Methodology Wood Work (Wood for Carpentry Works)
Wood has always taken a pride of place in Building construction and furnishing. However, the size and form of its usage has changed considerably over the years. From old days of Chettinad rosewood or Mahogany cabinet to the lightweight, sleek particle-board cabinets, wood has been through several transformations. The differing grains, colors, and expressions inherent in the material give wood a warm lively quality found in few other materials. Teak wood still rules the field and a favorite of builders, architects and users alike. There are several other species available in India, though large part is imported from neighboring countries, due to different types of controls and regulations against deforestation in our country.
Various hard woods available are:
Teak: This is the most commonly used hard wood for decorative purposes in India. Almost 80 per cent of all wood for decoration is teak. The price of teak makes it a ubiquitous choice for users. It is used in cabinets, doors and frames. The advantage of teak is that it has high dimension stability, which prevents it from warping when exposed to different seasons, and it can resist termite attacks. It is suitable equally for indoor and outdoor use. The wood needs to be polished to bring out its natural sheen and look attractive. Teak is imported from Ivory Coast and Africa as also available in Central parts of India like Nagpur and Madhya Pradesh, known as C.P. Teak. The African Teak is available less than C.P.Teak or Ivory Coast Teak. This has a specific gravity of 0.63 when dry, though may vary in different species.
Rose Wood: For furniture, it has beautiful grains, and is very stable and durable. However, as it is quite expensive and increasingly rare, it is not being used a lot these days.
Burma Teak: It is probably the best and reminds one of old days when it was the common wood to be used even in Railway sleepers, beams, purlins and floors of buildings not to say for doors and windows. The high cost of the wood, makes it a hard to afford. Only very few builders still recommend it. It is now being used only for decorative purposes.
Saal wood: This is another common variety of hard wood used in building construction. This is strong wood and almost similar to Teak in mechanical properties but does not take good polish and is used for beams, purlins, and hidden wood work. This is still available in Eastern and North eastern parts of India but the old forests have practically all been cut and re- plantations only survives. The `ballas’ of saal are used for scantling and scaffolding works but for carpentry work the saal variety is mostly available from imports
Vengi Wood: This is probably the most used wood in the construction industry. This hard wood is used extensively for doorframes, interior of sofas and any paneling. As there are no grains in the wood and because it presents a dull look when it is lacquered/polished, the Vengi wood at most times is painted. The easy workability of the wood makes it quite popular in the construction industry, especially in South India.
Champ Wood: This is found in Bengal and North Eastern India. This is good hard wood and has grains resembling Teak. However it does not take polish as well as Teak and has wider grain. It is used for construction of doors, windows and frames. Furniture is also made from this wood in many parts of country.
Hollock Wood: This is similar to champ but is used for works requiring lesser and rougher finish and is cheaper than Champ.
Marandi Wood: This is reddish yellow in color. This is imported wood from Malaysia. This is used for door window work.
Rajak Wood: This is in the same range as Hollock.
Soft wood: Soft woods like Cedar, Pine, Fir, mango and deodar are not useful for engineering requirements as they do not withstand wear and tear as also mechanically weaker, for bearing load. These are generally used for packing cases, crates etc. However, these woods are used in manufacturing various boards’ ply’s etc. Places where wall paneling of solid wood is to be done, the soft wood planks can be used. These being soft woods, carving etc. can be easily done and are preferred. These woods may have specific gravity ranging between 0.4 to 0.35, when dry.
Plywood: Plywood is probably the most widely available manufactured board material. It is manufactured by pasting thin ply’s of natural wood, soft or hard wood or a combination of the two, with synthetic resins which are set and cured by heating. There is always an odd number of veneers/sheets and the direction of the grain runs alternately to give the material strength; the more veneers used, the stronger the ply board. Ply boards are dimensionally stable, however all ply boards unless properly supported will sag under load though gradually with time. It is easy to work with and can be finished using paint; the edges are required to be covered with a trim to hide the different layers. Both the type of glue and veneers determine the suitability of a sheet for a particular application. Commercial ply boards use water soluble adhesives and are not suitable for outdoor use. The finish quality of plywood varies enormously; some have attractive grains with decorative laminates or veneers while others can have a large number of knots.
