I can't give much advice with your questions except to say that Waterlox was originally developed as a floor finish. It is certainly well-suited to the task, although not as modern as some other finish options.

No experience with it on floors, but I would be very hesitant to have people apply it to my floors who weren't familiar with it. When Waterlox goes wrong, it goes really wrong (you can read some of the problems people have had with it if you search this forum). It's great when it's done right but I can't imagine what a mess it would be if it went wrong on floors.

Fir is a soft wood with expansion and contraction. Be sure to finish both sides of your counter to help with this. Another option is tung oil(multiple coats)

Here's my ca.1906 yellow pine floor with waterlox finish.
Before:

First coat:

4th and last coat:

I hand sanded to 150 grit, most pros would stop at 100 grit. The finer than average sanding and the penetrating oil of the waterlox brought out a lot of depth in this simple pine floor.
Casey

Casey - those floors are gorgeous, just gorgeous. I read a few threads on the flooring forum where you talked about your experiences with Waterlox. If I can't find a local flooring person familiar with it, I am going to have my very capable carpenter finish the floors for me. Can you tell me the process you used: how many coats, how much sanding, etc?

dan1888 - yes, fir for countertops is not really ideal, but it will fit the age of the house and the very vintage vibe I'm going for in my kitchen. My carpenter is making the tops out of a very old, huge beam from an old warehouse in Seattle. Hopefully the old growth wood should be more stable.

Hi Rosylady. I'm just down the road/Sound from you. When I had my new oak hardwoods laid in 2011, my installers claimed that most of their customers use the Bona water based floor finish instead of Swedish. They claimed that Swedish was on its way out in our state for enviro reasons. And this is a large, regional wood floor company. I'm not sure if they go to BI or not.

FWIW, I used Osmo Polyx Oil on my black walnut island top. It's a greener product than Waterlox.

I have used Waterlox on countertops and floors ...

1 - Put a couple of coats on the underside of your counters to prevent warping.

I didn't do it on a small test counter and even though it was laminated beech, it warped almost an inch in the center.

2 - You can sand between coats with a fine sandpaper if you want, or not.

I wiped it on with a lint-free cloth in thin coats - 3 or 4

The floor was sanded with 80, then 120 grit, then several coats
The countertops were sanded with 120 or 150 grit

The first coat really soaks in, apply it liberally. The second coat soaks in some places where the wood is most absorbent. By the 4th coat, you should be wiping on a thin coat and having even coverage.

The wood is holding up well - some scuffing and scratching on the kitchen counters, but it is patina in the making.

Breezygirl - I did some reading about the Swedish finish online and it was a little scary. The Northwest is one of the few places in the country where it's still being used, it's been banned in many states for environmental reasons.

How did you find out about the Osmo? Did your flooring people recommend it? I vaguely remember when you posted about all this during your remodel...

Surprising that we here in the liberal, green, PNW still allow Swedish where most parts of the country have banned it. Usually it the other way around!

I was planning on Waterlox for my island top, but the local woodworker I hired to make the top recommended Osmo. He's been using it for years on his wood counters without issue and believes in the more environmentally safe product. I'd never heard of it, but decided to go with his recommendation, especially since he hadn't used Waterlox in quite some time so I didn't want him applying a product with which he wasn't entirely comfortable. I've read enough stories around here to know of the application difficulties some encounter.

Someone on the forum, I'm blanking on the name but I think she was from Oregon, DIY'd Osmo on their floors with some issue.