Help with crumbling plaster

hev_2

First, please be kind - I know that I should have seen to this ages ago, and I am really rubbish at anything DIY, so please be tolerant if what I am asking sounds a bit obvious.

I live in a terrace with my kitchen in the cellar. When we moved in over ten years ago there was no problem with damp. The damp has been getting worse.

Trying to keep it short and include relevant info:

Next door's washing machine waste water previously did not come out of a pipe but through brick work into the shared sunk drain. I paid to have that fixed. Drain will occasionally back up and now does not flood the kitchen because I have had the drain repointed but previously kitchen was regularly flooded. Once fixed I waited for the kitchen/dining area in cellar to dry out and it didn't.

Pestered my local water board to check the drains and they did, cleared a huge blockage in sewer outside in street, I waited for kitchen/dining area to dry out and it didn't.

At the bottom of the steps down to the kitchen the plaster is damp, coming off the walls and there seems to be some white furry stuff coming out between the bricks. On one side of the house there is wallpaper coming off the wall and that is the side against the neighbours with a hole in the roof (and the landlord won't fix it!). They are lovely neighbours, they rent, we own.

Finally get to the question. I need to ask a professional to have a look as I have no idea where to start. But who do I ask? Surveyor, builder or should I ask our insurance (if it is a problem from next door?) It is probably obvious what needs doing to you lovely people, but I do not know where to start! Any pointers about who to start calling would be appreciated. Next door's landlord will not be co-operative.

Many thanks

Hev

home_alone

Start with your insurance as it may become expensive to fix.

gary

hev_2

I should add, I have a dehumidifier that is supposed to be able to empty 14 litres out of the air per day and I empty the tank twice a day so I think it is running at capacity

home_alone

After the insurance see a builder.

gary