I doubt it's the concrete mix. Certainly looks like a workmanship issue. Definitely not enough control joints for that span. Also very surprised that they didn't have a layer of stone beneath the pour. I think it's acceptable to lag the concrete to the house with rebar but in my opinion it would be preferable to add an expansion joint. I would call in a pro for a professional opinion so you have so ammo to go back after the builder. Good luck.

Laura, It sounds like you are dealing with contraction joints, not expansion joints. These joints are just meant to control cracking. The self-leveling sealer should work fine, however, I have to be honest I have limited experience with concrete patios. I design large concrete pavements for runways and airports. The applications are a little different. We seal our contraction joints with self-leveling silicone. My only fear is that your expectations might be a little overreaching. Your concrete is always going expand and contract, it's the nature of the beast. The sealer is really meant to eliminate water infiltration, not to provide a completely smooth surface. The troweled joints that you have may be very shallow as well, which might lend to the potential for the sealant to be pulled out due to the lack of vertical surfaces to adhere to. You might want to check with someone who pours concrete patio's or driveways and get their feedback. I don't think it could hurt to try it on a small area though to see if it meets your expectations. Let me know if I can be of any more assistance. Riles

Just to let you know I used that Sikaflex and in some places I have to much movement in my driveway that it broke the seal and now it looks bad. In other places it looks great. And if you do use it you better make sure that you don't have an opening that goes into the ground, all the sealant will run into the hole. Plug the big holes or gaps below the surface with some thicker caulking and then poor the Sikaflex into the crack...

Actually, no. That is not correct. It is actually best to keep expansion joints waterproofed, although this should not be done for at least a year after the concrete has been in place, to allow for full shrinkage. I've not done mine, but I have looked into it. https://www.homerepairtutor.com/concrete-expansion-joints/ https://trim-a-slab.com/how-it-works/ https://www.pavepatch.com/slabgasket-c-40.html?gclid=Cj0KCQjw6uT4BRD5ARIsADwJQ1_NkdmyI8ObuMDHDfC-l7pHcx5edF1pQU-FUrKoD82WZ1iTbNuSPO0aAk6UEALw_wcB https://www.concretenetwork.com/concrete-joints/sealing-filling.html