Help! Polyurethane gone wrong....


Old 03-06-13, 09:26 PM
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Join Date: Mar 2013
Location: USA
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Help! Polyurethane gone wrong....

We have sanded a very old floor after removing wall to wall carpet, and used dewaxed shellac as a base coat (aka Zinnser Sealcoat sanding sealer). After two coats, it dried over nite. Today, I sanded with 220 and then layed water based poly. It went down great, except in a certain area where it dried opaque and almost crystalized. I sanded this area down with 220, and it seemed to come out, then wiped/vacumed and went onto the second coat. While wet the spots had a dark appearance, and now as it dries it is once again opaque.

Before the Zinsser universal floor sealer (aka dewaxed shellace) I wiped everything down with clean rags and mineral spirits. The shellace went down even without any issues.

This area of the floor has a large dark stain and I wasnt able to get it out with a drum sander and 24 grit paper. When I did the shellace, I onyl did one coat on this area as I wanted to try and darken the rest of the floor to make this stand out less. Any idea on what to do? I assume it is some sort of contaminant leaking through from the stain....


Dark area to right of banister after shellac, no spots...

After water based poly....

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Old 03-06-13, 09:30 PM
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Join Date: Mar 2013
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And a close up.....
Old 03-07-13, 04:35 AM
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Welcome to the forums!

While I've successfully applied oil base poly over shellac finishes I've never tried it with water base poly.

It looks like you'll need something heavier than 220 to sand off that area. I wouldn't think the lack of a 2nd coat of shellac over that area would have been an issue but....... Hopefully some of the others will have more insight.
Old 03-07-13, 06:21 AM
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Why did you use shellac? It's not wrong but I can't figure out what you think it was going to do for you. Personally, all I would have used would have been oil based polyurethane on the floor.

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