Not every surface defect on a quartz or engineered stone slab comes from the resin or the raw material. Some have their root in the mould: the condition of the mould surface, the type of release agent and how it is applied. This article summarises the most common mould-related surface defects and how to prevent them.
1. Sticking and tear-outs
Difficult release from the mould or carrier shows up as torn edges or a rough surface. It usually comes from an insufficient or uneven release film, the film losing effectiveness at curing temperature, or build-up on the mould surface.
Prevention: A product suited to curing conditions, regular mould cleaning and even application.
2. Marks, stains or residue
A release agent that is over-applied or incompatible with the resin system can leave marks and residue on the slab face or back. This returns as extra grinding/polishing and scrap.
Prevention: Aim for the thinnest film possible, track dosage against consumption and confirm compatibility with the resin through a trial.
3. Mould surface deterioration
Rubber moulds and belts hardening, cracking or losing their surface texture over time is reflected directly on the slab. An unsuitable release agent and insufficient cleaning can speed this up.
Prevention: Use a product compatible with the mould material and check mould condition regularly.
4. Uneven gloss and shade variation
Different gloss or shade across a slab can be linked to uneven distribution of the release agent, especially with manual application where film thickness varies from area to area.
Prevention: A product suited to the application method and, where possible, automatic or standardised application.
Quick checklist for root-cause analysis
- Does the defect appear on specific moulds or across the whole line?
- Has release agent consumption changed recently?
- Has there been any change in resin, curing temperature or curing time?
- Has the mould cleaning routine slipped?
- Is the defect concentrated in the first slabs after application?
From Biyopol Kimya: We can review the surface issues on your line together and run a trial with a release agent suited to your process. Request samples via our Quartz and Engineered Stone page.