New Basement Concrete slab questions

branimal · Apr 17, 2026

I'm getting ready to get my basement slab replaced with 4" of concrete. Currently I have tile + and old 2" slab on top of dirt. Plan is to have one giant room with LVP on top of the concrete.

I was initially thinking about patching the valleys with sand topping mix and then topping everything with self leveling concrete to get a smooth finish. The variation in heights from the high point is mind boggling for me to figure out how this will work. Plus I'd need quite a bit of man power to pour the SLC. This has been holding up my renovation project b/c I've been dilly dallying.

Here's the plan so far... please critique as necessary:

1. 4000 PSI Concrete with normal set time - i Don't need access down there right away
2. 10-15 mil vapor barrier
3. No gravel. I know gravel is recommended, but getting gravel into the basement will be difficult.
4. Wire mesh
5. There will be some digging to get the floor level. 1-2" of moving dirt around.
6. No floor drains. There is a boiler room in the back that has floor drains. This area is not getting a new slab.
7. Staircase is getting ripped out b/f the pour.

Price is $8500 for 720 sq ft, incl. demo and dumpster.

Here's some pictures of the basement from each end.

theoldwizard1 · Apr 17, 2026

This might cost more, but you will have more COMFORTABLE results. Installed a raised sub-floor, like DriCore, instead of replacing the concrete. (The remainder of that tile will come off quickly with the correct tools.) Installed correctly it will be perfectly level. Any minor leaks will find their way to the existing drain.

Best of all, IT WILL ALWAYS BE DRY AND WARMER THAN CONCRETE !

branimal · Apr 17, 2026

theoldwizard1 said:
This might cost more, but you will have more COMFORTABLE results. Installed a raised sub-floor, like DriCore, instead of replacing the concrete. (The remainder of that tile will come off quickly with the correct tools.) Installed correctly it will be perfectly level. Any minor leaks will find their way to the existing drain.

Best of all, IT WILL ALWAYS BE DRY AND WARMER THAN CONCRETE !

My floor /slab height variation is too great for dri core I think. Lows are 2 1/4" lower than the high point. And its not the tile that's causing the problem. ITs the slab.

Heres a rough height map of my floor. High point is in the upper left corner (near the 1/4"). The measurements indicate how much lower each spot is to the high point.

bluedog225 · Apr 17, 2026

I know people use self leveling concrete with success. But when I did it, the ”sand” in it made hills that were tough to level. Ended up out of level. I thought it would flow out. Did not. Even though instructions followed.

ConCretin · Apr 17, 2026

branimal said:
1. 4000 PSI Concrete with normal set time - i Don't need access down there right away
2. 10-15 mil vapor barrier
3. No gravel. I know gravel is recommended, but getting gravel into the basement will be difficult.
4. Wire mesh
5. There will be some digging to get the floor level. 1-2" of moving dirt around.
6. No floor drains. There is a boiler room in the back that has floor drains. This area is not getting a new slab.
7. Staircase is getting ripped out b/f the pour.

Price is $8500 for 720 sq ft, incl. demo and dumpster.

Let me take me take it point by point. I'll be a bit picky but it's intended to be helpful rather than offensive so bear with me.

#1 - You don't need 4000 psi concrete. Your comment about 'normal set time' suggests a lack of understanding. You can walk on any strength concrete in 12 hours.

#2 - There is a world of difference between a 10 mil vapor barrier that is typically polyethylene and a 15 mil product such as Stegowrap. Either is probably fine but the cost difference and performance is very different, Make sure you know what your are paying for.

#3 - Gravel may be recommended for a new slab but yours is basically an overlay. I don't see any benefit to adding gravel in your situation.

#4 - wire mesh is probably a good idea. Make sure it's properly supported rather than depending on the crew to pull it up during the placement.

#5 - I wouldn't spend too much effort leveling the sub grade - just pour over what is there.

#6 - no comment. Floor drains are optional.

#7 - no comment

$8,500 ($12.00/sf) to place an overlay with little or no prep seems pretty high. These things very considerably by region but that price seems crazy.

Don't over think your situation. If the higher floor elevation doesn't create issues with headroom, doors , etc just find someone to place and finish a concrete overlay. If it was in my area, I wouldn't expect it to cost more than a few thousand bucks and that includes a concrete pump.

Feel free to reach out here or by Pm if I can be of further assistance.

branimal · Apr 18, 2026

@ConCretin thanks for the detailed reply!!!

One clarification --> The crew is ripping out the existing slab (2") + tile.

