Where plaster is used for filling dents and cracks in plasterwork, fillers are used for filling larger indentations in wood. The main difference is that fillers have to match the colour of the piece of wood and require an elastic nature to cope with the movement of wood. It is also important that the right type of filler is used. Bear in mind the type of finish you want to achieve and the way the wood will be used, from a tough durable repair to exterior woodwork (such as doors and window frames) where the repair will be painted over; a repair to a floorboard; or a repair to a piece of fine wooden furniture. The most common fillers are cellulose, wood stopping, plastic wood, epoxy resin-based filler, and shellac and wax sticks.
Cellulose fillers come in powder form for mixing with water, or ready mixed in tubs or tubes. These are ideal for repairing holes in particle board because an exact match can be difficult, even with a stain or pigment. Wood stopping is a traditional filler with very good adhesion, which can be smoothed and shaped when hard.
Wood stopping is available in both interior and exterior grades.
Plastic wood is available in two-part or one-part form. It is formulated to resemble wood when dry and comes in several wood shades to provide a close colour match. Plastic wood dries out very quickly, so always replace the lid immediately. To get a good strong adhesion, the wood must be clean and dust free. Plastic wood is solvent-based, so you’ll need to work in a well-ventilated area or wear a mask. Once set, it shrinks a little, so leave it a little thick to dry, then shape it and smooth it just like wood.
Epoxy resin-based fillers also come in wood colours and provide a very strong adhesion. The wood needs to be treated first with a hardening agent in order to ‘toughen up’ any soft wood fibres. These fillers set by chemical action, which, once started, cannot be stopped. The filler and hardening agent are mixed together according to manufacturers’ instructions; only mix enough at a time to work for a few minutes to avoid waste.
Shellac and wax sticks are generally used for repairs to fine furniture and under traditional finishes. Shellac sticks are sold in a variety of colours and are a concentrated form of the shellac used in French polishing. The manufacturers of wax finishes also make wax sticks for small repairs. These coloured sticks are designed for use on surfaces, which will be waxed, or on pieces that are already polished. Wax and shellac sticks need to be warmed with a soldering iron and the molten wax or shellac pushed into the chip or hole in the wood with a small filling knife and any excess scraped off carefully when dry.