Confusion about Sanding in between coats

[Tegmark]

With oil based PolyU where you want to prevent cutting into the stain, My understanding is you can lightly sand the 1st few coats with only 800-1200g without sealing the bottom coat & preventing good adhesion of second. Because the clear hasn't fully cured, which takes a few days depending on how thick.


Is this correct?

Finally can you see 400grit scratches in the clear after next or final coat is applied?

thanks

[Tahlee]

I'd be interested in the replies.

I have used a card scraper (lightly) in the past to ease out shellac nibs and it seemed to work OK

Regards

Rob

[q9]

Light sand with 400 should do.

[Tegmark]

Light sand with 400 should do.

But If the clear hasn't fully cured I don't think a higher grit even 2000 will affect adhesion of the next coat much which is what I want to confirm.

[q9]

If it isn't fully cured it will clog up your paper, and will provide no actual benefit. 400 between coats

[Tegmark]

If it isn't fully cured it will clog up your paper, and will provide no actual benefit. 400 between coats

My thinking is the time specified for sand & recoat is when the clear is almost cured, but not enough to stop adhesion. You certainly can notice the hardness over time. Long after it has said to be cured, it still emits an odor & gets a little harder.

[artful bodger]

You really have to be careful with PU in the winter time. If the top coat has not fully cured then it does not matter what grit you light sand with between coats......there will be big trouble ahead. Found out the hard way about a year ago.
As for the grit size...I guess it is up to how good ones eyes are and how the finish is applied.
Have sanded back with 180 grit between coats before and never had a complaint or anything.