Concrete – How to increase height of existing concrete slab

concrete

An existing patio has flag stones set over a concrete slab. If you were to remove the flag stones and thinset, what would be the best way to raise the level of the existing slab to make up for the lost height once the flagstones are removed? Height difference is about 1".

Is there a recommended mix for this? Are there any additives, bonding agents, mesh or anything along those lines that would be recommended?

Best Answer

Something got lost in translation and the question I asked here was totally different than what the person asking had in mind. Not a patio and they didn't even want to raise the height of the slab! That said... I still found the answer to the question I asked by contacting Sakrete, a manufacturer of bagged concrete mixes found in many home improvement and hardware stores in the US.

They recommended:

  1. Surface be thoroughly cleaned and all thinset or tile adhesive completely removed. Any cracks should be repaired.
  2. Existing slab should be painted with their Concrete Bonder and Fortifier and allowed to dry.
  3. They recommended their Sand Mix which as far as I can tell has either no, less or smaller aggregate. It's used for pouring 1/2" to 2" thick. For the liquid, use the bag recommendation but replace half of the water with Bonder and Fortifier. Combine the admix with water before adding to cement.
  4. Any expansion joints in the original slab need to be duplicated on the top coat.

No mesh or fibers necessary.

I called Sakrete because that's what's easiest for me to get locally. Quikrete has a similar Sand/Topping Mix and an Acrylic Fortifier. You can mix your own sand mix I guess if you're into that sort of thing.

One of the comments above about being lucky to last a year was a bit extreme. I have seen a heavily trafficked sidewalk leveled with some straight out of the bag mix that held up for over 10 years in the NYC area. DIY job with no bonding agents or other additives.

I have personally used Quikrete's acrylic fortifier and can attest that it creates a better bond.

I agree it's always better to rip out the old slab and pour a new one but sometimes the added labor and budget isn't always practical.

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