PLYWOOD INFORMATION

   

 Plywood is a manufactured wood panel made from thin sheets of wood veneer. It is one of the most widely used wood products. It is flexible, inexpensive, workable, and re-usable, and usually can be manufactured locally. Plywood is used instead of plain wood because of plywood's resistance to cracking, shrinkage, splitting, and twisting/warping, and because of its generally high strength.
Plywood layers (called veneers) are glued together, with adjacent plies having their wood grain at right angles to each other, to form a composite material. This alternation of the grain is called cross-graining and has several important benefits: it reduces the tendency of wood to split when nailed at the edges; it reduces expansion and shrinkage, providing improved dimensional stability; and it makes the strength of the panel consistent across both directions. There is usually an odd number of plies, so that the sheet is balanced—this reduces warping. Because plywood is bonded with grains running against one another and with an odd number of composite parts, it is very hard to bend it perpendicular to the grain direction.
History

Plywood was invented about 3400 B.C. by the Ancient Mesopotamians, who attached several thinner layers of wood together to make one thick layer. They originally did this during a shortage of quality wood, gluing very thin layers of quality wood over lesser-quality wood.

Different varieties of plywood exist for different applications:

Softwood plywood

Softwood panel is usually made either of cedar, Douglas fir or spruce, pine, and fir (collectively known as spruce-pine-fir or SPF) or redwood and is typically used for construction and industrial purposes

Hardwood plywood

Used for demanding end uses. Birch plywood is characterized by its excellent strength, stiffness and resistance to creep. It has a high planar shear strength and impact resistance, which make it especially suitable for heavy-duty floor and wall structures. Oriented plywood construction has a high wheel-carrying capacity. Birch plywood has excellent surface hardness, and damage- and wear-resistance

Tropical plywood

Tropical plywood is made of mixed species of tropical wood. Originally from the Asian region, it is now also manufactured in African and South American countries. Tropical plywood is superior to softwood plywood due to its density, strength, evenness of layers, and high quality.

Special-purpose plywood

Certain plywoods do not have alternating plies. These are designed for specific purposes

Aircraft plywood

High-strength plywood also known as aircraft plywood, is made from mahogany and/or birch, and uses adhesives with increased resistance to heat and humidity. It was used for several World War II fighter aircraft. Although the British-built Mosquito bomber, nicknamed "The Wooden Wonder", was constructed of a plywood monocoque, this was formed in moulds from individual veneers of birch, balsa and birch  rather than machined from pre-laminated plywood sheets.

Decorative plywood (overlaid plywood)

 

Usually faced with hardwood, including ash, oak, red oak, birch, maple, mahogany, Philippine mahogany (often called lauan, luan or meranti and having no relation to true mahogany), rose wood, teak and a large number of other hardwoods. However, Formica, metal and resin-impregnated paper or fabric bonded are also added on top of plywood at both side as a kind of ready for use in the decoration field. This plywood is a lot easier to dye and draw on than any other plywoods.

Flexible plywood

Flexible plywood is very flexible and is designed for making curved parts. In the UK this is sometimes known as "Hatters Ply" as it was used to make stovepipe hats in Victorian times .It is also often referred to as "Bendy Ply" due to its flexibility. However these may not be termed plywood in some countries because the basic description of plywood is layers of veneered wood laid on top of each other with the grain of each layer perpendicular to the grain of the next. In the U.S., the terms "Bender Board" and "Wiggle Board" are commonly used.

Marine plywood

Marine plywood is manufactured from durable face and core veneers, with few defects so it performs longer in humid and wet conditions and resists delaminating and fungal attack. Its construction is such that it can be used in environments where it is exposed to moisture for long periods. More recently, tropical producers have become dominant in the marine plywood market. Okoumé from Gabon is now the accepted standard for marine plywood, even though the wood is not very resistant to rot and decay. Each wood veneer will be from tropical hardwoods, have negligible core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond. It uses an exterior Water and Boil Proof (WBP) glue similar to most exterior plywoods.

