What's a fair price for a new 10' x 20' concrete slab?

[studio_drums]

I just got a quote for $3300 to have my old slab taken out, and a new monolithic reinforced slab put in, with footers.

10' x 20', 5 inches thick, 3500 psi

To be completely level and isolated from surrounding garage foundation walls.

Is this a fair price?

Makes me want to rent a jackhammer...

Any advice appreciated. I am moving forward with the project now...

[russoloco]

Everything around here is quoted around $6 per square foot (4"- thick) and around $8 for 6" so for just the concrete work that seems a little high but since you're having them do the demo and disposal work to it might be fair. I don't know what disposal costs are like in your area.

[sharward]

I did most of the work on my slab myself. It was a lot of work, and I had no experience with concrete beforehand.

I rented a concrete saw and purchased a diamond blade for the saw. My friend towed it to my place. He ran the saw while I did my best to control the water flow to prevent/mitigate damage to objects in the garage. The rental was around $70 I think and the blade might have been around $85. I still have the blade -- there's about 50% of its life left on it.

I rented an electric impact hammer and broke the floor up into manageable pieces over two partial days. That cost around $60 I think...?

I removed the chunks of concrete and carried them to a dumpster that I had delivered to my house. I recall the dumpster and the haul-off cost me about $250.

I spent weeks removing the crushed granite base (saved for later use) and excavating thick, sticky clay soil from the area with a shovel. I still have a big pile of dirt in the back yard from that experience, and it's even visible on the "bird's eye view" photos on Zillow.com!

I then had to use an electric demolition hammer to chip off messy chunks of concrete off the foundation that had spilled out under the forms when the foundation was originally poured. What had been inconsequential under the original slab was (I believed) relevant, if not critical, in my effort to build an isolated slab. The demo hammer rentals cost around $100 for the all the days that I used them. I spent much of Thanksgiving Day chipping away at the foundation.

I bought 12" tall concrete forms and stakes ($100?), cut them to correct length, and then installed them (level).

I had to add more stakes later to make them more stable, this time using steel stakes (more expensive, around $35-40?).

I had a yard or so of crused granite delivered to my house, which I then moved one shovel at a time into the "pit." The crused granite delivery cost around $200 I think. (I kept no records. I suck! ) I also used the crushed granite that I salvaged from beneath the original slab.

I tamped all the crushed granite with a hand tamper.

I hired a professional concrete contractor to lay down plastic, insert all the rebar ($250), and position the J-bolts that I bought previously ($40?) in final preparation for the pour.

I had our pest control company treat the soil with Termidor termiticide ($550). I also plumbed a "termiticide injection system" that will allow for the area to be retreated in later years (every 5?) without having to drill into the slab. With a gap around the slab, I was quite concerned about termites forming mud tunnels and destroying the walls over time, unbeknownst to me or anyone because of inaccessibility and inability to see the damage until it was much too late. Perhaps this was overkill/paranoia, but I learned a lot about termites at that time, and it's scary!

I passed my concrete forms inspection (the building permit requires this).

I hired the same professional concrete contractor to handle the pour and finishing. The concrete delivery (5 yards, 3,000 psi, plus fiber mesh) was $770 and the bill for his time was around $300 I think.

There was an additional one yard "mini pour" that I had to do in an L-shaped area where the old slab met the new. I did all that work myself, with the exception of renting the mixer filled with concerete... That was a couple hundred bucks, and I was able to use my concerete contractor's rebar bender free of charge.

Overall, I'm very pleased with the outcome, but it took me a looooooooooooong time, as can be found in my project thread. I too had considered hiring a pro to do everything at first, but I had trouble finding a licensed professional contractor to do the work amidst the peak of the building boom out here. I wasn't getting calls returned -- I guess the job was too small to care about from their perspective.

I should also point out that at the time I did this, we did not yet have the benefit of Rod's book. I probably would have done things differently, such as not set forms at all for the new slab, instead using a foam board/roll around the perimiter, figuring that would provide sufficient isolation from the rest of the structure. I also think I worried too much about flanking across the slab at the time, because that was an era on the forum when floating floors were seen as typically necessary, whereas the tides have shifted considerably since then.

Sorry for the ramble... Hopefully there's some useful information in there somewhere...

--Keith

[studio_drums]

Thanks Keith,

Your posts are always useful!

So you don't think I need forms?

I'm going to get this done, can you please advise me what to specify for the perimeter, to fill in the 1.5" air gap?

How about wire screen instead of rebar to reinforce?

Maybe I can talk them down...

[sharward]

Definitely check out studio911's project, in particular Rod's comments about the rebar work that was done on that one.

Perhaps closed cell foam boards can be affixed with Liquid Nails onto the foundation, the tops of which would be level and flush with the surface of the slab to be poured?

I think that would technically still cause some physicial bridging of the old concrete and new, but based on what I've learned since I did my pour in terms of how the ground dampens slabs from resonating too much, that may be sufficient for you.

I hesitate to be too authoritative on this though...

--Keith

[studio_drums]

PLEASE tell me if I need to change anything!

Details of the pour:

-10 x 20 monolithic slab with footers: 4" crushed stone, 5" pad, 8" footers

-3500 psi mix

-Reinforced with "screen"- not rebar. (their terminology)

Is this okay? Will screen be enough to prevent the slab from cracking or do I definitely need rebar?

-Perimeter to be formed to leave 2" airgap between new slab and existing block wall foundation.

-Slab will be supporting single stud(wood) room with 3 or 4 layers of drywall(one side only).

I appreciate all input!

[studio_drums]

I amended the contract to specify rebar instead of screen.

Thanks

[sharward]

I would also highly recommend J-bolts for your soleplates.



They're generally positioned with small pieces of wood with holes drilled in them nailed to the forms before the pour is done.



The soleplates of the walls are really secure with this method.



Don't forget to have a plastic sheet put down to prevent/minimize moisture from wicking into the slab! This goes down over the crushed rock, before the rebar goes in.

--Keith

[studio_drums]

Thanks Keith!

[KellyRobert]

I force need to realize what sort of slab to utilize and how much if utilizing a 10' x 20' casing and how much steel bars or is it essential on the off chance that I utilize new concrete.

[Soundman2020]

I force need to realize what sort of slab to utilize and how much if utilizing a 10' x 20' casing and how much steel bars or is it essential on the off chance that I utilize new concrete.

You are replying to a thread that is OVER TEN YEARS OLD.

- Stuart -