Sealant? Make it yourself

In household practice, a sealing paste known as “Mendeleev’s putty” has long been used: it is commonly used to seal the joints of the frame and glass walls of aquariums.

This sealant is plastic at temperatures above approximately +45°C and does not crack after hardening. And although it is diluted by many organic solvents, it is better to soften it not with them but by heating.

The composition of “Mendeleev’s putty” is fairly simple (Table 1). By varying the ratio of rosin, wax, and linseed oil (boiled oil), sealants of different plasticity can be obtained.

“Mendeleev’s putty” is prepared as follows. Wax is melted in a metal (but not tinned!) vessel over low heat, preferably in a water bath, and crushed rosin is added with stirring, and after the foam disappears — sifted mummy (or ochre).

Heating with stirring continues until a homogeneous mass is obtained. Only after this is the linseed oil (or raw linseed oil) added to the melt; the hardness of the finished paste depends mainly on its amount. The process is stopped after the foam disappears, and the finished putty is poured into paper molds for storage. When used, the sealant is heated and applied to the product in a paste-like state.

Wax can be replaced with paraffin or stearin, and mummy (or ochre) with other powdered substances. However, this worsens the quality of the sealant; the same applies to using vegetable oil instead of boiled linseed oil in the composition.

“Mendeleev’s putty” is poorly suited for filling gaps between rubber gaskets and glass or metal due to the adverse effect of boiled linseed oil on rubber, so it is not used by motorists. However, some modification of the paste composition allows it to be used effectively for sealing joints of rubber with glass and metal as well. Thus, instead of boiled linseed oil (to which rubber is not resistant), castor oil can be used (to which rubber is resistant), and the filler in the form of mummy is replaced with ochre or most often simply omitted from the recipe (although this is not desirable).

The “automotive” homemade sealant is prepared from natural wax (paraffin, stearin), rosin, and castor oil. First, as with traditional “Mendeleev’s putty,” wax and rosin are melted in a water bath. The more rosin is added, the harder the sealant will be. Medium hardness is achieved with a rosin-to-wax ratio of 2:1 (when using paraffin or stearin, the composition must be determined experimentally).

After foaming stops while stirring the melt, castor oil is added — from 5 to 25 percent of the total amount of wax and rosin.

Note that omitting the dispersed filler from the recipe reduces the heat resistance of the sealant, so when the car is parked in hot sun the putty may begin to soften and run out of the gaps. However, when adding fillers it must be borne in mind that not all of them are neutral (Table 2). Thus, for example, ochre, mummy, soot, and graphite powder are unsuitable due to their tendency to promote corrosion, while aluminum and zinc powder, lead white, or red lead will, on the contrary, give the sealant anticorrosion properties.

To give the composition the desired color, a small amount of the appropriate dry pigment can be added, using the table as a guide; paste pigment can also be added.

The plasticity of the sealant depends on the amount of castor oil. Practice shows that the best results are obtained with putty whose viscosity after hardening is similar to hardened grease (solidol).

The sealant is applied into the gap between rubber and glass (metal) in molten form using a smooth wooden spatula; excess is easily removed with gasoline.

Putty made according to the proposed recipe has all the necessary consumer properties — it does not crack in cold weather and does not run in strong sun.

“Modelist-Konstruktor” No. 4’99, M. VEVCHOROVSKY