Refinishing chop block counter top

Question

I have bought my first house. I am DIYing my kitchen renovation. I have chop block countertops from IKEA and an undermount stainless steel kitchen sink. I know its not wise to undermount with a wood countertop but my mom has a similar set up and it has looked great for the past 15 years.

I want to protect the countertop. I am using the Varathane Polyurethane for the first time "Matte Interior" applying with a Wooster Pro brush

I have been reading everyones comments on procedures etc.

Two questions:

Have I made a mistake using a water based Polyurethane?

How do I know when to dry sand VS wet sand?

I live in Florida so I have been paying attention to humidity and sanding in-between coats with 3M 400 and 1500. I am 4 applications in at the moment

I am only half way into my project and did not realize there was two kinds of polyurethane. I guess I'm only a day late and a few dollars short at this point:)

Answer 1

In my own opinion I don't think that the owner of this top has figured out how is he/she going to use this top. If he /she are going to use it as it was intended, as a butcher block top, then a poly coat would flake off in time. But a regular coating of mineral oil, not vegetable oil, would be suffice. Vegetable oil would turn rancid.

Answer 2

In my opinion, you have not made a mistake using the water based poly.

I am a firm believer in the protective properties that oil based poly has, and have used it everywhere in all my cabinets I have built for my house and the results have been outstanding.

That said, what I know of oil based finishes as a rule, including poly, the finish is very brittle and with seasonal movement, will crack in areas, in your case where you need it most, at the interior edge at the sink and more importantly, at the meeting surface of the sink of the underside of the countertop. As a mention, the wood WILL move, and a highly flexible adhesive caulk must be used to seal the sink to the underside of the top. I do not suggest silicone, though many may swear by it. Its cleanup is atrocious. I use water based caulk in this type of place, since appearance is also important here.

Onto water based. Again, from research/reviews that I have heard from other folks, water based is a much more flexible finish and will be better suited for what you need. 4 coats is a good start. Depending on how much sanding you do between coats, I would go onto about 6, if not more. A note on OIL BASED, matte poly finishes. The more coats of finish you apply on a surface, the less matte a surface appears, and it takes on a more glossy appearance. I have seen this and limit my coats of finish to 3 coats, no more. If you have not noticed this with the water based, carry on.

About sanding wood finishes,in my opinion, 400 grit is great for in between coats. 1500G is for polishing surfaces to a near reflective finish and can be used with water, if the sandpaper is suited for it. The water clears the dust readily to keep the paper free of buildup of dust so it cuts the surface without clogging. There are grits that are more coarse, including 320G and more coarse still. I feel you will not need wet-or-dry sandpaper for this work.

The amount of sanding you do, truly needs to be watched at edges and corners. These areas are extremely easy to "burn through" all the coats of finish and in essence, still only have one coat on the surface.