Other plywoods

Other types of plywoods include fire-retardant, moisture-resistant, sign-grade and pressure-treated. However, the plywood may be treated with various chemicals to improve the plywood's fireproofing. Each of these products is designed to fill a need in industry.

Applications

 

Plywood is used in many applications that need high-quality, high-strength sheet material. Quality in this context means resistance to cracking, breaking, shrinkage, twisting and warping.
Exterior glued plywood is suitable for outdoor use, but because moisture affects the strength of wood, optimal performance is achieved in end uses where the wood's moisture content remains relatively low. On the other hand, subzero conditions don't affect plywood's dimensional or strength properties, which makes some special applications possible.

Typical end uses of spruce plywood are:

• Floors, walls and roofs in house constructions
• Wind bracing panels
• Vehicle internal body work
• Packages and boxes
• Fencing
• 
  
• 
  
•    There are many different types of wood-based man-made materials on the market. Each has its own purpose, drawbacks, and benefits. When most people hear the term plywood, they think of CDX (or whatever...) which is used to build houses. Yet in the wholesale wood products industry, plywood is a generic term for any sheet product regardless of construction (for example; MDF, VC, CDX.) The two terms are interchangeable, more-or-less.
  Medium Density Fiber Core Hardwood Plywood (MDF)
  
  MDF is made from fine wood dust mixed with a binder and heat-pressed into panels. The sheets can be sold as-is, or a veneer skin, like oak or maple, can be laid up on the sheet. (The veneered sheet is the most common form, but blank MDF sheets are available as Paint-Grade)
  This material is extremely stable to work with, and is typically very consistent from batch to batch. A 3/4" thick sheet purchased over a year ago is exactly the same thickness as a new sheet purchased today. The surface below the veneer is typically free of voids and blisters, resulting in a better veneer consistency and bond. With this better bonding of the wood veneer, there is less chipping during a crosscut operation. I have also observed that this material is easy to machine either by saw or router, and the cut edges are excellent for glue adhesion. (I have heard it mentioned that MDF is hard on cutters, but personally, I disagree with this statement. I feel that MDF is rather easy on the cutters.)
  The primary drawback to this product is weight. A 3/4" x 4' x 8' sheet can weigh as much as 70 to 90 pounds per sheet. The density of the core is expressed as the weight of a one cubic foot (1'x1'x1') block of the material. Therefore, an MDF sheet using a 48# (pound) core, will weigh 96 pounds. (48"x96"x3/4"= 2 cubic feet)
  Medium- and High-Density Overlay Plywood (MDO and HDO)
  
  MDO and HDO consist of a core material, like laminated fir veneer, overlaid with a pressed fiber material. In short, this is a typical veneer core plywood (common plywood) with an MDF surface. This gives the best of both worlds; the weight is lower than a full MDF, but the surface is more stable than a veneer core plywood.
  Veneer Core Hardwood Plywood (VC)
  
  Veneer Core plywood is made from alternating layers of fir slices (common plywood) with a surface veneer of a finished woodgrain such as oak or maple. This construction gives VC plywood a distinct advantage over others in strength. This is a light weight material, and easy to handle.
  The drawbacks of VC plywood are:
  

  
  • Voids in the core and face are common.
  • VC is not always consistent in thickness from sheet to sheet, or within the same sheet.
  • The pre-veneered surface is coarser, and does not accept veneer as well. This results in excessive chipping and tearout during machining.
  • No matter how you cut it, you will be ripping some layers, and crosscutting others. This makes cutting this material with a fine laminate blade more difficult, with a greater tendency to burn.
  • The saw-cut edges are not as clean and smooth as the other products, so this material does not take edge gluing as well.
  • The inconsistency in the pre-veneered surface can result in thin spots in the veneer.
  Lumber Core Plywood
  
  Lumber Core Plywood is manufactured from strips of solid lumber, typically basswood. The core is then surfaced and a veneer layer is applied. This is one of the most expensive plywood types to make, and is commonly used for applications where the edges cannot be concealed or need to be routed.
  As the popularity of this product diminishes, it is becoming more and more difficult to locate suppliers who are willing to carry high grade sheets. The quality of the core lumber is dropping in all but the best of grades. Most grades machine poorly. If the core is not glued up with consistent stock, voids can be present which will run the full length, or at least a portion of the full length, of the entire sheet.
  Because of this, care must be taken in selecting sheets if they are to be used for matched and sequenced door material, as a flaw in the core can wipe out an entire set of doors if they need to maintain grain matching from one to another.
  Particle Board Core Plywood (PBC)
  PBC uses a coarser wood dust than MDF. Because of this, it has a slightly lower weight, but the edges and surfaces are not as smooth and consistent. Most melamine products use PBC as the substrate.
  