1. Concrete PSI - I'll see if getting 3000 or 3500 PSI will make a decent difference in price.
3. Gravel - this is a new slab, but getting that much gravel (720 sq ft) down there will be costly.
4. Mesh support - My guess is they are going to pull up on the mesh. Since my old slab is 2" thick, can we use chunks of chipped concrete to space off the mesh?
5. Level - I don't think this is going to cost me too much more.

Cost breakdown below. This is the lowest price I got. These guys did a neighbors front yard. Looks decent. I'm going to go out there with an 8' straight edge to see how things actually turned out. Since I'm putting LVP on top, it has to be less than 3/16" flatness variation over 10'.

I'm going to call around for more concrete prices.

Labor: demo, disposal, level, compact, pour			3500
Concrete * yds	185	15	2775
Concrete pump			650
mesh			150
Vapor barrier		??
Dumpster			1350
dumpster permit			50
Total			8475

Overboost44 · Apr 18, 2026

Don't know where you are located but that dumpster cost is high. concrete can be recycled, so if there is C&D or rubble landfill nearby, cost should be minimal.

Stego 10 mil is $360 for 14' x 105' but then you also need tape. Not sure what the 15mil costs. Guessing that a large part of that labor cost is the demo part?

ConCretin · Apr 19, 2026

branimal said:
One clarification --> The crew is ripping out the existing slab (2") + tile

Ohhh, my mistake. Sorry bout that. That changes a couple things, not the least of which is cost. The $8,500 price tag seems a little more reasonable now. A couple other thoughts based on this scenario

You'll want to evaluate the base material under the existing slab just as you would any new slab. If the material is dry, stable and compact-able, you could place the new slab right over it even if the thickness varies a little. It might cost less for a little extra concrete than placing and compacting add'l gravel. If the existing slab failed structurally or the existing material is wet or unstable, you may need to remove some material and replace it with compacted gravel to ensure your new slab is properly supported.

This presumes you've factored in the net increase in floor elevation with regard to stair risers, door openings, headroom, etc. To maintain the existing elevations with a thicker slab will obviously require excavation.

It's great you know the flatness tolerance you need for your flooring. 3/16" in 10' is actually a pretty tight standard especially in a confined area. Make sure your contractor is comfortable with that.

I see that the question of vapor barrier is undecided. I would opt for a proper vapor barrier such as Stego. You don't want water vapor going thru the concrete and accumulating under your floor, especially if it's adhered. Poly is reasonably effective but degrades over time and is very susceptible to damage during construction.

I suppose you could use chunks of concrete from the old slab as supports for the wire mesh as long as they don't damage the vapor barrier. While not ideal, it is possible to pull the wire mesh during the placement but the crew needs to be very diligent and most aren't.

Take a look at my Guide to Floor Slabs in the link below for some additional thoughts on constructing a slab on grade and good luck with your project.

larry4406 · Apr 19, 2026

I think after taking out the slab, I would put in a perimeter drainage system with a sump crock with sealed lid.

This will address any drainage issue, should there be one, and give you the ability to install a radon vent that pulls vacuum sub slab.

Small cost add given where you are heading.

If you have appliances in the basement which generate condensate, a floor drain with trap piped to the new sump crock would also be wise.

Treeman · Apr 19, 2026

I, too was wondering why no sump crock is being installed, unless there is zero chance of water down there.

I would also consider renting a tamper to compact the base, unless I'm misunderstanding something.

Off topic..........please explain that tangle of flexible conduit!!!

red · Apr 20, 2026

larry4406 said:
I think after taking out the slab, I would put in a perimeter drainage system with a sump crock with sealed lid.

This will address any drainage issue, should there be one, and give you the ability to install a radon vent that pulls vacuum sub slab.

Small cost add given where you are heading.

If you have appliances in the basement which generate condensate, a floor drain with trap piped to the new sump crock would also be wise.

Couldn't agree more.
And if there's no water/drainage issue it could also be used for radon abatement (if that is even an issue in your area.) Cheap to put in just one side into a sump pit for future use if necessary.

My brother's house had water issues until we installed 4" solid perforated pipe on two sides of the basement perimeter he only had to use the pump after two days of constant rain. The gravel and drain pipe was enough to hold the water until the ground could absorb it. 1950's basement with no gravel and slab was barely two inches thick.

Djstorm100 · Apr 24, 2026

Overboost44 said:
Don't know where you are located but that dumpster cost is high. concrete can be recycled, so if there is C&D or rubble landfill nearby, cost should be minimal.

