Dilute polyester resin according to data sheet or freehand


In general, polyester resin can be thinned with different additives. However, not only the desired viscosity during processing must be considered, but the effect on the setting behavior. Curing degree, breaking strength and toughness are usually directly influenced.

Organic agents volatilize during curing

Usually and for new products also legally required is a data sheet of the manufacturer to polyester resin. It specifies the possible diluents and above all the correct dosages. The most common diluent is styrene but other organic solvents are useful.

As a chemical and physical reaction during the setting and curing of polyester resin, the diluent volatilizes by evaporation from the resin. Ideally, it acts only as a catalyst and does not affect the crosslinking of the molecules and structures in the polyester resin. For this, however, a sufficient amount of polyester resin must be present.

Hands-free thinning

If no data sheet is available or if a hands-free dilution is to be carried out for other reasons, in addition to styrene-based ready-to-use diluents, the following organic solvents may be used:

  • Nitroverdünnung
  • acetone
  • spirit
  • ethanol

The test is recommended with a sample quantity in which the conditions with regard to pot life, added amounts, curing behavior and material result can be evaluated. For all load-bearing or mechanically stressed components only styrene should be used as diluent.

Reference values ​​and dosage

In order to maintain approximately the original properties when diluting polyester resin, three reference values ​​must be taken into account:

  • The total volume
  • The amount of hardener
  • The amount of thinner

In general, an addition of hardener and diluent of more than ten percent on the total volume must be avoided. As a rule, the thinner shares are between five and eight percent. The lower the dilution, the smaller is the interference in the properties of the cured polyester resin.

The ratio between hardener and thinner should be affected as little as possible. In practice, this means that for five to ten parts of thinner, about one part of hardener should be added. However, the addition of hardener must not exceed four percent of the total volume.

Tips & Tricks

Almost all organic diluents belong to the hazard classes "Xn" for harmful and "F" for highly flammable. If possible use thinners only outdoors and / or with respiratory protection. Avoid embers, open fires and sparking machines near work.


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