Porcelain tile install - should I be concerned about this?

[Wakesurfer]

I'm in the middle of my porcelain tile project, and I noticed small cracks in the thinset in between some of the tiles once the thinset has dried overnight. It is only in a few places, but I wanted some input from the GJ Braintrust on what causes it and whether I should be concerned or take corrective action! The tiles are 18 x 18 set in C-Cure 907 thinset with 3/8" joints.

This is what it looks like:


Thanks,
WS

 

[Angelfire]

I'm going to let the pro's check in to give you a definitive answer but I'll take a stab at it before they arrive.

Looks to me that you are getting some shrinkage cracks as the thinset is curing. Probably won't be an issue under the tiles. Are you wetting the concrete before you burn in your thinset on the concrete? Dry concrete will **** the water right out of thinset and in some cases, can cause poor bonds. I typically have a spray bottle of water with me when doing tile and just spray the area I'm going to thinset just before burning in.

My only other input is that I typically removed the thinset between the tiles. Screwdriver/utility knife whatever.....once it sets up a bit, I just clean it out.....probably doesn't make a damned bit of difference to the install (other than costs me more on grout!) but thought I'd throw it out there.
Cheers.

 

[Dakota00]

It's just a shrinkage crack in the thinset from the exposed grout joint. There's nothing to worry about!! Do yourself a favor, clean out the joints. Most of the time I use a simple sharp pencil with a sponge to clean the joints out. Works great!

My only other input is that I typically removed the thinset between the tiles. Screwdriver/utility knife whatever.....once it sets up a bit, I just clean it out.....probably doesn't make a damned bit of difference to the install (other than costs me more on grout!) but thought I'd throw it out there.
Cheers.

Cleaning out the joints makes a difference. Dirty shallow grout joints, will be easier to damage, chip or crack. Clean joints will help to make for a more durable grout, which will have better integrity.

 

[Wakesurfer]

Thanks for the advice, Dakota. You talked me off the cliff! How far down do you recommend cleaning out the joint? The picture may not look like it, but I have cleaned out the joints about the equivalent of taking the 3/8" spacers and turning them on end and using them as a squeegee of sorts. It ends up being about a 3/8" deep channel. Is that too shallow for a solid grout joint?

 

[duneslider]

Consistent depth is most important. Highs and lows can lead to grout discoloration issues. I too would use spacers to clean joints then use a damp sponge to wipe them to make sure the upper edges were clean so grout looked good and there wasn't any thinset bleed through. You can clean joints pretty well the next day with a utility knife too.

Do you really have 3/8" grout joints? Or are they 3/16? Cause 3/8" is giant when it comes to grout.

 

[CNGsaves]

From what little I know about tile and grout, pretty sure you'll need sanded grout for that big an area. The sand will give strength to the wide grout joint.

 

[Wakesurfer]

Yes, 3/8"!!! Originally I was going to do 1/4", but since I went with 18 x 18" tiles on a floor that slopes to two drains, I was worried about lippage. Since I'm no pro, I figured a little play would help! I was concerned that 3/8" would look too big, but I think it looks nice with the large format tiles. Yes, I have sanded grout

 

[duneslider]

When you grout that, make sure the grout is more on the dry/thick side and not on the wet/runny side. With a joint that big you are more likely to get shrinkage and cracking. You will want to give it plenty of time to set up before sponging and cleaning or you will wash out too much of the grout and have low joints. Make sure you really pack the grout into the joint.