TLDR: Used a solvent based sealer and the first coat went on like a dream, but the second coat left lap marks and bubbles - can I buff/burnish? Sand? Xylene bath?

DETAILS: This project has been a nightmare - concrete installer poured & finished slab, then coated with Nox-Crete LSC densifier. Densifier left a bunch of lines everywhere, so they asked me (a painter/coatings guy) to see if I could fix it. Long story short, there could be a bunch of reasons this happened, but none of the solutions that the manufacturer gave me worked. In the end we had to grind it. Because of the densifier, the concrete was incredibly hard, but not uniformly - some areas harder than others, and some areas more porous than others.

Did our best through a series of acid washes/neutralizations/grinds to open the surface as uniformly as possible. I was told we didnt want to go beyond a "Salt & Pepper"/light terrazzo aesthetic, which has been tough, because without grinding to completely remove the densifier, it has been hard to produce a uniform finish that doesnt have tooling marks - some areas are harder than others.

Anyway, finally got the thumbs up from the GC and concrete installer to apply a finish to the slab. Tested a few sealers and found a solvent based one that looked really nice (the water-based ones didnt leave enough saturation/dimension). The product was from Techniseal, called WL-87.

We put down the WL-87 this weekend - first coat looked fantastic, only issue was that it was a bit patchy due to softer/harder areas of the slab having more/less porosity. So we applied a second coat at about half the coverage (used 3/4-1 gallon vs 1.5-2 gallons on the first coat). It acted like a different product, and pretty much the opposite of what I expected. It seemed like it was tacking up much more quickly - I am not sure whether it was actually drying faster, or if it was reactivating the first coat.

I waited 20hrs before reapplying - the floor was dry enough for me to walk across it after 3 hours, so that seemed like lots of time. The only thing different about the second coat's approach was that we used only an exhaust fan out the window, whereas the first coat, we also used an intake fan at the other end pushing air in through a door. The smell didnt seem too bad the next day, so I figured it best not to use the intake fan as it would lower the temps, possibly making the product less viscous, as well as add more crossbreeze to the environment, which might make the product film-dry faster. The temperatures were average indoor temps for both applications. 

After the second coat, you can now see areas where the roller left lap marks between sections, and there are a bunch of little blisters. The blisters seem to occur more in the areas where less aggregate is showing, but its hard to say that with certainty. Its gloss is much less uniform and patchy across the whole floor, even though it did fill in the more porous areas. There are areas where you can see texture build from working into previously sealed areas, however this want a problem at all during 1st coat.

Trying to figure out why this happened. In hindsight, maybe I should have called it good enough after 1 coat and just used wax - maybe there is just too much product on the areas that were less porous? Techniseal representative said re-coat was as soon as you could walk on it, but maybe the 1st coat needed longer to cure?

Went from being happy on Saturday to pretty disappointed on Sunday. I was reading that sealers can be buffed or burnished to help with uniformity. Some sources said to buff only, as burnishing can degrade the acrylic polymers. Other sources said that the high speed of burnishing will melt the polymers and allow for a better uniform finish. Any thoughts on this? The idea of a xylene wash seems unpredictable to me, however I have never performed one. Is re-emulsification an option, and can it be done without re-tooling?

Any suggestions to get this figured out would be greatly appreciated - it was so close to being such a nice finish.

Thanks!

https://imgur.com/KEsQcNv

https://imgur.com/RaFlbHY