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I have moisture under patio blocks laid over concrete. What can I do?

YGDbRu3MJQ | Posted in General Questions on

We bought a home that has a beautiful pool area with patio pavers all the way around. There is an area that retains moisture I couldn’t understand. I looked at the original lot map, the house had a concrete patio that looks to be the same size of the moisture issue. I believe they laid the pavers over the concrete and that area retains moisture. is there anything that I can to correct this or prevent moisture?

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  1. GBA Editor
    Martin Holladay | | #1

    What is the evidence of a problem? Do you have puddles, or just pavers that stay damp (even though adjacent pavers are dry)?

    If you have puddles, then there is a low spot that isn't draining properly. To fix such a low spot, the pavers would need to be removed and reset at the proper height to drain.

    If the pavers are always damp (but there is no puddle), you need to improve the drainage under the pavers. To do that, remove the damp pavers and examine the substrate. If the pavers are installed over a slab, the slab might need to be demolished. Improving the drainage below the pavers might require the installation of a layer of crushed stone and possibly a section of perforated drainage pipe that extends downhill to daylight.

  2. YGDbRu3MJQ | | #2

    Martin, thank you! You have confirmed what I suspected. No pooling, just the perfect outline of the old concrete patio. I have been hme for 2 days, (stationed in Saudi), saw mildew on some tiles. Everyone insisted it was becasue there was no sun, however it was too perfect an outline. That's when I found the plot plan and the old concrete patio was on it. No other drying problems anywhere, well....guess I have a project to work while my husband is still in Saudi! Good thing its warm in Florida! Thank you again very much for your time and knowledge,

  3. user-946029 | | #3

    Is the moisture currently causing a problem? Do you live in an area where freezing is a regular concern?

  4. YGDbRu3MJQ | | #4

    I am in Florida, and the moisture is growing mildew. It just won't dry out, all the way to the house. I know over time there is potential for rot. Possibility of freezing is slim, but could happen. The pavers stay damp and very cold to the touch, concerned after 4 years rebuilding in New Orleans at the potential mold and mildew have for causing problems, seen and unseen. I have dogs and grandchildren who spend time outside. I did power wash all of it and then bleach and water. It looks great but 4 days later completely wet.
    Did I give you enough info?

  5. user-946029 | | #5

    Yes, thanks Paula.

    If it were me, I'd first remove the pavers to see if they are helping to trap the water. If there's a low spot in the concrete underneath, such that the pavers have no effect on the water's presence, then removal of the slab may be in order. That would be unfortunate, because as I read it, it sounds like that is the original pool deck.

    One alternative you may have is installing a drain in the existing slab at the lowest point. Then, as Martin suggested, the drain would lead "downhill to daylight."

    Before taking any major action, it might not hurt to speak to two different concrete contractors. The Florida Concrete & Products Association (; 407.895.9333) would be a good first call to see who is doing such work in your area. Talk to Matt, and tell him I sent you.

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