Stego 10 mil is $360 for 14' x 105' but then you also need tape. Not sure what the 15mil costs. Guessing that a large part of that labor cost is the demo part?

Dang, I sell 15mil Yellowguard (same thing) for the same price. 14' x 150'

branimal · May 5, 2026

New slab project is underway. The crew got most of the concrete out. Tomorrow they will level the floor.

branimal · May 8, 2026

The crew got 90% of the slab poured. There was a plumbing mishap that needs to get addressed before they finish the remaining section.

They didn't cut control joints into the concrete. Should I cut 1" deep control joints into the concrete with my concrete saw?

-All floor penetrations and the room's perimeter were wrapped with expansion material - 1/4"x4" foam?? board.
-10mil poly sheeting
- wire mesh - pulled up during the pour
- smooth finish

I'm going to wet the floor and cover w/ plastic later today.

PCustoms · May 8, 2026

branimal said:
The crew got 90% of the slab poured. There was a plumbing mishap that needs to get addressed before they finish the remaining section.

They didn't cut control joints into the concrete. Should I cut 1" deep control joints into the concrete with my concrete saw?

-All floor penetrations and the room's perimeter were wrapped with expansion material - 1/4"x4" foam?? board.
-10mil poly sheeting
- wire mesh - pulled up during the pour
- smooth finish

I'm going to wet the floor and cover w/ plastic later today.

I'm not an expert I definitely have to read up again on control joints, but yes I would expect them. What was in the contract?

That finish looks a little rough...

Not sure I'd bother with plastic for a non weight bearing floor, it should cure fine

larry4406 · May 8, 2026

Too late now, but at the day job, we use zipstrips in the slabs and orient them from post to post and post to perimeter.

ConCretin · May 8, 2026

branimal said:
They didn't cut control joints into the concrete. Should I cut 1" deep control joints into the concrete with my concrete saw?

You could but the only potential difference will be that shrinkage cracks will be visible on the surface rather than hidden in the bottom of your saw cuts. I'm not sure it's worth the effort especially if the floor will be covered.

branimal · May 8, 2026

ConCretin said:
You could but the only potential difference will be that shrinkage cracks will be visible on the surface rather than hidden in the bottom of your saw cuts. I'm not sure it's worth the effort especially if the floor will be covered.

Yes the floor will be covered with LVP. I was reading the cracks could telegraph through and impact the LVP click lock system. Maybe that's an extreme case.

larry4406 · May 8, 2026

The LVP we use at the day job for basement applications is a floating floor. Not possible for it to be damaged by shrinkage cracks in the concrete.

Not sure what type you will be using.

branimal · May 8, 2026

How long after the pour can I put a ladder going from the 1st floor to the basement. I'll place the ladder on a piece of 3/4 ply. How long until I can start building a new set a stairs. (Old stairs was removed before the pour).

larry4406 · May 8, 2026

I would say 24 hours for foot traffic is more than adequate.

We don’t drive on a driveway apron for minimum of 3 days.

At the day job, we pour slabs today, next day put in construction entrance, next day deliver framing materials, and next day start framing.

branimal · May 9, 2026

There's some shallow bird baths. Biggest ones in the picture are 1/8" deep and 3/16" deep. In the back, on the right is where the crew first poured concrete, it still looked wet last night. I guess the first batch was wetter than the rest. But it's hard.

PCustoms · May 9, 2026

branimal said:
There's some shallow bird baths. Biggest ones in the picture are 1/8" deep and 3/16" deep. In the back, on the right is where the crew first poured concrete, it still looked wet last night. I guess the first batch was wetter than the rest. But it's hard.

Check the specs for your flooring, I bet that's going to be a problem

branimal · Sunday at 10:29 AM

The contractors that did my basement slab have disappeared. They under-ordered the concrete required. They needed ~12 yards and they ordered 10.5. Trying to maximize profits. I specifically told them to order extra and I'll pay for it.

Job was quoted at 9500. They got paid 5000. They damaged a water pipe, which was an expensive repair, but fortunately I was able to fix it. I guess they think the repair would be more expensive and it's time to cut their losses. Aside from hitting my water pipe and "GHOSTING" me, they were hard workers.

Whats left to finish....

a piece of the main slab. To tie the main slab together with the "to be poured slab", can i dowel 12" x 1/2" rebar? 6 inches on each side of the slab.
concrete walls for the house trap pit. How thick should those walls be?
basement areaway (external space before the basement entrance).

I'm guessing its 1.5-2 yards.

