Designing Kitchens and Bathrooms - bath tub / tile & mold ?

a little more than a year ago,i replaced a bath tub-installed fiber glass insulation in the outside wall covered it with 30lb felt-then hardi backer-used modified thinset/6" square tiles on the wall -w/ 1/16" grout lines & 1/8" color match grout at the tub/wall joint.
now at the "T" where the grout lines meet the caulk,for the 4-5 tiles closest to the shower end(wetest) on the outside wall, it apears tto be starting MOLD to come through from the back/ dark / black looking discoloring.

any ideas / cause/cure
thanks-mike

Did you leave the hardibacker about 1/2 - 1" off the tub lip? If not, the water maybe whicking up...

The grout still look good? No gaps, cracks, or anything?

all "looks" good except hhe discoloration that is starting.
an other member suggested,may be a proplwm in the fact that i 'did not' seal the grout lines-i guess alowing moisture to weep through the grout it self?
i was under the impression that the poly blend type grout did not need to be sealed?
any reply will be apretiated!

thanks mike

:confused:

:eek: The grout definetly needs to be sealed, a few times. Don't use that shower for a few days and then seal. Use a good quality sealer, and not the cheap $10 stuff.

thanks for info!
mike

Polyblend DOES NOT require a sealer. PolyBlend contains additives that preclude the need of a sealer.

Today's sealers are there to help to clean the grout when it becomes necessary and are not considered a waterproofing material. IN FACT - Today's sealers are "vapor-transmissive" to let moisture "out" so they could certainly also allow moisture "in".:)

Sealing PolyBlend isn't required but it also can't hurt if you understand why it is you are doing it and understand that sealers in most cases are a profit-center for retailers and so everyone says "SEAL IT"!

The problem here is a simple and (all-to-frequent) "caulk failure". Yes the moisture is wicking down the grout and getting behind the caulk but the caulk is also experiencing a cohesive failure and has separated from the wall enough to allow the growth of mold. Remove the caulk and do it again.:)

:confused: once again, thanks for the info!
question? thereis a void,i am guessing, about the size of - 1/2"x1/2"- behind the tile where the backer board stops-above the tub.should i try to add some of the soft set expanding foam spray in sealer (great stuff)? then re caulk the tille/tub joint?

mike

I've never heard someone recommend not sealing grout. :rolleyes:

If you want more mold and a hard to clean grout, then don't seal it.

Custom Building Products actually recommends sealing the grout to prevent all this.

:confused:
o/k, thanks again for info & fast reply!

mike