This is a stairway in a modular home, came as a clunky 2x4 walled in stairway, I cut that down to be an open stairway, rebuilt the cutouts with 2x4s, screws and glue.

Purchased custom glue-block 3/4" ash for the risers and treads, each one was custom cut and sanded to fit the space. Screws and glued-in wood dowels to cover, matching grain as much as possible.

We wanted a clean look and no "nosing" on the stairs. A coat of primer to even out the grain's dark areas and then a layer of gray floor paint and two coats of heavy-duty floor sealer to finish.

Sort of humorous: Had multiple go-rounds with the drywall guy who insisted it would separate from the drywall and leave cracks, but he finally did what I wanted and fit it to the shape. It's 4 years and heavy use later, no cracks. When you screw in ash on top of 2 inch pine, that thing does not move. It's the most solid part of the house. (Railing isn't the final solution, I'm getting a longer one to put on that wall.)