Can you pour concrete on dirt?

Question

My husband and I recently removed a plastic pond from our sunroom and want to fill in the hole where it was with concrete like the rest of the room.There is some dirt that was around the outside of the pond that we were going to shovel in the hole and then fill in the rest with cement but we have had someone tell us we need to remove the excess dirt before pouring the cement, others say just shovel the dirt in and level it off with cement... any advice?

Answer 1

The problem is what other answerers have brought up: the weight of the added concrete will compact the dirt, resulting in cracking around the edge of the added concrete, unless you properly reinforce the concrete patch.

The best way to do this would be to use a 1/2-inch masonry bit to drill a few holes into the sides of the existing concrete, insert a piece of rebar into each hole (about 2/3 the diameter of the hole), and tie them together with wire. Then you can pour the new concrete to fill in the hole. If you use something like ReadyCrete or QuickCrete, try adding about a cup of lime powder or Portland cement for each bag of concrete for added hardness.

You should also tamp down the dirt as much as you can to compact it before installing the rebar. And, the thickness of the added patch should be at least as thick as the existing concrete.

Answer 2

You need at least 4" of room for concrete. You can use the dirt but you have to compact it good with a hand tamper. You also want to clean the edge of the concrete on the existing hole and paint on some liquid bonding agent on the edges-let it dry before you pour the concrete in the hole.

Pour the new concrete so it's just a little higher than the existing. As the water leaves the new concrete it will cause the concrete to settle down about an 1/8". This is why you don't want to pour the new flush with the old - keep it up just a little bit and don't over work it with a trowel.

Pour it and float it in so it's fairly smooth. Let it set up for 30 - 45 minutes, then hit it again with a steel trowel. Let set for another 15-30 minutes until you see the water sheen leave the surface. One last pass with trowel and your done. This last pass is when you want it to be flush with the old.

Answer 3

Be sure the soil is compacted well, or your concrete will crack and subside.

Answer 4

Perhaps you should tamp the earth, lay screen reinforcement in the hole so that you will stabilize the earth and then do your pouring and leveling. What you do not want is for the new pouring to sink below the level of the present floor. You might ask some people who work with concrete the best way to do the job.

Answer 5

Compact the dirt, but more importantly, lay down plastic as a vapor shield, otherwise you will have a damp spot where moisture in the soil is wicked up through the concrete.  You might ask if this applies to a sunroom, but it certainly applies in my garage when it has be regularly wet outside (unlike right now where it has been over 100 for several weeks and about  0.01 rain.)

Answer 6

you can fill over the dirt as long as it is compacted very well and has no organic matter that will be in contact with the cement. you should also remember to leave enough room to have a full 4" of concrete throughout the area of the pour. and be sure to use re enforcing screen.(Lowe's or home depot for very low cost).

good luck, and remember not to skimp on the prep work.