Salt retardant backing if dry lining?

[AlexO]

Hi sorry to jump straight into a question post and being new to the forum. I am usually able to sort sort DIY stuff my self so never needed to join a forum.

Our new property (1920 solid brick partial concrete and partially suspended wood floor) came with a damp survey and recommendations were a chemical dpc. Removal of plaster upto 1m and a salt retardant backing plaster added. Lower external ground level and 4 more air bricks.

My question is we were planning on dry lining(because the house is cold) possibly with kingspan insulation between steel studwork. Do you need to use a salt retardant backing over the exposed brick work upto the 1m previously removed? por would you just remove all the plaster back to the brick work to ceiling height and then stud, insulate and board then skim. Another thing do I need to add a vapour barrier?. I don't want to end up trapping moisture behind the stud wall.

I know ultimately that external insulation and rendering would be best but that works out quite expensive and I don't know how good I would be at rendering an external wall with how large a surface that would be having only plastered a handful of walls and ceilings.

 

[endecotp]

Lower external ground level and 4 more air bricks.

do that first and see if the damp problem goes away. If so, no need to worry about anything else.

 

[Doggit]

Once you've done the DPC, you need to let the wall dry out. And you need to replaster with either a salt retardant plaster, or cement with a waterproofer in it, using washed sand thhat won't attract moisture from the air. Now the wall would normally take about 6 months to a year to dry out, but you want to put insulation on the inside, so the danger is that it would condense onto the back of the insulation.

I'd hack the plaster off, inject a silicone dpc, and then put a dehumidifier in the room to try and draw as much moisture out. And I don't think I'd do the insulation till I new the damp had been completely cured, otherwise you're storing up problems for yourself. You could paint the wall with Safeguard Drybase after the plaster has been removed, and then install the insulation, and use stainless steel screws to fix the bars on, but you stil wouldn't know if the jobs been done properly.

The EWI would have similar issues, and would cost more, but would be a much better job. With internal insulation the outside of the house gets cold, and the inside gets smaller, and you have to have the heating on all day. With external insulation, the house stays warmer all day, and requires less heating to keep it warm.

It's fairly straightforward to put up the Insulation externally, but needs a bit more practice to do the base layer, but the final coats easy.

 

[AlexO]

Thanks for your replies. I like the sound of both. Crack on with making it dry first then. It was recommended to leave it upto 9 months for drying out from the damp survey. Will need to invest in a decent dehumidifier too. Cheers guys