Prepping for Porcelain...cracks

[Angelfire]

Hiya folks,
I finally found the time to get my porcelain floor down. I’ve cleared the area and have started giving the concrete a good clean. When I first saw a couple of cracks, I thought they were pretty much just hairline cracks. However after vacuuming them, they’re more like 1/16”. I have a couple of sawcuts to fill already but am wondering if I need to gives these cracks more attention.

I’m in NM and moisture is definitely not a concern. The slab has been down for 5 years and I haven’t seen any movement since these cracks appeared just after being poured. I have a fair amount of flattening to be done and was planning on borrowing Dakota’s trick of using thinset for this. Over the cracks and saw cuts I’ll be generously applying Aquadefense after the flattening is done. I am planning to use Flexbond thinset throughout.

So, do these cracks warrant additional attention such as chasing them with a grinder and filled or would it be ok to thinset over them as part of the leveling activity and then the aquadefense?

 

[cgrutt]

I'd seal the cracks with a polyurethane concrete sealer such as Sika self leveling sealant and strongly consider setting tiles with a decoupling membrane such as Ditra.

 

[johnnyradiant]

Membrane and carry on.

 

[Dakota00]

Angelfire,

Do you have a better pic? Is this crack in correlation to the control joint(s)?

 

[Angelfire]

Dakota,
The crack is not associated with the saw cut although it does cross the saw cut at a right angle. When my concrete guy cut the slab, he simply divided the space in half and cut. It ended up being 16’ from the edges whereas I had asked him to divide it into thirds. The cracks have now divided it into thirds for me!

See if these photos help a bit and thank you!

 

[Dakota00]

Perfect!
Nothing to worry about that crack, do your flattening of the area as intended and then aquadefense as per our discussion.

 

[Angelfire]

Just out of curiosity, what were you looking for Dakota? Were you concerned the cracks were emanating from the saw cut? Thanks for the help!

 

[Dakota00]

Yes... Which isn't the case. It's a simple stress crack where a control joint should have been cut in.

 

[rustyjames]

I think Flexbond thinset is overkill for going over concrete, Versabond would be fine.

 

[Dakota00]

Flexbond is not overkill, yes it's more money than Versabond. Sure Versabond could be a good enough thinset. Key factor Flexbond is a flexible thinset with excellent bonding strength. Which is very important for a floor that will take a lot of abuse, plus any slight movement in the slab's control joints will be absorbed by the AquaDefense and the thinset not in results of cracked tiles.

 

[rustyjames]

I could see using Flexbond over wood framed structures but for a surface like concrete unnecessary. Versabond has plenty of bond strength, even on drywall or wood framing. Just my opinion.