How to Use Microporous Membranes to Stop Leaks

The following blog post is a transcript of the Belzona “Solve It Session” webinar on Microporous Membranes, as can be seen here:


A membrane is a selective barrier that allows the passage of certain items but restricts others.

If the membrane was not microporous, any trapped moisture would have to find a different way out. But in the meantime it could cause dampness within a structure and weaken it.

Whereas, microporous membranes have been designed to prevent water ingress whilst allowing any trapped water vapour to escape through the membrane and reinforcing sheet.

Therefore using these materials protects interiors from leaks. Whether that’s people, electric equipment, other liquids, the list goes on. Or, if a structure is already experiencing corrosion, membranes cut off the water supply.

Ultimately, microporous membranes are used to repair structures and prevent damage.

A visual representation of how a membrane works
A visual representation of how a membrane works

Application Areas


Sometimes it feels like, especially on flat roofs, the potential for problems is almost impossible to avoid. On a flat roof, any rain can easily start to pool. Even if there are gutters or a slight incline to try and prevent it, this may not be enough. The weight of pooling water can lead to deflection and subsequent issues.


In Belzona’s decades of experience, we have found that 90% of a roofs problems are actually found in only 10% of the areas. How did we come to this logic? If you think of a flat roof which has air conditioning ducting coming through the roof – the weak point will be the ducting.

So the troublesome 10% include: skylights, joints and seams, protrusions, glazing bars and gutters.


Anything that penetrates through the roof needs sealing. In this case a pitch pan or exhaust vent, almost all sealers used will crack eventually due to loss of plasticizer or ageing. If it is not stabilised or repaired, the vibration or movement of the roof can cause the sealant to crack.

The sealant used at metal penetration flashings may eventually deteriorate with exposure and may not seal if the flashing has not been properly cleaned before installation. They may also leak if the wrong diameter flashing has been used or if the cover is not correctly installed.

How would you combat this? By using microporous membranes which can adhere onto different materials and be applied to complex geometries.

All of the movement of a building is concentrated at the weak points. These can occur between either, two separate parts of a building or two dissimilar building materials. Therefore when leakage occurs, its origin can generally be traced back to these weak points,  so a flexible solution would be ideal for this repair. In this application, they purposefully chose a membrane like this, because it could be used for just the joints and they didn’t have to coat the whole roof.

Glazing bars and skylights generally fail because of the sealant. The problem is made worse due to movement because of natural expansion and contraction of the roof. The conventional repair would be to remove all of the dried out sealant and replace it. However, this will not solve the problem, as it will happen again.

In both cases where we have two dissimilar materials with movement, a liquid-applied membrane can give great adhesion to different substrates but also offers watertight and weatherproof properties.

Gutters are obviously designed to contain water, which run off the roof surface. Gutters can leak at the joints, through bolt holes, or at the junction of the gutter and the downspouts. A general repair would be to rip out the old gutter and replace it or a microporous membrane can be applied to create a seamless transition from the roof into the gutter, preventing any water ingress between the two.


It’s not just roofs where you can use microporous membranes, there are many other areas where they have been used over the years. Below are some of the problems which can effect these areas.

Electrical inspection boxes, which have been incorrectly sealed, can cause costly damage to electricity and gas utility companies. This is due to water ingress into the electric components through the failed seals.

In the above picture, you can see an example of how the harsh environment of the offshore industry can cause leaks. Again, this has the potential to create electrical damage which can put cranes out of action for weeks and cost the platform thousands of pounds.

HVAC systems are often left unmaintained and put under enormous strain, particularly in summer and winter months. The joints and seams of air conditioning ducting can become loose and damaged over time, particularly at areas such as elbows and T-pieces.

Installation of specific furniture into trains can cause cracks and holes in the train roof. This can cause damage to all internal fittings which would be costly to replace and wouldn’t be an enjoyable journey for passengers especially if the roof was not weatherproofed.

Above ground industrial storage tanks and their contents are extremely valuable assets that need to be protected.

Storage tanks can be exposed to extreme weather and operating conditions such as rain, heat and loading. Conventional sealing methods, such as mastic tapes, are subject to shrinkage and UV attack which do not allow moisture to escape

As turbines and blades increase in size, ensuring the stable foundations of these structures is essential. Therefore, any defects in the base must be quickly rectified before failure or even better prevented.


