Drying a damp wall before replastering

[BoftheP]

The top back room of our victorian terrace has a damp wall, we think it's caused by the chimney so its scheduled to be knocked out. The wall underneath was partially tanked but the damp has seeped through any weaknesses, like the join between the celing and wall and any holes hammered in for pictures. We've hacked off all the plaster in this room and were due to have Insulated board put up straight away but I now think the wall is too wet to have an impermeable surface put on straight away.

So my question is, does it need to dry before I do anything?

[PigletJohn]

it's not a basement room, so where is the water coming from? You need to find the cause, and cure it. Covering it up is quite the wring thing to do.

Maybe an overflowing gutter or downpipe.

[BoftheP]

Most of the damp is upstairs but is coming down were the chimney breast used to be in the room below it. we hope removing the chimney entirely will stop the water coming in, but the wall will still be wet, won't it? We've hacked plaster off the walls right down to the brick upstairs ready for insulation board to go up a few days after the chimney is removed. I'm now thinking it would be best to let the wall dry first, get dehumidifier or something and wait a few months? It's a NE facing external wall so it rarely gets any sunlight, just gets wet and cold.

[PigletJohn]

is the chimney ventilated top and bottom? Are you planning to remove it from the top down and reinstate the roof over the hole? If you leave the top in place it will need steelwork to hold it up.

has anyone said that the flaunching or leadwork at the top of the chimney is letting rain in? Can you see poor pointing or cracked bricks (borrow binoculars)?

Is the damp staining brown, yellow or clear?

Does water come down in rainy weather?

[Procrastinatingpeacock]

Don't just assume it's the chimney. We have a very similar issue which we assumed was caused by the chimney, but is in fact due to the lead flashing along our valley gutter being completely shot. Maybe get a roofer up to take a look before doing anything? We have had the whole house replaatered (skimmed) and our plasterer was quite clear that there was no point doing that room until the wall has totally dried out. We have stripped it back to brick (the damp plaster can't just be skimmed over) and have the radiator on and the window open a little. May invest in a dehumidifier if that doesn't work.

[Procrastinatingpeacock]

Oh and obviously we have had to get the gutter fixed as well!

[BoftheP]

Chimney is coming down as I write. The entire back extension roof where this chimney breast is is being re felted and re tiled and GRP. We replaced all guttering last year with new industrial sized guttering which is on the opposite wall. Various builders and roofers have looked at the pointing and bricks on the outside and have confirmed that it's fine. I'm confidant that the problem will be fixed after this work is done but the question remains, will the wall still be damp? Is it wise to get the insulation board ( this includes adding some kind of impermeable membrane before the board goes up) up straight away?

[PigletJohn]

preferable to put a powerful fan blowing over the surface of the wall for (at least) a few weeks. This will evaporate the moisture off the surface, and ventilation will take the water vapour out of the house. It will be more effective than turning the heating up.

Or you could hire a builders dehumidifier, which is bigger and noisier than a domestic one (like a washing machine) and set it to blow at the wet wall. It will release some heat as a by-product.

Not covering up the wet patch will also enable you to monitor the wet patch and to confirm that it is drying out.

[BoftheP]

Thanks. Hadn't thought of using a fan.