threshold or quarter round first?
Floor transition piece or wall molding first just depends on which is easier to cut a matching joint to. Transitions usually have a simple straight sided profile so cutting base to fit over it may be easier. On other hand transition may butt against a flat portion of base and if transition ever has to come up you don't have to remove base.
Maybe we should just stop saying plinth. ( Though it is fun to say.) Call it another transition. When you have two dissimilar molding profiles meeting you need a transition between them. Sometimes you can do that with coping one on to other, sometimes by cutting an angle on end of one, sometimes by adding a return, some times by coping onto the return or cope return onto other. In this case I think the plain "plinth" block idea would be easy and look fine.
As to material, shoot you could use a block of PVC or make one from a chunk of 2x construction grade. MDF takes paint well, doesn't shrink or swell unless it gets actually wet, and this is or is near a kitchen, and might not withstands bangs that a outside corner gets. Poplar is nice and hard, can take being kicked, fairly dimensionally stable. So is ash. Oak grain shows thru paint. ( I dunno what else they got at big box.)
What ever the plinthition piece is, it should be noticably thicker than what ever butts against it, at least an inch thick more likely 5/4,
so you get handdrive's reveal. Then it looks like its supposed to be that way. Trying to flush outer edges or too little reveal looks like you didn't know what you were doing and just slapped something in. And don't try to blend butt joints with curved cuts or caulk, make um nice and sharp and square.
Don,t worry about confusing me, jim, I been confused a long time. Sannitig pro'lly clicked "ignore" on me a long time ago. It is a good idea to check what you're grabbing out of the bins at big box, folks will put quarter shoe into round base bin.
Measure twice, cut once.
Look at the nail, not the hammer. Watch the fence, not the blade.
If you hook your thumb over your belt you won't hit it with the hammer or leave it layin on the saw table.
Last edited by notmrjohn; 10-30-2012 at 04:31 PM.