A Mexican paver is just a clay tile. I have been sealing them for over 20 yerars and have never had to wait 1 week and deffinately not 3 weeks. The problem began with the fact that there was grout left on the surface which is a big no no. Then you started to get them wet with a lot of water. This activated the lime and started the efflorescence.
Efflorescence is created from the water.
The paver tiles have lime in them and the moisture from the setting material will dissapate up thru the tile bring with it the salts. So Ash you are right it is efflorescence. But if you keep cleaning them with water the efflorescence won't stop. You just keep creating it. Soluble salts present in the setting bed of the material installed.