Ocaña suggests you take a swallow before you hit it the first time since you may well be disappointed. It's true. But play around with it, stick it in a corner and play it, get used to your tapa and how to strike it, and it's true character will likely reveal itself to be a lot better than your first impression. After giving it some time and practice, i have grown to love this one as it is, and i haven't taken it much further than the original design (e.g. by coating the inside with glue as Ocaña suggests, trying other tapas, placing wood inside to direct the waves, whatever). The snare, though: You will probably want to spend some time on your snare.
Ocaña recommends not gluing the tapa. Apparently some builders glue it, probably because it's easier to make but possibly because it seals better. Many cajon players, myself included, like the top corners of the tapa to be free (thus the lack of screws there, or with glued tapas, the lack of glue in the top third) in order to get a slapping sound as the tapa corner hits the frame (Inserting paper shims in the corners to raise them up a tad may help you get a good corner sound.) So the seal may not be as gravely important as it's made out to be, but perhaps the overall seal over the perimeter of the tapa really does matter. Having the corners lifted with shims in conjunction with slightly loosening the screws that abut the corners didn't seem to affect the bass sound much, as compared to no shims and all the screws tightened.
Ocaña recommends being generous with the number of screws. The tapa of this cajon lifts off a tiny amount at the edges, probably because of a slight, natural deformation from the tension of the screws. I am confident that the seal is nonetheless good. Drilling pilot holes is probably a good idea for the tapa screws to as to avoid splitting the hardwood frame. Before affixing the tapa, of course, you want to ensure (through sanding, if necessary) that the internal frame is appropriately flush with the edges of the plywood sides, top, and bottom. (I may even have tapered the plywood back a hair to make sure that the tapa contacted the frame fully, which may also help explain the slight gap between the tapa and the plywood.)
Straight-up organic locally-grown homemade fresh-squozed beet juice was used to dye the wood. As for the tapa, Ocaña recommends rigid finishes only as oil would soften or dampen the resonance. Not sure if he feels the same about the other faces: I think he advocates using similarly rigid finishes on the interior at least (or the glue method he described). It's hard to imagine that it matters on the external non-tapa faces. Anyway, given the horrid environmental and health aspects of most finishes, beet juice was used. As for finishing the tapa, it was left unfinished and we'll let nature slowly break down the plywood (which, of course, is itself full of toxic glues and will probably last lifetimes.) After the beet juice dried, a light pass with unrefined walnut oil, which is purported to be a "true drying finish", and is about as natural as it gets in that department, was applied. The inside is also unfinished.
Beet juice fades very quickly. A test piece faded dramatically after a week or two of mild sunlight. But it's beautiful, and you can always add another coat. Once totally dry it does not rub off on your clothes, though if it got wet it may well. I don't know if the walnut oil will make it harder to re-juice. I keep it under a cloth when not playing it in the hopes that the fading has more to do with ultraviolet light. Maybe the oil will help if in fact it has more to do with oxidation. Time will tell. After three weeks it still looks very strong, as opposed to the test piece, so maybe the combination of oil and storing under a cloth will work. Update: After 1 year the cajon was still nice and red, though it could maybe have used a fresh coat. After 2+ years it's more pinkish now. Still nice enough, but definitely ready for another juicing. This whole time i've kept a cloth on it to cut down on the UV.
The finish work basically involved making the edges meet up through the magic of sanding. All three of the top non-tapa edges were all generously rounded - it's definitely worth it! After sanding, the moisture in the beet juice will cause the wood to regain a rough texture, so don't spend too much time making it perfectly smooth, as obsessively fun as that is. Apparently you can sand, wet down the surface with water to bring out the grain, let it dry, then sand again, and this will cut down on the roughening phenomena.
Isn't it so beautiful?