Dark mould on oak veneer skirting

Discussion in 'Builders' Talk' started by pcoul, Nov 9, 2019.

  1. pcoul

    pcoul New Member

    I renovated my house 3 years back, replacing all skirting and door frames to oak veneer skirting.

    The skirting is damp proof and varnished front and back before going on the walls. The problem is that black mould seems to grow in the skirting (I have cut through some and it’s the whole way through the board).

    For the past couple of years we have replaced several boards and the same thing happens again after a few months (see photos attached)

    I can be almost sure I have no leaks, and when you take the board off there are no signs of damp whatsoever on the wall, in fact the damp reading shows nothing either. I also used the same varnish on a test piece of board which I didn’t fit, just to be sure the varnish wasn’t causing issues, but it shows no black marks at all.

    This happens mostly on internal walls. Would rising damp do this and show no other signs? What would my best steps of action be now?

    Thanks in advance!

    Attached Files:

  2. Astramax

    Astramax Super Member

    Had you sealed the edge that fits on the floor.
  3. Astramax

    Astramax Super Member

    Are the floors washed with water.
  4. frosty82

    frosty82 Active Member

    As Astamax has said and I wonder if you clean with a steam mop?
    Astramax likes this.
  5. KIAB

    KIAB Super Member

    It the tannin in the oak.
    Your didn't used steel wool on skirting before varnishing?

    And how did you fix skirting to wall, if steel screws then they will react to the tannin.
    Last edited: Nov 9, 2019
  6. pcoul

    pcoul New Member

    The side that fits to floor has been sealed, with a couple of coats of varnish, and no steel wool has been used, just sand paper if at all.

    As for mopping, we stay well away from the skirting to avoid this. In fact, this is happening in areas that are carpeted as well!

    If we had rising damp should I not at least expect to see something on the plaster when the skirting is taken off?
  7. pcoul

    pcoul New Member

    Nails have been mostly used, but a couple of boards were fitted with siliconed on. Same thing happens there.
  8. KIAB

    KIAB Super Member

    Well they will be ferrous like steel screws.
  9. frosty82

    frosty82 Active Member

    Maybe the boards still had a degree of moisture in them. When varnished on all sides and edges, this would trap any remaining moisture within them.
    Maybe try replacing a damaged board and just using an oil that will protect but allow the wood to breathe and see what happens in a month or so. As long as you don't slap too much on and soak the veneer, it shouldn't delaminate it.
  10. collectors

    collectors Member

    That is definitely damp or water getting on the oak. I got the same with my windowsills that i fitted with oak & thought i had sealed them with 3 coats of varnish "Wrong" Black stains started to appear & ended up having to painting them white gloss.
    Astramax likes this.
  11. Astramax

    Astramax Super Member

    Rarely use varnish these days ...........since I found Osmo products! :)
    frosty82 and KIAB like this.
  12. pcoul

    pcoul New Member

    Unfortunately it’s got to the stage I think that painting them white might be the only option. Was just worried that eventually it would show on the paint , or bubble..
  13. KIAB

    KIAB Super Member

    Old fashion varnish, far superior products available now.:)

  14. Nails have not caused the staining/discolouring you have.
  15. Astramax

    Astramax Super Member

    May be able to remove the stains using Oxylic acid (Wood Bleach) look for a Liberon stockist such as Brewers. Used it a few times now on so called Mahogany front doors that go black in places after weather exposure.

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