Well, I thought it would be easy to apply a shellac seal coat, using Parks' Universal Sealer (which is a 1.5 or 1 lb cut specially made for floors). Big mistake for a rookie (warning to rookies). It's not that easy to apply a fast-drying substance like shellac, and I ended up with a nice array of lap marks and drips, even though I tried my best to avoid them and smoothe them out as I went. It didn't help that I stepped in the paint tray early on!! I was actually able to smoothe out that disaster, but it gave me a big covered area in the middle of the floor and messed up my whole plan of attack.

So, can anyone suggest a good way to repair my lap marks? I'm looking at "feet" of marks, not 2-3 isolated ones. Could I sand them out with a random orbital sander or pole sander? Can I do anything with alchohol to blend them in, or wash them out an apply new shellac?

It's very disheartening. Wish I'd used bona kemi's drifast sealer or some oil product instead.

NOFMA Sand and Finish States:

Apply finish in parallel strips across the room. Always
maintain a “wet” edge. Don’t retouch missed areas
(holidays) if finish has begun to skim over. The next
coat will fill these areas. Allow to dry overnight.

NOFMA standards also state:
VARNISH AND SHELLAC - These products were commonly used as floor finishes before today’s modern formulations were introduced. However, they are rarely used today, and generally are not considered
as durable as the modern finishes. Shellac is not recommended for use as a floor finish since it shows water spots readily. NITRO-CELLULOSE
LACQUERS are hard and brittle and scratch easily
(very flammable when applied).

Ray, I'm just using the shellac - a 2lb cut by Zinnser sold as Parks' Universal Sealer - as the seal coat under water base. From what I've been told it's pretty common for this, especially with the stricter VOC laws in many states ... but it is probably harder to apply than a slower curing oil-base sealer, which I wish I'd taken into consideration.

I got advice on another forum that the sealer is self-dissolving, so one way to work out the lap marks is to apply fresh sealer on them, work them down and then brush that out. I'm going to try, and if all fails it'll be some unwanted sanding, I guess.

Why can't you screen it out, before the second coat?

Austinbirdman, Dewaxed shellac does not screen well.

You can wipe the lap marks with a rag soaked with denatured alcohol being careful not to wipe too much off causing a light spot.

Or, the easiest way for me to get rid of lap marks with dewaxed shellac is to wait till the lap mark is dry and hand rub them out with a maroon pad, again being careful not to take off too much sealer causing a light spot. A light spot in the sealer would show through a clear water-based finish.

You should be able to screen those lap marks out. Use fine grit sanding tape (150-180) on a maroon pad. Those top layers of water-based will hide/blend a lot, as long as you do some type of abrading first.

We worked this out more easily than I feared. Following tips here and at another forum, we first applied denatured alcohol to the lap marks and few spots. We worked it into the spots with 4" brushes, giving 2-3 brushfuls for the problem area, working down the problems, then feathering out. This first step eliminated the rings completely. For two big ridges where I had left a lap mark (a "beach") by not starting properly at the wall, the alchohol knocked down the ridge and almost blended the two spots, except that the process tended to take most of the shellac off the low part of the ridge. So then we cut the 2lb Universal Sealer to 1lb by adding 2/3 : 1 part alcohol, per directions, and we reapplied this diluted shellac to the areas we'd corrected. End result is perfect almost everywhere and the few remaining marks and ridges are barely noticeable.

When we brushed out the final spots with diluted sealer, we were able to work it along the lines of the boards and easily feather the sides (if it was not up against a wall). Blended perfectly. And my wife became quite good at it, sparing me most of the work.

Thanks for the suggestions.