Bathroom cabinet advice

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I am building a cabinet for an unused nook in my bathroom.  This is about 13" wide by 70" tall by 30 " deep.

The cabinet is already built using 3/4" alder plywood with a 1/2" ply back.  There is one shelf built into it with middle of the carcass and there is holes for pins along both levels for other shelves.  To accommodate the height I want the shelf to be for trimming it out, I have raised the area by placing two 2x4s at the front, middle and back of the alcove to support the bottom of the shelf.  I am pretty sure it will be well supported but had second thoughts.  Should this have a solid base under this cabinet?

I am finishing the interior of the cabinet with two coats of Zar varnish.  The cabinet will be enclosed in a nook but it is in a small bathroom which will get steamy but with a timer on the exhaust fan it should only be 20 minutes at a time.  Should i seal or varnish the exterior of the cabinet in any way?

[jteneyck]

Commercial vanities aren't finished where you can't see them.  

John

[fredhargis]

I wouldn't, for the reason John  stated. Was that an oil based varnish you used on the interior?

[EricU]

I wouldn't, for the reason John  stated. Was that an oil based varnish you used on the interior?

I couldn't tell if he had already done it.  Just about the only finish that doesn't stink for inside a box is shellac.  That's why most things aren't finished on the inside

[Admiral]

I couldn't tell if he had already done it.  Just about the only finish that doesn't stink for inside a box is shellac.  That's why most things aren't finished on the inside

I built a pair of cherry vanities for the master bath, and finished the insides with 3 coats of my roll your own wiping varnish, oil poly cut 50-50 with MS.  No stink.  I do like shellac however.

[Stwood_]

I never sealed cabinet sides that weren't exposed.

[Arlin Eastman]

Just wondering about the finishes.  You guys say you do not do it where it does not show, but would that not affect the wood warping or expansion or contraction in a humid place??

[jteneyck]

Just wondering about the finishes.  You guys say you do not do it where it does not show, but would that not affect the wood warping or expansion or contraction in a humid place??

I haven't seen any bath or kitchen cabinets (also not finished where it doesn't show), commercial ones or ones I've made, warp or otherwise misbehave.   The boxes of these cabinets are plywood, particle board, etc., stuff that has little seasonal expansion so there is no concern about them moving.  I'm talking about the boxes here.  Doors and drawer fronts often are solid wood, and they are always finished on all sides.   

If you look at antiques they weren't finished anyplace you couldn't see either, even though they were built with solid wood.  The ones that were built well by folks who understood about seasonal wood movement are still around.  

John

[mikefm101]

For the base the 2x4s are plenty sturdy. Often a base is made with 3/4” plywood scrap so you are ok with the 2x4.

If possible level the 2x4 with shims, then place the cabinet on top. I think that’s what you were thinking anyway.

With a ply back I concur with others no finish is required but it isn’t going to hurt if you do finish and it won’t take any more time to apply anyway.

Mike

[jteneyck]

2 x 4's make a poor base.  Strong, yes, but unless they are really dry they will shrink over time.  The cabinet back is screwed to the wall studs so nothing will happen there, but the front will droop down as the base shrinks.  On a narrow cabinet it probably won't be noticed, might not even happen if the cabinet is built well and not heavily loaded, but it definitely will happen on a wide cabinet like a kitchen base.  I know.  

The better way to make cabinet bases is with 2 layers of 3/4" plywood glued and screwed together.  Shim up level then add vertical blocks, glued and screwed to the base, to lock it in position.  

John