Rising Damp in Cascais: Bilinear Cavity Injection System

In this second thermal image, the temperature increases to 21.8°C, showing the transition from the cooler damp zone to the warmer, drier area.

Thermal image showing a purple damp zone at 21.3°C, with temperatures increasing and colours warming as the scan moves into the drier area.

Mechanism of Rising Damp in Cascais wall

Rising damp in CascaisPRICING typically develops when groundwater migrates vertically through the pore structure of masonry by capillary action. In hollow-core brickwork the internal voids provide additional storage volume and interconnected pathways, so liquid water and dissolved salts are transported more rapidly and over greater heights than in dense solid brick assemblies.

What are the Limitations of Conventional Chemical DPC Injection

Conventional silane or siloxane injectable DPC creams are engineered for solid brick or stone substrates, in which the product can be absorbed into a relatively continuous mortar bed. In hollow-core Cascais wall constructions, standard 10 mm injection drilling at 120 mm spacing frequently results in uncontrolled loss of material into large internal cavities. The active agents do not remain confined to the intended treatment horizon and a continuous damp-proof course is not formed, even with elevated material consumption. This behaviour renders conventional injection methods unreliable for engineered rising damp remediation.

Concept of the Bilinear Cavity Injection System

The Bilinear Cavity Injection System is a dedicated preparation and injection methodology for rising damp in hollow-core brickwork. The objective is to convert a discontinuous cavity-rich zone into a stabilised internal mortar band, creating a defined absorption layer into which a silane or siloxane injectable DPC cream can migrate laterally and form an effective chemical barrier.

1. Primary Mortar Injection Line

A first line of 12 mm diameter boreholes is established along the design DPC level at 80 mm centre-to-centre spacing. A flowable, cementitious injection mortar is introduced using a high-pressure mortar injection pump. The material is driven into interconnected voids, progressively forming the lower component of an internal consolidation band.

2. Secondary Staggered Mortar Injection Line

A second line of 12 mm boreholes is drilled 50 mm above the primary line, staggered midway between the existing holes. Injection along this upper line promotes hydraulic communication between upper and lower cavities and eliminates residual unfilled pockets. The combined effect of the two injection lines is the creation of a bilinear, internally linked mortar structure across the treatment zone.

3. High-Pressure Delivery and Reaction Support

Mortar placement is carried out with a high-pressure injection pump configured for cementitious grout delivery. A reaction support device incorporating a weighted base is used to maintain constant contact pressure between the pump outlet and the borehole during injection. This arrangement improves operator control, minimises back flow at the wall surface and enhances penetration into the cavity network.

4. Curing Phase of the Internal Mortar Band

Following completion of both injection lines, the filler mortar is allowed to hydrate and cure for a nominal period of 14 days. This curing window is sufficient for the formation of a mechanically stable and dimensionally coherent internal band, without requiring the full 28-day structural design strength typically associated with load-bearing concrete elements.

5. Installation of the Chemical Damp-Proof Course

After curing, 10 mm diameter injection holes at 120 mm spacing are drilled into the consolidated mortar band along the original treatment horizon. A silane or siloxane injectable DPC cream is then introduced under controlled conditions. In this stabilised environment the material remains confined to the design plane, enabling lateral migration and the formation of a continuous chemical damp-proof course suitable for long-term control of Rising damp in Cascais

6.Compatibility of DPC Cream With Mortar or Concrete

Silane or siloxane injectable DPC formulations are not intended to be mixed directly into fresh mortar or concrete. If combined, the reactive components become immobilised within the cementitious matrix and are unable to migrate through the pore system of the wall. As a result, a functional chemical damp-proof course is not established. Cavity backfilling and chemical DPC installation are therefore treated as sequential, not simultaneous, operations.

7.Salt-Contaminated Plaster and Finishes

In many rising damp cases, pre-existing internal plaster layers contain significant concentrations of hygroscopic salts. Even after the moisture source is interrupted, these salts can continue to attract atmospheric moisture, leading to ongoing damage to finishes. In such situations removal of the contaminated plaster up to approximately one metre above finished floor level and replacement with a breathable, salt-resistant render system is typically indicated.

8.Drying Behaviour After Remediation

Post-remediation drying time is a function of wall thickness, material composition, internal and external climate and ventilation regimes. Typical drying periods range from approximately three to six months for summer conditions, with extended durations likely during winter or in low-ventilation spaces. Periodic moisture-meter surveys are used to quantify drying progress.

Conclusion

The Bilinear Cavity Injection System provides a technically robust framework for rising damp remediation in hollow-core brick constructions typical of Cascais and similar regions. By first generating a stabilised internal mortar band and then installing a silane or siloxane based chemical damp-proof course within this controlled absorption layer, a durable and predictable barrier to capillary moisture rise is achieved.

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