We have moved into our new house in May and about a month ago some bubbles/ blisters started appearing on our hardwood floor in the kitchen, which has a water based polyurethane finish. The installer inspected and advised we had spilt something on it. We could not recall spilling anything however had to accept the verdict. About 6 weeks later we were away for a week and returned to find more blisters in another area of the kitchen. Again the installer inspected sending photos to the supplier of the polyurethane and advised us again we had spilt something on the floor. We are confident we didn't as after the first bubbles we have been so careful/ obsessive with not spilling anything, and two, we were away at the time. We live in a subtropical area and both times the blisters appeared was after a hot few days of weather - perhaps coincidental? Please see some photos here: https://www.dropbox.com/sh/d8btg6hjdwj1 ... wcuca?dl=0
Can anyone shed some light onto what may be the cause please?

This looks like an adhesion issue. Since the installer will not take responsibility you may want to call your homeowners insurance agent to see if this is covered with your homeowners policy. Sometimes the fire/casualty coverage will pay for your loss. These seem to be spot repairs not a whole refinish.

many thanks for your reply. It's hard to see in the photo, but when looking at the bubbles under a magnifying glass they look like a bunch on grapes of multiple little bubbles bunched together. Is that reflective of an adhesion issue?

Could be that something is preventing the finish from adhering to the coating below in these spots. I have had soda spilled onto the floor in between coats of finish near a sliding door which made the next coat of finish turn white in spots.

Many thanks again- but why has it taken 6 months to occur & is emerging at different times/ places?