  Melamine
  
  Melamine plywood is a thermally fused, resin saturated paper finish over a particle board core. It is highly stain and abrasion resistant. As a cabinet maker, I use a lot of this material. Even though glue manufactures claim to have developed an adhesive which bonds to the surface, I (personally) am not willing to take the chance; after all, this is a "paper" surface. (My personal recommendation to any one using this product is to dado the joints for better bonding.)
  Contrary to popular belief among many woodworkers, melamine is not the name of the paper finish; it's the name of the resin used to impregnate the paper liner (chemically C₃H₆N₆). Even among manufacturers of this type of sheet product, however, it is still called melamine.
  This material comes in a variety of colors, is highly stain and mar resistant, and is commonly used in the cabinet industry for carcass construction.
  Depending on the grade of melamine, it can be brittle or soft, coarse or smooth. Typically, the higher grades of melamine are more brittle and will chip during machining but have a thicker surface and greater resistance to abrasion.
  I have found that the best blade for cutting melamine is a triple-chip laminate blade set with a blade height of about 1" above the top of the wood. With a higher blade height, there will be excessive chipping on the back of the sheet, and with a lower blade height, there will be some chipping on the top of the sheet. The reason for the top-side chipping with a low blade height is due to the teeth striking the surface veneer nearly perpendicular, and throwing chips forward.
  
  High Density Maple/Birch (Baltic Birch or Appleply)
  
  High density plywoods (HDP) typically come in either maple or birch specie. Unlike common plywood, HDP has many more plies, is generally void free, and uses a stronger species than fir. HDP is commonly used for drawer side material as it is strong, stable, and has a moderately attractive edge
  Baltic Birch
  
  Baltic birch is probably the most common type of HDP, and uses birch as the substrate. This will come in 5' x 5' sheets. For a 1/2" sheet, there are typically 7 to 9 plies. Being birch, the surface does not finish as nicely as the maple counterpart, and there is a tendency for splintering at the edge of a machined cut.
  Appleply
  
  Appleply is a manufacturer's name for high density maple plywood. From a fabrication stand point, it is similar to Baltic Birch, in that it carries about the same number of plies, except Appleply comes in standard 4'x8' sheets. Because the surface is maple, there will be slightly more grain pattern on the surface, and the surface will sand much smoother. There is less splintering of the machined edges, and those splinters which do appear will be shorter and less inclined to align with the edge.
  
  

TYPES OF PORTLAND CEMENT

                                               Cement

       Crystals precipitated from solutions within a pore or
void space.
       Major process involved in lithification of carbonate
sediments.
       Can be syndepositional to late diagenetic .            
     

  TYPES OF PORTLAND CEMENT 

Portland cement (often referred to as OPC, from Ordinary Portland Cement) is the most common type of cement in general use around the world because it is a basic ingredient ofconcrete, mortar, stucco and most non-specialty grout. It usually originates from limestone. It is a fine powder produced by grinding Portland cement clinker (more than 90%), a limited amount of calcium sulfate (which controls the set time) and up to 5% minor constituents as allowed by various standards such as the European Standard EN197-1:

     Portland cement is a closely controlled chemical combination of calcium, silicon, 
aluminum, iron and small amounts of other compounds, to which gypsum is added 
in the final grinding process to regulate the setting time of the concrete. Some of 
the raw materials used to manufacture cement are limestone, shells, and chalk or 
marl, combined with shale, clay, slate or blast furnace slag, silica sand, and iron 
ore. Lime and silica make up approximately 85 percent of the mass (1). 
The term "Portland" in Portland cement originated in 1824 when an English mason 
obtained a patent for his product, which he named Portland Cement. This was 
because his cement blend produced concrete that resembled the color of the 
natural limestone quarried on the Isle of Portland in the English Channel. 
Different types of portland cement are manufactured to meet different physical and 
chemical requirements for specific purposes. The American Society for Testing and 
Materials (ASTM) Designation C 150 provides for eight types of portland cement: 

