re-grouting tiles

[steeve]

hi, i m trying to regrout area where it s loose, i took out the broken grout cleaned the spacings.etc..For some reason when the new grout cures doesn't stick to the old grout, and later on cracks again du to the vibration of the floor. i used the latex ahesive to get more flex, no change. :?

[Tom R]

I've had similar problems in the past. The only way I could make it work was by completely removing the old grout and starting over. Never any fun. Maybe cleaning the area with TSP first would help? Also, if it's coming loose because of 'vibration', maybe you don't have the necessary 'double' sub-floor (minimum 1 1/4" thick) you need for ceramic tile.

[steeve]

it's a 50 year old house, when a truck passes, everything shakes,
i have the original subflor,3/4"hardwood,3/4" plywood...should be anough...
maybe some grout sealer would help..
thanks