I've already built a few simple projects, but I find that the ignorance
lingers, even as regards some very basic concepts. I learned a ways back
(the hard way) that "modern" ply can't be sanded a great deal without
the substrate peeking through. My error stems from '70 era high-school
shop training that was better suited to solid wood, and the memory of
older plywood whose top veneer was more than a few molecules thick.
So my question is this: How should I sand?
I'm considering building some plywood bookcases; tall (7'?) narrow (24"
x 15"?) tower-shaped things to flank a wide window. Birch, or maybe oak.
I've been told here that I need not start with coarse paper on ply, but
I'd like some details.
I'd be using a very old third-sheet orbital sander. It's what I've got,
and it seems to work well. The weight seems to damp some of the
So what grits should I use? And how long should I sand each area? This
project, should it actually become reality, would require sanding the
better part of three sheets of ply on both sides, not including whatever
I use for the backs. I'd like to be efficient.
As an aside, what should I use for the backs, anyway? I'm sure 3/4" is
not necessary, but what do you recommend?
As always, thanks in advance.
There are two main reasons for sanding...
1. to make the surface flat
2. to make the surface smooth
Hardwood plywood is already about as flat as it will ever be; it is also
generally pretty smooth. If it isn't smooth enough for you, you can make it
smooth by sanding the finish, not the wood. If you just gotta sand the wood
I would suggest a grit no coarser than 180. How long to sand? Until your
fingers tell you is is at the smoothness that you want.
One of the better things to use if you need to sand the ply is a sanding
sponge. I'm talking about the ones about 4x5x1/4. Fine or superfine grit.
They are good because the sponge deforms so that slightly depressed areas
get sanded without cutting down the higher ones excessively. The bad news
is that you do it by hand; the good news is that it takes very little time.
For backs, 1/4 ply works just fine. So does 1/2, ditto 3/4. Be sure to
build in some way of securing the cases to the wall as they *WILL* tip.
You missed a very important reason for sanding, or planing.
For finishing you want fresh wood, not wood that has oxidized. It does
make a difference. The wood should not be exposed for too long, or the
finish MAY be less than it could be.
On Dec 5, 10:45 pm, tiredofspam <nospam.nospam.com> wrote:
Hmmm. I'll remember that. Thanks.
Being the finishing ignoramus that I am, I do a lot of "testing".
Every time I have used any sort of finish, I put some on different
kinds of scrap as well; oak, maple, ply, even a planed-down bit of 2x4
once. But I don't usually bother to sand them first. Sometimes it
seems as if the finish doesn't penetrate very well.
On Thursday, December 6, 2012 6:06:44 AM UTC-6, Greg Guarino wrote:
Many finishes don't/can't penetrate at all, but just lay on top. *I am aware that you will apply your finish coats to raw wood, hence your testing on raw wood. Just because a finish doesn't penetrate (Deeply? How deep?) doesn't mean your application has failed.
What symptoms/results are you referencing/experiencing, for your assuming the finish doesn't penetrate (isn't penetrating) very well? *I'm wondering if your term "penetrate" is the appropriate term for the results you are getting "Sometimes, it seems....".
Stains, conditioners, sealers and oil finishes may/will readily penetrate raw wood. A subsequent top coat is exactly that, i.e., lays on top. A finishing varnish, shellac, lacquer, poly coat - not proceeded by a stain, conditioner or sealer - will penetrate raw wood, to some extent.... a particular specie of wood can/does dictate how a finish (alone) is absorbed, if at all. That's one of the reasons for doing test applications, to see how the different applications (or combinations of, i.e., w/ stain, conditioner, sealer, etc.) apply.
I agree, you want fresh wood, to be finished.... or stained, conditioned, sealed, etc., also. You want clean wood, also, hence, use of a tack cloth or vacuuming may be beneficial, after sanding.
Assuming that the surface is in good shape and you are actually using
cabinet grade plywood there is no need to start any coarser than 180
grit and I never use any thin any finer. And still, be careful.
On Wednesday, December 5, 2012 12:10:31 PM UTC-8, Greg Guarino wrote:
I would only sand by hand with a rubber or other block and just use 220. Really just need to knock down a few fibers and equalize the surface scratching on any decent ply so any stain of finish will look consistent.
For what you describe above, minimum of 1/2" plywood, with the back
preferably dadoed into the end panels, top and floor; and with fasteners
through the back into stationary shelving, as below.
Face frame, or frameless?
If face frame, at least one built in, stationary shelf that spans the
inside width, preferably dadoed/glued into the end panels. The rest of
the shelves can be adjustable.
If frameless, consider using 3/4" ply for the back, with two built in,
stationary shelves that span the inside width, preferably dadoed/glued
into both the back and the end panels. The rest of the shelves can be
For any standalone piece that tall you will need to either attach them
to the wall in some manner, or you will need an "anti-tip" device of
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