1. “Re-roofing of old roofs – Liquid Applied Membrane
with Moisture Triggered Polyurethane Technology
-- a new dimension”
Key words: re-roofing, liquid membrane, PU, bituminous roof.
Abstract:
One of the most agonizing and painful concerns for all the building and property owners in India remains a
“leaking roof”… this becomes more troublesome as the solution to fix an already waterproofed roof with
commonly used products based on bituminous systems and other coatings etc. is much more challenging
and most of the times unsuccessful with repeated cost of maintenance severely affecting the “peace of
mind” for the owners!
In this paper, the latest technology development in the field of liquid applied membranes based on state of
the art “Moisture Triggered Chemistry” based Polyurethane system to tackle such difficult and challenging
leaking roofs have been discussed with special mentions on the key benefits and associated return on
investments.
Re-roofing – major challenges:
Refurbishment of an old, leaking roof is always very difficult as it comes with various challenges:
• Removal of existing layer (like bitumen) : time, risk, debris management, extra cost
• Lack of information on the previous installation
• Lots of detailing, congestion and lack of open space
• Direct bonding with existing bitumen layer
• Dead load
• Inconvenience to owner / end user (sound pollution, access to the area, time loss and shut
down, loss of production and revenue, additional cost of repair, loss of peace of mind)
To overcome the above pain area, construction professionals worldwide have tried and tested various repair
methods for an old, leaking roof with different degree of success. However, in modern times, with the advent
of special type of chemistry, known as “Moisture Triggered Chemistry” - based high end polyurethane
membranes in liquid form has given a new dimension to the re-roofing segment with it’s various additional
benefits to ensure an easy, fast and reliable refurbishment solution for such old, leaking roofs.
Author biography:
Arijit Basu is a marketing professional with more than 13 years of cross functional experience in the field of
construction chemicals in Indian market. He has been instrumental in new technology introduction and
concept selling for entire part of his career. He has been associated with the Swiss multinational SIKA AG
as Head- Strategic Business Unit of Waterproofing & Roofing business in India. His core competence in
strategic marketing, business communication and presentations and his track record of introducing and
successfully establishing new technologies in competitive markets have been appreciated and well
recognized in the construction chemical industry.
He is a Bachelor in Science with Chemistry Major and also a Post Graduate Diploma holder in Business
Management. But his biggest strength is what he has learnt ‘hands on’ over the years.
He is a thorough professional with clear vision and also a person who comes across friendly and easy to
approach. He loves reading, music, travelling and spending quality time with his family.
He may be reached at basu.arijit@in.sika.com or arijitsika@yahoo.com
Arijit Basu, Sika India Pvt Limited

2. “Re-roofing of old roofs – Liquid Applied Membrane
with Moisture Triggered Polyurethane Technology
-- a new dimension”
Introduction:
One of the most agonizing and painful concerns for all the building and property owners in India
remains a “leaking roof”… this becomes more troublesome as the solution to fix an already
waterproofed roof with commonly used products based on bituminous systems and other
coatings etc. is much more challenging and most of the times unsuccessful with repeated cost of
maintenance severely affecting the “peace of mind” for the owners!
In this paper, the latest technology development in the field of liquid applied membranes based
on state of the art “Moisture Triggered Chemistry” based Polyurethane system to tackle such
difficult and challenging leaking roofs have been discussed with special mentions on the key
benefits and associated return on investments.
Re-roofing – major challenges:
Refurbishment of an old, leaking roof is always very difficult as it comes with various challenges:
• Removal of existing layer (like bitumen) : time, risk, debris management, extra cost
• Lack of information on the previous installation
• Lots of detailing, congestion and lack of open space
• Direct bonding with existing bitumen layer
• Dead load
• Inconvenience to owner / end user (sound pollution, access to the area, time loss
and shut down, loss of production and revenue, additional cost of repair, loss of
peace of mind)
Moreover, as a general practice, most of the roofs in new conditions are being treated with rigid
waterproofing system like cementitios acrylic coatings or bituminous membranes. Also, the use of
conventional systems like brick bat coba or tiles are very much popular in many parts of India still
today.
Though such conventional methods are having their own merits within the technical limitations,
however, when used on a general basis even for roofs with complex geometry or higher detailing
areas, they fail to deliver the desired results. Also, workmanship issues and lack of pre
engineered details with conventional systems lead to higher propensity of a leaking roof.
Once, however, a roof starts to leak, it becomes very difficult to refurbish the same and make it
watertight. On the other hand, a leaking roof remains a perennial problem for the building owner
and end users in both commercial and industrial buildings.
To overcome the above pain area, construction professionals worldwide have tried and tested
various repair methods for an old, leaking roof with different degree of success. However, in
modern times, with the advent of special type of chemistry, known as “Moisture Triggered
Chemistry” - based high end polyurethane membranes in liquid form has given a new dimension
to the re-roofing segment with it’s various additional benefits to ensure an easy, fast and reliable
refurbishment solution for such old, leaking roofs.
Arijit Basu, Sika India Pvt Limited

