And, coming into the classification so, we saw the ingredient part. So, this sealant
is converted in 2 different classified products. So, one is called as one part and
other is called as 2 part . So, the one part is is a ready mix you might have seen in the
market a 300 ml cartridge or a 600 ml sausage pouch. So, that is a ready mix material .
So, if you see a carpenter or a or a window sealer coming to our house or somebody sealing
your kitchen or somebody coming to your bathroom and doing some joint applications
with sealant, you would have seen them coming with a small plastic cartridge under dispensing
equipment. So, this is like a small dispenser . So, this is called as an one part.
The formulation the ingredients what we saw before, everything is being bundled and put
inside the cartridge . So, while packing it is pin packed in certain atmosphere and where
it does not trigger any reaction to happen within that particular tube . So, once you
open cut it and then apply this reacts with the moisture in the air and start secure .
So, this way the product you know starts curing where reacting some moisture in the
air. So, when the moisture enters through the sealant after application, then there
is a initial cure which happens on the area, which is in contact with the air. And, you
can see the paste form of the silicone is getting converted into a rubber form ok.
So, then the moisture penetrates slightly through slightly through then you can see
that the rubber component becomes more and more deeper so, but with a with a single component
the constraint is if you have only and one side exposed cure to the air where the
moisture can penetrate. The maximum depth what can what you can do with single part
is 15 millimeters. So, beyond 15 millimeters the reaction will
be very very slow. So, you would not get a fully cured sealant to give you the desired
from mechanical or the physical properties . So, this can be changed by having a dual
you know air for systems by using an open cell spacer or an open cell baker rod.
So, where then there can be allowed to pass through from both the ends and then the depth
can be increased. But, essentially for a single seal with a
one sided open ended applications like what we do in the weather seals the maximum depth
waters you know been can be cured as only 15 millimeters . So, and this cure
rate takes time. So, the time it takes to cure 15 millimeter is general thumb rule is
2 weeks' time. So, A 1 millimetre per day is a general thumb rule for joints which are
done beyond 10 millimeters , but if you really look at you know in the applications
we do not do except on some of the structural joint applications 15 millimeter.
So, what is important to understand is by feeling more and more sealant into a
joint for a wider depth using a single point single part; you are essentially not achieving
anything beyond 15 millimeters ok. Whereas, this particular limitation or what we call
it as the constrain is completely not there for the 2 part. The 2 part it does not require
the moisture to you know react and cure it is an automatically, when the 2 components
of the sealant like part A and part B they are mixed together. So, there is a catalytic
reaction which happens and then the sealant cures only the by-products catalyst. Even
on a single exposed joint obligations you can go to a depth of 30 or 40 millimeters
and essentially that cures in say 24 to 48 hours time.
So, the rate of cure for the 2 part is much faster than the one part So, that is the
only difference between these 2. So, for a project which are of large scale and where
you do not have a space to keep the panels for cure? And you want to move them out faster
in day or 2. Then 2 part is one of the you know preferred product used by most of
the high end and you know fabricators or the facade manufacturers, because they want the
panels which are done today to be dispatched or you know ready for instruction tomorrow.
So, this can be easily achieved by using 2 part, other than essentially between 1 part
and 2 part there is no change in terms of design. So, it can also happen that the broken
glasses in an unitized system on a facade needs to be fixed using 1 part, because sometimes
2 part is not possible to be you know applied or done though there are some new products,
which have been introduced by some of the manufacturers have come in to do that, but
essentially if you look at most of the times. So, 1 part is always used for those applications
where, you cannot move the pump to the site or do some applications with 2 part.
So, the design in terms of the load or the capability for both is different only
the cure rates are different ok . So, now, we are going to essentially look at one of
the application called structural glazing. So, what is structural glazing? It is the
method of retaining glass to the frame using silicone on all 4 sides ok . So, any load
coming on to the glass is transferred to the frame through the silicon.
So, we are going to talk about this in detail and essentially if you look at a a a picture
like this like a building, where in the areas where you can clearly see this is the
area where, we are talk going to talk about the facades is the structural glazing part.
So, this is a curtain wall. So, in India probably still some when I say curtain wall
most of the people might think that this is a mechanically fixed system.
So, what is interesting to understand is the glass can be fixed to the building in different
ways. The way we are talking about here is using a silicone sealant to burn the glass
with a frame. So, this is one of the very proven technology very energy efficient
you know method, and it has to go through a series of quality check for doing the application
. So, which we will you know which I will take you through .
So, other than that silicone can be used for various other applications, it can be used
for fixing solid materials like composite panel or high pressure laminate or thin stones.
