a Vietnamese. Another chinese guy came by

I asked him, who also do flooring but without license, He looked and said it would be because the floor has sands, not clean just like you said. But it is 13mm thick, small sand like 4-5 mm can cause a 4-5mm bump on surface?  There are not very high, they are about 1mm high, you can barely feels.  So you think they are unclean cause those bumps too?  not moisture? or both?  how long the bumps show up if it is from the sand?