Exterior grade plywood (WBP – Weather and Boil Proof) is specially made using a water-resistant adhesive to withstand a certain amount of moisture and can be used for outdoor constructions – sheds etc. and is sometimes used as a cladding material, particularly for insert panels under windows. WBP does require additional protection (paint or varnish) to protect the outer veneer.
Internal plywood is of a similar quality as Exterior grade but it does not use water resistant adhesive. It can be used for wall paneling, flooring and furniture.
Shuttering Ply is used in the construction industry for making shuttering boxes for containing concrete temporarily. Although water resistance to a degree, the sides of this material are not finished with a decorative veneer and is generally not suitable for use where a quality finish is required.
Marine Plywood is made with waterproof adhesive so that it will stand immersion in water, the veneers themselves will not last forever under water so the material should still be finished with paint or varnish.
Plywood is normally available in 2440 x 1220 sheets (or subdivisions) and in thicknesses from 4 mm to 35 mm. The ply boards commercially are available in 4 mm, 6 mm, 8mm, 12mm, 19mm, and 25mm thickness. The price of water proof ply boards is about 10-20% more than commercial ply boards, depending upon the Brand and thickness of ply board. The rates are practically in proportion to thickness of the ply boards, which vary from 4mm ply to 25 mm ply for a branded material. Shuttering ply boards are normally of 12 mm thickness and should be of water proof quality.
Plain Particle board: Unlamented Particle board is the cheapest and weakest material. It is generally unsuitable for shelving or any structural purpose, further the finish is also poor. This is however used for wall paneling or false ceiling as it improves the acoustic character of the space. Particle board is made by bonding together wood particles with an adhesive under heat and pressure to form a rigid board with a relatively smooth surface. Particle board is available in a number of densities; normal, medium and high-density. Normal density is fairly soft and ‘flaky’, high-density is very solid and hard (often used for tabletops and fire exit doors) – medium density is somewhere in between.
There are exterior grades of particle board available but most are only suitable for internal use as all but high-density tend to soak up water like a sponge. Once water logged, particle board tends to swell and breakdown.
Laminated Particle board: Laminated particle board is cheaper than solid timber and comes in a number of different types of veneer. It is not as strong as solid timber and will tend to sag except under a very light load. This is used for temporary shelf for exhibitions, fairs etc., partitions, panels etc. 12mm laminated thick particle board will support the shelf at no greater than 300mm centers for all but the lightest of loads, or /8mm particle board with supports no greater than 700mm apart. Sometimes this is also used for internal doors for mass housing schemes, with thickness of 25 mm. High- density particle board is often used as a basis for the shelves of kitchen furniture, table tops, and flooring – this is hardwearing, rigid and heavy.
Particle board is normally available in 2440 x 1220 sheets (or subdivisions), finished veneered sheets are available in smaller sheets so that the four decorated edges do not need to be cut. Thicknesses range from 9mm, 12 mm, 18 mm and 25mm.. The exterior use boards are appx. 10-20% costlier.
Pre-laminated particle boards are normally available laminated on one side at an additional cost for interior quality (OSD) & interior quality (BSD). Laminated softwood board (pine board etc.) – made up of strips of
Softwood (typically 25 to 100mm wide) glued edge to edge, to achieve finished boards .This is typically as strong as solid timber of soft wood. These are used in flush doors for inside use. These can be worked with normal carpentry tools.
Boards are available in a number of thicknesses (15, 18, 25, 30mm), widths (400, 450, 500, 600 mm) and lengths (1.2m to 2.1m). This wide choice means that the appropriate sheets can be selected to suit the job while minimizing waste.
