Grout Discolouration - The Question ?

[alba820]

Hi Folks
A newbee to the forum and joined up prior to starting a total refurb of our small en-suit shower room (timber frame bungalow).
Have taken a lot of time ensuring things prep'd and finished with care, new walls, floor, plumbing etc.
Have hit the problem of patchy discolouration of some of the grout lines on two of the walls !!!!!
The room has not yet been used and the tiles after fixing were not grouted for several days.
Bal flexible blue star white adhesive used and white bal grout to finish.
Interestingly the discolouration is on both a wall finished with mapei shower waterproofing kit and one that was not.
Substrate is green plasterboard, sealed with mapei primer - all walls.
Having just checked the depth of discolouration, it seems to be in the top 1mm and I assume is bleed from the biscuit. Still to explore further in other areas
THE QUESTION to you whizz kids: If I rake this out & re-grout, is the discolouration likely to re-occur and if so would spraying the joint with grout sealant, pre grouting, resolve the issue ?
Have found the forum to be a source of great help over the last few weeks - many thanks to you all.

 

[Gazzer]

Working logically you have to discount the Mapei waterproofing kit if its on walls with and without. So it must be down to either contamination during the grouting or after.
Is the discolouring on outside walls ?
Also, what colour is the discolouration.

 

[nybor62]

any pics please

 

[Rich]

If the stain is just on the surface then it would suggest that it was caused by something after the grouting was done, cutting out/regrouting/sealing the grout would sort this out. However if thats not what has caused it it may not be so simple.

Pics would help.

 

[DHTiling]

How thick was the adhesive used on the walls..???

 

[alba820]

Thanks for your prompt replies.
The problem has occurred on inside walls. The discolouration is a straw yellow colour on the surface and does not seem to be full depth
The adhesive thickness is apx 4 - 5mm
Grout line 3mm
The grouting was done over a couple of days and the discolouration is evident in places from each day.
Grout applied with a rubber float and cleaned off with tilers sponge.
Some photos attached below



Look forward to your further thoughts.
Cheers