Hi, there. Several questions here but if I understand you your primary concern is whether your cork floor can be permeable.
I can't think of any finish which would be super-durable and also permeable -- I'm referring to your intention to put "many layers of varnish" on the cork floor.
- If you're going to do that, ie you expect lots of wear, might you consider another material?Cork is not particularly resistant to heavy wear, eg dog claws.
- As far as under the cork, you can only install cork over concrete if it's really dry. You can test for that: look up ASTM F 1869 calcium chloride test, should not exceed 3lbs/24hrs/1000sq ft. This sounds like a technical test, but isn't.
- If you want something breathable to coat the concrete with, use a concrete sealer based on siloxane. AFM Safecoat makes a couple of products of that type and they are excellent.
Your best source for lots of great material on cork flooring and on putting it over concrete specifically is the Expanko website. Check their installation guidelines here.
One way of avoiding all moisture problems on an otherwise dry floor is to use dri-core squares available from Home Depot. They have a plastic raised backing covered with wood.
- Not particularly environmentally-friendly, but you can put almost anything over that as a substrate without moisture problems, and it's vapor permeable.
- You would still have to resist coating the cork with lots of layers of poly or other impermeable coating if you want the whole area to breathe.
For more information:
Check our basement flooring Q&A to see what other homeowners and contractors are saying about cork, carpet, laminate, etc."