Introduction

Cracks in timber beams need not affect the overall integrity of the structure. Indeed, cracks in timber beams can be taken as a positive visual feature of the timber, which, in conjunction with the timber grain, distinguish timber from the more uniform man-made materials such as steel and concrete.

In spite of this, there is a steady demand amongst specifiers for crack-injection of beams for the following reasons:

1. To improve fire resistance

2. To improve resistance to weathering

3. To improve mechanical performance

4. To prevent parasitic attack

Repair Method

Cracks, shakes, warps and fissures are formed as a result of the timber giving up moisture and shrinking. This may occur as part of initial drying or subsequent changes, during service, in the Equilibrium Moisture Content. The EMC of timbers inside buildings can range from 9% to 14%. Fibre saturation is reached in constructional softwoods at about 28%.

For cracks and splits that are greater than 5mm wide the void can be filled with an epoxy mortar, but if the crack penetrates more than 30% through the timber it will be necessary to provide dowels across the filled section in order to 'stitch' the two halves together. The advice of a Structural Engineer should be taken with regards to the number, diameter, length and spacing of the dowels. The dowels can be made of glassfibre, carbonfibre, steel or stainless steel. We normally recommend the use of epoxy/glass or epoxy coated steel, set in an epoxy adhesive.

Clean out cracks with a saw blade and vacuum clean. Fill cracks with epoxy mortar, using a primer for hardwoods.

Drill holes across the filled crack into sound timber on the opposite side.

Inject epoxy adhesive from the hole base outwards using an extension tube.

Fit dowels (into the epoxy adhesive) at 100-150mm intervals, to act as connectors. Cap off holes with epoxy mortar