely. Are they strips of linen canvas for art?
Nice job Alex. We use machined bamboo for uniform sizing, but looks like yours is natural. In that case you must sand the bamboo to scuff the shiny outer surface. You will want a minimum of 3 coats of varnish, sanding each time. Also pay attention to seal any gaps around the lugs. It helps if you can sand the edges of the lugs to be almost flush with the tubes. Happy Riding!