Delta Registered Installers, Renderseal Ltd were called upon to provide a waterproofing solution to an extremely narrow lightwell to a medical facility in North London.

The scope of the project was to facilitate a solution for a damp, salt and mould covered lightwell wall, which was impacting negatively on staff who thought their office views were unsightly and unhygienic.

After many years of the medical facility seeking to remedy the problem by repainting the wall, continuous maintenance issues due to water staining, salt patches and algae growth lingered.

A lightwell (also known as a light well or air shaft) is an architectural feature which allows natural light to enter an interior space of a building and can also promote good ventilation in areas which would otherwise require artificial light or have poor ventilation.

A lightwell can take form as a vertical shaft within the volume of a building that typically penetrates from roof level down to lower levels.  Lightwells can be an open space or with a roof making it an enclosed space.

Lightwells can be problematic if they are not drained correctly.


After surveying the issue and identifying the problem areas of the lightwell, Renderseal Ltd proposed a solution to modify the lightwell to mitigate any future problems.

The solution was to install a Delta PT Cavity Drain Membrane to the lightwell.   The Delta PT Membrane is a HDPE membrane which is suitable as an impermeable damp proofing base for plaster or shotcrete (as a water control and drainage membrane).

Due to the “air gap” technology, Delta PT would create an effective barrier to the transmission of moisture, humidity, water vapour and salts, whilst assisting drainage by directing any water ingress to suitable drainage facilities.

Once the Delta PT was installed, Renderseal incorporated vertical expansion joints to prevent the render from cracking, whilst installing a horizontal stainless-steel stop beads top and bottom.  They further applied a two-coat sand/cement, finished with a wood float to provide a surface ready for painting.

Case Study Results

Renderseal Ltd have furnished the medical facilities with a dry pleasant lightwell which will remain fully protected against the long-term effects of damp, salts and water vapour.

The works were carried out over 6 days and came in on budget.

The client painted the render once it had cured to reflect light into the office facilities and are delighted with the results.

Chat with a member of our team

Get in touch