Yup, another question that just hit me today.

I am going to be mixing and laying about 1 ton worth of concrete tonight in our basement where I tore out 1700 pounds of concrete for the new bathroom location. That comes out to about a 2 foot wide 'J' shaped trench that is about 32 sq feet of 4 inch thick concrete. Not a huge area, but still a bit of concrete...

Anyway, I've got surrounding concrete to use as the basic forms and to screed against, but what about curing? Do I need to lay some burlap tarp over it and keep it wet for a few days? I am trying to get the walls framed up down there on Friday afternoon/Saturday morning and want to make sure that it cured ok.

The basement isn't overly damp, but obviously isn't super dry either since it is underground. Weather forecast (if it matters) is highs in the upper 60's the next 3-4 days with rain off and on. So it isn't like this is in Arizona with their dry heat.

I want to do it right, but don't want to delay things longer than needed. Outside of the walls being framed on it this weekend, it will sit for 1 week before the plumber comes back to work on the room more.

I don't want to put a curing agent on top of it as I was told that it can take forever for the curing agent to go away and it can leave a slick, waxy surface that is hard for tiles to adhere to.

So any concrete curing tips for in a basement?
Any tips at all?

(I'm a concrete newbie, but tearing it out and putting the new in is saving me $900 after I factor in the cost of material and the mixer)

I think I'd pay the extra $900.

Bah... You big chicken...
Besides, the $900 savings is how I am justifying my VP180 purchase in a couple of months! Now that is some incentive to put a little (ok a lot) of sweat and muscle into this concrete work.

So back to my questions, does anyone know if I need to cover the concrete in the basement? I don't think that the rest of the floor was ever covered since it shows no marks from tarp or plastic. I doubt that they covered it when it was originally poured, and have never heard of people using the "pooling" method around here where they put a couple inches of water on it for several days...

Rick the Wid Man is the guy to talk to!

Hmmm... Rick hasn't posted anything in almost a week... I'll have to drop him a PM...

Concrete takes 28 days to cure. The most commonly used cur promotor is calcium chloride. It should be slick, but it is corrosive, so I wouldn't use it near pipes.

General rules for concrete:
- you can walk on it in ~4h
- you can drive on in 24h, but I wouldn't go anywhere near edges or corners.
- it's very brittle for about a week.
- cured enough for drilling and fastening in about 2 weeks, this is ~80% of cure strength
- fully cured in 4 weeks.

Hmmmm.... I need to attach stud walls to it this weekend. That is a far cry from 2 weeks. It won't be "used" for a couple of weeks, but definitely will be worked on this weekend and then again later next week when the plumber comes back. Right now, there are just PVC drain pipes that the concrete will be around, so it is still corrosive to PVC? I would think not, but just checking. As for securing, I am using one of those .22 "caliber" charge systems that drives a nail through the base plate 2x4 and into the concrete.



In the area that I am working, I would need to use about 7 nails (they go into the concrete 1 inch) to secure the walls to the concrete.

What can I do to make that happen?

Also, do I need to keep the surface covered and/or wet for a few days until I put the walls up?

Ooooo, those are fun, but wear safety glasses and ear plugs, especially in a basement. If the new concrete is supported on either side by older concrete, and your base plate is somewhere near the middle, you should be OK, but that first week is still a bit crumbly. You'll know pretty quickly if it's gonna hold. You can always go back with a hammer drill and some redheads later.

Correction from earlier post; CaCl2 should NOT be slick, however it does absorb water, so it will stay wet. Your plastic pipe should be fine - its already chlorinated

Nick: If Scott told me exactly what I should be doing in my basement, I'd just do it.

Oh, oh, TO your basement. Nevermind.

Seriously, where else can you get professional industrial chemistry advice?

Props from Bob! Nice.

According to concrete.org, you should be good to go in 6 days.

Props from Bob! Nice.

According to concrete.org you should be good to go in 6 days.

Good luck. Let us know how it turns out.

Nick, quick suggestion - do you have to secure the walls to the floor this weekend? Could you build them and temporarily anchor them by other means until the concrete is cured before you secure them permanently? When I refinished my basement I had a couple of walls that were a fairly snug fit between the subfloor below and floor joists overhead that easily held them in place with no anchoring. I of course did anchor them before finishing but they were solid enough for any other work that needed to be done before the drywall went up.