3. “Re-roofing of old roofs – Liquid Applied Membrane
with Moisture Triggered Polyurethane Technology
-- a new dimension”
What is the new dimension?
Polyurethane in liquid form is not a new idea and have already been extensively used worldwide
in re-roofing applications. It has a lot of merit in the form of roofing material, however, the
available “Moisture Cured Chemistry” based polyurethanes always have issues in case of “rain”
after installation. This poses a critical disadvantage for using such a system in Indian context as
most of the times re-roofing works are taken up during monsoon and in India the rain fall can be
very consistent, frequent and at times high in most parts.
This critical factor handicapped the use of otherwise very promising technology of liquid applied
PU systems for re-roofing applications.
Another key concern in a re-roofing work remains the “fire hazards” specially in an already
running building or industrial unit, which meant that systems involving open flame or similar
technique of application for the re-roofing work was “high risk” and banned in many countries.
However, with the latest development in the polyurethane chemistry with “Moisture Triggered
Chemistry” based Polyurethane in liquid form, there has been a leap frog movement in terms of
“technology” – “Performance” – “Reliability” and “Return on investment”.
This now provides a completely new dimension when it comes to planning for a re-roofing of an
old leaking roof, as this technology comes with several benefits which actually evolved by
addressing the genuine concerns and limitations of the earlier technology in liquid applied system
Introduction to Moisture Triggered Chemistry based Liquid Applied Membranes:
Background:
The most commonly used liquid coatings are based on Polyurethane resins (PUR). Liquid
coatings as waterproofing membranes for outside applications in the civil engineering structures
like roof are already known since 15-20 years.
Liquid coatings have been used for waterproofing on roofs throughout Europe since 10-15 years.
They have become popular due to the fact that special application details can be easier
waterproofed than with normal bitumen or synthetic waterproofing membranes.
However, in many parts of developing and emerging markets like India the most commonly used
liquid PUR coatings are bitumen or tar extended PU coatings due to it’s initial cheaper cost,
however, these are far less superior in terms of long term performance and also subject to
various quality assurance issues due to local manufacturing practices and poor application
standards.
Other raw materials in liquid membranes:
Liquid coatings are generally Duroplastic materials or also known as Reactive resins. The resins
are usually based of monomers or pre-polymers, which are chemically reacting by using
hardeners without mechanical or thermal influences. Special UV-stabilisers have to be added in
order to receive the requested UV-resistance of the liquid coatings.
Arijit Basu, Sika India Pvt Limited

4. “Re-roofing of old roofs – Liquid Applied Membrane
with Moisture Triggered Polyurethane Technology
-- a new dimension”
The main groups are the following:
- Acrylic resins (AC)
- Epoxy resins (EP)
- Polyurethane resins (PUR)
- Modified Polyester resins
There is only one major difference within the various types of liquid coatings. Most of the liquid
coatings are using either water- or solvent based resins. Also, when it comes to PUR coatings,
the aliphatic grades are the high performing ones.
As a summary, when used as a waterproofing or roofing membranes for external
applications, the liquid coating systems are based on polyurethane resins.
Basics of PU chemistry:
A conventional PU is made by mixing together the ingredient chemicals (isocyanate and
polyol) in predetermined proportions, which then react to form the polymer.
Polyurethanes has an unique way of utilization of simultaneous polymerization and
shaping of the part.
Apart from Polyol, the other most critical raw material in a PU system is the isocyanate.
Many commercial grades of isocyanates used for making PUs are aromatic in nature.
Each isocyanate will give different properties to the end product, requiring different
curing systems and, in most cases, different processing systems. An important property of
an isocyanate is its functionality, i.e. the number of isocyanate groups (-NCO) per
molecule. For cross linked PU applications the average functionality of the isocyanate is
usually a little over two. The higher functionality isocyanates are used for special
applications. When a di-functional isocyanate is used with a di-functional polyol a long
linear PU molecule for elastomeric applications is formed. The common isocyanates used
to make PUs are shown in figure 1.
Arijit Basu, Sika India Pvt Limited

5. “Re-roofing of old roofs – Liquid Applied Membrane
roofing
with Moisture Triggered Polyurethane Technology
-- a new dimension”
Figure 1. Typical isocyanates
Many PU products, such as flexible ones are made with toluene di-isocyanate (TDI).
ones, isocyanate
The other main isocyanate used is methylene diphenyl di
socyanate di-isocyanate (MDI)
Moisture Triggered Chemistry Based PU system
system:
The biggest advancement in the Moisture triggered based PU system is the introduction of
Aliphatic isophorone di-isocyantate
isocyantate.
Systems incorporate a unique technology that allows the material to use atmospheric moisture to
trigger the curing process.
This means the waterproofing membranes are capable of curing in a wide range of conditions.
Unlike traditional moisture curing sys
systems PUR Systems, moisture triggered curing based PU
systems do not release CO2, which causes gassing (foaming or bubbling) .
,
Soon after application the fresh applied membrane will show no adverse reaction to water,
show
which is impossible with a conventional moisture cured PU system.
Arijit Basu, Sika India Pvt Limited
,

