Mould Sealer — Sealing Porous Masters & Moulds

Primary uses

• Pattern pore sealing
• Release compatibility preparation
• Detail preservation

Applications

• Sealing plaster, wood, MDF and concrete patterns before mould rubber is applied
• Preparing porous masters for composite lay-up
• Protecting patterns that will be reused

Advantages

• Prevents mechanical lock between rubber and porous pattern, which is the most common cause of a destroyed pattern
• Lets release agents work as intended by giving them a non-absorbent surface to sit on
• Preserves patterns for reuse instead of treating them as consumables

Limitations to consider

• A heavy sealer coat fills fine detail, so application discipline matters on ornament work
• Not every sealer is compatible with every rubber system, and some cause cure inhibition
• Coverage, drying and compatibility are declared by the supplier for the exact product and substrate
• Decorative and architectural work is judged by eye. Colour, gloss, texture and translucency shift with batch, substrate, dosage and finishing method, so approve a physical sample panel made by your own process before a production run and keep it as the reference for later deliveries.
• Mix ratio, pot life, working time, demould time, full-cure schedule, hardness, tear strength, elongation, shrinkage, viscosity and temperature resistance are properties of one specific supplier system. They are never quoted here from memory or by analogy with a similar product; they are read from the supplier data sheet for the exact material offered and confirmed at quotation.

How to choose the right grade

• Start from the casting material and the number of parts the mould has to produce, because durability and detail pull in opposite directions
• Describe the pattern itself — its material, porosity, undercuts and whether it can be destroyed — since that decides the mould strategy before any product is chosen
• State the shop conditions the work happens in, including temperature, ventilation and whether the job is poured in a box or brushed on in place
• Name the pattern substrate and the rubber system, since the sealer has to satisfy both
• Confirm with the supplier that the sealer does not inhibit the cure of the rubber you intend to pour
• Mould-making and casting behaviour depends on the pattern, the shop temperature and humidity, the mixing method and the operator. A production-representative trial on your own pattern and in your own shop conditions is the only honest way to qualify a material before a run is committed.
• Exact specification is confirmed against supplier documentation at quotation.

Typical grades

• Solvent-borne and water-borne products as the supplier offers them
• Products the supplier matches to specific substrates and rubber chemistries
• Buyers search this category by grade name, and those names describe what the workshop needs rather than what is asserted here. Which grade a specific offer corresponds to, and what the supplier declares for it, is read from the technical documentation issued for the exact material quoted.
• Materials in this category interact: rubbers, releases, sealers, resins, pigments and fillers can inhibit cure, stain a surface or shorten mould life when they are combined outside the combinations the supplier has tested. State every material already in the process at enquiry so compatibility is checked against supplier documentation rather than discovered on the shop floor.
• Reactive materials age in the container, and moisture-sensitive systems age faster once opened. Order against real consumption rather than against a discount, and confirm the shelf life the supplier states for the exact product and pack.