TYPE I

Type I is a general purpose portland cement suitable for all uses where the special 

properties of other types are not required. It is used where cement or concrete is 

not subject to specific exposures, such as sulfate attack from soil or water, or to an 

objectionable temperature rise due to heat generated by hydration. Its uses include 

pavements and sidewalks, reinforced concrete buildings, bridges, railway 

structures, tanks, reservoirs, culverts, sewers, water pipes and masonry units. 

TYPE II

Type II portland cement is used where precaution against moderate sulfate attack 

is important, as in drainage structures where sulfate concentrations in 

groundwaters are higher than normal but not unusually severe (Table 2). Type II 

cement will usually generate less heat at a slower rate than Type I. With this 

moderate heat of hydration (an optional requirement), Type II cement can be used 

in structures of considerable mass, such as large piers, heavy abutments, and 

heavy retaining walls. Its use will reduce temperature rise -- especially important 

when the concrete is placed in warm weather. 

TYPE III

Type III is a high-early strength portland cement that provides high strengths at an 
early period, usually a week or less. It is used when forms are to be removed as 
soon as possible, or when the structure must be put into service quickly. In cold 
weather, its use permits a reduction in the controlled curing period. Although richer 
mixtures of Type I cement can be used to gain high early strength, Type III, highearly-strength portland cement, may provide it more satisfactorily and more 
economically. 


TYPE IA, IIA, IIIA

Specifications for three types of air-entraining portland cement (Types IA, IIA, and 
IIIA) are given in ASTM C 150. They correspond in composition to ASTM Types I, II, 
and III, respectively, except that small quantities of air-entraining materials are 
interground with the clinker during  manufacture to produce minute, welldistributed, and completely separated air bubbles. These cements produce concrete 
with improved resistance to freeze-thaw action. 

TYPE IV

Type IV is a low heat of hydration cement for use where the rate and amount of 
heat generated must be minimized. It develops strength at a slower rate than Type 
I cement. Type IV portland cement is  intended for use in massive concrete 
structures, such as large gravity dams, where the temperature rise resulting from 
heat generated during curing is a critical factor. 


TYPE V

Type V is a sulfate-resisting cement used only in concrete exposed to severe sulfate 
action -- principally where soils or groundwaters have a high sulfate content. Table 
1 describes sulfate concentrations requiring the use of Type V portland cement. Low 
Tricalcium Aluminate (C3A) content, generally 5% or less, is required when high 
sulfate resistance is needed.  For concrete pipe and precast box manufacturing, Type I or II cements are 
            generally used.

TYPES OF PORTLAND CEMENT

TYPES OF PORTLAND CEMENT 

bricks types and flyash bricks

                            Types of bricks 

There are literally thousands of different bricks, but they 
can be broken down into a handful of basic types. The vast 
majority are made from clay and are kiln-fired.  

Facing Bricks 

Quality, durable bricks with an attractive appearance for 
external use above ground


Wirecut 

The clay is continuously extruded to a 
required size and shaope and then cut into 
individual bricks by means of a wire, much 
like a cheese is cut by cheesewire. 
Thousands of variations in colour and 
texture. Usually the cheapest facings 
available as the manufacturing process is 
highly automated.  


Stock 

The clay is wetted to a so-called "soft mud" 
and then moulded to shape, before being 
allowed to dry prior to firing in the kiln. 
Much of the process is automated. Tend to 
be slightly irregular in shape. Usually a bit 
more expensive than wirecuts.  
Stock bricks  

Handmade 

Usually made on a bench, in a mould, much 
as described above for a stock brick. 
Because the clay isn't firmly compacted by 
machine, each brick normally has 
distinctive creasing known as a 'smile'. 
Very desirable, and the most expensive of 
the facings, but well worth it on prestige 
jobs.  


