Try looking for concrete bonding primer, that's what you'll need to make sure it bonds well with the existing subfloor.

Forming can be done by anything that holds the concrete and doesn't absorb too much water. A couple pieces of wood will do fine most of the time for small jobs. If you have some melamine coated particle board which you can rip into strips it will work even better. You can use some cheap caulk to make sure the forms don't leak.

Normally you can walk on the concrete in about a day. However, it takes about a week before you can put a heavy load on it, and a full month before it's fully cured. If you can put flooring on it depends on the amount of moisture in the concrete. You can test this by putting a piece of clear plastic on the floor. If it isn't wet on the bottom after a day, it's dry enough.

Do we need to drill holes throughout the 4x6 area so that the concrete has something to set itself into? I'm thinking 4 holes about 2-4" inches deep to prevent movement or would the bonding primer do that?

It certainly wouldn't hurt to drill a couple of holes and run in a couple of tapcon concrete anchors. If you leave them sticking out a bit they'll act as pieces of rebar linking everything together.

If it is only 1", I would go with a concrete leveler either SikaLevel 50 lb. Self-Leveling Underlayment Concrete Floor Leveler or Rapid Set 50 lb. CTS Concrete Leveler.

It is the more expensive option but much easier to work with and less risk of cracking.

At 1", 1 bag will cover 5 sf, so you would need 5 bags

You need to prime the floor with an Underlayment Primer

So, $200-$250

The cheaper option would be to use a Sand/Topping mix witha fortifier and the primer, around $100.

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Forms... depending on the working area you can use plywood, 2x4, etc. You just need to make sure nothing can run out of the bottom or corners. The self level has a milkshake consistency if there is a space in any of the forms it will find it.

We plan on polishing the whole level, so it doesn't need to be exactly level, we're just looking to get that front entrance area back on level with the rest of the floor. We plan on doing stained/painted concrete for the immediate fix and might do LVP in the future.

I'm worried about the self-lever breaking through the forms, which is why we are willing to go the concrete route.

Do you mind linking some products so I know what you're referring to?

Both are at Home Depot since that is the store closest to me, Lowes will have similar products. The specifications and instructions are pretty straightforward if you want to dive in to the details.

https://www.homedepot.com/p/Rapid-Set-50-lb-CTS-Concrete-Leveler-186010050/204414391

https://www.homedepot.com/p/Sika-SikaLevel-50-lb-Self-Leveling-Underlayment-Concrete-Floor-Leveler-517004/207086698

Can you stain and seal the floor leveler?

We had holes drilled through our concrete slab to repair our foundation and we're left with obviously different filled concrete holes from the rest of the slab.

I'm thinking of applying a thin layer of self-leveler throughout the entire floor which could give us a new concrete slab look. Our plans are to stain/seal the entire floor but I'd like to get a clean starting point and with the holes glaringly obvious, I'm not sure we'll ever get that unless we cover or obscure them in some way.

Not the person you’re responding to- but I just poured (and messed up, and re-poured on top) a 10x12 room with self-leveling “underlayment” concrete before adding LVP.

Tons of videos online- this one is a good example of a team of professionals making it seem super easy.

https://m.youtube.com/watch?v=5GyXWeSzY_0

Your first attempt will probably not go so smooth- strong recommend some practice on a small area.

It is not intended as the “wear” surface- not the same durability as “regular” concrete; it’s designed to self level AND set quick- can’t also be crazy strong.

Happy to answer any questions

Yeah, that's what I was thinking, it's not intended but is the tradeoff small cracks down the line? Because, honestly, small cracks would be an upgrade relative to the large apparent holes we have showcasing themselves.

The holes have since dried but we have ~8 of these through the main living area. They dried a shade lighter than the rest of the slab. https://imgur.com/a/9T3n5oP

What about grinding down the uneven surface? Given I'm going to be filling the area roughly 1-2" deep, does it matter if the surface is relatively ground down to an even level?

Personally, I have never tried to stain concrete, it's just not a look that I like. If I was in your situation, I would level and go with an LVP floor.

Looking at your photos, one would assume the floor is level. However before applying floor leveler, I would verify that with a long level just to make sure

I 100% agree, I would prefer to go with LVP but as a cheaper immediate fix, we're going with a stained look.