Moisture coming thru concrete floor

23 Feb 2010
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United Kingdom
I've got a storeroom which is slowly getting growing mould on lots of stuff. It's got breeze block walls, plus a concrete floor and has zero air circulation.

From reading on the forum I figured the first thing I'll do is put in a ventilation fan to start air moving through the room, plus wipe the existing mould off with diluted bleach.

But I also noticed that the concrete floor in one corner in particular appears quite damp. There is a drain sump below it on the other side of the floor/wall which has water in it. The water level is usually 1.5 -> 2 feet below the concrete floor level.

Is it a worry to see dampness coming thru the concrete? Should it be waterproof, or is this expected for something so close to a drain?

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It will depend if a waterproof membrane was laid down before the concrete.....if there wasn't, moisture will surely wick through!
John :)
Your problem is condensation. You are best leaving it closed in and running a dehumidifier.
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I've left the door to the room open the last day and while it's a securiy risk, the wet patch on the floor has gone.

When is it better to use a dehumidifyer as opposed to a ventilation fan?
Your problem is condensation. You are best leaving it closed in and running a dehumidifier.

Awful, awful advice! How can you possibly know for sure it is condensation and why would it occur on the floor and not the walls/ceiling where condensation tends to appear as mold. And if it was condensation the solution is not to run a dehumidifier but ventilate the space!

To the OP just because the damp has disapeared does not automatically mean it was/is condensation, it just means that the damp is evaporating quicker than it is being absorbed by the slab.
The mould isn't really on the walls or ceiling, it's basically on stuff stored in room that has the capability to rot - cloth, cardboard, paper, even wood.

Nothing outside the room has mould. Outside being an underground garage, which has some ventilation via mesh garage door.

Since nothing outside the room gets mouldy, hopefully if I put some ventilation in to make the conditions similar in the room to outside the room, it should resolve itself.

Now I know water wicks thru concrete I'm not too concerned about it, especially as it disappears when there is air movement. Thanks again

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