I have sanded a very old floor after removing wall to wall carpet, and used dewaxed shellac as a base coat. 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. Any idea on what to do? I assume it is some sort of contaminant leaking through from the stain....



Sean



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


After water poly....


Close Up....

Obviously there is a contaminant is the wood. You should rip it out.

Removing the wood is not an option for us.....

As the shellac stage looked OK, I am thinkig I should sand it back to bare wood, do some cleaning, and then double coat shellac again to seal it in before goin to poly.


I am debaing bleach, or just more mineral spirits. When I did the shellac, I only single coated the area in question as I was trying to darken the rest of the floor a bit to make this area blend in. The single coat obviously as not enough to seal in the contaminent...

Any more thoughts?

Sean

dont tack waterborne finish with mineral spirits better yet never tack with mineral spirits. Over the years mineral spirits has gotten really low quality lots of recycled product in it nowadays. PUre virgin white mineral spirits is ok but the other is a problem waiting to happen. Use water to tack water borne finishes. looks like someone tried to get that pee/water stain out using a chemical and didndt get it off/encapsulated/ neutralized. resand and put two coats of dws before the poly.

Also, be careful about tacking the bare wood with mineral spirits. IF you have an excellent vacuum with the right attachment , you shouldn't need to tack anything. that's up to you . But on that note, mineral spirits and shellac don't mix so be sure to let the mineral spirits gas off for a significant time before applying shellac.