We've worked with KOMA only once before but over the next month we'll be at it again. We'll be using it for interior trim and, as such, will be routing, planing, and sanding it. We'll probably try drooling and shaping it, too, to see how it works.
We're not familiar with KOMA (or AZEK) being used for interior work, so it's all a bit of an experiment. We bring this up because, if anyone had any requests, or anything they'd like tried, just drop us a line.
Having worked mostly with AZEK before, these new experiences with KOMA have already been enlightening.
First off, whereas AZEK does not require painting - indeed, is very difficult to paint - KOMA is paintable. In fact, in exterior applications paint is a requirement. The broad surfaces are milled in a way that gives them a good tooth to receive paint. That milling opens the pores of the air-entrained PVC that makes up the KOMA. That, in turn, forms an ideal environment for the growth of mold and algae. Even simply priming your exterior KOMA fills the pores and keeps it mold- and algae-free.
KOMA is famously harder and more durable than AZEK. Spears has a display provided by KOMA that allows you to pound AZEK against KOMA, demonstrating that the KOMA does not dent where the AZEK here pretty well beaten up.
Similarly, KOMA is much less floppy than AZEK. It is much more rigid than AZEK, and does not belly between eaves.
We will be using it for mopboards and door/window trim in the Little Easy. We'll let you know how it goes.
Our experiment is ongoing but we thought we'd throw in notes as we figured things out.
We've noticed, on three occasions, that when we are milling KOMA we develop symptoms of the common cold. We sneeze, get runny noses, packed sinuses, headaches, and a cough. We also get that generally cruddy sensation that goes with having a cold.
We have a long term problem with our lungs following our years in Iraq and Afghanistan ( the VA is smugly confident we're wrong); this may be relevant to our response to KOMA but we'd recommend wearing at least a dust mask when milling the stuff.
Note that we're talking about putting dozens of feet of KOMA through the table saw and two routers, and then sanding it. We've no reason to think that cutting KOMA to length and screwing it into place would cause anyone any difficulty.
We've had great success with KOMA when we've attacked it with miter saws, a table saw, routers, sanders, and drills. We've cut it squarely, at angles, and at bevels. We've rounded over the ends and relieved the edges, edge-forming with 1/8", 5/8", and 3/4" bits. We've sanded with conventional sanders, a bench-mount belt sander, and detail sanders.
We've also used KOMA for hundreds of shims to square window- and door-frames into the framing. By using our bench sander we've had no problem calibrating our shims to hundredths of an inch. We use a 100 grit belt and a 120 grit disc. It's easy to trim the shims squarely or with a taper. Were there a reason to do so we think it would be very easy to form the shims with a convex curve.
KOMA Does Have Limitations
We've used a handheld power planer to reduce the backs of baseboards to fit inconsistencies in the framing and it has worked fine. The KOMA is more prone to scalloping from the planer knives, though, and we think it would be difficult to form a smooth surface with the planer.
However, we had a real problem running KOMA through the stationary planer. Although it worked well a few times the KOMA shattered once, firing PVC shrapnel all over the shop. We opted never to try it again.
Another concern we have at this point regards KOMA's durability. Milling the stuff removes its tougher exterior so edgeforming leaves a porous, softer surface. We will be primer and paint shopping with this in mind, looking for a finish that will harden the KOMA up again.
We also need the primer and paint to have enough body to make the surface smooth. Right now the surface is toothy, not unlike pumice but much less coarse.
Not that we ever make mistakes that we have to go back and fix - perish the thought - but if we had we would have found screws can be removed and reinstalled without much drama. This is in stark contrast to AZEK. If you have to remove a piece of AZEK you'll need to throw it out and install a new one; KOMA isn't destroyed by the removal of screws.
Scuffs and scratches on KOMA can be filled or painted over. With AZEK any ding is permanent and unrepairable.
Speaking of which, we've located a filler that sounds ideal. We'll update as events warrant.