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Internal Drain Cover or Condensation Cause of Rising Damp in Bungalow?

Postby silverfx » Tue Feb 09, 2016 10:46 pm

After moving into his retirement bungalow, my father discovered mould in an extension bedroom, and threw out the underlay and carpet which was going to be replaced anyway. Applied antifungal wash to the concrete floor. The plaster was mouldy above the skirting board for about two feet upwards, so I took hammer and chisel to it for him and chipped off the skim coat plaster about 5mm deep.

Applied anti-fungal wash to the plaster but yet to skim it (been told that an anti-fungal plaster should be used?). That was several months ago and no mould has returned, so will be skimming soon :-)

We think the cause was condensation rather than rising or penetrating damp; just a cold room where previous occupants may have dried clothes etc. However, taking up the carpet revealed an internal drain cover, fitted by a previous owner, where two out of four corner screws have corroded and gone greenish.

Question: Is the screw corrosion due to the damp underlay and carpet from condensation, or due to damp rising up from the drain below either around the screw holes or the cover seal?

Hoping it's not rising damp, but prepared to replace the cover with a new double sealed one if necessary, or as a cheaper fix, apply silicone around the existing screws and all around the cover seal if that made it rising-damp tight.

Any ideas much appreciated.
screw 2.jpg
Less corroded screw
screw 1.jpg
Most corroded screw
internal drain cover.jpg
Internal drain cover, iron hooks near corner screws
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Simply Build It

Postby thedoctor » Fri Feb 12, 2016 2:10 pm

If all walls were affected its very unlikely to be rising damp and almost certainly condensation. Check for an old leak to a radiator for cause of floor damp on screws to manhole cover. This could alse be caused by heavy condensation seeping into carpet although in both cases a lack of a damp proof membrane under the floor slab cannot be ruled out until properly investigated. The damp returning to the walls in a properly ventilated ròom will be a sign that its damp rather than condensation.

Take a look at our main website where we have many project pages on all forms of damp and a very comprehensive page on condensation.
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