How to damp proof a brick shed – Real life case study

In this article we will be looking at how to damp proof a brick shed. This is based on a real life case study, where I personally converted a brick shed into a small outdoor office.

how to damp proof a brick shed

The shed originally contained an outdoor toilet, and a bin store. It was also suffering from a small amount of penetrating damp. This was mainly coming through one of the external walls and the roof needed a tiny bit of patching.

Ripping out and cleaning the shed

the first job was to remove the toilet, and the non-load bearing wall between the toilet and the bin store. This was a small job and only took an afternoon. The toilet was out of use and I had a plumber disconnect the system and cap it off.

Once this was completed, we removed the toilet and the system from the wall. I then preceded to remove the wall that was dividing the brick shed into two sections.

When I had removed all the rubble and completely cleaned all the internal surfaces. I proceeded to fill in the hole Where the toilet had been removed.

I achieved this by tightly packing the u-bend with toilet paper. This was around 2 foot below ground level. once sufficiently packed I filled behind the paper with expanding foam. This completely blocked the pipe off.

The logic behind this, was the toilet paper served as a plug, to stop the foam getting down the pipe. Essentially, if the toilet paper were washed away later, it would cause no issues in the drains. Once the foam had fully expanded and set, I was confident this would not move. Therefore, it would cause no drainage issues.

Once the foam had completely expanded and set, it reached above the floor level. I dug this out again two around 6 inches below. Then proceeded to fill this with cement, completely sealing off the waste pipe.

Identify and fix any existing penetrating damp

My next job was to identify any existing damp. This is damp proofing 101. If you want to completely stop damp, you first need to resolve any existing issues.

The shed itself was not that damp. There was a small amount of penetrating damp coming through one wall and there had been a small issue with the roof.

Thankfully, the roof issue had previously been fixed by my neighbour. His brick shed joins onto mine. There had been a small issue where the felt for my roof joined his.

This had been patched up and sealed the previous month. To do this, he had cut away a strip of the felt. Next, he added a new strip overlapping the previous joint and sealed it with blackjack liquid DPM. This proved to be extremely effective, it completely addressed the small amount of damp that was penetrating the top corner of the ceiling.

If you need a DIY solution to completely damp proof your entire flat roof. You can see a good video guide below.

The next job was to stop the penetrating damp that was coming through the wall. This was being caused by some old pointing. To address this, I scraped out the old pointing and repointed the effected wall.

Luckily, the pointing was only an issue on one side. Also, the top half of the external walls was pebble dashed. Thankfully, this was in good condition and needed no repairs.

If you need a tutorial to help you with repointing, you can see another good video below:

If pointing is not the issue, you can learn more about identifying and fixing other penetrating damp issues here

Is rising damp an issue in your shed?

Thankfully when damp proofing my brick shed. Rising damp was not an issue. However, I did take precautions to avoid this becoming an issue in the future.

In my case I used a tanking slurry. I applied this to the floor in two coats.

As the brick shed was set on a concrete slab. I probably would have done the same thing if there was rising damp.

With that said, there are various options when you are damp proofing a concrete floor. You can see a few more examples for damp proofing a concrete floor here

Choosing a damp proof membrane

As I mentioned previously, I used a tanking slurry for the floor. I decided I would also use this to tank the walls and I even added it to the ceiling.

At the time I was considering two different options for tanking my shed. The first option was to use a plastic membrane, the second was to use a tanking slurry.

In the end I decided to go with the tanking slurry. I think either solution would have offered a very similar affect. The only real reason I chose a tanking slurry was the ease of application.

To apply the tanking slurry, you simply need to mix and paint directly onto the walls. It requires two coats and the first was dry in a couple of hours. So, I managed to get both coats added in one day.

To read more about the tanking slurry I used, and the process involved, you can read the full tanking slurry guide here

Choosing a finish for internal walls

If you decide to go down the same route I did, and use a tanking slurry, there are several ways you can finish the walls.

The finish you go for will depend on the final use of your shed. If it is just going to be used for storage, then you may leave the tanking slurry as your final finish. or perhaps you will paint the tanking slurry.

You can use any water based paint over tanking slurry. This could be a standard emulsion, or if you wanted even more protection you could opt for a masonry paint.

If like me, your shed will be used as a functional room (in my case an office) Then you may be looking for a higher quality finish.

If this is the case, then you may consider boarding and plastering. Again, this can be achieved in a variety of ways. The most popular options can be seen below:

  • dot dab directly onto your tanking slurry. This can be done, although it may not be the best solution. However, we do have a full article you can read on dot dabbing over tanking slurry here

  • batten the walls and fix boards directly to the timber battens. This is another great option and can be very effective, particularly if the walls you are fixing to are straight and plumb.

  • Build an internal stud wall. This was the option I chose, as I thought it would give the best protection against condensation. This was because, I could insulate the studwork, and avoid dew points that may have existed on the existing brick walls. I could also create a small cavity for extra air circulation

Insulating and avoiding condensation

The disadvantage of choosing an internal stud wall, is that it takes up more space. Because of this, I opted for 2×2 timber as opposed to 3×2. This was mainly to save an inch on each wall. It was also a perfect fit for 50mm Kingspan insulation.

One word of warning. 2×2 generally comes as sawn timber, this is usually lower quality than 3×2 scant or CLS. For this reason, you should go choose your own timber.

Do not rely on the builder’s merchant to deliver the best quality, straightest timber. Take some time to go down and choose your own.

When constructing my stud walls, I Left a 20 millimetre cavity between the studwork and the brick shed wall. This would allow air to circulate behind the studwork and stop condensation. Luckily, the shed already had an airbrick, so I placed an air grate in my studwork, this enabled better air circulation behind the stud wall.

This combined with 50mm Kingspan insulation, meant there should be no condensation behind the stud wall, or on the surface, as there was no dew point.

One last thing I did, was to add a plastic damp proof membrane under the soleplate of my studwork. For this, I simply used a roll of damp proof course. Which I laid on the floor underneath the timber. I fixed this into the floor using plugs and screws.

As one final precaution. I injected silicone into the holes before plugging and screwing. My intention here was to avoid damp coming through the tanking slurry on the floor.     

Final points and conclusion

There were a couple of other things, that I did not mention in this guide. These include:

  • Hiring an electrician to add lights and sockets.

  • New UPVC window and door installed. I had a local fitter install this for me.

  • Decorating. I am not a big fan of painting. So, whilst I could have done this myself, I know a good decorator and just paid them to do it.

  • Flooring. This is the only other place where I added any other damp proofing. This was in the form of an underlay with built in DPM. Following this I laid a laminate floor to finish.

In total the entire job cost just over £2000 and the shed is completely damp proofed.

Hopefully, this guide has shown you how to damp proof a brick shed. If you do have any questions, please feel free to send me a message via the contact page and I will do my best to help.