6. “Re-roofing of old roofs – Liquid Applied Membrane
roofing
with Moisture Triggered Polyurethane Technology
-- a new dimension”
Where does a Liquid Applied PU membrane make sense:
here
• Renovation / repair of bituminous roof
• Other types of conventional roofing renovation like asbestos, tile, thin metal deck, brick
bat coba.
• Small congested areas
• Areas with lots of penetrations
Typical built up of Liquid Applied Moisture triggered PU roofing installations:
• Warm roof design:
• Inverted roof design:
Note : There are many other possibilities available with such a versatile system based on design
requirements
Arijit Basu, Sika India Pvt Limited
,

7. “Re-roofing of old roofs – Liquid Applied Membrane
with Moisture Triggered Polyurethane Technology
-- a new dimension”
What about the critical detail:
Most of the conventional roofing and re-roofing applications fail actually from the detailing areas.
Generally, with a conventional method of application, a glass or polyester based mesh is
introduced into a liquid applied membrane system as reinforcement which surely increases the
tensile properties of a liquid applied system like a conventional PU membrane, however, when it
comes to critical and congested detailing areas, it becomes very difficult to apply such a system
and keep it watertight at those critical detailing areas.
The new generation moisture triggered chemistry based PU liquid applied membranes has a
special glass fibre reinforcement which spreads randomly during the application into the liquid
matrix thereby ensuring all the critical detailing areas are securely and professionally reinforced.
This is the biggest technical benefit of a moisture triggered based PU system over conventional
PU or other liquid applied membrane system.
The following pictures will demonstrate the capacity of such a system to handle congested and
critical areas on a roof top:
Arijit Basu, Sika India Pvt Limited

8. “Re-roofing of old roofs – Liquid Applied Membrane
with Moisture Triggered Polyurethane Technology
-- a new dimension”
Case study on Re-roofing of an old, bituminous roof in Gandhi Bhavan,Chandigarh, India:
Before After
Before After
View of Gandhi Bhavan
roof from outside
Arijit Basu, Sika India Pvt Limited

9. “Re-roofing of old roofs – Liquid Applied Membrane
with Moisture Triggered Polyurethane Technology
-- a new dimension”
Case Study on roofing of a congested roof in East Midland Airport, Englad:
Before After
Before After
Arijit Basu, Sika India Pvt Limited

10. “Re-roofing of old roofs – Liquid Applied Membrane
with Moisture Triggered Polyurethane Technology
-- a new dimension”
Summary of benefits of a moisture triggered chemistry based PU liquid applied system:
• No Flame, No Seam, Easy and Fast installation
• Fully reinforced detailing with special glass fiber reinforcement
• Excellent option for refurbishment of Bituminous roof for it’s ability to bond directly on
bituminous materials
• Moisture Triggered Chemistry – No threat from imminent Rain !!
• High standards with worldwide approvals like FM, ASTM, BS, ENERGY SMART etc.
• BBA approved for long life expectancy – high life expectancy
• Also an excellent option for asbestos sheet roofing, old metal deck, clay tile roof and
many other complicated roofing!
Life Cycle Analysis based costing of Moisture Triggered PU systems:
The initial higher investment on a moisture Triggered PU system can be well justified by LCA
based approach with “Total Investment” relative to “return on investment”.
The following tables will be helpful to capture the point as mentioned above:
Arijit Basu, Sika India Pvt Limited

11. “Re-roofing of old roofs – Liquid Applied Membrane
with Moisture Triggered Polyurethane Technology
-- a new dimension”
Conclusions:
Finally, it’s important and crucial to realize that though liquid applied systems look very easy in
terms of application, which is actually true, but due to the ease of application, there are also a lot
of careless mistakes during application and poor workmanship which leads to failure of such a
technology.
Moreover, in a re-roofing application, proper cleaning and preparation of substrate, selection of
suitable primer if required, correct adaptations in detailing and finally a very well trained applicator
and an experienced manufacturer with core know-how is very crucial for the success of a
refurbishment of an old, leaking roof…. With an advanced system like a Moisture Triggered
Polyurethane liquid applied system, it’s high time to go for that little more investment in case there
is an unfortunate situation of a leaking roof to be refurbished!
References:
1) Sikalastic application manual
2) Liquid Plastics, UK
3) Azom.com
4) Punjab University, Gandhi Bhavan Re-roofing Case study (Sika@Work, No.08/2011)
Arijit Basu, Sika India Pvt Limited