Plastering after damp proofing – How long should you wait?

Major damp issues in a property can cause serious cosmetic issues internally. This can involve unsightly damage to decoration and internal plaster.

Because of this, it is likely you will need to do remedial work after the damp proofing is complete. This will often include some, or all of the following:

• Replastering
• Redecorating
• Adding new skirting and architraves
• New carpets
• Replacing floorboards
• And in more serious cases you may need to replace structural timbers, such as floor joists.

The most common item from this list is plastering after damp proofing and redecorating. However, it is not advised that you do this straight after the damp proofing has been carried out. The walls need adequate time to completely dry before new plaster is applied.

Most experts would recommend a period of at least 14 days after damp proofing, before new plaster is applied. However, this period could increase if the damp problems were particularly bad. The surface should be checked with a damp meter to discover if moisture is still present,

You want the wall to be completely free of moisture before you add a new coat of plaster. If the wall is not dry this could lead to future problems.

When you plaster over a damp wall moisture and hygroscopic salts are still present. These could come through the new plaster after the work is completed. This would give the impression that damp proofing did not work. When in fact, it would be trapped moisture causing your new problem, and not new penetrating or rising damp.

Drying a wall after damp proofing

The good news is that after your damp treatment, the wall should not take on any new moisture. The only problem you have at this point is the water and salts that are already present in the wall.

Ideally you need to remove as much of this moisture as possible before plastering. You can speed up this process by taking some of the following steps.

• Maintaining a good temperature. This can be achieved with your central heating or an electric heater. Extra heat will help the excess moisture to be evaporated from the wall.
  
  
• Keep the area well ventilated and allow good airflow. By doing this you will allow moist air to be removed from the room.
  
  
• Use fans to help the air circulate. This could include standing fans, as well as extractor fans.
  
  
• Using a dehumidifier can also be a fantastic way of extracting moisture from the air. It will take in moist air and pass it over an internal refrigerated coil. This process will cause moisture to condense and collect in a bucket inside the dehumidifier.

All the above can help to speed up the drying process. However, you must make sure that you are testing the wall with a damp meter. This is the best way to determine if it is still damp. The wall may look completely dry, but this does not mean there is not moisture trapped inside. A damp meter is really the only way to test this.

Damp meters can be expensive, but there are some good models for less than £20 that are surprisingly accurate. We recommend the Brennenstuhl Moisture Detector you can click here to learn more and read over 7k customer reviews

How to apply plaster after damp proofing

There are several ways you can plaster after damp proofing. The three most common ways can be seen below:

1 – Plastering straight on to the brickwork

This will usually require two coats. The first should be a salt resistant, damp proof plaster system. A good option for this is Dryzone damp resistant plaster. This offers a highly breathable coat of plaster, that will prevent moisture and salts from passing through.

You can learn more about Dryzone damp resitant plaster and read customer reviews of this product by clicking here

Once the first coat is dry, you can skim over the top with a standard multi finish plaster.

2 – Applying a damp proof membrane

Another option is to fix a damp proof membrane and plaster over. Damp proof membranes are made from a high density polyethylene. This makes them completely water resistant to moisture and salts.

Once the membrane has been installed you can plaster directly onto the surface. Alternatively, you can dot dab over the membrane.

In theory you could dot and dab without a membrane. However, there is always a chance that moisture could pass through the board adhesive. This means the membrane gives an extra level of protection.

3 – Baton and moisture barrier boards

The final option is to use timber batons and fix vapour barrier plaster boards.

To add extra protection, you could also add a thin plastic DPM, or plastic packers behind the batons to keep the timber off the wall. The timber should be fixed with plugs and screws and you will need to make sure they are plumb, level and provide a flat and straight surface.

Once your timber is fixed to the wall, the boards can be fitted straight to the timber batons with drywall screws. When installing your batons, you should set them at 400mm centres. This will mean you do not need to cut the boards.

Finally, you can skim the boards with finishing plaster. You can use either a multi finish, or board finish for good results.

All three of these options can work great. The one you choose will depend on various factors. For example, the size of the job, are you just patching a smaller area or is it a full wall?

If you are plastering up to existing plaster, then option one or two might make the most sense. This is because you will need to finish at the same level as the existing plaster.

If you are doing an entire wall, then option 3 might make more sense. Not only is it very effective at stopping damp from penetrating, due to the gap and vapour barrier. But it also creates a cavity that allows airflow behind the boards. This can be a great way to avoid condensation.

Conclusion

As we have discussed, you should always let your walls completely dry when plastering after damp proofing. Hopefully, this article has helped you to speed up this process.

Also, the 3 methods of applying your new plaster should give you some options when it comes to finishing your walls. Each one has its own benefits, but they will all get the job done.