Epoxy and Urethane

Both the polymers are versatile products and used extensively in industries like paints, sealants, adhesives, foams and resins. Both  are very similar in polymer composition, however understanding its application for different situations is key to yield the best results for any material’s life.

Colour & Texture – In paint and resin industry, both the products are extensivley used and they possess distinct qualities in view of protection of paint. Epoxy  is not resistant to UV light, thereby resulting in yellowing of colour over a period of time. It also becomes chalky and brittle at touch when exposed to UV for longer periods. On the other hand, Urethane is resistant to ultra violet light, thus maintaining the longevity of the paint finish and remains smooth throughout its life.

Chemical Resistance – Here Epoxy is highly resistant to acids and bases, thus providing strong protection against corrosion, whereas Urethane wears off and start corroding over prolonged exposure to harmful atmospheric gases.

Therefore for metal (particularly mild steel) painting, epoxy is always recommended to be used as  base primer and finised with urethane coating especially when it is done in outdoors. Epoxy base coating may not be necessary with aluminium, stainless steel or titanium. Also, urethane provides the sheen and glossy texture to the metals. 

Concrete Repairs – The general rule for this is that if concrete needs to be structurally repaired with very good compressive strength material then the choice is an Epoxy. Epoxy comes in different viscosities from ultra thin to paste like to accommodate the cracks of different widths. Colour pigments can also be added to match the existing colour.

If the crack in concrete only needs to be repaired for water leakage , polyurethane is an ideal choice. It is an elastomeric, fast setting foam that is effective alternative to seal the crack for any leakage only and not structurally. Since it is an elastomeric, it doesnt crack due to concrete’s movement owing to weathering.

Floor Coating – In floor coatings the principle is same as metal paints i.e. recommendation of using epoxy as base coating for better adhesion with concrete as per required build up owing to availibility of ranging viscosity, and then top coating with polyurethane as sealer layer for better resistance to wearing and abrasion. Sometimes, epoxy coating is also used as finished top coating depending upon particluar use and desired outcomes.

Advertisements

Common Glossary of Environmental Design

Dry Bulb Temperature – It is a measure of ambient air temperature . When people talk about temperature, they are generally referring to dry bulb temperature.

It is called Dry bulb because while recording the temperature by thermometer, the bulb is dry and not affected by moisture content in the air Expressed in degree celcius or degrees fahrenheit.

Wet Bulb Temperature – It is meaured by a thermometer that has its bulb wrapped in cloth and mositened with distilled water. The evaporation of water from the thermometer and resulting cooling effect is indicated by wet bulb temperature. It is always lower than dry bulb temperature unless the RH is 100%. More the evaporation, the lower the temperature. Or higher the humidity, higher the temperature recorded that would be closer to dry bulb temperature.

Dewpoint – It is the temperature at which water vapour starts to condense out of the air i.e. after RH reaches 100%.

The capacity of holding water vapour reduces with the cooling of air, leading to rise in the relative humidity. It will rise until it reaches 100% making the air saturated.

If moisture condenses on a cold bottle taken out from a refrigerator , it means dewpoint temperature of air outside is above the temperature in the refrigerator.

Relative Humidity (RH) – In simple terms, it is the amount of moisture in the air (water vapour density at a given time) compared to what the air can hold (saturated vapour density at same time) at a given temperature and pressure. It is expressed in percentage.

Relative Humidity =  (actual vapor density / saturation vapor density )x 100%

Our human body’s relation to humidity is quite significant in light of feeling comfortable and pleasant. Our bodies rely on the air to get rid of sweat and thus keeping us cool and maintain its body temperature. If the RH is 100% and air is saturated, the sweat will not evaporate into the air. This unevaporated seat makes us feel uncomfortable and feel much hotter than the current temperature.

Hence, areas with high RH should encourage more natural breeze or fan to help in moving or replacing the surrounding air and consequently evaporating the sweat faster.

People tend to feel most comfortable at a relative humidity level of about 45%.

Above all the properties are represented in psychrometric charts used to access the physical and thermodynamic properties of gas vapour mixtures at a constant pressure.

Natural Stone

For centuries, stone is being used in building construction across the globe. It is one of the oldest material known to mankind,  and still as popular as thousands years ago. They offer wide range of surface finishes, colour, textures and durability,  and consequently wider range of applications in construction industry.

