How do I put this room back together?

[sjee6]

Hi, I bought this house in December 2022 and soon realised there was a damp and rot issue (didn't get a survey done, stupid I know). I began by getting quotes from various damp proofers and builders but they all wanted to charge me a fortune - £8000 to do the floor, £5000 to inject a new DPC and re-plaster. I work minimum wage so being able to afford these costs just wasn't an option, and none of them were addressing the real issue which was the source of the damp. So I decided to do It myself. These are some of the issues I discovered and why It looks like it does right now:

- the hearth was sitting on a bed of sand which was heavily saturated
- damp spots all over the walls from hydroscopic salts
- cavity wall had insulation which I've had extracted
- removed vestibule to improve sub floor air circulation (sub wall had no air bricks)
- poorly wrapped joists, some of them wrapped in plastic

I think that's It, the moisture is coming in through the air bricks when It rains. It's an old terrace and there's about 20 houses joined together and I'm right in the middle. The street is on a bit of a slope, so I guess It only takes one person to have an issue and the water will travel through all the houses. I'm hoping If I rake up the floor so It's smooth and there's no obstructions, the water will just travel straight through and not cause any damage.

Here's my plan for putting It back together:

- clean up and repoint the fireplace (I bought some brick acid, say's it's 30% hydrochloric acid, will that be enough? Lots of thick sutt on the wall)
- replaster external wall using lime and sand
- plasterboard the ceiling where I've removed the vestibule using screws and skim over it
- Install new joists by laying them on three sub walls with air-bricks and putting slate under the joists

I don't know about the utility box or what to do about the gap in the door, can I just fill it in with foam?
I also don't know how to finish the walls. I'd prefer the walls to be breathable but there's quite a bit of gypsum and there's some crinkly paint that's impossible to get off on one of the walls.
I'm really just looking for any observations, tips advice you can give me before I make a start because I'm a complete DIY novice and I've already made some mistakes like smashing up the hearth, I probably should've kept that.

 

[Koolpc]

Make sure u have plenty of airflow under the new floors. Insulate between the new joists.

 

[Ivor Windybottom]

Nothing wrong with not bothering with a survey, it would probably only have told you what you already knew and taken some of the money you needed to fix it. They don't usually find anything that's not obvious anyway.

Check the outside soil levels, ideally it needs to be about 150mm below the internal floor level. Also if there's any kind of paved surface then check its level to ensure it tips water away from the building. Rain doesn't normally enter air bricks.

We've had some heavy rain recently. Have you actually seen running water in the subfloor?

Ignore some of the internet knowall crackpots and conspiracy theorists - rising damp definitely exists! It looks like that's what you have. But you can DIY inject a treatment, it's pretty simple and you definitely don't need to pay £1000s to cowboys.

Brick acid will be more likely to remove the pointing than the soot.