Cracks between boards shinier than floor after second coat of poly

Q: After our second coat of satin poly there are shiny places along some of the cracks between boards. We waited 24 hours then used a pole sander with 180 grit screen to sand after the first coat. My theory is that these are low places where the poly pooled.

We had already planned to sand again with the 180 grit screen before the 3rd coat. Do you think it will still happen after the 3rd coat and if so, what can we do to prevent it?

Next question: there is a spot I missed with the second coat of poly. Should I tape it off sand and finish like I have seen you suggest to others that have missed spots, or will the 3rd coat cover the mistake? Thanks for your help. I wish I would have found this website sooner!

A: I would give the missed spot a quick rub with some abrasive and give it a thin coat. Hard to know what the shiny spot is all about. Is it entirely dry or is it sticky? All the various shines except gloss have a paste which serves to reduce the shine. These finishes generally need to be thoroughly stirred to disperse the silica throughout the product. When you apply it, this is suppose to settle to the bottom of the film. If it sets up and dries too fast this can be prevented and you end up with a more shiny finish and even at times shiny spots. I’m not so sure this is what has happened in this case. Make sure you thoroughly sand before the last coat. Don’t miss any spots. Remember, thin coats are always better than thick coats and generally the spread rate will be 500 feet per gallon.

Follow-up: Thanks for your reply. To answer your question, the spots feel very dry and it has been about 60 hours since we finished the second coat. The sheen is very consistent throughout the rooms other than in the cracks. I’m using Minwax oil based poly. It recommends 600 feet gallon and I’ve applied it very close to that rate. Hopefully the picture will help explain what I’m seeing.

A: Possibly a contaminant between the boards. Why not put some wood filler in those cracks and stain it. Or better yet get a tube of colored filler such as Color Rite. It comes in hundreds of colors and is easy to use.

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