Here I would run through quick basic anatomy of stone and popular types of stones available in the market along with the possible finishes on them. All the stones seen today are broadly categorized into 4 categories; sedimentary rocks, metamorphic rocks, igneous rocks and manmade stones.

1.) Sedimentary Rocks – It is formed out of sedimentation of various particles from rivers, glaciers, river plants and accumulated to form rock beds. They were bonded through millions of years of heat and pressure. The primary examples of this rock are

Limestone – Mainly consist of calcite and lime from sea water. This stone doesn’t show much veins or crystalline structure. The surface is pretty smooth granular that comes in earthy brown and greys shade.  It is a beautiful natural earthy stone that is popularly used in decorative wall cladding and flooring where earthy appearance is been envisaged. The other benefit of this stone is the consistency of the stone texture and colour quarried over many years, hence making it a great choice when future expansion is in mind. However, this stone does stain therefore this would require a sealer to protect it.

limestone       images (1)

Sandstone – It comprises of sand and quatz grains( the common mineral found in earth’s crust) . It is commonly found in light browns, yellows  or red colours. Since it resist weathering, it is a very popular material for building exterior/interior  applications and landscape paving. Majority of Indian palaces, forts have been done in Sandstone. It comes in smooth texture with fluidic patterns over it.

download (1)images (3)

Travertine – This is formed by accumulation of calcite in hot springs, similar to limestone, but uniquely characterized by natural cavity and various patterns on it. These cavities are required to be filled with synthetic resins or cement grouts. Similar to limestone, it is bit porous in nature hence it requires artificial sealer over it once installed. The common colours are creams and light red shades. Commonly found in Italy and France. It gives elegant and pleasing appearance of expensive marble.

download (4)images (2)

2.) Metamorphic Rocks – It is formed from one type of stone to another type by immense heat and pressure inside the earth.  In this process, it develops crystalline formation, a texture change or a colour change. The primary examples of this rocks are

Marble – It is a recrystallized limestone formed under  heat and pressure. It mainly consist of magnesium carbonate. It ranges in many colours and comes with lot of long veins .It has been used from roman baths to old minuments traditionally. It is relatively hard , but not as hard as granite. Populary used in public and private building interiors.

download (5)download (6)

Slate – This stone is formed from clay or quartz. It is quite thin and easily breakable. Commonly found in black, grey or green.

images (6)download (8)

3.) Igneous Rocks – This is formed through volcanic material such as magma, getting solidified along with other minerals resulting in new crystalline formations with various colours. The primary examples are:

Granite – It mainly comprises of Quartz, Feldspar and Potassium. It is very granular in appearance and very strong material compared to any other above explained stones.. The only stone harder than granite is diamond, sapphires and ruby.  It is a maintenance free material, long life with minimum deterioration, scratch and strain resistant. Hence, it is a very popular choise for institutional and public buildings. Granite is the all time favorite as countertop materials for its unique colors and patterns, proven durability and lasting value.

images (7)download (9)

4.) Manmade Stones – There are made from artificial resins or cement mixed with stone chips. The main example is Terrazzo made of marble and granite chips embedded in a cement composition.

download (11) download (12)

In a follow up blog to this, I would discuss the all possible finishes that can be applied to a natural stone.

Curtain Wall

A curtain wall is defined as aluminium framed wall, containing infill panels of glass metals or stone. It is the non-structural entity that does not carry any building loads. The wind loads and gravity loads are transferred to building structure, usually at the floors levels and column connections.

Extruded Aluminium members is the preferred choice for curtain wall framing because of its light weight, thus reducing the structural cost. Although, very earlier curtain walls were done in steel.

The curtain wall is designed to resist wind loads, air leakage, rain penetration, condensation, thermal expansion & contraction , control vapour diffusion, building sway and seismic loads. In addition, it is also designed to provide optimum acoustics and fore rating.

There are 3 types of curtain walls available:

1.) the stick system ( or semi-unitized system) – this is the oldest system of all. The full cladding system is hung from the building structure. It is an assembly of various hardware components like mullions (vertical tubes), transom ( horizontal tubes), Integrated glass units, spandrel glass, insulation, steel anchors, aluminium sheets, pressure plates to hold the IGU, external capping system, structural silicon sealants, EPDM, neoprene and gaskets. All the connections are done at site in this system.