It can be also used for you know elastomeric coatings can be given on the rear facades,
where you want a good excellent waterproofing to be you know part of the facade. So, it
was also we have got insulation blankets, which are very very thin amount of insulation
blanket we can achieve very high insulation. And, also what is also essentially understand
is there are some new technologies coming up which can give you a clear crystal clear
method of bonding a glass to the frame or in a fin or could be in weather seal or
on the point fixing, where there are essentially a clear technologies, which are coming into
picture, where you can avoid drilling a hole in the glass in the some sometimes in
the façade. So, on the essentially coming back to the
structural glazing part the way the silicone is applied on a facade today is characterized
into you know classified into 2 types; one is called fully unitized system and semi
unitized system . So, the fully unitized system is normally these frames are floor to floor
in height or could be you know different dimensions where multiple panels can be put
in one frame . So, they take the frame in the horizontal
direction put the glass in a in a double sided tape to hold it in place and apply silicone
around the perimeter. And, then allow there to cure and after it has cured this frame
is moved to the side and fixed . So, this is called as fully unitized system. And, essentially
these are done in a factory atmosphere, where there is a clean and dust free room
is maintained with temperature control and the the advantage is you do not see
any grid work done on the building except the fastness part. And, this gets clamped
onto the fastness and then you know there is a male female join which are again fixed
onto the building and you can do the you know the completion very fast.
So, you need a capability to do a fully unitized system at factory and you also need a good
capability to handle these large units, which are much heavier to the site and fix them.
So, but this is essentially available in India there are many top class facade manufacturers
today. Who have successfully doing many projects using fully unitized system? The the second
system which is also predominantly common and used in India is semi unitized system
not only in India, these are the 2 systems which are being used worldwide is you know
fully unitized and semi unitized system. The semi unitized system will find a grid
work in the building. So, which is we already put on the building. And, essentially there
will be a sub frame in the factory and individual glasses will be bonded to each
and every sub-frame. This sub-frame will be then fixed to the mainframe. So, again it
is not only glass you can use different materials to bond silicone to the frame. And, this
subframe can be then moved to the side and fix to the mainframe and you get a externally
what you see is a clean good façade. And, also there is one more system which is
being also used for some of the applications essentially on a fin you know total vision
system, or a fin system, or a or a 2 sided captive systems, it is a stick. So, again
in the glass will be mechanically held by others other systems and the silicone will
be used to bond either 2 sides And, this is again lot of quality control needs to be
done, because when we are going to apply silicone at side you know the side conditions, where
the side conditions are not always dust free, or not clean, or it is not essentially you
know maintain with the temperature is hot humid dust.
So, we need to ensure that the proper cleaning is done before the sealant is applied. And,
the sealant is applied properly with the right temperatures and also the quality chicks of
these needs to be done. So, this needs lot of quality control. So,
essentially somebody is doing a 4 sided fixing for a broken glass again it requires a vigilant
mechanism to monitor. So, it is not generally advisable to do this as a system for a whole
project, if your broken glass is here and there where we can access it is a quality
control, then this is one of the methods which has been followed today for bonding the glass,
but not for the complete project ok. So, this is showing you the picture on the
fully unitized system, you can see there is a larger frame with multiple parallels in
one frame ok. It is fully unitized and this is semi unitized where in there is a single
subframe. Where the glass is bonded and this is then fixed with the main frame using mechanical
plates because the glass has bonded with the subframe using silicone sealants.
So, the case histories what it has been shown here or all the projects, which are done with
a fully unitized system and you can also still see some of the systems have a 2 sided mechanical
capping, because of the requirement and an architectural feature or sometimes they are
also designed to take the loads . So, what is essentially a critical to understand here
is, you can you can also see these are the projects which are like the world's tallest
towers standing today which are the it is the finished structure Burj Khalifa has been
done with such a system, and also the top wave type a 1 0 1, which has got lot of earthquakes
and tycoons or typhoons. So, and also you can see the climate like
Malaysia, which is similar to what we have in Indian coastal climates again the Burj
Al Arab. So, these are all the cases which have been standing tall for 10 20 15 years
you know and then these are proven that the technology what has been used or the product
is really working. So, what is the difference you saw from the
previous picture to this picture is here you do not see any mechanical fixing or an aluminium,
which is holding the capping, which is holding the glass from outside . So, what
does it essentially mean is all 4 sides of the glass is bonded using silicone sealant?
Ok. You can get a completely clean facade by using this technology. So, you do not need
to have an additional mechanical feature to hold them.
So, you can you have what you have to do is we need to design. And, then apply and and
then install. So, what is possible is these are the new trends and you can see in India
many many many projects, which have been done using this technology in last 15 20 years
. So, I want to quickly take you through one of the important slide on this particular
application is a dissection of an structural joint.
So, this is the glass and this an aluminium. So, the glass is bonded using silicone, which
is applied behind the glass . So, this is called a structural silicone and this is what
we have been talking about so far . So, any load coming onto this glass is transferred
through this silicone to the frame . So, the contact width between glass of the frame is
called as structural bite. . So, this needs to be calculated and this is
calculated based on a formula which is again designed on a rigid plate blending theory.
