Putty and Fillers
It’s inevitable – a little scratch here, a tiny crack there, an unwanted gouge, or an unsightly nail hole. Just about every woodworker will run into a defect of one type or another on a project – more often on older furniture, cabinetry, or trim work. Sanding is one way to deal with some of these defects. An alternative approach is to use wood putty or wood filler. In this article we’ll look at the difference between the two.
On surfaces that have been sanded and top coated, you can use small amounts of putty to fill in tiny dents. Different colours of the same putty can be mixed together to get an accurate colour match.
Putty doesn't harden like filler does. It stays slightly soft and is less likely to crack down the road. It will either say "putty,” "non-hardening" or both on the container.
Dry Time Indicator
DAP's stainable wood filler has a time indicator on it, so it goes on pink and dries to a natural colour. This allows the user to clearly see when the filler is dry, and can be sanded.
The primary ingredients of wood putty are hydrous magnesium silicate (aka “talc,” a naturally occurring clay mineral), titanium dioxide (a common anti-caking and whitening mineral used in paint), and crystalline silica (quartz dust). Putty has a texture much like paste wax or play dough and is both flexible and non-hardening, which makes it easy to use, particularly with a putty knife. Because it doesn’t harden, putty expands and contracts with wood movement, making it less prone to crack or break. However, it doesn’t sand well, so you should use it on surfaces that are already sanded and top coated. Wood putty is available in a range of basic wood tones, and you can blend the colours to get a perfect match for the job at hand.
Painter’s putty is a white, non-hardening putty that can be used indoors or outdoors to fill cracks and nail holes in trim and other woodwork. Wood should be primed before painter’s putty is applied and painted after the putty has skinned over.
There are two general types of wood fillers – those used to fill holes and cracks in wood, and those used to fill pores in open-grained wood when you want to achieve a super smooth finish as found on pianos and highly polished furniture. This latter group of fillers are more properly called “pore fillers” or “grain fillers” (for more information read “Pore Fillers” in the Oct/Nov 2017 issue).
Wood filler for holes and cracks is typically made of natural materials like silica (quartz dust) or limestone, latex, titanium dioxide and various solvents. Some contain wood fibres. They can be either solvent or water based and come in neutral as well as various wood shades. Most are made for interior use – for exterior use make sure you check the product label. Unlike putty, fillers dry quickly and hard. Once dry they can be sanded, stained or top coated. You’ll also find that some contain a dry time indicator – they go on pink and then dry to a neutral colour.
Plastic wood can either be a putty or a filler. If the product description states “non-hardening,” then it’s putty; otherwise, it’s wood filler.
Epoxy putty refers to a wide variety of special-purpose polymer putties for bonding metals, plastics, glass and wood, available in a two-part mixable format (an epoxy resin and a hardener) or an all-in-one kneadable stick. Epoxy putty made specifically for wood can be sanded, stained and painted.
Bondo is a brand name for automotive putty, and like epoxy putty it’s a two-part putty consisting of a resin and a hardener that dries very quickly but is not flexible.
So, there you go. Use a putty on surfaces that are already sanded and top coated, and a wood filler on bare surfaces before staining, sanding or topcoating.