Painting - Remove only the poly overcoat?

A year ago my wife acquired a nifty idea for painting a faux marble finish on our basement floor. It started as two coats of latex on the cleaned and acid etched concrete, followed by some random sponging of two or three contrasting colors, and then one of the three recommended coats of polyurethane. The thing is, we weren't aware enough of the yellowing effect of the poly and it never occurred to us to test it on a small area first. Well, of course, she doesn't want yellow floors and wants them redone.

Now, we found out after this that water based poly doesn't yellow as does the oil-based that we used, so the working theory for now is to try to sand off the old poly, repaint as needed and apply water-based.

First, is this likely to work without pulling up most of the paint, too?
Second, hand sand or machine?
Third, will the water-based poly dry as clear as we are told?
Finally, will the water-based be sufficiently tough for this floor... with kid traffic... some in the new kitchen?

Thanks for any help.

To remove only the polyurethane, sanding is likely the best course of action. Stripping will tend to remove all the finish. I would be inclined to use a sander for so much space.

Water-based polyurethane does not yellow.

Some brands of polyurethane are used for basketball courts, so durability is an achievable quality. Choose a brand carefully, and follow the instructions for application.

Hope this helps.

I know of no way to remove just the oil-based poly w/o affecting the faux underneath

I prefer oil-based poly for floors, but today's quality water-based floor polys aren't too bad

Thanks for your comments. And now, the rest of the story.

I had always expected that sanding would mean that the majority of the paint would come up, too, which then would mean pretty much a complete repeat of the job. As loathe as I am to add money to this pepetual project, I thought I would end up putting down some laminate because repainting everything would take many more days than we want spend. At least that would be fairly quick. :(

What I didn't expect is that even with 20 grit paper, I could hardly get any of the offending poly off the floor! I spend several minutes in the same 2x4 foot space and saw very little affect, only a bit of dust, and then only after I swept it together! :o

Well, after plenty of fretting and a few phone calls to the paint store, we decided to just scuff off the surface and start again, painting over the top. They tell me it should adhere O.K. Not what I was planning to do this week, but perhaps it is a good sign that the original top coat is so tough with only one coat; with three of the real stuff it'll last forever! :)

Just for curiosity's sake, we noticed way back when, that wherever we have a rug or pad on the floor, the yellow is much darker than where it is exposed. What's that about?

I don't know the technical reasons but surfaces with poly/varnish always amber differently with different exposure to light and air. You may have also noticed differences on varnished walls where pictures have hung. Oil base enamel can do the same thing under similiar conditions.

I'm baaack! Well last year we only reworked the main, "public" areas and left the bathroom and sewing room for later. Well, now is later and I am wondering if there is a better way to sand off the old, oil-based poly. Last time I used a common circular floor buffer/sander with 20 grit disks with verly little effect as far as I could tell. Should I use a different type of sander perhaps?

The other issue is that the water based seems to be not nearly as tough, as it seems to scratch under the chair legs, etc. We used MinWax before from the blue box store. Is there something new and amazing available now that will be as clear but tougher?

Thanks,
Mike

I don't know that there is an easy way to sand of a finish - except maybe let someone else do it :D

Not all water based polys are created equal. Minwax and other readily available latex polys are probably the softest. I don't remember the name but there is atleast one waterbased poly that requires an activator/hardner. It's one of the harder drying water based polys but IMO the oil base dries to the hardest - longest wearing film.

Bona Kemi makes a two part waterbase,"Traffic", that's as tough as anything. There are other two part floor finish manufacturers. You might ask on the flooring forum about two part waterbase finishs.