MDF (Medium Density Fiberboard): MDF is stronger than Particle board and is easy to work with. MDF can be finished using paint to suit the decor or just sealed with a varnish. Use 18mm MDF as a minimum and support the shelf at no greater than 500mm centers for all but the lightest of loads. 25mm MDF board can be used for shelves, with supports no greater than 700mm apart. In India MDF is sold as NUWUD and is used in furniture making as well as flush or paneled doors. These boards are available in sizes 6mm, 8mm, 12mm, 18mm, 25mm, 30mm, and 35 mm.
These are available in
i) Furniture grade
ii) Interior grade
iii) Exterior grade.
MDF soaks water even from humid air and is not very stable in shape.
Block board: Block board is composed of a core of softwood strips (up to about 25mm wide) placed edge to edge and sandwiched between veneers of hardwood, the ‘sandwich’ is then bonded under high pressure.
An interior grade adhesive is normally used, so block board is not suitable for use out of doors.
When using block board for such items as a door or a long table, make sure the core runs lengthways to give maximum strength. Block board can be used for shelves, doors, paneling and partitions (with the core running lengthways) is stronger than particle board and is less likely to sag. It is easy to work with and can be finished using paint; the edges will probably need to be covered with a trim to hide the different strips. Block board is normally available in 2440 x 1220 sheets (or subdivisions), thicknesses tend to be limited to around 25 mm.
Gypsum Board: Gypsum boards are used for false ceiling work and are available in tiles of 600×600 mm. They are marketed in 9.5 mm and 12 mm thicknesses.
Laminates: Laminated plastics are available in many colors, patterns and designs. They can be used for countertops, tabletops and many other surfacing applications. The sheets are available in dull or gloss finish.
Laminated plastic is made from layers of paper that are first impregnated with resin and then bonded together under pressure and high temperature, forming a rigid sheet.
Decorative laminates like Formica, Sun mica, green mica etc. are available in thickness of 0.8 mm and 1.0 mm. These are water proof and pasted to the wooden surface with synthetic glues.
Every house uses timber in its construction or decoration, and while it can last a long time, it is a dried material and nature has various methods of making it decay unless it is looked after. Providing it is well maintained, timber will last many life times.
Below two areas of timber rot found normally are addressed – dry rot and wet rot.
Dry Rot: Dry-rot fungus is often thought of as a building cancer, rampaging through buildings and rapidly destroying any timber in its path. The fungus, which thrives in moist unventilated conditions, will penetrate brickwork to get to more timber and can cause widespread destruction of structural timbers, skirting boards and door frames, and wood flooring. In short, the fungus can be thought of as ‘living in masonry and eating wood’, and because the fungus thrives in damp, unventilated conditions, it can occur in the areas of a property that are not often seen, such as floor voids, or behind timber paneling, so damage may be extensive before the attack is discovered.
What to look for: Initially the fungus appears as off-white felt-like or cotton-wool like sheets on brickwork and timber, and, in later stages, can develop fungal strands as thick as your finger. Where the fungus is exposed to light, it often has a lemon-yellowish tinge. Damage is often confined to timber but large flat mushroom-like fruiting bodies can easily grow through finishes such as plaster or paint. These fruiting bodies may be the first visible sign of a problem, and they produce numerous spores which are normally brick-red in color.
Entirely dry-rot decayed timber can be crumbled between your fingers. The fungus leaves deep cracks running across the grain, and there is often evidence of off-white sheets of the fungus on the wood.
Treatment: The term dry-rot came from the belief that the fungus is able to transport moisture from a source many meters away, to attack dry wood. In fact, although the fungus can transport moisture over several meters, it cannot transport anywhere near enough moisture to attack wood that is otherwise dry. Treating dry-rot can involve removal of the affected timber (including all timber for a meter beyond the visible signs of the fungus), and extensive chemical fungicide treatments for all adjacent timber and the brickwork of any contaminated walls and plaster. However, this approach is expensive and unnecessary.
