slab curing time? Newbie Forum Discuss slab curing time? in the Good Background Information forums; Just out of interest how long do you usually wait after laying the stand slab before you start on the ...

[crwdtb]

Just out of interest how long do you usually wait after laying the stand slab before you start on the dome? I know it might change depending on weather ,but someone told me 3 to 4 weeks which seems a little excessive but he was a builder!
cheers

[Tscarborough]

If you did it right, you can strip forms the next day and get right after it. To be safe, a couple of days won't hurt.

[dmun]

The official word on this is one week. The slab continues to cure for a month, but it's as strong as it's gonna be in a week or so. As Tscarborough says, it's solid the next day, but don't neglect to keep it dampish for the next week or so.

[crwdtb]

thanks guys for your response, I just didnt want the wt of the dome to sag it! not that it should with a heap of rebar in it. reason I was worried is that i layed concrete bricks on foundation slab 2 days after it was layed and it sunk about 5mm on one corner, not alot I know but I probably should have waited a week. When you say keep it damp, do you spray it with hose? forgive me if that sounds stupid but ive never done any of this before.
cheers
Dave

[fxpose]

Originally Posted by crwdtb

....reason I was worried is that i layed concrete bricks on foundation slab 2 days after it was layed and it sunk about 5mm on one corner....

Something is not right. Concrete should be fairly rock solid after 2 days and 5mm is considerable movement or settling. When you say the slab sunk 5mm on one corner, then did it rise 5mm on the other end? Did you pour concrete over solid hard packed soil?
Or are you saying that the bricks sunk into the concrete, which is very unlikely?

[Tscarborough]

That was not the concrete's fault, it was a base or sub-base issue.

Every day, 12' CMU walls are laid on slabs poured 2 days before. A pizza stand is a little different in that it has formwork supporting it (which is generally left in place for a week in commercial work), and it is not usually done to ASTM or UBI standards (usually it is overbuilt, going by what I see here), but the placement and composition of concrete is very important in relation to the strength curve.

The general rule is, the longer the better, but I will tell you that formwork gets progressively harder to remove the longer it is in place. For edge boards and anything not supporting horizontal concrete, remove it the next day at the latest.

[crwdtb]

we had the largest amount of rain in 100 yrs the day after I layed blocks and I was away so it sat soaked in water for 4 days till i got back maybe it was just a bit of mortar that was under the first row that eroded while sitting in water, it is layed ontop of concrete for the foundation of the house so I doubt it can move anymore.I didnt notice it untill I formed it for the second slab and noticed the differnence slightly against the form. I am away again for a while and when I get back I will pour 2nd slab which will be level so when its bricked you will never see it, not that you can really now. your saw pic its not out that much, as you probably cant even tell.

[crwdtb]

I am known to be a bit of a perfectionist which annoys me to no end, but in the scheme of things this isnt a skyscaper and im sure will be more than sufficent to hold the weight of a pizza oven? with all that steel and concrete surely its overkill as TScar said?

[Tscarborough]

Again, from what I have seen on here, most bases are built 2-10 times stronger than they need to be in regards to steel and cell grouting. However! That is assuming that the concrete is proportioned and placed properly, which is the hardest aspect of the construction for DIY'ers, so for the small additional cost it is probably the best plan of action to over engineer it.

[crwdtb]

So tscar what you are saying is that it should be fine? it looks fine to me, as I said I will just make up for that 4 mm or so on the next slab so it is even, that is all that matters cause I am 100 % sure the thing aint going to fall over or anything like that. Thanks for your reply.
cheers