I understand the need of grout lines and I did have grout lines for bathroom and kitchen project. But as a DIY with request from the spouse (who hates seeing the grout lines), we plan to cover the raised concrete fireplace hearth with porcelain tiles and no grout.
Something like this (picture shown tiles fitting closed to each other - Not fireplace specific):
Obviously I have never done tile without grout before. I did some research and people said two things about grout:
Tiles can move --> But it's a fireplace hearth only 70x10x10 and we won't even turn on the fire. So it's less likely the concrete expanding itself from inside out to cause cracking.
Dirt getting inside, hard to clean --> But it's way closed, the gap is not visible to see. Plus I can put non-sanded grout and run through after things done.
Will I regret doing this without grout? Please advise