With a putty knife at hand

In today's car repair technology, a lot has changed and it is difficult to find a person who will spend as much time modelling large surfaces as they did a few years ago. Nowadays, the focus is mainly on the time and quality of the repair. But is it possible to completely abandon the use of putty? Of course not, because puttying is the basic skill that a painter learns at the very beginning of their training. This method is sometimes irreplaceable for levelling surface irregularities caused by hail or after bodywork.

Putty is, by definition, a filling compound that, after modelling and hardening, becomes resistant to many adverse chemical or physical conditions. Putty is intended to replace the damaged sheet metal and should combine two characteristics:

• be soft to work with, so that we can model any shape, which is then sanded in the preparatory process;
• form a hard coating after drying, which will provide a durable base for a full paint repair.

The basic and most important component of putty is a filler in the form of talc, of which there are many varieties on the market with different properties. Nowadays, so-called glass microspheres are also increasingly used in light fillers, which ensure better flow of the filler with lower viscosity, and at the same time are more chemically stable. It is also important to mention the right hardener, which is usually sold with the putty. We should use the hardener recommended by the manufacturer. This will ensure proper hardening and will not contribute to the formation of paint defects later on. The hardener contains organic peroxide, which binds all the putty components, but it is dangerous to the body and we must not forget about personal protective equipment when working with putty.

There are various types of filler available, which are used depending on the purpose, but most importantly, on the type of surface being repaired. Filling compounds can be categorised according to different properties. The first type of filler that should be mentioned is the so-called construction filler, which is used for large fillings. It contains glass or carbon fibres, which have a reinforcing function (e.g. CP 336 Glass by Profix). The resulting structure is durable and resistant to cracking, because the larger the surface, the greater the forces. It is recommended to use this product during repairs where the damage is significant and it is not possible to replace the element with an original one.

Another putty that is very popular is the so-called metallic putty, which can be recognised by the aluminium particles it contains (e.g. CP 335 Metallic by Profix). Thanks to the addition of metal to the filler, we obtain a characteristic feature, which is the even distribution of heat throughout the element and the absence of intense stresses that can result in cracking at the application site. It is especially recommended for components that are exposed to intense sunlight, are in a horizontal position or are exposed to engine heat. As aluminium rims have become increasingly popular, this type of putty has become the ideal solution for painters and is used for repairs.

Products characterised by high elasticity should also be mentioned. They are used for plastic parts that are exposed to higher stress (e.g. CP 341 Plastic by Profix).

Traditional polyester fillers with the general name Soft are used for thin layers (e.g. CP 334 Soft plus by Profix). They are used where the surface needs to be gently corrected to ensure an optimal repair result. Here, the new generation of light fillers should be mentioned, which are characterised by their reduced density (e.g. CP 339 Perfectly light by Profix). This is achieved by replacing heavy talc with a modern filler, such as microsphere beads.

For larger jobs, where it is necessary to apply filler to large surfaces with complex shapes, we use sprayable polyester putty (e.g. CP 332 finish by Profix). It is used especially in the reconstruction and restoration of vintage cars.

How to apply filler correctly?

First of all, we should get tools to make our work easier: metal ‘Japanese’ spatulas, plastic spatulas, rubber spatulas or trays on which we mix the filler with the hardener. The correct procedure for filling requires us to first clean the surface with a remover (e.g. CP 015 by Profix) to remove any dirt, dust, silicone or wax residues. Then, we protect the neighbouring elements with foil or paper so that we do not damage or stain them. Next, we can start sanding the surface to make it adhesive. Remember to use the sandpaper grade recommended by the putty manufacturer.

It is best to remove any sanding dust residue with a vacuum cleaner and then clean it again with silicone remover. The putty is made of two components in the proportions specified by the manufacturers (there are also one-component putties). To make working with the putty easier, putty manufacturers have used different colours for the hardener and putty, which, when mixed correctly, form a uniform colour.

An interesting solution is to facilitate the dispensing of the hardener into the putty using dispensers. In this case, we squeeze out the putty and hardener in the correct proportions, which can be adjusted depending on the ambient temperature. After mixing the putty, we only have a few minutes to apply it. We apply the putty to the repair area as needed, achieving a similar shape. After the filler has dried, we start sanding – tools such as sanding blocks, hand sanders and an orbital sander, preferably with dust extraction, will be necessary here. We use the indicated grades of dry sandpaper to sand the filler, preparing the surface for the next stage of the process, i.e. the filling primer.

Finally, here are some important tips to keep in mind when using putty.

• Remember that adding more hardener will not speed up the drying process, but it will certainly cause discolouration on the top layers of the paint. That is why it is so important to use the proportions recommended by the manufacturer.
• Do not apply too thick a layer of filler at once, as cracks may appear in the filler during drying.
• Dry putty at an ambient temperature above 5°C or with a radiator. However, the technical data sheets for the product in question will be necessary here, as too low or too high a temperature can affect hardening.
• It is not advisable to sand wet putty because it absorbs water, which can lead to corrosion and difficulty in drying. A puttied surface exposed to high humidity should be insulated with a primer as soon as possible.
• Use suitable thinners; for polyester putties, a polyester thinner is essential.
• When dealing with a one-component putty, remember that it may be sensitive to thinners contained in primers and varnishes.
• Do not apply polyester putty to reactive primers, as you will not achieve adhesion to the substrate.
• Before applying the putty, make sure which substrate you will be working with and choose a product with the right properties for it.