This is the plan that came with the quote for the work by a contractor. The parts in green are where a polypropylene membrane will be attached to the wall. The parts in red are where a chemical damp proof cream will be injected. The text is my comment about joining membraned wall with not membraned wall.

I wasn’t happy with this because the walls with the membrane are attached to walls without the membrane, meaning that moisture behind the membrane could escape through the attached wall.

I decided to do the job my self and make sure the entire middle wall was completely covered in membrane. So bought a SDS drill and some damp proof cream and a polypropylene membrane kit.

Before starting the work, here are some pictures of the damp in the walls, which is effecting the plaster and skirting boards.

As you can see, the situation is not great. But also not really bad.

Having removed the radiator it became apparent that the vent had been blocked up with expanding foam. I removed this and tested the flue with some smoke pelts. It became clear that this chimney had not been capped, and had been collecting rainwater for about 20 years! In hindsight I probably could have unblocked this and left it to dry out without doing any more work. But I was already committed, so I decided to continue as planned.

Next came the plaster removal. I decided that since the membrane kit came as a roll 1.5m high and 20m long I would chisel the plaster off to a height of 1.5m. This and the disposal of the waste was much harder than I expected. I estimate about 1 or 2 tons of waste were generated. Fortunately I was able to dump this at the bottom of the garden where nature would reclaim it eventually.

I worked behind some polythene sheets to try to contain the majority of the dust. This worked to some extent, but dust still managed to work its way into every corner of the house. It was really hard work, even with the power drill. This took about 2 days. One of the days I forgot to wear gloves, and my hand felt numb from the vibration for about 1 week afterwards.

I then spent about 1/2 day chiselling out the bricked up fire place. It was really damp in there so I’m fairly confident this was the root cause of the damp problem.

Having cleaned up, and fixed up the chimney breast rendering, these are the bare walls to be damp proofed. I added a new concrete lintel in line with the original fire place design, but decide not to change this just now as I was pushed for time. I may revisit this some time enlarging the fire place to the height and width of the new lintel. Care was taken to keep the brick work in place by adding a steel strap. I should have used acros, but they didn’t have any for rent at the DIY shop.

Next came the attachment of the membrane. This was the fun part 🙂 It was quite difficult to get it tight around the corners, also since the walls are not perfectly straight, the tension was different up and down the wall. I added about 2x the number of plugs as shown here, with mastic sealant to make water tight. I also added the damp proof cream at the base.

Next the plastering. About 2 tons of sand + cement + water proofer as the base layer. If id know better i’d have hired a cement mixer for this. I used a drill whisk attachment and could mix about 1 sqm at a time. I spent a lot of time mixing. In the end I removed the plug socket on the right. This was the first wall section I did, and I forgot to put the wires and shielding behind the membrane.

After some finishing coats of plaster (by a pro, not me…), and decorating here is the finished product. As you can see, the kitchen fire place now vented, and the radiator has been moved to a different wall to a) stop all the heat going up the vent, and b) preventing holes being dried into the membrane.

Happy days 🙂

In hindsight I’m about 50/50 as to whether I should have let contractors do this. None of them spotted the blocked vent, or considered this as a possibility during their inspection, and I doubt they would have spent 1/2 day chiselling the bricked up fireplace out. Chiselling out the fireplace was really hard work, but worth it as so much damp soot came out. Overall a success. Probably paid about the same in the end, but I fixed the root cause, so probably have a better result.

Hi /r/DIY.