What is a Damp Proof Course?

A Damp Proof Course (or DPC) is a barrier that prevents water from travelling through the pores in conventional masonry. Made from a variety of materials, damp proof courses were first used in the 19th Century (circa 1860) and were designed to combat the issue of rising damp.

Rising damp describes the process of groundwater travelling up the walls of a building via the capillary-like pores in masonry. Due to the nature of the materials we use for building, rising damp is technically unavoidable, but DPCs form a barrier around 150mm above ground level, preventing water from travelling any further upwards.

If rising damp is left unattended and your house lacks a DPC or has a damaged one, then it can cause very serious damp and structural issues for the building. The most obvious symptom of a rising damp problem is tide mark staining. This is a yellow-brown mark on the internal walls, indicating where the water has risen. Other key signs are salt deposits left on your wall, wooden features on or near the wall showing signs of rot and black mould beginning to develop. Some of these features could indicate other forms of damp as well as rising damp, so be sure to consult a professional before instructing any work.

What Causes Rising Damp?

As mentioned previously, rising damp is the result of water travelling up the wall via small holes in the masonry, in the same way as water travels up through a straw. Most modern houses will have a damp proof course to prevent this from happening, but there are still situations that can bypass your DPC and lead to rising damp. These include the following:

Your Damp Proof Course is Below Ground Level

If your DPC is below ground level then water will settle and seep into the wall above it, this bridging of the damp proofing can allow water to rise up the wall.

External Bridging

During a cavity wall installation, debris can get trapped between the walls. If the debris is situated particularly poorly, then water can begin to pool within the cavity and seep into the wall. This will bridge the damp proofing and lead to rising damp.

Neighbourhood Bridging

Though rare, it’s possible for rising damp to affect your house through shared masonry with another property. If you can’t locate a reason or cause for your rising damp, then it’s worth considering the positioning of your neighbour’s walls, especially if only specific areas of your house are being affected.

Again, to be 100% sure of rising damp, the cause and the most effective solution, it’s always best to instruct the assistance of a professional.

How to Install a Chemical Damp Proof Course

Whilst traditional DPCs were made using a variety of materials from slate to pitch, modern DPCs are created using chemical creams, gels and fluids. A chemical Damp Proof Course is the best solution to DPC issues in your property but requires a specific set of steps to work correctly, which is why most individuals entrust trade specialists with the responsibility. Currently, our team use Tri-Gel as our DPC solution.

Chemical DPCs work by being injected into the masonry at the base of the affected walls. The DPC then spreads throughout the masonry, coating the pores in water-repellent silicone resin which prevents water from passing through. To ensure an effective damp proofing installation, the injection of the cream or gel must be at the correct depth and spacing.

However, before installation can begin, it’s important to remove any damp plaster from the inside walls. This is vital for the DPC to dry correctly after it has been injected. After all of the affected plaster has been removed, an analysis of your walls is required to ensure the correct technique is used when drilling and injecting. To help explain the method, we have prepared some diagrams on drilling angles and patterns.

All chemical Damp Proof Courses should be installed at least 150mm above ground level, with the holes drilled approximately 110mm apart dependent on construction. It is strongly advised that you do not drill into the brick itself without a professional on hand, as this can lead to structural issues if done incorrectly.

From here, the chemical Damp Proof Course can be injected into the wall and left to penetrate the masonry surrounding each hole. The DPC must then be left to dry for up to six weeks depending on the specific product being used. Re-plastering must be delayed until after the DPC has dried. Finally, use sand and cement to fill the boreholes on the outside of the property.

Chemical Damp Proof Course Cost

Chemical DPC installation can vary in price depending on many variables, including:

  • Wall size
  • Wall location
  • Wall type
  • Number of walls affected
  • House type
  • DPC product
  • The extent to which your property has already been affected by rising damp

The only way to truly know the price is to get a quote from a qualified professional like our team here at Garratt’s Damp & Timber. Get in touch with us today for a free survey and quote for your property.

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