My basement floor has control joints and some have opened up. Floor was poured 5 years ago and the cracks are stable now.

The worst section is 3/16ths wide.

What caulk should I use to seal this? I want something safe for indoor use.

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  • What is your purpose in wanting to caulk it?
    – FreeMan
    Jul 20, 2022 at 13:28
  • Primary purpose is to seal any soil gas coming up from imperfect vapor barrier install below the slab. We have a radon mitigation system as well. I have no idea how accurately that vapor barrier is fit… Jul 20, 2022 at 17:03
  • I would use polyurethane caulk. either the DAP or SILKA products, the waterproof one...
    – mark f
    Jul 21, 2022 at 15:08

1 Answer 1


I've used this stuff in many a basement or garage. It is designed to bond to the concrete, the color blends into undyed concrete, and it can be applied with a caulking gun (much easier than the squeezy tubes for doing long cracks).

You don't really have to worry about Radon infiltration if you already have a mitigation system, even if the vapor barrier isn't perfectly sealed. It's not under pressure or anything so that system of sub-slab pipes and vent stack already provides a path of least resistance for the gas to bypass you and escape to atmosphere. In high-Radon areas like where I used to live, builders install a fan to pull a slight vacuum as well.

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Note: this is not a specific product recommendation FWIW. Quite a few brands produce this type of sealer.

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