I just installed some Cap-A-Tread vinyl stair treads. Basically, these are 5/8" thick MDF boards that wrap around existing treads and give them a new "look" because of a thin vinyl layer. The vinyl is a wood pattern that matches my floors.
The steps have an exposed side, and the Cap-A-Tread have mitered "returns" to deal with this. However, the miters aren't great, and there are decent-sized gaps on the outside corners. With crown molding, this isn't a problem as it's usually all white so a combination of caulk and paint could effectively hide any gaps. With dark wood grain, I don't really have this option.
What's the best way to hide the gap of a mediocre miter on wood-look vinyl?
Best Answer
I would probably use the same stuff you use to fill gaps in other laminate products. I don't know how well it will hold up on the edge of a stair (in terms of working its way out of the gaps over time), but it'll at least blend in with the floor. That stuff is made by a few companies in many colors to match a variety of laminates. Should be available at your local big box hardware store.
For anyone in the dark about the Cap-A-Tread product, it's a laminate product designed to go over existing stair treads. Kind of like the granite countertop systems that just lay on top of existing laminate countertops. Looks like this:
It can also be ordered with a mitered edge piece that covers up the exposed stair end in the case of an open stair end, as OP is describing. Basically a one-piece alternative to plank-and-bullnose for laminate on stairs.