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When I had my hardwood floors professionally sanded and refinished, the contractor put down satin polyurethane for the base coat, then gloss for the top coat.

I'm now refinishing a floor myself. Is there any reason why I shouldn't use the same gloss for both coats? I want the top coat to be gloss, and it's cheaper for me to buy a big bucket of gloss polyurethane and use it for both coats, instead of smaller buckets in different sheens.

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Yes, but you better be right on the money with your re-coat times.

A second layer of paint bonds to the first layer one of two ways. Either Mechanically by the paint grabbing onto the last coat, or chemically by the paint diffusing into the last coat.

"Chemically" requires that you hit very specific "re-coat windows" that are documented on the paint label/instructions.

"Mechanical" doesn't work on gloss paint, because it has a finish like glass.

Their use of flat paint is partly to "cover" them against missing their re-coat window.

However gloss paint can be made re-paint-able by scuff-sanding it, i.e. sanding it with something like a Scotchbrite pad to remove the gloss. (if you're removing layers of paint at corners and edges, you're sanding much too hard). This roughens the surface to give it some "tooth" for the next coat to bond to. I am the master of missing my re-coat window, and that's how I handle that.

Paint also tends to be quite soft and vulnerable during the re-coat window, so unless you're Tom Cruise, painting a floor might be a bit of a problem!

  • Thanks for the explanation. I was asking about polyurethane for hardwood flooring, rather than paint. Does the same logic apply for polyurethane? – painter48179 May 18 at 16:45
  • Same principles apply. Yeah, that's just a style of speech where you leave off the noun: The Met (don't say Opera), The Henry Ford (don't say Museum), Polyurethane (don't say paint), built-in (don't say cabinets), mini-split (don't say heat pump). It's still that thing. Some people claim it's too good to be called "paint", fine call it a "coating"... tomayto tomahto. – Harper May 18 at 17:51

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