Timber is one of the oldest building materials known to man, having been utilised as a principal construction material over 10,000 years ago. Timber has a high tensile strength parallel to the grain. Naturally, there will be cracks or splits in the case of the old beams, especially when the large size members are used. Also, some timber species are more liable to crack without any major weakening of strength. But a cut or knot or drilled hole at the wrong place may weaken it. Therefore, it is essential to know how to handle and conserve such natural and man-made defects in timber members. This blog precisely explores some of the common defects in timber structures and the ways we can repair them.
List of Contents
1. Common Defects in Timber Members
1.1 Outward Leaning Pitched Roofs
In many of the old buildings, the thickness of the wall may vary from bottom to top after plastering especially with earth walls. This should not be mistaken as an outward leaning wall. Horizontal cracks in the walls of a building near eaves level appear on the inside walls when there is an outward movement of the portion of the wall above. Roofs exert an outward thrust when there has been over-loading of the structural roof members or the tie which had been provided in the original design gets damaged because of fungal or insect attack.
1.2 Leaning and Sagging of Structural Timber
In numerous historic buildings’ structural timber members, there will be modest deviations from the straight level and plumb. If the structural timber is visibly leaning or sagging and it is becoming worse, it should not be ignored. If neglected, this causes damage to the joinery and the nearby timber members. Jacking the timber members in the middle may take care of some of the bendings but, it may also damage the tenons on either end. Temporary supports in a structurally damaged building should be done carefully as per the instructions of a structural engineer.
1.3 Damages in Timber Flooring Members
Timber floors are common in many historic buildings. In a hot climate, the damage will be mostly caused due to termites which would have found entry below the timber planks. In many cases, the damage around the perimeter of the floor is more, especially near the external walls of the building. The floorboards may fail, but the main damage may be confined to the beams and may not be readily visible. In the case of a cool climate, the ventilation below the timber floor would have been blocked by subsequent interventions. If the damage is at the ends of the beams, it is more likely by wet rot, but if it is widespread, the more chances are dry rot (or) fungal attack. Rising dampness problems can also cause wet rot in the timber planks. Too often the flooring has been unnecessarily replaced, destroyed by heavy sanding, suffocated by blocked ventilation and coated with unsympathetic synthetic coatings.
If there are no signs of fungal or insect attack, check the quality of the boards and other defects such as knots, splits or shakes. Another reason for the damage of the floor might be over-loading because of the change of use.
Let us move on to know more about how to repair such defects in timber structures.
2. Treating the Defects in Timber Structures
2.1 Repair of Timber Columns
In some circumstances, the foundations in particular areas of the building sink, causing the timber columns to sink. In other cases, the termites will attack the column from below. This will be aggravated by the presence of moisture because of the splashing rain. In many traditional buildings, timber columns are made to rest on granite bases, which is a sensible thing to do. Granite can help in protecting the base of the column from getting wet.
In the case of the decayed timber columns, the decayed portion should be cut out and replaced with new timber to match the cross-sectional area. As far as possible, one should try to match the direction of the grains as well. In joining, one can use water-proof glue. Timber or steel dowels may be inserted for gaining more strength.
2.2 Repair of Timber Rafters, Beams and Ties
In the case of the rafters and beams, the damage normally occurs at either end. Termite attack can happen at any part of the member, but it is usually close to any sapwood (outer layers). The general rule in all timber repairs is to replace the defective part with another timber section of sufficient cross-sectional area.
2.3 Repair of Mouldings & Carvings
The carving or moulding in many of the old buildings will be of great value and have to be preserved at any cost. But in some cases, where there is substantial damage, the geometrical figures can be carved again. Human figures and other figurines are not to be carved even though good craftsmanship is still available in India.
In other cases of slight damage, once the cause of decay is removed, it may be possible to make the design of the timber members in such a way that the decorative timber will have to carry its own weight only. It can also be suspended from above or made to hang from a steel beam. The main advantage of such an approach is that the painted ceiling or the decorative carving is not dismantled from its original location.
3. Conclusion
It is safe to conclude that the usage of timber in construction has increased over the last century, and this trend appears to be accelerating. But, preservation of the authentic and original structural timber is of prime importance. When quality materials and good craftsmanship are used in repairs, they become a part of the original structure. In many of the buildings, there is a demand from the craftsmen to do the carving again even if a major portion of the original carving is still surviving. It is better to avoid replacing the decayed timber carvings in a building. The principle of replacing only what is necessary applies to timber planks, mouldings and carvings. While repairing defects in timber structures is labour-intensive, the cost of purchasing high-quality repair materials is minimal.
To know more about the other defects in timber and the suitable timber treatment methods, visit the links given below:
