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 still ongoing but here's where we're at so far:
Our blueprint for the Little Easy called for two inches of rigid insulation outside the sheathing, so the windows and doors had to extend three inches beyond our vapor barrier. That meant the jamb extensions would all be quite deep.
That much jamb extension and windowsill seemed like a higher than normal risk for moisture damage from condensation and accidental train intrusion. We wanted our surfaces to be as smooth and featureless as possible, and the two considerations made PVC sound an appealing alternative to wood.
We hadn't ever seen PVC used for interior trim but it didn't seem a bad idea, and research supported the idea.
We've worked with AZEK a number of times and do not enjoy it. It's finicky, unforgiving, floppy, and damage prone.
KOMA is a similar product with better rigidity and impact residence. It's also a little easier to manipulate.
AZEK does not require paint and cannot be painted. It has a skin of sorts that seals the air/PVC matrix. KOMA cannot be exposed to the elements without paint, as the advance of that "skin" creates an ideal substrate for algae and mold. Both are expensive but KOMA is a little steeper.
What PVC offers, though, justifies the expense. AZEK without paint, and KOMA with paint are completely unaffected by water, sun, and age. They don't appreciably swell or shrink due to moisture or temperature. They don't warp, fade, bleach, or yellow for to sun or age. They don't degrade over time. PVC has no grain, which makes for smoother surfaces and easier milling.
We've noticed that when we mill 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 contribute to a sensitivity to KOMA dust (indeed, any dust) but we'd recommend wearing at least a dust mask when milling the stuff.
Note that we're talking about putting hundreds 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.
It's extremely easy to cut, mill, rout, drill, and sand. After maybe 300 lineal feet we've not had to replace any blade or router bit; they still appear new, which I put down to the softness of the material.
We've been using laminate/non-ferrous blades on the circular, take, and miter saws and they've worked perfectly. In all likelihood regular (wood) finish blades would have worked fine but we wanted to be sure.
We've also used KOMA for hundreds of shims to square window- and door-frames and jamb extensions into place. 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 convex and conclave curves.
Using PVC for shims seems smarter than using wood, especially given the garbage cedar that most commercially available shims are made of. PVC doesn't absorb water, so it doesn't swell, it doesn't degrade over time, and it doesn't compress under load the way low density cedar does. (Cedar is probably out favorite wood, for a number of reasons, but the culled shingles sold as shims don't make the cut).
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 than wood 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.
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