I have a very unique and serious problem on my hands concerning the sump pump in my basement and I am very eager to hear of any suggestions or possible solution(s) as soon as possible. The problem I have is that basement wall waterproofing sealant/tar is coming in through the foundation drain pipe and into the sump pump basin and it causing the sump pump to keep malfunctioning.

A basement waterproofing company recently rebuilt a whole basement wall and half of another basement wall and then they waterproofed both of these walls. They finished the job about three weeks ago.

This problem with the sump pump started three days ago after it rained real hard here for several days. I heard the sump pump making a strange noise, and upon investigating it, I found that the black waterproofing sealant/tar was floating on top of the water. After studying what was happening, I found that the external sump pump float was stuck to the bottom of the water level sensor because it was was covered in waterproofing tar. After removing about a pound this black tar from the sides of the sump pump and from the float and the post it rides on, the sump pump functioned normally again.

It has been raining here a lot the past few days and after every heavy downpour, a steady stream of black waterproofing tar will come in with the water from the foundation drain pipe into the sump pump basin and it begins to collect on the surface of the water as the water rises. I've had to clean out the sump pump basin and clean off the sump pump & float at least 10 times over the past few days to keep it going. The last time I cleaned it, I think there was about 2 pounds worth of tar that I scraped out. I can't keep doing this. I'm afraid I'm going to get poisoned by the tar or pick up some bad disease from the water.

I talked to the basement wall contractor several times over the past few days and he thinks this is a very unusual situation but he is refusing to do anything about it because 'he stands behind the quality of his work' and he will not offer any solutions to stop this problem. His only suggestion was for me to get a sump pump that uses an internal float.

What I believe is happening, and the contractor strongly disagrees with this hypothesis, is that the waterproofing tar did not set/cure before they put the rocks and dirt back around the foundation, and so after every heavy rainfall, the hydro-static pressure of the water pushing against the basement wall is pushing the waterproofing tar off the basement wall and then gravity is pulling it down and into the foundation water pipe system.

I think I will probably end up suing this contractor to reimburse me for me hiring another basement contractor to dig up around the foundation again and to redo the basement wall waterproofing.

Yet, in the meantime, I need a workaround solution to stopping the waterproofing from coming into the sump pump basin. I am thinking that perhaps I can buy and pour some kind of chemical along the top of the the basement walls, which will then seep down along the walls and chemically mix with the waterproofing sealant so it will then get hard/cured. Any thoughts on this particular idea of mine?

So, how do you stop basement waterproofing sealant that is coming into the sump pump basin from the foundation drain pipe?

  • What product did they use when waterproofing/damp-proofing the basement? Was it water- or solvent-based, asphaltic or polymeric? May 18, 2020 at 4:04
  • 2
    I'm not an expert but I don't believe water proofing material should be water soluble. You'd better start a detailed file with dates, documents, samples of the material, pictures, etc.. May 18, 2020 at 4:44
  • @ThreePhaseEel, I'm not sure, I'll have to ask the contractor that question. I live in Ohio, is there a particular waterproofing sealant that should be used in this state based on the soil we have here and the amount of rain that this state usually gets each year?
    – user117409
    May 18, 2020 at 9:50
  • 2
    The very definition of NOT "standing behind the quality of his work."
    – Ecnerwal
    May 18, 2020 at 11:34
  • 2
    one bit of good news: the water is yucky, but it shouldn't have diseases in it to worry about. The tar shouldn't be very hazardous through casual dermal contact either.
    – dandavis
    May 18, 2020 at 12:44

1 Answer 1


I just called and spoke with the housing inspector who had been out here inspecting the contractor's work and he said that it's normal for some waterproofing material to make its way down into the foundation drainage system after a basement wall waterproofing job. He said that I will probably need to keep cleaning off the sump pump for another 2-3 weeks and then it will stop coming in and everything should be good after that. He said that he had spent many years as a new home construction plumber and that he often saw this issue happen whenever there was a long period of days with heavy rainfall right after a waterproofing job had been completed.


Update: I decided to buy heavy tarps from The Home Depot and I placed these outside along the length of the two basement walls that had been rebuilt. I did this to stop any fast moving torrents of water that were probably coming down off the siding and then flowing down along the basement walls stripping off the waterproofing tar and then depositing it down around the foundation drainage system. So far, there has not been any tar coming into the sump pump basin. I hope that the hot dry summer weather will now cure all the tar on the basement walls and I can then remove the tarps.

  • 1
    Wow. That seems unusual. Thanks for following up! It would be great if you would come update your answer in a couple of weeks to let us all know if the issue does clear up or if it continues. Of course, that may be rain dependent. If this does clear up, but then next spring's rains bring the problem back, you're more than welcome to update your answer next year with that additional info.
    – FreeMan
    May 18, 2020 at 13:29
  • 1
    I would also suggest talking with the inspector again to define what "some waterproofing material" is. You indicated you're taking pounds at a time out of the sump. Confirm with him that this is within what he considers "normal".
    – FreeMan
    May 18, 2020 at 13:58
  • @ FreeMan, that's a good idea. I will add an update to this thread in about two weeks.
    – user117409
    May 18, 2020 at 14:33

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