Liquid vs Sheet DPM: Which Damp Proof Membrane is Best?

In any property construction, one of the biggest considerations is protecting from rising damp. Damp-proof membranes (DPMs) play an invaluable role in ensuring all buildings are safe from the issues damp can cause.

For generations, damp proof membrane sheets have been a go-to option for dealing with rising damp. However, there are now many liquid DPM options, often promising simpler and more effective solutions. So, what’s the best option for construction today?

Liquid vs Sheet DPM: The Pros and Cons

First things first, quality liquid and sheet DPMs both do the same job. When applied professionally, both of them are more than capable of protecting buildings from rising damp.

However, the different nature of each product means that they each suit different types of jobs.

What is Liquid DPM?

As the name suggests, liquid DPM is a modern damp proofing solution that is applied as a liquid coating. Once cured, it forms a seamless waterproof membrane that prevents moisture from travelling through floors and substrates. Often applied via a paint roller or spray, it creates a waterproof barrier once set.

Because it is fluid when applied, liquid DPM is an excellent choice whenever working in tight, awkward spaces. It is commonly used beneath flooring systems such as vinyl, tiles, and laminate, and is a go-to choice for remedial works, where it can be sprayed into holes to provide consistent coverage in spaces where a traditional sheet wouldn’t fit.

The big disadvantage with liquid DPM is that the skill level required to use it effectively is much higher. While sheets automatically provide a consistently thick cover, liquid applications require extra care to ensure the damp proofing is the right thickness across the whole surface.

What is Sheet DPM?

Sheet DPM is the most common choice when it comes to effective damp proofing. Sold as rolls of thin plastic, sheet DPM provides unparalleled consistency and reliability, particularly when working across large, square areas. Because it’s a sheet, there’s also no waiting around for it to set – work can continue straight after it has been applied.

The main weakness of a sheet DPM is that it does not offer continuous coverage by default. While liquid DPM is seamless, sheets have to overlap and be carefully sealed together with DPM jointing tape, or water vapours can seep through. Another issue with sheet DPM is its inflexibility – these sheets are great for large coverage of a square surface, such as in new builds, but if you’re trying to fit them into tight spaces, it can be awkward to get the sheets secured.

Is Liquid or Sheet DPM Best for Your Project?

There are advantages to both liquid and sheet DPMs, so which is best for you will depend on the exact nature of your project. However, as a general guide:

• Liquid DPM is great for remedial work – it fits into tight, small spaces to create a seamless seal.
• Sheet DPM is great for new builds and larger work – its consistency, ease of application and cost-effectiveness mean it's still the go-to when covering a large underfloor space.

Of course, there may be factors in your project that mean the following isn’t correct. For example, if your building foundation covers a lot of awkward pipework, liquid DPM could help negotiate those spaces. Meanwhile, the level of remedial work needed on a property may well merit using sheet DPM for more reliably consistent coverage. This is why it’s always worth seeking a professional’s opinion before beginning your damp proofing work.