Appendix 5: Wood Fillers

The fills mentioned are ones used traditionally by cabinet makers or in the conservation field. This list of fills is an introduction to this broad subject and is not extensive. Experiments often will be needed to determine the best type of fill for a specific object.

Gypsum Plaster

• is mixed with polyvinyl acetate AV 101 and methyl methacrylate AC 135 in proportions of 3:1:1 with 2.5% methyl cellulose; and
• is a strong fill which can be worked and coloured.

Shellac Burning-in Stick

• traditionally used to fill cracks on wood where French polish has been applied; and
• skill is needed to apply this material but it is easy to sand and colour.

Two-part Filler

• uses an epoxy or polyester resin;
• can be mixed with micro-balloons, fine sawdust or an epoxy filler to produce hard fills which can be worked as well as coloured with pigments or paint; and
• the fills yellow with age.

Paraloid B-72

• a 15 % solution in either acetone or ethanol can be mixed with micro-balloons to produce a fill which can be carved, sanded and coloured with pigments or paints;
• this type of fill can be soft or hard depending on the quantity of micro-balloons used; and
• it will not yellow with age, unlike epoxy or polyester fills.

Plaster of Paris

• may be mixed with micro-balloons to make a lightweight fill;
• can be moulded, carved, sanded, tooled, coloured with pigments, painted, waxed and so on; and
• traditionally, linseed oil was applied over plaster to make a transparent fill. This yellows with age.

Polyfilla

• is a cellulose derivative;
• may be mixed with sawdust or micro-balloons to produce a very lightweight material which can be easily worked and coloured; and
• should not be used for fills that will be stressed or strained.

PVA

• polyvinyl acetate adhesive or white glue is best mixed with fine sawdust or micro-balloons to prevent shrinkage of the fill; and
• it can be easily worked but may be difficult to colour.

Vulcanising Silicone Resin (RTV)

• the RTV resin (Dow Corning 734 and 738) may be mixed with micro-balloons (2-3 parts resin to 1 part micro-balloons) to produce a lightweight fill which can be moulded, carved, sanded and painted; and
• do not use on wooden objects which have metal components as it may enhance corrosion.

Wax

• beeswax, microcrystalline wax and carnauba have been used for fills;
• these waxes may be used individually or mixed to vary the individual qualities of the waxes (e.g. to increase hardness);
• they may be purchased coloured or may be coloured with pigments; and
• fills made from wax can be moulded, carved and worked with heat and solvents.

Wax and Resin

• tree resin such as dammar is often mixed and melted together with flakes of shellac;
• sawdust and micro-balloons may be added to the molten mixture to make a lightweight fill; and
• this fill is difficult to sand, carve, colour with pigments or paint.