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I hired a guy to refinish hardwood floors. I am not happy with his work so far because he didn't sand into the wood at all. He basically just sanded off the old floor finish and then started applying polyurethane on top. The sanded floor doesn't look that different from before the project started, except now it's a little shinier because of the new polyurethane.

When I asked him why he didn't sand deeper, he claimed that because the flooring is pine (it looks like oak to me, but he says pine -- whatever), sanding into it would create blotches and discoloration. Is that true at all? It's also an old floor (about 100 years), if that matters, but it is in good shape overall -- very few nail heads are showing, and the boards are at least a half-inch thick (I pulled one up to check).

I was under the impression that when you refinish a floor of any type of wood, unless it is really thin, you sand it down to the bare wood. I realize you might not be able to sand deep enough to get out every stain or dent, but I thought that you at least have raw wood before you apply new finish.

Is this guy taking me for a ride, or is it true that you can't sand into pine without having problems?

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    Even sanding completely can leave spots where the original sealer soaked in deeper this is more of an issue with pine as it is softer and will absorbe further in the soft grain. Although the boards are 1/2" if the boards are sanded two much the tong and gruve will start cracking on the edges of the gruves if sanded two thin and then the floor is toast. With this possibility your contractor may just have saved quite a bit as that old tight grain wood is not really available in most areas and it cost big time (more than new oak)
    – Ed Beal
    Sep 11, 2018 at 18:38
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    It isn't clear from your question why you expected the sanding to be deeper. If you are changing the stain color, you need to sand enough to get the old stained wood off. But if you are just applying polyurethane, you want to remove the minimum material to leave a clean surface that the new poly will bond to.
    – fixer1234
    Sep 12, 2018 at 0:33

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I don’t buy the “blotchy or discoloration” claim. Sanding doesn’t bring the blotchy problem out. If it wasn’t blotchy before, it won’t all of a sudden develop a blotchy appearance.

Blotchy areas are caused by pockets of sap, chemicals, stacking problems, etc. Here is an article that explains:

https://hardwoodfloorsmag.com/2018/07/31/common-stains-discolorations/

Yes, refinishing wood floors are sanded down through the finish. Often we’ll refinish school gym floors. The finish (and painted lines) are sanded until they’re gone. Then we use a light “pre-stain” to help eliminate any possibility of blotchy finish.

The real sanding depth issue is sanding down so many times that the nail head begins to show. Usually we can sand a gym floor 3-4 times before we need to replace it.

BTW, I doubt that it’s pine. Floors are made from hardwoods.

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    Depending on the region a hundred year old pine floor is perfectly reasonable.
    – Matthew Gauthier
    Sep 12, 2018 at 0:18

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