So, how you when you bend the rigid plate? So, what does the trapezoidal distribution
of stress coming out? So, based on that the formula has been developed for this technology
and this is proving out to be the successful formula for last 45 years.
The thickness of this particular silicone is called as glue line. Function of the glue
line is want to gun the silicone into this joint and second when there is a thermal moment
happening between the glass and aluminium, this glue line accommodates that thermal movement
ok. So, this takes the load and this takes the movement. And, what is that you see here
is also a spacer tape? So, the function of the spacer tape is to provide the gap and
also the keep the glass in place till the sealant cures, you might have seen in many
applications where there is a single glass being used and there is a double sided tape
has been applied. So, essentially you can see that the adhesive would leave the glass
in no time ok. So, what is holding the glass permanently
to the frame is silicone. So, we need to understand this is the product which is going to be holding
that for the long term . So, this you may not see from outside because nowadays people
use performance glasses, people also use double glasses. So, what we generally see from outside
is the whether silicone. Again, there is a minimum joint design required for weather
seal in terms of the width and depth and this is what is you know really providing against
a watertight seal ok. So, the the essential components what you
see it is glass aluminum whereas, there are 2 types of silicone is being shown here. This
is called as split joint design, where the silicone has applied from inside there is
a spacer and somebody also can use a baker rod here and this is the weather silicone.
So, this is the formula I was talking to you about how we have derived at the formula for
determining the structural bite is by you know doing a stress distribution theory
using the trapezoidal you know a way. So, here the maximum stress you can see how it
is happening around the you know 50 percent of the short side and somewhere here
on the long sides. So, the formula comes by multiplying the 0.5 into short side into
window, which is in the kilopascal divided by the sealant design load. In most of the
cases we this you know the point phi and sealant design load is almost common, depending upon
the glass size and the wind load the you can essentially determine the structural bite.
So, the concept is same for a single and double glass. So, in case of a double glass if this
is a double glass which is made from the glass purchases factory, the structural silicone
is applied behind the glass ok, inboard glass. So, this is a fixed unit where you can see
the sizes of both inboard and outboard DGU is you know glasses same. So, in that case
you normally apply the silicone behind the inboard glass of the insulating glass unit.
So, this is a spacer tape, again it is a fully unitized system you can see a male and a female
joint, and also you can see the weather seal here which is controlled by putting a baker
rod here. So, there are 3 types of sealants being shown
in this picture; one is the structural sealant, second with the insulating glass and the weather
seal. Just to give you a few you know idea. So, there are 3 products and they have different
application requirement. The structural silicone is used for holding the glass to the frame
and any load coming on to this unit glass has transferred through this out of the frame.
The insulating glass sealant is do you know designed to take the keep these 2 units together,
whether seal is you know acting as a seal not to allow the water to come in and take
the movements. So, any of one of this fail you may have if weather seal phase water will
come in, if the secondary seal of the DGU fails you will have a fogging and if this
fails you may have this class coming down . So, they are very critical and also in terms
of the quantity if you look at normally a glass of 1.5 meter by 2 meter or a 2.5 meter
with a windload of 2 kpa, generally the silicone required to supported against windload is
hardly 12 millimeters. Such a huge glass a 3 square meter glass what you need is essentially
12 millimeters of silicone. But, the critical device what is important
is designing the product applying it and then selecting them is very very very important
for the for this to perform. And, it is like any other thing it is not that is
you need to do extra care for silicone, it is essentially important for any manufacturing
process that you need to have a proper design, proper product, and proper application.
So, just to sum up what we have seen here is the silicone is taking loads. So, what
are the loads it takes up? There are a large area load which comes onto the building, which
is called as the windload this is a full area load. So, the wind will be hitting the building
either through the positive or the negative. So, the positive is a compression you know
and then negative is the suction. So, when the glass is pulled out what is holding the
glass to the frame is essentially the silicone sealant here ok. So, this is the sealant which
is essentially holding it. So, this has to be design to take against the windload. So,
which can be design we have seen the formula. The second thing what we need to understand
is sometimes in the facade we may have provisions not to have the you know we cannot we may
not be able to support the weight of the glass. So, which is not a good practice essentially
we need to support the weight of the glass as part of the section under setting blocks
and using setting blocks. So, if not what happens is this silicone is also have to be
designed to take the weight of the glass which is a shear. So, there is a different formula
which has to be followed to take the weight of the glass. So, which will depend upon the
weight, and the perimeter of the sealant length, and also the sealant design factor
for the deadload ok. So, it could be possible that in some of the
facades you may not have a just straight façade you might you might have an inclined facade.
So, you have a deadload support, but this the still there is a some angle of inclination
because of which there is a load acting on the sealant. So, we may have to determine
both windload and deadload see which is more, and we need to see the combined stress,
and recommend the bite according to the stress which is acting on the sealant.
