Another Tile Grout Question (floor, installed, sealer, exterior)

[riaelise]

This is a newly laid floor by an installer that I've used (and trusted) over many years. For some reason the sanded grout is start to erode and/or crumble. For example, if I rub too hard some of it will come off. It is sealed. Any ideas for why this is happening? Grout lines are fairly narrow.

Thanks.

[Hemlock140]

That can happen when the grout starts to set up, and the installer adds water to make it last longer. Also, if the sealer was put on before it had fully set and dried.

[K'ledgeBldr]

Probably-
Grout was too wet when initially installed.

[Treenoid]

I mixed some grout to fill in some gaps in the exterior brick - actually it was mortar mix... once it was in place I tried to clean it up a little more and found that it was coming apart with very little effort..
The mortar mix was too old.. I think that stuff has a shelf life and if your guy used old grout it may also be part of the problem.. The previous owner of this house left a large bag of mortar mix - that stuff would not even mix with water