Can concrete be poured over a river rock floor?

Answered by Jeffrey Anderson ~ March 4, 2013 ~ No Comments

We have a room that began as a patio outside. The floor is river rock and it has wood paneling on the walls. I have been looking at ways to cover the river rock and solve the dampness seeping in between the original house and the patio slab. We have sealed part of the crack with a cement product and it seems to work. I read that you can cover the whole floor with cement and bring it to the level with the house. Is this feasible? Will it help with the connection to the original house? If not, how do we go about beginning the remodeling project?

John L. -- FL

Jeffrey Anderson

John, this is one of those projects where it's almost impossible to give good advice without visiting the jobsite. Based on your description, I see two issues that could affect how you should proceed with this remodeling project: the difference in elevation between the patio and the rest of the house and the fact that there is already paneling on the perimeter walls.

If you pour concrete, any framing or other wood it comes into contact with should be pressure treated. Some localities accept installing a moisture barrier between the two materials in lieu of using treated wood. Considering how much rain Florida receives, I'm not sure if this would be an option in your area. It might be worth a call to your local building inspector if you decide that pouring concrete is the way to go. Removing the paneling and installing treated plywood to protect the existing framing could be fairly expensive and a lot of work.

The best solution may be installing sleepers or floor joists over the river rock and putting down a plywood subfloor. However, this might be difficult if the difference in elevation between the house's floor and the patio is only an inch or two. The sleepers should be treated, 2-inch material that would be supported by the river rock and attached with joist hangers at the perimeter walls. In order to use this system, the river rock and its base would need to be structurally sound. An engineer should inspect the existing patio floor prior to installing any sleepers.

If the difference in elevation is six inches or more, a better option might be installing a floor joist system that is tied into your perimeter walls. Depending on the size of the patio, you may need some support for the floor system in the center of the room as well. A joist system should allow a perfect match in elevation with your home's existing finished floor height.

Regardless of what system is used, a moisture barrier should be installed over the river rock before installing the new floor. I also recommend having an architect or engineer visit your home as they may have some other ideas on how to address the situation. It might cost you a little for their inspection, but could save you a lot of money in the long run.

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