A moment of panic

[n74tg]

This post is sort of a continuation of the "Concrete Curing Compounds" post.

I poured the first half of my basement slab yesterday.  It was 95 degrees when concrete arrived.  The pour went smoothly.  The driver helped me screed off the slab with a 2x4, showed me how to use the bull float I'd rented and helped me float the edges with a magnesium hand trowel.  It looked pretty good as we cleaned up all the tools and he washed out the truck.  

He drives away and 30 minutes later I start seeing spider web looking cracks start showing up in the slab.  First, one, then two or three more.  Cracks varying in length anywhere from a foot to 3 foot and widths of 1-2 mm.  All the cracks are in the middle of the slab.  

I call the concrete company, but they've all gone home for the day.  I try to look up the name of company manager in phone book, no luck; same for concrete truck driver.  I realize I'm on my own.  

I hadn't planned to do anymore troweling figuring I'd just screw it up, but hey, what have I got to lose now.  So, out comes the water bucket and mag trowel... and hand floating begins.  The cracks close up nicely as I work the slab.  I end up re-working probably half of the 12'x12 slab.  When I'm finally finished I putter around for 30 minutes or so to see if any more cracks are gonna show...none.

So, I water it down good and cover it with visqueen and call it a day.  Needless to say last night was a worrisome night; couldn't wait til morning so I could go check it.  

What a relief...no new cracks overnight.  I rewatered the slab good again several times today, and recovered it each time.  Maybe tomorrow late, or next morning I'll uncover it and start removing forms.  

I'd post a pic, but all you'd see is a visqueen covered slab.

PEG688: Thanks for your advice on the curing compound post.  I got a lot of good advice from all of you, but your thought about "if it's that hard to find (curing compound) in your area, it's probably overkill".  That's what finally sealed it for me.  So, I just used water and visqueen.

Keeping my fingers crossed.  

[glenn kangiser]

I didn't see you mention using a tamp after screeding so it is possible it could have consolidated a bit more upon setting.  I don't always use a tamp either -- many times on bigger slabs I use a 21' long 6" dia.  pipe roller -handles on each end -- pull out to lock and screed --handles straight and loose to roll and tamp -- then just use the screen tamp in bad spots.  I usually limit my pours to 40' x 60' with 5 or so good helpers and finishers - .  Last one was 40x40 one day and 20x40 another day.

I wouldn't worry about your slab ---  If you are happy with what you see -that's good enough.  If it wants to crack it will -- even happens to the pro's  -- lately I would say especially to the pro's.  I worked on a laser screeded slab- about 6 acres in one building that had up to 1" differences in areas - smooth but still ups and downs.

Even poorly cured slabs will usually be fine.  It's only fake rock.  Don't let it bother you.  Just be ready for it on hot days or it can get away.

[n74tg]

Well, a couple of tiny cracks showed up today.  They are maybe a foot long and essentially they didn't "open up" any.  They occurred where an interior block wall will be (tornado shelter) where vertical rebar sticks up thru the slab which made it difficult to get that area covered well with visqueen.  I expect the water on the slab in that area all evaporated overnight and let the slab dry out in that area.  

It will be interesting to see if other cracks come back when I remove the visqueen for good; tomorrow.  It will have been on (and kept nice and wet underneath and on top too) for 3 full days.  

Still keeping fingers crossed.