Plywood

Plywood is one of the most important of the manufactured materials, namely for its structural characteristics. Plywood comes in sheets from the merchant, and as such is classified in a technical sense as a “sheet good”, or “sheet material”. Plywood draws its name from its layered construction of plies, also known as veneers. These layers are typically 1-2 mm in thickness and are glued together in a perpendicular pattern orientation wise. By assembling the sheets in this fashion, the instability of the thin veneers’ grain pattern is negated. The layers required for the construction of plywood are harvested from logs typically by a method of running them through a rotary veneer machine, which to all intents and purposes is like a giant vegetable peeler for logs. The log is rolled against sharp blades, and a continuous thin veneer is then harvested from the log. This long veneer is then sliced into smaller sections for use in the construction of plywood. 

Plywood is often called for as a sheathing material in the construction of structural stud walls, as it provides excellent resistance to racking as well as providing a physical level of protection from the elements. Due to its alternating grain pattern across its layers, plywood also has very good relative compressive and tensile strength across its face, making it a good choice for use in floor sheathing, as well as in flat roof constructions.  

Additionally, plywood is the most durable and weather resistant of all the timber sheet goods, making it a great choice for use in the construction of protective hoarding and covering down delicate floor surfaces.  

Plywood comes in an array of thickness and sheet sizes for use in different applications. It also comes in a few different classifications, with the most prominent distinctions being between structural plywood, and WBP (Weather & boil proof) Plywood, with the latter being made of more durable hardwood veneers, for use in weather prone applications. The distinction between types of plywood required to be used are always listed in the specifications related to the building requirements and regulations.  

The veneers that make up a sheet of plywood can be made from most woods that come from large trees, both softwood and hardwood. Construction ply is typically made from Douglas fir or Spruce.  

OSB (Oriented Strand Board)

OSB is another sheet material that is commonly used for structural applications within the construction industry. OSB was invented in 1963 by Armin Elmendorf and serves to turn the waste products from the timber milling process into a usable sheet material. OSB is an abbreviation of the material’s full name “Oriented Strand Board” and is also known as Sterling board in the UK - based on the primary manufacturer of the material. This material is formed by layering strands of wood in an alternating orientation like plywood and compressing the fibres in conjunction with the presence of an adhesive. The adhesive used is typically formaldehyde based; an unpleasant chemical concoction assumed to be a carcinogen. 

Whilst all types of OSB are susceptible to water damage, and will swell or plim after prolonged exposure, 4 different grades of OSB exist, with OSB/3 and OSB/4 being rated for use in potentially damp conditions, such as roof sheathing. All 4 types are constructed following a similar procedure, though OSB/1 and OSB/2 are not rated for the same structural applications that the other two are. Despite these categorizations, the most produced and sold type in the construction industry is OSB/3.  

When OSB gets wet, the glue holding it together can start to dissolve, and the sheet can start to become soft, soggy, and take on the mushy appearance. Despite this characteristic, OSB isn’t intended to get wet, and so in a correctly weathered application, this sheet good is a very effective structural material. Similarly to Plywood, OSB can often be specified on a set of drawings for use in sheathing structural walls to prevent racking, or for use in flat roof coverings. Due to the actual construction of this material, it posses relatively poor tensile strength across its face.  

Chipboard (Low Density Fibreboard)

Chipboard, also known as low density fibreboard, or particle board in the US, is an engineered timber product that puts to use the waste materials from the timber milling process in a similar way to the creation of OSB. It is created by taking smaller chips of wood and compressing them in combination with sawdust and resin or glue to produce sheets. These sheets are often used in the creation of cheap furniture and for modern tongue and groove floorboards. The component materials are mixed and shaped under high pressure and heat to produce the resulting material, which has many applications. Chipboard doesn't mix well with water and becomes soggy and biscuity when water is allowed to permeate it. Because of the glue used in the creation of floorboards and the shiny smooth surface that is produced on the boards, they can be resistant to some water or rain, if water isn’t allowed to sit on top of them for prolonged periods.  

Chipboard is a very cost-effective method of producing a usable sheet material, as the base wood component is essentially wood chips. Uses include floorboards, flat pack furniture cores as well as kitchen worktop and panel cores. Due to a lack of continuity within its structure, chipboard is rather susceptible to breaking under load and must be adequately supported when used in a flooring capacity. Chipboard works well for cheap furniture when veneers are applied.  