Tank bases are one of the key areas where microporous membranes can be utilised.

Storage tanks are generally placed onto a concrete pedestal with a bed of sand. However, if the tanks move, this can cause the conventional sealant to fail between the tank and base. Overtime this results in corrosion at the chime angle annular ring or on the track underneath the base due to:

  • Water ingress
  • Poor drainage
  • Sloping foundations

Meaning that in the long term it could cause loss of containment.

The Belzona solution is to apply microporous membranes onto both the concrete base and the steel tank, with addition of bridging tape to allow smooth transition onto both substrates.

The solution can also be inspected with NDT equipment

Tank Base Sealing


As well as tanks, roofs, and everywhere else, membranes can also be used on pipework. This is to prevent Corrosion Under Insulation (CUI). CUI is often unforeseen and it can potentially cause equipment failure, so it is essential that pipework and vessels are inspected regularly for this.

Traditional metal cladding materials have inherent weaknesses at joints. These can be damaged by mishandling and impact, for example workers walking across the pipes damaging the protective cladding. As a result, this causes further gaps between the joints increasing the risk of water penetration.

If there is any water present then ideal corrosion conditions may be created within the insulation layer as the rockwool / foam glass can absorb the moisture.

The result could be general corrosion of the surface of the equipment or, even more seriously, localised pitting corrosion which can lead to premature failure of equipment.


Fundamentally, you use a membrane to encapsulate a problem area, sealing it and protecting it, rather than just patching it up.

Plus, because these microporous membranes are liquid applied, you can use them on even complex geometries. As well as this, thanks to the reinforcement sheet, they are able to flex with the substrate beneath.

In the below video, we put these membranes to the test to showcase their properties.


Case Studies


So if we look at this case study from Poland, this is a perfect example of the troublesome 10%.

In this situation only the skylights required repairing, rather than the whole roof. They were suffering from deteriorated sealant and every time it rained, it leaked into the offices below. The solution was to apply a two coat microporous membrane incorporating a reinforcement sheet to the joints between the skylights and roof. The next time it rained the customer found no leaks and was therefore very happy with the application.


This application took place in France at the beginning of the year. Unlike a typical ‘repair’ using a membrane, this time a material was required to protect these new build structures from any potential damage.

The customer applied Belzona 3111 on the curved walls and roof of these buildings before using an adhesive to bond small white tiles on top. This left the buildings perfectly protected but also with the aesthetic finish the customer wanted.


Rain water and moisture seeped into the ground and then into the wind turbine structure through the base between the tower structure. This over time affected the concrete base with propagated cracks and corrosion at the base of the tower beginning to occur.

In this case the current coating failed due to UV degradation leading to delamination from the concrete surface.

The customer could have used a type of concrete filler but needed extra flexibility in that area so decided on a Belzona solution to seal the base of the structure.

Belzona 3111 was an easy way to seal the base between the structure and the concrete. The application was simple and proved to be a cost-effective solution with minimal down-time and interruption to the operation of the turbine.


This is a tank base sealing application where, although there was an existing system in place, it had failed due to it rigidity. This resulted in water ingress, causing corrosion at the base of the tank

Therefore, Belzona 3111 was used to provide waterproof protection at the base of the tank. Three years after inspection, in 2007, it was found to be in good condition with no signs of corrosion. Then it was reinspected in 2017 and still in excellent condition.

So, all in all, the customer was very pleased with the application and its longevity in service. Especially since, unlike competitor systems, it is possible to inspect the thickness of the annular ring through Belzona 3111.


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This Post Has 2 Comments

  1. Draco Jean-Luc

    I have worked with microporous boards in furnace applications along with membrane systems for microfiltration of H2O. But I have never heard of microporous membranes. This sounds very interesting. Has there been a study as to what the life expectancy or duration of the microporous membrane is? I know that might be a bit difficult to answer since there are many variables involved such as the application, the environment, and etc. But I was just curious as to what kind of data you have available on the life expectancy of this product when applied. I was thinking this might be a good product for some of the home projects or facilities that we do work in.

  2. hebert

    excelente …como siempre!!!!

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