2 coats is standard. it takes extra time and materials costs to do more coats. you can request them to apply extra coats at an additional cost to cover the extra time and materials.

Don't forget that it also depends on the type of wood you have...some take stain better than others...I have red oak... I decided to do English Chestnut. In theory I love a dark floor but I worried about dust and maintenance and scratches showing. Another BIG factor was that I always do very dark funiture...so I wanted some contrast....The color did come out a little lighter than I thought, but I definitely don't think it's red bc I hate reddish floors...I'd say it's a nice medium, neutral tone...the dark tones really work well with the dark furniture. Here are some pix: This is when we first moved in...with our temporary old loveseat and rug, etc..it looks pathetic LOL..but it shows the floor with natural light which is how it usually looks...oh, it's a satin finish top coat

Should be o.k., but test on a sample board. If you have trouble with adherence, it will peel off once it dries. You're supposed to be able to put a coat of shellac between incompatible finishes, but I found that didn't work too well. For what it's worth, I used the waterborne polycrylic on a bathroom vanity and it's held up well for 5 or 6 years. No water spots. I don't think the water based has the depth to it that the oil based does, but it's sure a lot faster between coats.

You are mixing chemicals (mastic adhesive + mineral spirits + polyurethane + concrete moisture) and have had a reaction. I've heard this done...but only by high-end epoxy finishers that deal with plastics and chemicals every day; all day. There is a reason why the epoxy finishers are some of the highest paid flooring professionals around...you need a degree in chemistry to understand epoxy. And polyurethane for wood is a vastly different product than polyurethane for concrete. There are so many things that could have gone wrong (didn't rinse the floor after the mineral spirits; wrong polyurethane; moisture coming up from the slab; mastic reacting with the polyurethane; etc) that it is hard to figure out what is happening. Mastic is an aggressive material. It doesn't like anything but vinyl backed stuff. One man's adhesive (mastic) is another man's solvent (polyurethane). Good luck. My guess is you will be using a diamond grinder to get this down to raw concrete so that you can start over.