What is this brown gunk coming up from a new floor?

We live at an apartment where the "maintenance" is a total joke. Nothing is done correctly, so I'd imagine the same applies here. They came and redid the bathroom floor the other day, and we've been having all this milky off-white stuff coming up from the cracks any time the floor gets damp or wet. They never told us whether anything had to dry or set up, so we just started using it like normal right away. For reference, it's wood lookalike linoleum or whatever. I'd appreciate some help on what's going on here!