Concrete base (please help!)

[wrighty208]

Hi all,

Hope I have this in the correct forum.....I have water entering my sheds through the concrete and causing condensation.

I have a concrete base in my garden with 2 x 10'x8' metal sheds on. The base is approx 14' x 22' with the sheds at each end facing each other.

I have sealed both sheds on the inside with a weatherproof silicone sealant (http://www.screwfix.com/prods/62431/Sealants-Adhesives/Sealants/All-Weather-Sealants/Dow-Corning-791-Weatherproof-Silicone-Black)

The base was made approx 1 year ago and the top layer is about 2" thick of Sand and cement only.

Now, I have witnessed that when it rains, the water seems to be drawn into the concrete on the outside and drawn up into the sheds on the inside from the shed walls heading towards the centre depending how much rain there is.

I have made sure the silicone sealant is bonded to the metal of the shed and the concrete base so the water must be drawn through the concrete.

What can I do to prevent the water entering the sheds? I have given the concrete a couple coats of 'concrete sealer' from wickes but it still seems to enter a bit - I also have some garage paint but don't want to use it until I know it's safe too and won't get ruined by water coming up from underneath.

Any advise appreciated.

Thanks

 

[r896neo]

Your problem sounds like it is not neccessarily the concrete but its the 2 inches of mortar on top. Concrete is reasonably waterproof but sand and cement only i.e mortar is not.

Why is this 2 inches of mortar on there? if your sheds have a decent overhang and drip edge you could consider putting dpc under the bearers but that depends how the floor is made.

 

[wrighty208]

unfortunetely it's a metal shed without a base, the frame is bolted down to the concrete base.

The base has sand, cement, balast for most of the depth (about 4" approx) and the remaining approx 2" is sand/cement/water.

I think the problem is the top layer of sand/cement is absorbing the water so I need something to seal the base and make it waterproof/less porous?

 

[Deluks]

Anything else in there that might be giving off moisture?

It's a common problem with metal sheds, you really need to get the structure off of the concrete.

You might get away with painting a liquid damp proof membrane on the floor, then either putting down more concrete or 2x2 joists and ply or osb deck.

 

[wrighty208]

nothing else giving off moisture - I have emptied both sheds completely for the time being.

I was thinking about give the whole base (in and out) another coat of concrete sealer (from Wickes) and then giving it a paint with some garage paint on the inside. This should seal off the inside, I just hope the moisture isn't still drawn through ruining the paint!

The sheds are too big and awkward to raise on a wooden base I think.

 

[fastneattrowel]

Is it possible to spread out 3 x 8ft 100mm x 65mm plank lintels ie one on each end one in the middle and fix shed too those,then put some boarding on,must be like a swimming pool today if you had the rain what we had

 

[r896neo]

The mortar layer on top will just suck up water but i assume it is not in contact with soil? all exposed areas of the base not covered by the shed need a fall to discourage water from getting under there