...and the winner is...

Flooring
Originally uploaded by radioflyer007

...well, it was hard for me to decide since it wasn't a clean-cut right or wrong. There were a couple of detailed responses (and good ones at that), and one that was simply referring to a part of the house but didn't say why and how the buckets were used. "E" Hettinger has won the IKEA coupon because she had guessed correctly the application of the buckets. Here are the details on the buckets:

The buckets (there were 35-40 buckets in all) were not used for the concrete patio at all. They were staged there since all the flooring on the first level (carpet and linoleum flooring) got ripped up.

As you can see from the photo, we had hardwood floors installed. Part of the hardwood was installed directly on the concrete slab as opposed to the wood subfloors in the raised living room. Since they could only glue the wood to the concrete (and not glue AND nail the planks as in the living room), the installers had to rely on clamps to hold the planks tight against each other and heavy weight to ensure a tight bond between plank and floor.

That's where the heavy buckets with water came into play.

Soo . . . the buckets were used as weights. And why water in trash bags? I guess so it made transporting them easier (no sloshed water on wood floors).

Great guesses!