Bob, I'm not "questioning" the advice, just asking more questions.

I was just down in the basement prepping for the concrete fun tonight. There is 1 wall that will secure into the surrounding existing concrete, and another wall will me 3/4 on existing concrete. The back wall will be 100% on NEW concrete. There are also some shower surrounds that will be 100% on new concrete, BUT I think that I will play it safe and secure what I can to the existing floor, and then secure the walls that are over the new concrete to the ones over the old... Go on my business trip, and then late next Wednesday night or early Thursday just fire a few nails into the new stuff. Seems doable and lets the concrete do its stuff.

I did pick up some accelerator stuff. Gotta factor that into the recipe (starting to think that it would have been a lot better to have gotten Quikrete since it is already mixed and just add water and accelerator)...

Hopefully that will help. Well, time to make some calculations and then off to rent the mixer.

Thanks all!

It's not a problem to shoot into the concrete after about 24 hours. In fact, it's much easier while the concrete is still green.

You don't need to do anything special to cure it in a basement. That's only an issue if you're outdoors where the sun or wind could dry the surface faster. Like you mentioned, it's better not to use a curing compound so you avoid issues with flooring later.

I wouldn't bother with an accelerator either. It'll just make the finishing job more stressful if the concrete sets up too fast. Just pour and finish it tonight, and you'll be good to go tomorrow night.

By the way, concrete reaches it's design strength in 28 days, but continues to cure and get stronger and harder for 50-100 years.

Well, you posted those tips about 2 hours too late. ;-)

Anyway, the concrete is all in. I did use some of the set accelerator in there too. You are right, for someone who isn't experienced, it made the first "batch" a little more difficult when it was time to screed and float, but it is done. I noticed that the existing floor wasn't 100% level either, so that didn't help. I may have to put down a thin layer of self-leveling compound or whatever before we tile, but I haven't even looked into what that is all about.

Glad it is done. My back and knees are sore... And even though I wore a dust mask, I still sneezed portland cement...

new screen name nickmason

LOL

I would ABSOLUTELY encourage you to use a self-leveling compound before you tile. Tile wants flat. Bad. Like, Calista Flockhart.

Check out the John Bridge Tile Forums for tips.

Tom, you forgot the " ™ " after Calista Flockhart™.

I've obtained exclusive use of her name on this forum when referring to flatness.

My attorney's letter is on it's way.

Sorry I missed this but the advice you got was spot on.

Pffft.

Rick's been hanging out waiting for someone else to come up with the correct answer first.

Like that guy that reaches for the check, but not very quickly!

(Rick, you're not hanging out here as much as you used to. Don't you miss us?)

Don't you already "own" Suzanne Vega? It's not like she had to give up the accordion during puberty---like Connie Francis did.

glad the pour went well!

personally, I have no problem with the ibtc... just saying.

OK. So the concrete turned out OK. It was odd though. It seemed like the area around each of the 3 PVC pipes (shower drain, toilet drain, and the vent/vanity drain) all was higher than the rest. I had the hardest time screeding around those areas last night, but it is like they climbed up the pipes...

Gave me an excuse to buy a new tool and make a HUGE mess. I picked up an angle grinder and a diamond cup wheel. I suspected (and was right) that the "free" masonry grinding wheel would be crap, so I picked up the double cup wheel. Holy crap does that thing go through the concrete. Even with the shop vac on, there was way too much high flying particles to capture and the entire basement has a layer of dust on it. I was picking small rock/concrete bits out of my hair and a lot more was trapped in there until I took a shower.

Now things look pretty level and came out pretty good according to my 6 foot metal level used to see if it "teetered" on any high spots.

At least now it will just come down to *maybe* having to slightly fill some lower spots, but only when it is time to tile.

Whew. Glad that is over. My daughter is singing at the Iowa Speedway (pretty decent race track) tomorrow night, so I am not going to work on it tomorrow, but I will get the walls up Sat/Sun and keep on truckin'.... Thanks for all of the help.