I have spotted a damp patch in the corner of my patio doors (pictures below). Things I have tried so far:

  • Reseal the door inside and out
  • patch up some mortar on the outside that was crumbling away
  • reduce humidity in the room to rule out condensation
  • Glued down some parts of the door that were loose

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There is a draft coming through when I pull the carpet back. And there is an air brick below the door on the outside

Any ideas appreciated

  • what's the height difference between the paving outside and the floor inside? what is the floor structure (concrete / wood )?
    – Jasen
    Dec 6, 2022 at 8:59
  • The height difference between the paving slap and the floor is 11 inches, the floor structure is concrete. and as you can see in the last picture there is a slight gap between the door and the start of the concrete floor and some kind of filler at the top, I assume holding the plastic door cover in place
    – User1
    Dec 6, 2022 at 10:13
  • 1
    It looks to me as if water is being forced around the edge of the door from outside. It likely was not installed properly. You could try some caulking on the outside and see if you can seal it up. Keep in mind that it may be entering the door frame higher up and coming in to the house at the bottom.
    – jwh20
    Dec 6, 2022 at 11:49
  • 2
    Further to @jwh20's comment, it would be reasonable to carefully scrape off all the caulking on the outside of the door then replace it all. It's difficult to patch caulking and do a good job of it, so remove/replace is a better option. Also, the cause of the damp patch is likely water, though it could be milk (to answer the actual question asked).
    – FreeMan
    Dec 6, 2022 at 13:43
  • 1
    Generally a defect in the flashing that's letting water in, but since there are no outside pictures, and it may not even show up in pictures, difficult to be sure. As a rule, look up, since water runs downhill. It could be coming in above this and running down the wall to this point. But the top of the doorframe itself is where I'd start looking.
    – Ecnerwal
    Dec 6, 2022 at 13:53


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