Q: I’ve just had a 100 yr old Kauri pine floor sanded and finished with a 2 pack water based polyurethane. The sanding looks fine and the finish is great, except that there are pale spots / blotches evident in the wood in a number of areas, some quite large, some small. These were evident after applying the sealer, but I was assured would disappear with the urethane finish (4 coats) but they haven’t, and then I was told this sometimes happens with Kauri pine.
This doesn’t sound right to me. Are you able to confirm what is the likely cause and if it can be rectified?
A: This pine is native to New Zealand so I’ve not worked with it. However, it is probably much like other pine in that it contains resins. The presence of the resins can vary from piece to piece. You likely are getting interaction between that and the finish. Unless there is a sealer which can be applied to block that there isn’t much to be done except live with it and consider it natural for that species of wood.
Related Q: I have yellow pine. I have sanded the floor. I’ve been trying to apply polyurethane (water base). It looks like wax on top, or like a glazed over floor. What could be the reason for this?
A: If you sanded to clean wood you will still have to be aware that this wood can contain a lot of resin. There are sealers designed to be applied first and serve as blockers, but those are professional coatings that you won’t buy at the hardware store. Also because the wood is so soft and water borne coatings do not have as high a solids content as solvent based coatings you would likely need 3 or possibly 4 coats of the product you are using.