The Old Harrods Repository Repaired Using Koster Waterproofing Products

Harrods Repository showing the domes on top of the entrance which have been waterproofed with Koster Products

Koster products have been used to solve a serious water ingress issue in one of the domes of the old Harrods Repository building in London.

Having been built in 1914 as a warehouse for Harrods department sotre, this grade 2 listed building (which has been converted to up-market apartments) was causing concern due to the condition of one of the prominent domes on top of the main entrance.

The domes were constructed using the revolutionary "Khan" technique which involved incorporating flat steel reinforcement bars into the centre of the moulded concrete form. The concrete domes weree then tiled in glazed terracotta tiles. Over time water has filtered through the weathered tiles allowing water to enter the structure. This moisture started to corrode the steel reinforceing bars and damaged the surrounding concrete.

We understand that several years ago an attempt was made at preventing water ingress by re-pointing the terracotta tiles, but this had achieved no appreciable improvement in the condition of the structure.

The Waterproofing Contractor had been contacted by the owners of the building to conduct extensive repair work to this iconic structure and on a personal recommendation, contacted Koster Aquatecnic to conduct an extensive investigation and propose a suitable solution.

Alex Lynn, Technical Manager for Koster Aquatecnic visited the site and produced a comprehensive plan to:
*Protect the exterior of the dome
*Carry out concrete repairs within the dome
*Re-inforce the internal joints
*Create a flexible yet watertight seal to the flagpole penetration
*Waterproof the internal dome

The inside of the dome before restoration work showing corroded steel reinforcements, damaged concrete and moisture

Protection of the Exterior of the Dome 

Products Used

Koster Facade Cream, Koster Repair Mortar Plus, Koster SB Bonding Emulsion

Preparation and Application

All loose mortar was removed and the area was thoroughly cleaned to remove any traces of mould, organic growth or de-bonding materials. Areas with missing mortar were made good using Koster Repair Mortar Plus, with added SB Bonding Emulsion. After all cleaning and repair work was completed, Koster Façade Cream, (a highly active hydrophobic impregnation) was brush applied to all the mortar joints and worked over the glazed terracotta tiles as well as the ornate stonework around the flag pole.

Protection of the Internal Dome

Internal Concrete and Steel Repairs

Products Used

Koster Betomor Multi A

Preparation and Application

The inside of the dome was cleaned to remove any de-bonding material and reveal the original concrete.  All exposed steel work was mechanically wire brushed, removing all surface rust and taking the steel back to its original shiny appearance. Any loose concrete was removed.

Having completed the cleaning, the Betomor Multi A was packed tightly around the steels using a trowel. The repair was built up until flush with the surrounding concrete.

Betomor Multi A is a three in one concrete repair system providing anti-corrosion, course filler and a smooth finish coat all within the one product.  It is perfect for smaller areas of concrete repair with exposed steelwork.

Reinforcement of Internal Joints

Products Used

Koster Repair Mortar Plus, Koster SB Bonding Emulsion

Preparation and Application

Koster Repair Mortar Plus with added SB Bonding Emulsion was used to create a fillet detail in all the internal angles including the wall to floor joint, around the brick support for the flagpole and around the base of the flagpole. To create the fillet, the material was trowel broadcast into the junctions and then smoothed over using a 100mm section of plastic pipe, creating a concave profile to evenly distribute movement stresses. Koster Repair Mortar Plus is a slightly expanding, high strength waterproof mortar.


Creation of a Flexible but Watertight Seal to the Flagpole Penetration

Products Used

Koster KB PUR IN 5 (PU Elastic Solid-Body Resin), Koster Repair Mortar Plus

Preparation and Application

A previous attempt had been made to seal the flagpole penetration with expanding foam, so the first step was to remove this failed material.  The concrete flanks were scraped clean of as much dirt and contamination as possible. A closed cell backing rod was inserted into the gap between the pole and the dome and positioned to create a 100mm void above it.  A hole was then drilled through the surrounding concrete at a 45 degrees angle to intersect the void and a 10mm Koster injection packer inserted. A 20mm layer of Koster Repair Mortar plus was troweled into the bottom of the void below the backing rod.  Once cured a Koster hand pump was used to inject the KB PUR IN 5 through the injection packer and into the void until it was completely filled. KB Pur IN 5 is an elastic, solid body resin providing a strong but flexible watertight seal.

Waterproofing the Internal Dome

Products Used

Koster Polysil TG 500, Koster NB1 Grey, Koster SB Bonding Emulsion, Koster 21,

Koster Flex Fabric

Preparation and Application

The inside of the dome was sprayed with Polysil TG 500 using a hand pump sprayer. The Polysil primes and strengthens mineral surfaces as well as blocking salts within the substrate.

NB1 Grey crystallising sealing slurry with added SB Bonding Emulsion was applied over the entire area, including wall, floor and flagpole base. The SB Bonding emulsion makes the NB1 Grey creamier for a smoother application as well as giving the finished coating some flexibility.  The products were applied in two coats using a block brush to an overall thickness of approx. 2mm.

The following day a finishing layer of Koster 21 was applied.  This synthetic, crack bridging material provides a bright white finish, with excellent adhesion to the NB1 grey.  By utilising a high strength mineral coating with an elastic crack bridging finish we were able to combine the best of both worlds and an extremely robust waterproofing was achieved.  Koster 21 can be applied by brush, trowel or spray.  On this project the material was applied in two coats by brush.  On the floor area of the dome Koster Flex Fabric was embedded into the fresh first coat of the Koster 21, providing good resistance against occasional foot traffic. 

The Completed Project

After 5 days of work by the Contractor the restored dome is now watertight and stabilised for the foreseeable future. The Contractor was very impressed with the quality of the Koster products, the technical knowledge of Koster Aquatecnic’s Technical Team and the company’s commitment to customer service. 



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