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Remove Drylock before rigid foam?

metsfan978 | Posted in General Questions on

I’m finishing part of my basement and will be using rigid foam to insulate the block foundation wall.  The basement never feels humid and never had a musty smell, but twice in 10 years we’ve had some water weep through the walls.  The previous owner dealt with water issues by using something like Drylok (it’s a yellowish/off white color) on the walls, which was done at least 20 years ago.  I repaired the storm drains (old Orangeburg pipe is gone and storm water makes it to the street again) and have an interior french drain going in soon.  They’ll also drill weep holes into the bottom block to keep the voids in the block from filling with water.  That should limit the water against the foundation and give it a place to go if it comes in.

My plan is to put a dimple membrane on the wall to allow any water that weeps through to run down into the drain and then rigid foam over that. The existing Drylok is a good shape other than a few areas where it’s flaked off. Is there any issue covering the wall as is, or should I try to strip the old coating off?  When I’m done the wall will be covered with XPS, and I’m not sure if the existing Drylok will cause any issues once the wall is sealed with rigid foam.  Bare block and XPS aren’t surfaces mold can grow on, but I’m not sure about whatever this old coating is.  Once the foam is up the wall won’t be able to dry to inside as easily as it can now.  I’m in climate zone 5a

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  1. Expert Member
    Zephyr7 | | #1

    I see no reason to remove the drylok coating. Even if you try, drylok penetrates the block by design, so it's almost impossible to completely remove it. I would just put up your dimple mat and insulation and call it good. If you have any water leaking in, it will self-remove the drylok for you anyway, and the dimple mat will provide a drainage path so you shouldn't have any problems.


    1. metsfan978 | | #2

      Yes, I know how hard it is to remove. About half my basement is staying unfinished and I recoated those walls. White looks better and the old Drylok was peeling a lot more in that section. The french drain is going around there too, so the fresh coat was for aesthetics and not moisture. A big grinder and wire wheel made short work of the peeling sections, but any place it was well applied barely came off. I'd probably need to grind the wall down to expose bare block again.

      Covering the wall up as is will save a lot of work, but if I had to do anything it's a lot easier to do it now than later.

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