So, we saw windload we saw a deadload and also there is a differential thermal movement.
You know there are climates which are like you go to Hyderabad, Delhi, Bangalore, Pune,
you may have a minimum and maximum which is quite high. Essentially, you may have a minimum
of say 15 if you go to Delhi it is minimum of say 5 6 degrees maximum of 45 degrees,
this is an air temperature. When you talk about the air temperature the substrate temperatures
are much much higher. So, there is a temperature gradient of close to 70 degrees we are talking
about. So, there is going to be a thermal expansion and contraction which is going to
happen between glass and aluminium. So, essentially when there is a thermal expansion
and contraction happening. The silicone which is a tough rubber, but it is also flexible.
So, it has to allow certain amount of movement to happen, it is not like a chewing gum that
you need to allow that movement otherwise nobody will go near the building. What we
are talking about this the rubber which is tough, but flexible. So, you, but it accommodates
the movement. So, that the glass moves and then you accommodate
the movement. So, that it does lead into any failures. So, the silicones do that and there
are you know the movement capability has been built in as part of the product characteristics,
which is also considered while designing the product for this joint, design.
So, I am quickly taking you through some of the way how do you calculate the bite? So,
if you take a glass size of 2000 by 1200 millimeters, and if you see how to calculate the windload
is if there is a design windload of 1.5 kpa. So, you take 0.5 into the short side into
windload in kpa divided by sealant design load which is 140 kpa you get 6.5 rounded
up to 7 and at a millimeter tolerance and always maintain 8 millimeter. So, that your
glasses you know essentially designed to take care of the with the silicone to take
care of the windload. So, when there is deadload support the silicone
will take the windload and here the setting blocks are takes in the weight of the glass
which is again transferred to this deadload to the section. But, in some cases this may
not be done this way. So, where the deadload is also taken by the sealant again this is
a formula where we need to use for calculating the deadload structural bite, where the plate
will act into play. So, here the weight upon you know perimeter into this is the sealant
design factor for the deadload. Ok. And, an example to talk about is if you have
a same glass size with the 6 millimeter thick where the weight is 36 kg and if you apply
the you know. So, you have a perimeter of 6.4 meters, and also you have a 36 kg.
And, when you do the calculations you are getting 8 millimeters through this. So, we
got 7 in the windload and 8 in the deadload. So, we have to use 8 millimeter for this particular
glass to take the weight load . So, whatever is higher we need to do that.
So, when there is a particular angle then we need to actually take the angle of inclination
and accordingly calculate the deadload size for those buildings which are inclined.
So, this is essentially showing you how the movement happens with expansion and contraction,
because of the temperature change you can see the how silicone is moving. So, essentially
both the structural and the weather seal joints are you know tough, but they can move and
take this movements . Just to recap on our first part. So, the
minimum structural bite has to be always to domain by the windload, also the thickness
has to be determined by doing the thermal dilatation calculations. If there is a deadload
which is acting on the silicone we need to determine the deadload as per the formula.
And, minimum 6 millimeter of bite has to be maintained in spite of calculations and also
a minimum thickness of 6 millimeter is made to be maintained regardless of any calculations.
So, the bite should be always equal or greater than the glue line. So, if you are doing an
8 millimeter glue line and your bite comes to 6 millimeter, then automatically to accommodate
the you know equal you need to make the bite of first 8 millimeters. So, there is a ratio
between the bite to the glue line the width to the height. So, 1 is to 1 to 3 is to
1 is the ratio for a 6 millimeter thickness or the glue line you can go up to an 18 millimeter
structural bite. The important thing what is also essential to understand here is the
structural joint should be easily able to be which up to able to fill into the joint.
It should not be so, complex you can show in the drawing, but practically it may not
be possible for you to apply. So, such designs are not really a proper design for applying
silicone ok. So, one side should be always exposed to the
air for the silicone to cure which I explained in my initial slides. So, these are all minimum
guidelines. So, you should always contact your manufacturer or the suppliers representative
for any complications or design challenges. So, essentially this is a technology, which
has been used for now 45 years and it gives you an excellent benefit you get a completely
clean glass façade, there is a flexible anchor which is holding the glass to the frame. This
takes windloads, this can be designed to take hurricanes, typhoons, it is a flexible anchor,
it can take seismic loads, it is uv resistant, it it is a long term weather able weather
resistance product, it is a flexible cushions. So, it is one of the most reliable method
which is being proven for more than you know 45 years. So, it is a proven technology for
us to really take that as a right method of doing the glass mixing today ok.
So, this is my first part and I am also going to you know take you through a a small video
in my now to show you on some of the essential things of how you really apply a
silicone into a structural joint. And, what are the quality controls you need to follow
while doing this joint application.