protecting the concrete base of a shed

by Jeanette
(France)

Hi, We have built a 3-meter x 3-meter concrete slab for our wooden shed which will be 2.98 meters x 2.98 meters at its base. The slab sits on a slight slope so the back two sides of the slab are lower than the ground height. We have plastic sheeting underneath the slab to protect it from the moisture in the earth underneath.

We have about 5 inches clearance between the slope and the concrete slab which we plan to fill with small stones to improve drainage around the slab.

Questions:

1. Should I paint the sides of the concrete slab and the shed which will be below ground level with bituminous paint before I pour the stones into the gap? (or) Should I place a piece of plastic vertically against the slab and shed before pouring the stones?

2. Would you recommend painting the surface of the concrete slab with some sort of 'basement' paint to give the interior of the shed a more protected finish?

Thanks for your help!

Jeanette

Shecman says:

Hi Jeanette,

Thanks for your question.

Firstly well done on having the plastic sheeting beneath the slab, this will act as a sort of damp proof membrane. It will help to restrict the amount of water from the ground that can pass through or be absorbed into the slab.

With regard to your questions:

1. I would try to ensure that no ground is in contact with the timber of the shed at all. If timber is in contact with the ground it will sooner or later initiate decay, due to the damp. If possible I would build a low retaining wall behind the shed so that there is a gap between the shed wall and the ground.

2. Secondly, I think that painting the slab is an excellent idea if you want to prevent the rough concrete surface ‘dusting up’.

Firstly you will need to seal the floor. You can do this with some proprietary brush/roller applied concrete floor sealant. Or you could use PVA which is commonly used in a watered down version to seal absorbent surfaces such as concrete to help with the adhesion of secondary coatings. PVA is commonly available at builders merchants but you should check that it is compatible with the paint system that you choose.

Once the floor is sealed then you can add the wearing surface of paint to match whatever colour you prefer. There are several brands that are available, you are best to go along to your local builders' merchant and chat it through with them to see what they stock.

Sounds like a great project

All the best

John