Koster NB1 Spray

Waterproofing the tunnels of a World War ll Gun emplacement

Koster NB1 Spray



During our time spent at The Gunnery in Kingsdown, renovating the existing property which was previously a World War II gun emplacement, Universal Basement Waterproofing Limited were also sought after to successfully waterproofing a series of tunnels and rooms within the structure that required adequate levels of waterproofing in order to install the high level finishes required by our client.

There were numerous waterproofing to cause concern. Around the ground level of the structure, exterior ground levels varied, with some ground levels being in excess of 0.2m higher than the internal ground floor. This meant that it is highly possible that laterally migrating damp could penetrate into the buildings.

In the tunnels and small rooms throughout the property there were mixtures of construction techniques used and different combinations of exterior ground levels, with some tunnels being completed built in the ground. There were some obvious signs of historic water ingress, damp staining suggested in many locations throughout the property that water had previously transferred into the property between the wall floor joint, especially where ground levels were high.

In the areas that required waterproofing, several systems were discussed with the client, main contractor and architects. One of the initial systems envisioned was to install a membrane system, however, due to the lack of head height and extensive excavation required another solution was needed. We put forward the idea of installing a Koster NB1 Grey Waterproofing Slurry system. This system is designed and manufactured to seal against pressurized water. It is a crystallizing mineral compound that is used as a capillary plugging agent, effectively sealing all capillaries found within a structure’s substrate.

This system was agreed upon by all parties involved as it held many advantages over the use of other systems. Primarily, the use of NB1 Grey Waterproofing Slurry means that very minimal space is lost in the areas where it is applied. It can also be applied using a specialised spraying machine which improves the speed at which the NB1 Slurry can be applied, this also provides a more even coverage of every area receiving the remedial woprk and also provides a greater bond to the substrate when applied in this nature.


In order to successfully install this waterproofing system, our technicians first had to prepare every surface that was intended to receive the remedial work. This would include mechanical preparation to the wall and floor substrates in order to remove the laitance of the concrete,

this is an important step in applying a successful waterproofing system. In many cases, a waterproofing system is only as good as the substrate that it is applied to, thus meaning preparation is key. By removing the very top layer of the concrete’s laitance, dirt etc this exposes the many thousands of capillaries within the substrate.

he preparation of the substrates was carried out by sand blasting the concrete substrate. This sand blasting substrate preparation is the process of using a specialist machine sprayer that fires out fine sand at exceptionally high velocities. Once the sand hits the concretes surface, it begins to break up and remove the concretes weak, exposed top layer. Once the sand blasting preparation is completed, the concrete substrate is left clean of all dirt and debris, and its capillaries are exposed, ready for the waterproofing system to be applied.

Having access to these capillaries allows the Koster NB1 Grey Waterproofing Slurry to perform at the level it is required to. Having the capillaries of the concrete exposed means that the NB1 slurry can migrate into the concrete, where it “plugs” each and every capillary. The NB1 Slurry was the perfect waterproofing solution for this environment as it is designed to provide both positive and negative waterproofing against pressurised water, it is resistant against chlorides, sulphates and phosphates which helps keep damaging salts at bay. NB1 also inhibits the movement of any salts in the substrate when used in conjunction with Polysil TG-500 which is an anti-lime coating product.

Bearing in mind the differing heights of external ground levels, and the varying locations of the ingress of any water, the NB1 Grey Waterproofing Slurry provided our client with one product that was easily applied to all the different areas, delivering consistency and high-performance waterproofing.

As well as the Koster NB1 Grey Waterproofing Slurry and Polysil TG-500 solution, the use of a Koster Repair Mortar+ cove fillet detail was also installed. This was in order to be confident that no water ingress could penetrate through the weak wall/floor joint, where historically it had, potentially due to the high external ground levels.

As part of the second phase of installing this waterproofing the system the Koster Repair Mortar+ cove fillet detail would act in providing strength to the wall/floor joint where water had previously entered into the property. The Koster Repair Mortar+ product delivers high quality waterproofing to these areas by providing incredible adhesion to substrate materials, it used for delivering watertight repairs, and its excellent strength and resilience makes it perfect for the use in cove fillet details.

The shape of the Koster Repair Mortar+ cove fillet detail means that strength and weight of the wall is better transferred into the floor, this is how it helps provide rigidity to the structure and facilitates the structures ability to try remain watertight.


Upon the completion of the waterproofing works our client was provided with spaces that were now dry and watertight and ready for the further renovation works.

The products used in accordance with British Standards on waterproofing were perfect for supplying a waterproofing solution for the areas in question. Due to its ability to follow the contours of any buildings shape and structure whilst still providing the same consistency of waterproofing grade throughout means that even in the tightest of spaces the Koster NB1 Grey Waterproofing Slurry provides a high-quality waterproofing solution.

After the successful application of the waterproofing system this meant that even the most extreme areas such as the tunnels of the property were totally watertight. Koster NB1 Grey Waterproofing Slurry is a highly durable and easily appliable product that is perfect for any waterproofing needs.

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