Damp on bottom of wall?

stuart45

Get yourself a cheap surface thermometer is you want to be sure about condensation forming.

paperclap

I have considered gravel and/or French drains, yeah.

Just want to get this blasted skirting down!

Eldi_Dos

If room layout allows can you place bedhead against internal wall, that would allow better airflow on external wall.

ThisIsWeird

paperclap said:

1950s bungalow, made up of brick and mortar, cavity wall, with cavity insulation. No joists. Two air bricks on the other side (outside) of this wall.

Outside of this wall is a car port with a concrete ground.

No joists = solid floor? Which would make sense, as these air vents are seemingly above DPC layer, so more likely to be ventilating the cavity? And, good news, as you shouldn't have to worry about slowly-developing rot

The presence of a car port makes penetrating due to direct rain also very unlikely, tho' it can always come from above, say down the cavity, even from the sides. So I guess that leaves cond, or rising.

Rising is also not very likely there, and the breached DPC is only the outer wall skin, not the inner. There's a possibility of a breached cavity, as Stuart pointed out, but - against my initial thoughts - cond is looking more likely now.

Is one of these vents close to where you have the issue? If so, unscrew/prise off he cover and have a gander/feel inside?

paperclap

This is the only room layout I’m afraid!

Behind those air brick covers are clay (I think?) air bricks. Back when I put these covers on about 2 years ago, didn’t notice they were blocked. Siliconed around the top and side edges to attach them, leaving the bottom not siliconed, so as to let any water drain out if it does get there.

Given the mould on the floor and the underside of the mattress, I do feel this does point to condensation.

Before this bed was in here, before the laminate down, etc, etc, this entire room had lining paper (which couldn’t see any signs of peeling that I remember), solid wood skirtings (couldn’t see any mould), before the reroof… but there was no furniture against that wall. Literally nothing there.

ThisIsWeird

Can you keep the bed clear off that wall? Perhaps replace it with a 'frame' type, on legs with plenty of air circulation? 
You can still store stuff under it in baskets or whatevs, but allowing a good gap all around.

FIREmenow

If it has a cavity, modern bricks and modern sand/cement pointing then walls needing to breathe is less of an issue.

Was also wondering what your floors are if no joists. Is ground level in this room higher or lower than ground level outside and in your car port? What is the story with the grey cement-like stuff behind the skirting, is it just there or is the whole wall plastered with it?

Seems to be pointing to condensation. Is this your main bedroom or a spare? Making sure radiators are not totally off in winter, keeping door and window open regularly for ventilation (trickle vents?), thinking about what moisture you bring in there - breathing, drying washing on an airer etc. and how it can get out again should help. Pulling bed slightly off wall and having about a foot of space underneath clear of storage should help. 

But if you've had a mouldy mattress that suggests a very damp and cold room so maybe you need a dehumidifier, you can get them with a HEPA filter - so you aren't breathing that mould in.

If surface mould is going to be an ongoing thing to treat then I'd avoid Matt paint on the skirting boards as it won't be wipeable.