Repairing a cracked bumper, sealing a boat, or maybe building a pond liner? For these tasks, the classic duo of polyester resin and glass matting is second to none. It is a cheaper solution than epoxies and ideal for repair or construction work.
Although the laminating process may seem simple, it is easy to make mistakes that will ruin the result. What proportions should you use? How long does the laminate take to dry? We answer the most important questions.
What is polyester-glass laminate?
Laminate is a composite made by combining two materials with completely different properties:
- Glass matting – serves as reinforcement (the skeleton). It is responsible for mechanical strength.
- Polyester resin – serves as a binder (filler). It provides shape, seals the surface, and protects the fibers.
Step 1: Surface preparation – the key to success
Before you open the resin can, you must perfectly prepare the substrate. Even the best resin will peel off a greasy or smooth surface.
- Matting: Sand the surface with sandpaper to increase mechanical adhesion.
- Degreasing: This is a mandatory step. Use technical acetone, which effectively removes grease and evaporates quickly. Avoid naphtha, which can leave a greasy film.
Step 2: Resin and hardener – how much to add?
The most common question from beginners is: how much hardener should be added to polyester resin?
- Polyester resins (e.g., structural) usually require the addition of a hardener (initiator) in an amount of 1% to 3% by weight.
- Important: Always check the product label!
What happens if the proportions are wrong?
- Too little hardener: The curing process may not occur at all or may take forever, and the laminate will remain sticky.
- Too much hardener: The mixture will heat up quickly (exothermic reaction) and harden in the cup before you have time to apply it. It may also crack after drying.
Step 3: Applying the matting (Laminating)
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Prepare the matting: Cut the glass matting into appropriate pieces.
Pro tip: If you are joining pieces with an overlap, do not cut them with scissors, but tear them by hand. This will leave ragged edges that will become invisible when saturated with resin. - Priming: Apply a thin layer of resin mixed with hardener to the prepared surface.
- Application: Lay down the matting and saturate it with resin using a brush or roller. Do not paint it like paint! Use a "stippling" motion (tapping the tip of the brush) to thoroughly press the resin into the fibers.
- De-airing: This is a crucial step. You must push out all the air bubbles trapped under the matting. Leaving air inside weakens the laminate.
Polyester resin drying time – how long do you need to wait?
Many customers ask about the drying time of polyester resin. This process (gelation) usually begins within 15–25 minutes of adding the hardener (at room temperature).
- After this time, the resin stops being liquid and becomes jelly-like (no more corrections can be made!).
- Preliminary curing occurs after a few hours.
- The laminate usually achieves full mechanical hardness and chemical resistance after a few days.
Which matting should you choose?
At Gaz-Bud, you will find various types of reinforcement. The most popular is 450 glass matting (450 g/m²). It is versatile – thick enough to build layers quickly, yet still flexible.
- For precise details and complex shapes, choose thinner matting (e.g., 150 g/m²).
- Thicker matting is used for large, flat surfaces (e.g., building tanks).
Do you need materials for your project?
See our selection of glass matting and polyester resins.
