Properly prepared linseed oil putty is ecological and consists of natural raw materials – linseed oil and selected chalks. It is especially favored in window restoration and traditional construction, where longevity is crucial and linseed oil paints are used. It possesses very good adhesion to glass. Linseed oil putty can be used for both interior and exterior works, as well as for filling small cracks and nail holes.
Before application, the putty must be properly prepared. Excess oil should be removed, and the putty must be kneaded thoroughly so that it does not stick to fingers.
Surfaces must be clean and dry. Before applying the putty, the window rabbet (groove) must be primed with linseed oil varnish. In certain cases, linseed oil paint in a chosen tone is also used. Once the varnish or linseed oil paint has dried, the window rabbet should be coated with shellac to prevent the wood from absorbing the oil from the putty, which would cause it to become brittle and crack over time. The applied window putty can be painted immediately, but there are conditions where it is better to wait for it to dry slightly. If the putty is used for window glazing (sealing), it is better to wait 1–2 days after application for the top layer to form a skin; applying paint with a brush that has stiffer bristles may cause streaks in the putty, resulting in an uneven finish. Paint can be applied sooner if using a brush with softer bristles. Correct practice involves coating the putty with linseed oil paint, especially on the exterior of the window. This allows it to maintain elasticity in the long term.
Linseed oil putty is also useful for filling cracks in wood. For cracks of 3–4 mm, putty alone can be used. This method of crack filling is suitable for windows, floorboards, and cladding boards. The putty can also be tinted, making it suitable for floorboards that will be finished with tinted hard wax oils. A condition to observe: cracks must be primed with linseed oil or linseed oil varnish before applying the putty. Deeper cracks in log buildings should also be saturated with linseed oil varnish, then tightly filled with tow (oakum) that has also been soaked in linseed oil, and finally covered with linseed oil putty. The top surface of the putty should be coated with varnish or linseed oil paint, which provides better resistance to solar UV rays.
The compatibility of linseed oil coatings with natural linseed oil putty is a recipe tested over centuries. Properly performed puttying works protect the wood in the long term, which is particularly significant for windows exposed to increased moisture levels. Use natural and proven wood finishing materials!