Yellowing Grout [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-20-2008, 12:34 PM
Got a problem occurring in the new basement bath. It started by the tile grout slowly yellowing. At first I thought it was because I never go around to sealing the grout.

However, problem is getting worse - not only are areas of the walls yellowing (at joints where jointing compound used) but also towels and bathmats

The only thing that I can think of is I used DensArmor Plus paperless mold-resistant drywall.

There is no moisture or odors and only afftecting the bath (not other rooms). The bath has a corner shower unit, sink & toilet (5'x8' room).

Any ideas?


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02-20-2008, 03:30 PM
Some more info

The shower is very seldomly used - only as overspill when we have guests which is 2-3 times a year maybe for a week at a time. It has an exhast fan.

It really does not look like mold.

While basement tends to be cold, never feels damp and never see condesation on the tiles.

02-20-2008, 03:39 PM
Hi Mark
Tell us what type of mortar was used to set the tile.
Is there a vapor barrier behind the backer board?
What was used to seal the seams of the backer?
Do you have well water or on a municipal system?

John Bridge
02-20-2008, 04:12 PM
Hi Mark, :)

IS there backer board behind the tile or just sheetrock?

02-20-2008, 05:53 PM

No backer board, just DensArmor Plus paperless mold-resistant drywall.

1 wall is exterior, 2 of the walls adjoin a Theater room so also insulated for sound. So on 3 walls there is insulation with the Kraft backing paper facing the drywall. On last wall no insulation - yellowing occurs on all 4 walls.

I used a white versagauard mold resitant thinset and a white polyblend non-sanded grout......the grout was a year or two old from a previous tiling job.

As was working on other parts of basement I forgot to seal - but bath room was not really being used. The yellowing started quite quickly and now after a year all grout is yellowed.

Water is municipal system.

I've tried a Zep brand mold/mildrew cleaner with no impact.

02-20-2008, 06:01 PM
Here is a pic of the issue.

crow wing
02-20-2008, 06:39 PM
I know Denishild is a great backer for showers but not sure about Denisarmor
and two year old grout ? I try to write the year on my containers so it gets tossed at 1 to 2 yrs so it doesnt end up 4-5 yrs.
could be the city water too.
might want to try a more powerful cleaner

02-20-2008, 07:03 PM
maybe something you guys are cleaning it with ?

02-21-2008, 07:46 AM

So far my wife has just used a damp it rarely gets used been no reason to to get any cleaners out.

02-21-2008, 11:31 AM
Is the yellow all the way thru the grout or just on the surface?

02-21-2008, 01:27 PM

It would appear it is on the surface......scrubing with a household cleaner or a mold/mildrew cleaner does not have much impact but if I scrap a 1/16th off with a stanley blade I get back to white grout.

So it does look like some kind of mold spore issue.

So is my best option to remove top surface of grout, bleach and then replace with a mold resitant grout and seal?

And recomendations for:
- removing grout
- mold resistant grout?

02-21-2008, 03:08 PM
You might try some CLR cleaner in a spot. Which you can get at the grocery store. Or you might think of staining it. You can go to and check it out.

02-21-2008, 05:27 PM
might be something on your water.
you have well water ?

I have seen this happen a few time, but never followed it to see what made it happen.

02-21-2008, 08:26 PM

Water is municipal system.


My wife today scrubed the grout with laundry detergent and then with bleach. Big improvement but still some discoloration. I then used a toothbrush with neat CLR - more improvement but a think I'm still going to have to scrape some areas of grout and grout again.

If anyone has recommendation for a good mold resistant grout I;d really appreciate it.

02-21-2008, 08:31 PM
Almost all grout now days has a mold resistance in the formula.

with the appearance of the stain on the surface you should be able to remove it with the utility knife blade. Just be careful not to scratch the tile.
or cut you. go slow.
Seal after grouting. A couple coats.

Good Luck