Below are some characteristics of the curtain wall:

  • This system is installed by hanging mullions from floor slab with a steel bracket.
  • The approximate distance between two mullions varies from 1 M to 1.8 M depending upon wind stresses and seismic zone, and aesthetic choice.
  • The transoms are fixed to mullions making the frames for vision glass and spandrel panels.
  • The glass is tucked into the aluminium frame tube and fixed it by using pressure plates from outside. It is sealed with gaskets (neoprene or EPDM) on the both the sides and capped from outside to get neat facade lines.
  • The drainage and venting mechanism is inbuilt in capping system with slots or holes provided at regular intervals in transomes.
  • EPDM gasket also acts as a thermal break between the cold internal mullion and hot cap/pressure plate externally. This helps in avoiding condensation
  • All the calculations for air tightness, water penetration, pressure equalisation are performed by Glazing contractor/consultant.

In spandrel units, the outer panel is an opaque glass, usually frit, or vinyl sheet pasted from inside in any colour. The spandrel covers can also be experimented with lots of other materials like stainless steel sheets, copper sheets, textured aluminium panels or granite stone. The spandrel unit is enclosed with metal sheet from inside with high density glass fibre or mineral fibre insulation filled in between the inside metal sheet and outer face panel. It works for thermal insulation and vapour barrier.

2.) the unitized (or panel system) – In this system, only brackets are fixed to walls at site. Rest all the complete curtain wall system (same componenst as explained above in stick system) are assembled in factory under controlled working conditions, and brought to the site for final installation. There should be a warranty for silicone sealant for at least 20 years.

It does promote quality assembly and speedy construction of envlope, though it require a precision supervision while installing.

3.) the structural glazing system (capless vertical joints) –  The basic anatomy of curtain wall remains same as above except the capping on outer face. All the vertical and horizontal joints are sealed with silicon sealants ( visually appear as a groove) for a flush exterior appearance. In this system, the depth of mullions is generally deeper (250mm approx.) compared to capped system ( 180mm – 200mm approx.). In cases of high humidity, silicone sealant may need a beading of butyl selant tp resist vapour penetration.

Good detail drawing references can be found at below link;

https://www.alcoa.com/kawneer/united_kingdom/en/doc_login.asp

 

Thermal Comfort

The term ‘Thermal Comfort’ defines the person’s state of mind in terms of whether they are feeling too hot or too cold. It is important for person’s productivity in a given work place.

There are large variation from person to person in terms of physiological and psychological satisfaction , it is hard to find an optimal temperature for everyone in a given space. However, it is very important to achieve thermal comfort for every person because it affects the concentration for a particular task and increases the risk of making errors. There are six primary factors that directly affect thermal comfort that can be grouped in two categories:

1) Personal Factors

a) metabolic rate – the more heat we produce while doing the work, the more heat needs to be lost in surroundings. Therefore, considering metabolic rate while evaluating thermal comfort becomes critical. Hence, people with different age, weight, sex, size, fitness level would have different level of comfort even if temperature, air speed and relative humidity are constant.

and b) clothing level – this is another important factor defining the degree of insulation worn over the body. This is also  one of the adaptive strategies to cope with thermal comfort i.e. by adding or removing the layer of clothing to feel thermally comfortable.

Other factors are like acclimatisation, state of health and expectation of comfort level also defines the satisfaction level in a given space.

2) Environmental Factors 

c) air temperature – this is the temperature of the air surrounding the human body, generally represented in degree celsius or fahreneit.

d) mean radiant temperature – it is the measure of the average temperature of the surfaces that surrounds the human body with which it will exchange the heat. It has a gretaer influence than air temperaure since it defines how we lose or gain the heat from/to the environment. For example, radiant heat sources like sun, fire, equipments, hot machinery generate lot of radiant heat.

e) air speed – it is the speed of the air that a person is in contact with. It is generally represented in m/s. The more the speed of the air, the greater the exchange of heat between the person and air. Moving air in warm or humid climate cam make us feel cooler due to convective heat loss.

f) and relative humidity – it is the ratio between the actual amount of water vapout in the air and maximum amount of water vapour that air can hold at that air temperaature, expressed as percentage. the higher the RH, the more difficlut is to lose the heat through the evaporation of sweat. The ideal RH is about between 50% – 70% for s space to be thermally comfortable.

The evaluation of above six methods is the way of measuring thermal comfort in any given workplace.

The point to be noted is that even if all these factors may vary with time, standards ususally refer to a steady state to study themal comfort just allowing limited temperature variatoons.  It may also be noticed that for some people air movement can be pleasant and provide comfort and for some people it may cause discomfort.

