Mouldy cold water storage tank lid

Discussion in 'Plumbers' Talk' started by jonesr91, Mar 18, 2019.

  1. jonesr91

    jonesr91 New Member

    Hi there,

    Im a DIY'er and after a bit of advice.

    The lid for my cold water storage tank in the loft fell into the water a couple of months ago. When i inspected it, I found that it wasn't the original plastic lid, but instead a very thin circular DIY lid, which wasn't very well cut to shape.

    I looked into buying a new circular plastic lid but found that my tank has warped so much that only a lid that is far too big would cover it, but wouldn't fit through my loft hatch. Its likely the same plastic circular tank that was installed when the house was built in '71.

    So, I did my own DIY job. Using 6mm plywood, I cut a circular lid and glued Celotex to the top to give it some insulation. I also gave it 3 coats of varnish to keep the moisture out.

    A few weeks later, after checking up on it, I found that the underside was covered in mould. Some black, some white and very furry.

    I cleaned the lid with bleach, let it dry, then added 2 more coats of varnish - I was sure that as long as moisture wouldn't get into the wood, it wouldn't go mouldy.
    A few weeks later again, I found it was covered in mould again!

    I cleaned with bleach again, let it dry and this time covered the underside of the lid with 2 coasts of black bituminous paint - Usually used for roofing to keep the moisture out.

    But sadly again, its totally mouldy.

    What are my options?
    Do I need to bite the bullet and get a new cold water storage tank with a fitted lid?
    Are there any other solutions to avoid a new tank+lid?

    Thanks in advance,
  2. KIAB

    KIAB Super Member

  3. Heat

    Heat Screwfix Select

    Also better that you had used heavy polythene sheet (heavy dpc) to wrap the ply lid with and joint in on the top using tape so to avoid damp effecting the joints or getting through them.
    Also fit a vent as said.
    Or get the tank replaced with a new tank and matching lid and bylaw kit.
    1971 is old for any tank.
    Must say round cold water storage tanks are by far the best and strongest tanks
  4. xednim

    xednim Active Member

    Heat likes this.
  5. gas monkey

    gas monkey Well-Known Member

    if you tank has miss shapend put a strop around it and pull it back into shap now old lid will fit no need for new tank jobs a gooden
  6. Heat

    Heat Screwfix Select

    Great idea about the “dent” and all tank lids should have been designed with that. Unfortunately most of the designers haven’t a clue
  7. Heat

    Heat Screwfix Select

    The round tanks misshape (go oval) due to the wooden bases being uneven, or not level.
  8. gas monkey

    gas monkey Well-Known Member

    thanks for the tip
    Heat likes this.
  9. Heat

    Heat Screwfix Select

    You probably knew that anyway.
    I always remember seeing a round tank that was oval shaped, which I discovered was due to the raised base having no middle support below the plywood
  10. gas monkey

    gas monkey Well-Known Member

    just keeping it light
  11. jonesr91

    jonesr91 New Member

    Thanks for all of the suggestions - There's some real good stuff here which I hadn't even considered.
    I'll give them a go, one by one, until the problem is sorted.

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