Chipboard was first invented in 1897 and really began to see widespread usage in the 1950’s, most notably as a more economical system of construction in contrast with older fashioned, resource intensive methods. From an economical perspective, it makes sense to replace the unseen solid timber cores of affordable furniture with more cost-effective manufactured materials like chipboard.  

MDF (Medium Density Fibreboard)

MDF, or medium density fibreboard, is another engineered timber product that follows the same general concept as the other materials that use timber waste as one of the material components. MDF is manufactured in a very similar way to chipboard, with timber waste, namely sawdust, being mixed with resins and glues and then formed under heat and pressure. MDF varies from chipboard in the sense that it is much denser and thus heavier by volume, as the sawdust and wood fibres are compressed into a much tighter finished product. MDF is also typically denser than plywood and OSB. Whilst still utilising waste materials in its construction, the shavings and chips must be further processed into appropriately sized dust and fibres for the creation of MDF sheets, and as such the price is often comparable to plywood or OSB.  

As far as timber products go in terms of hazards to health, MDF carries the largest risk through the formaldehyde-based glues and resins used in its construction. As such, MDF dust is considered carcinogenic and so proper respiratory protection should be used when cutting or sanding MDF. 

MDF shapes up very well and is very responsive to cutting, sanding, routing and drilling. It has a smooth and shiny surface, which is very receptive to taking finishes. It is a stable material in the presence of regular household humidity, though its strength and stability fail quickly in the presence of direct contact with water, making it a poor choice for bathroom and external applications.  

MDF is used for a variety of different applications within construction, though most notably it is the material of choice for most modern internal mouldings, with most skirtings, architraves, mouldings, window boards, and finished boxings being made from MDF. More advanced varieties of MDF can be purchased, with some being resistant to fire or water, due to additional chemicals being added to the mix during the manufacturing process. Whilst the material itself is relatively strong, it is not suitable for structural applications. The soft nature of the material means the corners and edges are prone to being damaged.   

Hardboard (High Density Fibreboard)

Hardboard, also known as high density fibreboard, is the densest variety of fibreboard, as the name implies. It is constructed from wood fibres that are produced from the waste resulting from the timber milling process. The process of manufacturing hardboard includes compressing the waste pulp under extreme weight, essentially mashing all the fibres together, with the process requiring no additional adhesives to bond the fibres together. This contrasts with chipboard and MDF, which both require the use of glue or resin to help bring the fibres and chips together. Hardboard possesses poor structural properties and performs very poorly in damp or wet conditions. Due to this it is not suitable for exterior use or in structural applications. Most commonly, hardboard can be found in applications such as cheap furniture back panels, and backers for products such as flooring or cork boards 

Because hardboard has no grain structure, it is very stable in dry conditions, meaning it doesn’t expand or contract as much as other wood materials. Due to this quality, in combination with its cheap cost of manufacture, hardboard is a good choice of material to use as a backer for applying wood veneers, or for painting over.       

Blockboard

Block board is an old fashioned, less common type of manufactured material. It is a style of laminated board and can sometimes be classified as a type of plywood. It consists of solid strips of wood that have been glued together and then sandwiched between two veneers. These veneers can be decorative, or ply veneers can be used, with the intention of adding a decorative veneer over the top after the fact. The strips of wood within the veneer sandwich are typically around an inch (25mm) thick and are glued together in a parallel arrangement. In the past these materials were used for creating door panels, kitchen components, as well as uses in furniture making. It is a strong and stable material, though the internal movement of the solid timber can sometimes compromise the outside veneers under extreme moisture or heat conditions. The applications of blockboard have been replaced by more economical and cost-effective materials such as plywood in modern construction. It still finds applications in more bespoke scenarios nowadays however, such as higher end worktops or tabletops.

Laminboard

Laminboard is a variation of blockboard, with the internal solid wood strips being much thinner in laminboard. The internal strips are not typically more than 12mm in thickness but are glued together in the same fashion as blockboard. The advantages of laminboard over blockboard exist in its ability to utilise a higher proportion of timber waste in its construction.