Fletton 

Also known as 'London Bricks'. A unique 
facing brick manufactured from the Lower 
Oxford clay found only in SE England. 

This clay contains coal traces, which burn during 
firing, reducing the amount of fuel needed 
for the kiln, which not only keeps down 
costs but also produces some interesting 
effects in the bricks themselves.  

What is fly ash?

Power plants fueled by coal produce more than half of the electricity we consume today. But in addition to electricity, these plants produce a material that is fast becoming a

vital ingredient for improving the performance of a wide range of concrete products.

That material is fly ash.

Fly ash is comprised of the non-combustible mineral portion of coal. When coal is consumed in a power plant, it is first ground to the fineness of powder. Blown into the power plant’s boiler, the carbon is consumed — leaving molten particles rich in silica, alumina and calcium. These particles solidify as microscopic, glassy spheres that are collected from the power plant’s exhaust before they can “fly” away — hence the product’s name: Fly Ash.

Chemically, fly ash is a pozzolan. When mixed with lime (calcium hydroxide), pozzolans combine to form cementitious compounds. Concrete containing fly ash becomes stronger, more durable, and more resistant to chemical attack.

Mechanically, fly ash also pays dividends for concrete production. Because fly ash particles are small, they effectively fill voids. Because fly ash particles are hard and round, they have a “ball bearing” effect that allows concrete to be produced using less water. Both characteristics contribute to enhanced concrete workability and durability.

Finally, fly ash use creates significant benefits for our environment. Fly ash use conserves natural resources and avoids landfill disposal of ash products. By making concrete more durable, life cycle costs of roads and structures are reduced. Furthermore, fly ash use partially displaces production of other concrete ingredients, resulting in significant energy savings and reductions in greenhouse gas emissions

Flyash bricks can be divided into the following types

 
Clay Flyash Bricks.

Manufacturing process of clay flyash bricks by manual or extrusion process involves mixing
of flyash (60 %) with clay of moderate plasticity. The green bricks are dried under ambient
atmospheric conditions or in shed to equilibrium moisture level of below 3 percent. Dried
bricks are fired in traditional brick kilns at 1000º ± 30º C with a soaking period of 5 – 7 hours
at maturing temperature. This technology has great potential to reduce not only precious top
soil and consumption of coal in making conventional clay bricks, but also requires minimum
charges in existing set up at kiln sites and not very much susceptible to quality of ash.

Flyash – Sand Lime Bricks.

In presence of moisture, fly ash reacts with lime at ordinary temperature and forms a
compound possessing cementitious properties. After reactions between lime and flyash,
calcium silicate hydrates are produced which are responsible for the high strength of the
compound.

This processes involves homogeneous mixing of raw materials (generally fly ash, sand and
lime), moulding of bricks and then curing of the green bricks. Some technologies call for
usage of chemical accelerator like gypsum. These processes are almost similar and vary
slightly from water curing to steam curing at low pressure or autoclaving at 10-14 kg/cm2.
Bricks made by mixing lime and flyash are, therefore, chemically bonded bricks. These
bricks are suitable for use in masonry just like common burnt clay bricks. These bricks posses
adequate crushing strength as a load-bearing member and are lighter in weight than ordinary
clay bricks.

Generally, dry fly ash available from power plants meets the properties specified in IS: 3812
and is suitable for manufacture of Fly Ash – lime bricks in accordance with the requirements
of IS: 12894.

Cold Bonded Lightweight Flyash Bricks, Blocks and Tiles

The material can be produced in a variety of building blocks, bricks and tiles, depending on
local markets and regulations. Keraton consists of cheap and ubiquitous raw materials such as
fly ash and / or other waste materials. These materials are mixed and a cold bonding agent is
added. The mixed raw material is cast in moulds, after which the moulds are processed in a
microwave oven for transportation to the building site.

The products can be applied as a lightweight material in the house building industry and utility building, such as stables, barns, garages, etc. A surface treatment or coating for coloring is possible. Strong points are the
ability to use fly ash, the insulation properties and the production flexibility.

