Just my 0.02 here.
Quartersawn sycamore can be unbelievably beautiful. I have seen small
pieces of furniture made from it, as well as musical instruments.
For anyone that hasn't seen the quartersawn stuff, here's a good look:
I finishes almost exactly like soft maple. That means that it is a
little unstable, and must be finished when properly dried.
If you are going to stain (ouch.... maybe just a toner of some sort to
highlight the flecks, not stain?) you will be unhappy if you don't use
a conditioner. Sycamore, particularly when quartersawn will have
rough spots that will feel smooth, but aren't, and will show up as
blotches with colorant. If you aren't going to spray dye, a good
conditioner (available everywhere) followed by a good gel stain will
give great results. Personally, I really like the "Old Masters" line
of gel stains.
Don't over sand, and change sand paper frequently. Sycamore has long
fibers that are quite bendy, and have a tendency to lay over, not to
be cut. Hence, more blotchy color. But the rough spots will also
come up when you put straight finish on the wood.
As a test to make sure you get the surface uniformly smooth, I would
flood the surface with anhydrous alcohol a small spot at a time and
see if anything raises. This is a good cleaner to wipe off pre-
colorant, but will also slightly raise the grain in any rough areas.
The only reason I would personally use shellac on a working cabinet or
one that sits directly on the floor (in the line of fire from shoe
traffic, vacuum cleaners, kids, me, etc.,) would be as a primer. And
the only way I would use a primer is if I felt my colorant would run.
In that case, use a dewaxed shellac as a base, sand and clean, then
apply your top coat.
If (in your testing you will know the answer) your colorant doesn't
run or lift with a first application of top coat, I wouldn't prime.
Rarely is primer needed on clean wood. Salvage, bottom of the pile
at your hardwood dealer, yes. Middle of the stack stuff, no.
For my top coat finish, (I always spray, but if you don't) check out
Leon's comments on his poly choice applied with a foam brush. His
finishing turns out great, and applying the way he does he gets great
control from his foam applicators. IIRC, he uses a General Finishes
coating, but I am not sure which one.
If I didn't want to jump in on a sprayed conversion finish, I would
certainly use poly. It is easy to apply, forgiving, and you can apply
two coats in one day. Remember, if you apply a second coat in about 8
hours, you don't have to sand unless you have flaws in your finish.
If you wait longer than that, you should scuff sand lightly to break
the surface and apply a second coat.
Again, nothing beats personal experience, so Leon may be good enough
to jump in here to give some hands on advice with his experience with
his favorite finish.
I don't use wipe on products personally. I don't like wipe on
products because they take WAAAAYYY to long to build a useful finish.
When you apply the wipe on stuff, you get as little as 1/8" of a mil
of dry finish after application.
Almost without fail, manufacturers recommend a final finish of 3 mil.
(Read their MSDS). Let's see.... 24 coats to get to a thickness?
While most home projects become treasures that are well taken care of,
it usually winds up that someone only puts on about 5 - 6 coats of
that wipe on stuff. You do the math.
REALISTICALLY, most final finish coats for home projects that use wipe
on products probably wind up with about a 1 mil thickness for home
use, which is okay for small projects.
But with brush or spray application, you lay down a 2-3 mil finish at
one pass, and depending on the thinners used, and will wind up with .
75 to 1.25 mil of cured finish per coat. So over conditioner, two
coats may do just fine.
Good luck! Let us know how it turns out.