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Annoying dampness in cellar


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Bit of history to this but converted an old inspection pit in a garage into a wine cellar during a conversion. Before it started, the pit was bone dry and dusty even in winter, and is just constructed of hollow 6” blocks with no infil.


A concrete lid was cast over the top, and an access left and the insulation and UFH in concrete over that, so probably 200-220mm of solid structure over a box that is 1m x 2.2m x 1.4m deep.


During fit out noticed that there was some water (gets 1-2mm max in one corner and condensation on the bottom row of blocks) in the bottom of the cellar and decided to tank using one of the cement based compounds and then add a layer of self levelling and standard floor paint. Walls are done with masonry paint, and yet we are still getting moisture forming on the bottom layer of blocks and also on the floor.


Its not from an external water leak, and it’s definitely not from the UFH, and it’s not that much although if you run a dehumidifier down there it will pull water out which I think is just down to if moving through the concrete and the cement joints in the blocks. 

The trapdoor is pretty airtight and there is no real place for the air to go anyway so don’t think it’s due to humid air getting in or a real difference in air temperatures as it barely changes if the trapdoor is open or closed.


Its now annoying as it’s stopping the final bit of what should be a quirky addition and it becoming a wine cellar !!! 

Given there seems to be little or no hydrostatic pressure, I’m considering parging the blockwork with a 3:1 sand cement and SBR slurry and then using one of the bitumen based sheet products as the cement based waterproofing seems pretty crap. I’ll need to then line it with something such as MR board but can’t think of any other way and it’s now starting to annoy me that I can’t work out what the cause is..!!


I did consider the “insulating / condensation paints” but I am suspect as to whether they actually work…! I am wondering if it’s because the floor is a glossy finish and just putting a layer of thin foam and some of those garage floor tiles down may help, but that won’t help with the bottom of the walls. 

Anyone got any ideas …?

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34 minutes ago, dpmiller said:

a wee circulating fan? PIV?

+1 to this idea provided the arrival rate from whereever is low. I had a similar issue in my underground workshop, tanked on the outside, and just running a 7w fan for the cheap rate period every night keeps it bone dry. 


I thought could be tiny amounts  of condensation given the workshop walls are at a constant temperature it only takes a slug of air and the dew point to create damp. If, in your case, the lining cannot absorb it its going to creep down and have a party in the lowest corner.

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Was thinking a fan - PC type thing - as got a duct into it so can feed in a cable.

Did look at how the spiral cellars do it and only issue is getting a vent to the outside wall which is over 8ft away ….!!! If I’d known this could be an issue I would have put ventilation in ..!


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