Roofing Question

Drip marks on bathroom ceiling - not condensation - please help?

Hi, we have the top flat in a modern block with a flat roof. For the last several months we constantly get drip marks in the centre of the bathroom ceiling (& centre of dining room ceiling). The flat roof was felted last year and looks perfect. There is some rockwool in the void roof space. There are mushroom vertical vents sticking out of the flat roof. Eventually, black mould keeps coming back every month so needs repainting regularly. Surely it can't be condensation from using the shower/cooker as the flat has been vacant for the last 2 weeks!? Has anyone come across this before? Very puzzling as the roofer said his felt is guaranteed 20 years and it does honestly look water-tight? Many thanks in advance.

Yes Timothy, we're cleaning black mould/stains off using HG mould-spray and then using stainblock spray then emulsion?

We're using Everbuild stainblock spray. Is that what professionals like yourself ever use?

I attach a photo link
Access to drill a hole for ventilation on the side wall would be difficult as it's the 3rd floor, so would drilling a hole in the flat roof and creating a mushroom vent for the loft-space solve this dampness in the loft-space?

2 Answers

Best Answer

sounds like condensation caused by lack of ventilation in the roof.
without looking at the issue its impossible to say what the best solution maybe, but cutting 1 hole in the flat roof will not solve the issue the flat roof need through ventilation properly done to prevent the build up of condensation.

Answered 8th Mar 2018

ADR Property Maintenance

Member since 1 Mar 2009

Hi. Seems likely to be condensation.
Are you cleaning the black mould off and repainting with emulsion?
If so, the spores will regrow more black mould indefinitely.
After cleaning you should block the spore/mould stains. I use 2 coats of zinsser b.i.n to do this. Then it can be painted over with any paint, but you should consider an anti-mould paint. The best of which is zinsser permawhite
Which stainblock? I use zinsser b.i.n because it does prevent spore re-growth ( having shellac as an ingredient)
No i havent used everbuild stain-block. I stick to zinsser b.i.n for the reasons ive given

Answered 8th Mar 2018

Timothy David Interiors

Member since 24 Jul 2017

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