I have to find someone that's willing to do a small job.

Should I break out those forms left on the slab? It's been 1.5 weeks since the pour. I was initially worried of chipping the slab face. I think the concrete is at 70% of 4000 psi by now.

PCustoms · Sunday at 11:03 AM

branimal said:
The contractors that did my basement slab have disappeared.

I'm shocked

mm08822 · Sunday at 1:25 PM

Any signed contract in place or just a post-it price?

If a contract is in place, read it carefully before you complete any of their remaining work.

Leave the forms for now, not hurting anything.

branimal · Sunday at 2:26 PM

mm08822 said:
Any signed contract in place or just a post-it price?

If a contract is in place, read it carefully before you complete any of their remaining work.

Leave the forms for now, not hurting anything.

I have a piece of paper with the job spec, price, etc. But it's effectively a post-it price. These guys are off to the next job. I wouldn't let them finish the remainder anyway. I had to run around before the pour to make sure all the forms were on mark. And make sure each stake was cut flush. It was constant babysitting.

When they ran out of concrete I asked them how much they ordered. "12 yards." I go out to the concrete truck and ask him for the bill. 10.5 yards.

Thanks I'll leave the forms on. My thinking was I can dowel the slab so the next contractor doesn't have to.

PCustoms · Sunday at 2:34 PM

Forms aren't doing anything at this point

Carchie · Tuesday at 12:06 AM

branimal said:
I'm getting ready to get my basement slab replaced with 4" of concrete. Currently I have tile + and old 2" slab on top of dirt. Plan is to have one giant room with LVP on top of the concrete.

I was initially thinking about patching the valleys with sand topping mix and then topping everything with self leveling concrete to get a smooth finish. The variation in heights from the high point is mind boggling for me to figure out how this will work. Plus I'd need quite a bit of man power to pour the SLC. This has been holding up my renovation project b/c I've been dilly dallying.

Here's the plan so far... please critique as necessary:

1. 4000 PSI Concrete with normal set time - i Don't need access down there right away
2. 10-15 mil vapor barrier
3. No gravel. I know gravel is recommended, but getting gravel into the basement will be difficult.
4. Wire mesh
5. There will be some digging to get the floor level. 1-2" of moving dirt around.
6. No floor drains. There is a boiler room in the back that has floor drains. This area is not getting a new slab.
7. Staircase is getting ripped out b/f the pour.

Price is $8500 for 720 sq ft, incl. demo and dumpster.

Here's some pictures of the basement from each end.

Skipping the gravel sub-base is risky since it provides crucial drainage and a capillary break to stop moisture from coming up through the dirt. If you must skip it, ensure that vapor barrier is taped perfectly.

ConCretin · Tuesday at 9:23 AM

branimal said:
The contractors that did my basement slab have disappeared. They under-ordered the concrete required. They needed ~12 yards and they ordered 10.5. Trying to maximize profits. I specifically told them to order extra and I'll pay for it.

Job was quoted at 9500. They got paid 5000. They damaged a water pipe, which was an expensive repair, but fortunately I was able to fix it. I guess they think the repair would be more expensive and it's time to cut their losses. Aside from hitting my water pipe and "GHOSTING" me, they were hard workers.

Whats left to finish....

a piece of the main slab. To tie the main slab together with the "to be poured slab", can i dowel 12" x 1/2" rebar? 6 inches on each side of the slab.

concrete walls for the house trap pit. How thick should those walls be?

basement areaway (external space before the basement entrance).

I'm guessing its 1.5-2 yards.

I have to find someone that's willing to do a small job.

Should I break out those forms left on the slab? It's been 1.5 weeks since the pour. I was initially worried of chipping the slab face. I think the concrete is at 70% of 4000 psi by now.

Sorry about your experience so far. At least you didn't pay too much up front. You're probably still above water as long as their work to date stands up although I'm not clear on the impact of under-ordering the concrete. Any chance you could finish it up yourself. A yard or two of concrete is manageable using bagged mix.

The birdbaths can be leveled up pretty easily if your the floor doesn't meet the tolerances required by your flooring. Ardex makes some good products. You can remove the forms anytime but they'll help protect the edges from chipping if you leave them until they are in the way.

It wouldn't hurt to install a few dowels to connect the slabs together but a rebar or smooth dowel every 12 or 18 inches is fine. The pit walls don't need to be any more than 4" thick. I'd hang a form and cast the pit with the surrounding floor. Construction can be challenging but keep plugging and you'll get it done. Good luck!

New Basement Concrete slab questions

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