The HVAC strategy for any workplace should cater to above all parameters in order to control th ethermal comfort levels .

Concrete

Here I am just sharing very basic understanding on concrete requisite for an architect to know. These are just thumb rules and shall not be considered for any construction puporse without any consent from certified Structural Engineer.

Concrete is a mix composed of cement (binder), aggregates (filler) and water (binder). The composition of three or adding the reinforcement to it depends upon the requirement of physical strength that is desired from hardened concrete, and workability of fluid concrete for the purpose of pouring and compaction. The fluid mix of three can be molded into any shape to create the fascinating structures or elements.

The desired compressive strength of concrete depends on complete process of concreting that involves quanitity of mix, types of admixtures and plasticizers, batching plant, pouring, compaction and finally curing.

A very generic formula for the proportion of cement, sand and coarse aggregate is 1 : n : 2n by volume. The different types of concrete mix designs are denoted by Letter ‘M‘ followed by a number where number represents the specific compressive strength of 20 cm cube at 28 days expressed in n/sqmm.

Following are the some types of concrete Mix:

  • M 10 – 1 : 3 : 6 ( thumb rule to remember is that the total comes to 10 for M 10)
  • M 15 – 1: 2 : 4
  • M 20 – 1 : 1.5 : 3
  • M 25 – 1 : 1 : 2
  • M30 onward are generally design mix according to requirement of various strengths.

Few thumbrules for quick awareness:

  • M25 and above shall be used for high strength where reinforcement is involved. ALl are design mix.
  • M15 and M 20 shall be used for normal strength in building construction, and not for structural loads.
  • M10 and PCC ( 1 : 4 : 8) are used for PCC in foundations, coping and other such areas.
  • In 7 days, concrete gains the strength of 67% of its total strength. For example M 30 in 7 days shall achieve 0.67 x 30 = 20.1 n/sqmm.
  • In 28 days, it usually 90 % of its total strength.
  • Concrete has a property to harden with age
  • Concrete itself has very low tensile strength, therefore is generally mixed with steel bars, steel fibers or glass fibers to increase the tensile strength.
  • The composition of Cement mortar is generally 1 : 4 ( cement : coarse sand)
  • The composition of plaster is generally is 1: 4 ( cement : fine sand)
  • The shuttering time and its removal is critical in view of concrete gaining adequate strength. For columns, beams and walls, 48 hours is the minimum for shuttering. In case slabs it is more than 7 days depending upon area of slab. As it span goes higher, the it requires more days  to remove shuttering.

 

 

Seasoning of Wood

lumber_air_drying

Seasoning is the controlled process of reducing the moisture content of the timber such that it is suitable for the environment and intended use. It is very important to get this done before using it for construction purpose. The advantages are as follows:

  • Seasoned wood will be lighter, stronger and reliable.
  • It is better against wood rot and other wooden parasites.
  • it will behave better against glue and adhesives
  • It will not warp or shrink further once seasoned.
  • It is easier to work with

There two common ways of seasoning are :

  1. Natural Seasoning ( Air)  – In this process, timber is stacked in the open air, preferable at site. Stacking is done with horizontal distance of atleast 25mm. End of boards should be sealed by using suitable sealer or cover to prevent too rapid drying out via the end grain. The stack pile should be kept raised above the ground to provide good circulation of air and free from rising dampness. Lastly, overhead cover should be placed to prevent from effects of direct sunlight. Softwood takes about 3 months, and hardwood about 12 months for seasoning.
  2. Artificial Seasoning ( Kiln) – In this process, the seasoning relies on controlled environment to dry out the timber. It either uses hot air ( air mixed with gases) or superheated steam with latter being more common. There are primarily two methods, compartmental and progressive seasoning. The time consumed in this is significantly less compared to traditional air seasoning. It is primarily used for large scale lumber seasoning.

The compartmental seasoning involves enclosed container/kiln equipped with large       fans/blowers and piped steam. The stacking should be done in similar way as it is                     described above.

In progressive kiln, timber is passed through the chamber with different air conditions to progressively dry the woods.

Crushed wood particles for chipboard are seasoned primarily in gas drum driers at temperatures up to 500°C.

The sheets of veneer are moved through the drier on roller conveyors to dry it. 

The wood is always tested for its moisture content before and after the seasoning. There are several equipments available in the market to do the same. Like Oven test ( more popular) and wood moisture meter ( hydrometer).