Flux Bonded Flyash Bricks Blocks and Tiles

The process is similar to the one in the conventional tile industry: fly ash is mixed with less
than 10 % plastic clay and a few additives and tiles, bricks or blocks are pressed. These
shapes are fired in the range of 900ºC to 1000ºC to make the final product. More than 85% of
flyash is used in the process.

The process is based on the formation of low melting fluxes at
the firing temperature, which partly react with the fly ash and form a high temperature
reactive glass binder phase. The bricks, tiles and blocks are brick red in colour, but changing
the initial composition can make a variety of colours.

 Difference between Flyash brick and Clay bricks

Flyash brick Uniform pleasing colour like cement	Normal clay brick Varying colour as per soil
Uniform in shape and smooth in finish	Uneven shape as hand made
Dense composition	Lightly bonded
No plastering required	Plastering required
Lighter in weight	Heavier in weight
Compressive strength is around 100 Kg/cm2	Compressive strength is around 35 Kg/cm2
Less porous	More porous
Thermal conductivity 0.90-1.05 W/m2 ºC	Thermal conductivity 1.25 – 1.35 W/m2 ºC
Water absorption 6-12%	Water absorption 20-25%

For manufacturing flyash bricks , most of the machine manufacturers suggest the following TWO mixing ratio, YOU CAN CHOOSE PROFITABLE MIXING RATIO TO SURVIVE IN THE MARKET if you are facing lowavailability of Flyash .

At the same time you should maintain the quality too.

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NORMAL METHOD

Process of Manufacture: 
Fly ash, Hydrated lime, Quarry dust and gypsum are manually fed into a pan mixer where water is added in the required proportion for intimate mixing. The proportion of the raw material is generally in the ratio

62%	fly ash
8%	lime
5%	Gypsum
25%	sand or Quarry Dust

 depending upon the quality of raw materials. 
After mixing, the mixture is shifted to the hydraulic Brick Making machines. The bricks are carried on wooden pellets to the open area where they are dried and water cured for 14 days. The bricks are tested and sorted before dispatch.

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PROFITABLE METHOD

20%	fly ash
15%	lime
5%	Gypsum
60%	sand or Quarry Dust

Cement bricks or concrete hollow bricks

   Cement concrete hollow blocks have an important place in modern building 
industry. They are cost effective and better  alternative to burnt clay bricks by 
virtue of their good durability, fire  resistance, partial resistance to sound, 
thermal insulation, small dead load and high speed of construction. Concrete 
hollow blocks being usually larger in size than the normal clay building bricks 
and less mortar is required, faster of construction is achieved.
Also building construction with cement concrete hollow blocks provides facility 
for concealing electrical conduit, water and sewer pipes wherever so desired and 
requires less plastering.

RAW MATERIALS
Concrete is a mixture of ordinary Portland cement, mineral aggregate (sand and 
stone chips) and water. The water used in preparing the concrete serves two 
purposes:
(1)It combines with the cement to form a hardened paste
(2)It lubricates the aggregates to form a plastic and workable mass
The water that combines with the cement varies from about 22 to 28% of the 
total amount of mixing water in concrete.
Mineral aggregates (sand and stone chips) are normally divided into two 
fractions based on their particle size. Aggregate particles passing through the 
No.4 or 4.7 mm Indian Standard sieve are known as fine aggregate. The 
particles retained on this sieve are designated as coarse aggregate. Natural sand 
is often used as fine aggregate in cement concrete mixture. Coarse aggregate are 
crushed stone chips.  Crushed stone  chips  broken into particle sizes passing 
through the 4.7 mm sieve may also be used as fine aggregate. The maximum 
size of the coarse aggregate that may be used in cement concrete hollow blocks 
is 12.5 mm. However, the particle size of the coarse aggregate should not 
exceed one third thickness of the thinnest web of the hollow blocks.
Ordinary Portland cement is  the cementing material used in cement concrete 
hollow blocks. Cement is  the highest priced material per unit weight of the 
concrete. Hence, the fine and coarse aggregates are combined in such 
proportions that the resulting concrete is workable and has minimum cement 
content for the desired quality.