Can you plaster over tanking slurry? Plus three good alternatives

Tanking slurry is a great way of creating a waterproof barrier on internal walls and floors. However. It does not always provide the best possible finish.

If you are tanking inside your home, in a room that will be used as a living space, then it is highly likely you want to apply a smooth finish after tanking has been applied.

Most properties will have a smooth plastered finish in most rooms, even those decorated with paper. It is quite reasonable to assume that people would plaster over a tanking slurry once it has been applied.

You can plaster over tanking slurry. However, you should use a dilute SRB to prime the surface before applying a plaster finish. It is advised, to use a 1:1 SRB and water mixture over the finished tanking slurry.

Wait until the primer is tacky (not completely dry), then apply the plaster finish.

The main problem with plastering over tanking slurry, is the slurry is non-porous. This means that it does not allow suction, and the wet plaster cannot penetrate the surface of the tanking slurry. The primer solves this by adding an intermediary layer that the plaster can key too.

If a primer is not used, the plaster could come away from the wall once dry.

Stopping damp issues before tanking

Whilst tanking can provide a damp proof barrier, it should not be used to just cover up damp issues. This may work in the short term, but if the source of damp remains, you are simply covering up the problem and trapping moisture in the walls.

If water builds up in the wall, it will apply more pressure to the tanking slurry. Eventually this pressure could cause the slurry to blow and come away from the wall.

Whats more, the trapped moisture can cause other issues, such as spalling in bricks due to freeze thaw cycles. Over time this can cause serious structural damage, due to deterioration of the brickwork.

Finally, there is always a chance that the excess moisture will simply find a way around the tanking. Unless you tank the whole house, it is likely that damp will find another way in.

Essentially, you need to locate the problem before the tanking is applied.

In most cases, damp entering from outside will be a form of penetrating damp. If the problem is near ground level, it is also possible that rising damp is the issue.

To learn more about penetrating damp click here. This article covers the subject in more detail, including how to identify penetrating damp, as well as potential solutions.

For a more detailed explanation of Rising damp click here

Once you have identified and fixed the root cause of damp, a tanking slurry is a great way to add additional internal protection.

Also, after damp issues are fixed, it is common for a small amount of moisture to remain in the wall. This moisture can still penetrate through, along with hygroscopic salts, that can ruin the decorative finish inside. A tanking slurry is a good way of stopping this issue.

Alternatives to plastering over tanking slurry

There are several alternatives to tanking slurry itself. For example, a plastic membrane could be applied to walls. You may also use a lime based render. Both are potential options, and both come with their own pros and cons.

The main advantage with a tanking slurry, is its ease of application. As a DIY damp solution, tanking slurry is the most simple to apply. If you can follow the mixing instructions and work a brush, you will not need any professional help (unless you would prefer to outsource the work)

Installing a membrane or a render on the other hand, are much more technical. Both could probably be done by a competent DIY’er, but they require far more expertise than painting a slurry onto your walls.

There are also alternatives to applying plaster straight on to the tanking slurry. This will usually involve applying a plaster board and skimming over. Again, this can be done in a variety of different ways.

You can see a few options below:

• Dot and dab boards over the tanking slurry and skim. This is a popular option and is relatively simple, boards are fixed to the tanking slurry with an adhesive and plaster is skimmed over the boards.
  
  However, this is not 100% straight forward. Due to the non-porous nature of the tanking slurry, it is not advised that a standard plasterboard adhesive is used. You can read more about dot and dab over tanking slurry by clicking here.
  
  
• Applying timber batons to the wall and fixing the plaster boards. This is another good option, although some might claim, that fixing batons to the wall could compromise the tanking slurry.
  
  To avoid this, you can inject silicone into the drilled holes. This will seal any holes in the slurry caused by plugging and screwing the batons.
  
  
• Building a stud wall with a small cavity between the tanking slurry. This is likely to be the least popular option, as it will result in the most loss of space. However, in some cases it could be the best option.

For example: if you are tanking a single skin brick wall, a stud wall could provide extra advantages. Such as the ability to add extra insulation.

Conclusion

So, to conclude you can plaster over tanking slurry. However, you must make sure the surface is primed correctly before applying plaster.

There are also a few other things that you should consider.

Firstly, you need to fix the root cause of the problem, this is very important for a long term damp solution.

And finally, consider the other methods of finishing. Plastering can be a good way, but it might not always be the best solution. Always weigh up the pros and cons before deciding which method to use.