There are many possible causes:
- excessive stain soaks into the cracks between boards;
- highly pigmented or very thick stain doesn’t dry before coating with finish;
- overly dry conditions at the time of staining dry the surface of the stain, trapping liquid stain below;
- solvents from the finish dissolve the excess stain and bring it to the surface.
If the bleed-back occurs before applying the sealer coat, wipe the excess stain or buff the floor with a white pad. Allow additional drying time. If bleed-back happens after applying one or more finish coats, complete re-sanding is required. Trowel filling a floor before staining keeps excess stain from between the boards. Buffing on the stain avoids excess application. Use a fast-drying sealer to minimize the chance of re-dissolving the stain.