How long for concrete to cure?

It will still be "green" after a day or so, but should take light foot traffic by then. If placing heavy loads like a car on it, then it needs at least 7 days. So three to four days for a shed sounds ok. It will achieve about 50 - 80% typically of its ultimate strength in a month (reaching "full" strength can take years!).

Once its set enough to stop the cement being washed away, water won't hurt it... (concrete will set when submerged)

Theoretically, concrete never completely hardens. However it is usually taken that it has achieved 90% of strength in 21 days. How fast it cures depends on how hot it is.. You should be able to walk on it in 24 hours. Erect you shed in three or four days.

IMPORTANT Keep it wet down and ideally covered with plastic sheet for the next few days. This adds to finished strength enormously. Not really very clever doing a job like this in two lots.

Thanks all for the info.

"Not really very clever doing a job like this in two lots"

As per a previous post I had no choice really, budget run out and heart condition, although excercise is good its not wise for me to keep at it until finished like the good old days.

Ignore him - it's a shed base, not the shuttle launch pad.

As others have said, few days, keep it damp until then.

On 04/08/2012 01:47, John Rumm wrote: ...

It is even carried by some long distance yachts as an emergency repair material for underwater holes.

Colin Bignell

Did you see how they fix leaking pipes, etc. on war ships? Cut wood to make a box around the leak and fill with concrete.

Depends on how ambitious you are in your shed ;-)

Indeed.