I first used unsanded grout (had the same trouble applying it) and it cracked. The advise I was given was that the spacing was to wide for unsanded. So I chisled out the grout and started again this time with sanded grout.
I finsihed one wall. The grout hasn't cracked. But it took me a whole day just to grout the wall with the facet :( It seems applying grout should go quicker than this.