The modern approach is to use environmental controls, such as isolation and ventilation, which ensure that the damp, unventilated conditions required by dry-rot do not occur. The techniques are simple ways to ensure that the timber in a property does not become damp enough for dry-rot to attack, for instance replacing dry-rot decayed joists with new timber using joist hangers, instead of building them back into the brickwork, or by using ventilated skirting board details to encourage ventilation of a floor void.
Replacement door frames should have a strip of damp-proof membrane around the outside, to fully isolate them from damp or potentially damp brickwork, so the timber would never become damp enough for dry-rot to `eat’.
If you have dry rot, it is probably best to have the problem looked at, and corrective action taken by a reputable specialist firm, so that you have a guarantee if the problems were to return.
Wet Rot: Compared with dry rot, wet rot is hardly a problem. It is basically the timber decaying naturally in the presence of high levels of moisture. There is almost always a structural defect causing the problem, it may be that the wall adjacent to the timber is suffering from damp, or water collecting on the timber. Any structural problem must be tackled at the same time as the timber is treated otherwise the problem is likely to reoccur. The problem may just be damaged paint finish on the timber allowing the actual wood to absorb excessive moisture. Damage is normally limited to the timber although the original structural problem may also cause other areas to be affected by damp (such as plaster or just decorations).
What to look for: Check vulnerable areas of timber, such as window and door frames, for signs of rot. The bottom of frames is more susceptible to rot where water can collect or the wall/floor is suffering from damp. If the paint finish is damaged, this can increase the risk of wet rot. However, although the paint may look sound, the timber underneath may be rotting from the back. You will often see a professional builder push a thin bladed knife into painted timber frames, the blade should stop after a very short distance; if it goes in up to the handle, it is almost certainly a sign of rot behind the paint. Timber suffering from wet rot will feel spongy (even through a coat of paint) and look darker than the surrounding timber. When dry, the timber will easily crack and crumble into fine particles. Timber in the roof can also be at risk especially where there is roof damage allowing rainwater to run onto the roof timbers.
Prevention: Ensure that all external timber frames are adequately painted to protect the timber from frontal ingress of water.
Be aware of any damp walls and address the problem, it could be a missing /damaged damp proof course (DPC), a bridged DPC or a bridged cavity. If necessary seek expert advice as the symptom may be just a sign of a bigger problem.
Make sure that any soil and other debris is cleared away from around the bottom of timber frames.
Check the roof space for the ingress of water, you may not see daylight through a hole in the roof, the water could be running down the underfelt behind the tiles onto timber some distance away from the hole. When it is raining, go into the roof with a torch, the shining of water on a timber or felt normally stand out very easily.
Other favored places for wet rot are under the kitchen sink, bath, shower, wash basins, toilet and behind the washing machine etc.; all areas where a small leak from either a water supply or drain could go unnoticed for a long time but where timber could become saturated with water.
Treatment: First of all treat any structural problem; there is no point in repairing the damage to the timber if it is going to reappear.
If wet rot occurs in structural timbers (such as roof trusses, floor joists), expert advice should be sought as the implication for structural integrity must be established.
In other areas, the rotten timbers should be removed and replaced; if the damaged area is fairly small, it can be cut away and a new piece of timber joined to that remaining. If the damage is confined to a very small area, an epoxy based repair kit can be used to fill the damaged area once it has been cut back to sound timber and the new surface of the wood treated with a suitable primer. Preservative tablets are available which are inserted into the timber adjacent to the repaired area to protect the timber from within’. If there is any doubt that the structural problem has been eliminated, the new and adjoining timber should be treated with a proprietary wet rot treatment before redecorating.
After repair, external timbers should be protected with adequate coats of paint or some other suitable timber treatment/preservative.