Mystery Question: Wet Cement & a Locked Door Murder


Useless Carlon PVC Grey Conduit Cement

The cement is normally very useful but this can and another were useless. I had used two cans and left them out, tightly sealed. It had been a sunny day and then it rained that night. When I opened the first one up, which I had almost finished off the day before, I discovered it was nearly full of water! How bizarre. The cement was useless. How did the water get in there?

Then I opened the second can which I had just started on the evening before and it too was full of water on top of the cement that was in it! Totally Bizarre. Once is strange. Twice is obviously a conspiracy!

While I pondered this I went and got another can of PVC conduit cement from my private hardware store in the chiller. (Everyone needs a hardware store on-farm!) The can stored indoors out of the rain was fine. After much thinking I figured out what mechanism had probably put the water inside the tightly closed cans of PVC conduit cement. Can you figure it out?

I’ll give you some clues:

1) A can stored on its side outdoors had no water in it.

2) Three cans stored upright indoors in an open area (so same air flow as outdoors) had no water in them.


3) A can stored like this upside down outdoors would have no water in it.


4) Cans stored in window frames like this would have no water in them. I had two test subjects for this case.

5) Cans with a bent top such that the upper surface was at an angle had no water in them.

6) It had been a warm sunny day and then it cooled off in the evening.

7) It had rained gently most of the night.

8) All the cans were tightly screwed shut.

This is sort of like a locked door murder. Who dunnit?!? Or rather, what mechanism of physics is our culprit?

Leave your ideas of how the water got in and why as well in comments. I’ll leave a comment with my answer, which I’m pretty sure is right after having thought about this puzzle. Let’s see what we come up with…

Outdoors: 59°F/46°F Overcast
Tiny Cottage: 68°F/66°F

Interesting Names: Vladimir B. Brik in Wisconsin works in masonry

The Carlon brand PVC Grey Cement is my favorite and it in and of itself is not useless. I don’t mean to be disparaging of them or their product at all. The stuff works great, as long as it stays dry. This little mystery is not about cement but physics. The fact that it was Carlon brand had no impact on the mystery at hand.

About Walter Jeffries

Tinker, Tailor...
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12 Responses to Mystery Question: Wet Cement & a Locked Door Murder

  1. John Tucker says:

    When the cans cooled over night there was a partial vacuum created inside the cans that was enough of a pressure difference to pull water in through the screw threads?

  2. Servius says:

    The water falls on the lid builds up behind the rim and seals the bottom of the cap. Up till this point the air pressure inside the can and outside the can had been the same.

    Then the air pressure outside the can rises after the rain has passed as a normal event in the weather.

    Now there is greater pressure outside the can than inside the can and the water on the lid gets forced into the container until the water level on the top of the can has lowered to the point where the seal is broken.

  3. Jack says:

    The decrease in temperature caused a phase change inside the can creating a vacuum as the volitile compounds condensed. This vacuum pulled water, trapped in a puddle by the seam-sealed upper can edge, past the imperfect seal of the lid to the interior of the can.

  4. Jeff says:

    My guess is that :
    1-during the sunny warm day the contents of the can expanded forcing air out
    2-the lip of the can filled with rain water covering the bottom of the screw cap
    3-as the can cooled a vacuum was created sucking water from the lip of the can into the can spoiling the cement.

  5. David says:

    My guess would be that the water gathered on top in the ring and when the can cooled during the night it sucked it up through the metal to metal “seal” that the screw on lid has. Either through the screw on cap or through the metal seams where the can is put together on the top.

  6. Larry says:

    The heat of the day caused the contents of the can to expand and push air out, the rain pooled around the top of the can and then the cooling of the evening caused everything to contract in the can and since water now covered the lip of the lid, it sucked the water into the vacuum. With clean surfaces and a rubber seal between the metal lid and body of the can, it would have sealed like a canning jar taken from a hot water bath.

  7. Tim says:

    I believe I see solvent on the top of the can that had water in it. That would indicate that you set some get on the threads of the can while you were using it.
    The solvent is flammable. Left in the sun the pressure within the can would rise to the point that it would escape the can around the solvent between the can and cap.
    The rain cooled the can reducing the pressure until it became a vacuum.
    The rim on the outer edge of the can looks higher than the bottom of the cap. that would hold the water that was drawn into the can.

  8. marc says:

    The warm day caused the gases above the cement to expand, then at night when the can was cooled off be the rain, the gases contracted, creating a vacuum, drawing in the water, something that could only happen if the lid was upright, able to retain water.Whereas the can on its side did not retain water, so it couldn’t draw the water in. Thus saving the can.

  9. Jessie N says:

    Fun mystery Walter! Here’s my guess. The temperature change from warm day to cool night caused the metal to contract as it cooled. Apparently the cap is a different gauge or type of metal because it contracted less than can’s threading. This caused the screw cap to no longer be tightly sealed, which allowed water into the cans left out under open sky. When the cans are checked the next day the temperature has once again increased, so the metal will expand back to the original dimensions and the caps will once again be tightly screwed shut.

  10. Jody Burgess (elnini) says:

    My guess is that the recessed top filled with water, covering the bottom of the screw cap. As the temp dropped the pressure inside the can did too, sucking water in under the cap.

    Cheers :-)

  11. Woody says:

    I would say that a vacuum was created by the glue cooling over night and the steady rain kept the top of the can supplied with enough water to hold the seal until the pressure was equalized.

    • Yes! And we have a winner, actually lots of winners, everyone was right but Woody got the last detail: the steady rain kept the top of the can supplied with enough water to hold the seal until the pressure was equalized. This key detail is what filled the cans with water. The top of the can didn’t contain enough water to fill the cans but with the sky constantly adding a little while the pressure differential sucked water in until the cans were nearly full and the pressure was equalized.

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