Sheet Moulding Compound (SMC) Compression Moulding for Sanitary Ware Material Selection, Process Characteristics and Manufacturing Considerations for Shower Trays and Basin Tops
A MANUFACTURER'S TECHNICAL WHITEPAPER
Jerry Wong
Homietek New Material Technology Co., Ltd.
No. 1699, Zuchongzhi Middle Road, Bacheng Town, Kunshan, Jiangsu, China
https://shower.homietek.com
November 2026
Abstract Sheet moulding compound (SMC) is a glass-fibre-reinforced thermoset composite supplied as a ready-to-mould sheet and shaped by compression moulding in heated steel tools. This whitepaper summarises, from a manufacturer's perspective, how SMC is selected and processed for sanitary ware — principally shower trays and wash basin tops — covering the material system, typical industry material parameters, the compression moulding cycle, tooling economics, quality control points, and the limitations that buyers and product designers should weigh against alternative
materials and processes. All process figures given are typical industry values for SMC moulding; product-specific data for Homietek products are published separately in the product documentation.
1. Introduction Shower trays and basin tops are demanding mouldings: they must hold precise dimensions over large, thin sections, resist hot water and household chemicals, present a cleanable, cosmetically consistent surface, and survive decades of daily use. Candidate processes include acrylic thermoforming with reinforcement, cast stone-resin (mineral casting), ceramic, and compression-moulded SMC. SMC occupies a distinctive position in this set: because the part is formed under high pressure in a closed, heated mould, dimensions and drain positions are defined by the tool steel rather than by downstream trimming, and both faces of the part replicate mould surfaces. This paper explains the material and process characteristics behind those properties, and the trade-offs they impose.
2. The SMC Material System SMC is a sheet-form intermediate consisting of: • an unsaturated polyester (or vinyl ester) resin paste; • chopped glass fibre reinforcement, randomly oriented in the plane of the sheet; • mineral fillers, low-profile additives, pigments, release agents and thickeners. The sheet is produced by metering resin paste onto a carrier film, distributing chopped glass fibre over it, sandwiching it with a second paste-coated film, and compacting the sandwich so the paste fully wets the fibres. After a maturation period in which the paste thickens to a leather-like consistency, the sheet is cut to charge blanks and compression moulded. Formulation is adjusted to the end use. Established formulation families include water-boiling-resistant grades, flame-retardant
grades, Class-A surface grades for visible cosmetic parts, highstrength grades, and low-density grades. Sanitary ware normally specifies a formulation direction combining hot-water resistance with a Class-A cosmetic surface, because the part lives in continuous contact with hot water and is judged first by its visible finish.
3. Typical Material Parameters (Industry Reference) The values below are typical published ranges for SMC sheet and moulding practice across the composites industry. They are provided as orientation for designers and buyers, and are not test results for any specific Homietek product. Parameter
Typical range
Sheet width
0.45 – 1.5 m
Sheet thickness
1.3 – 6.4 mm
Glass fibre content Fibre length Fibre orientation
20% – 35% by weight
12 – 50 mm
Random, in-plane
Charge weight
Typically within ±0.1
control
kg of target
Moulding cycle (single part)
3 – 5 minutes
Qualitatively, cured SMC is characterised by high dimensional stability and low mould shrinkage, good resistance to hot water and common bathroom chemicals, electrical insulation, and a hard, dense surface (commonly assessed by Barcol hardness, ASTM D2583). Water absorption is measured per ISO 62 in product qualification programmes.
4. The Compression Moulding Process Compression moulding of SMC proceeds in four steps: 1. Charge placement — a pre-cut, weighed blank of matured SMC sheet is placed into the open, heated mould. 2. Mould closing and flow — the press closes; under heat and pressure the compound softens, flows to fill the cavity, and conforms to fine surface detail. 3. Cure — the thermoset cross-links in the hot tool; the part rigidifies in its final geometry. 4. Demoulding and finishing — the part is ejected, deflashed, and passed to inspection and any secondary operations (drilling, assembly, packing). Three process consequences matter for sanitary ware: • Geometry is tool-defined. The part's dimensions, wall profile and drain position are guaranteed by the closed mould cavity, which is why moulded trays hold tight size tolerances across long production runs. • The cycle is short and repeatable. At a typical 3–5 minutes per part, with stable quality from part to part, the process suits volume production of identical parts. • Surface quality is replicated, not applied. Finish and texture transfer from the mould surface to both faces of the part; there is no gel-coat or paint step between the buyer and the base material.
5. Tooling and Production Economics Because every geometry requires its own steel mould, the economics of SMC differ fundamentally from cut-and-form processes: • Development lead time. A new product — from drawing and mould design through mould machining, trials and approval — typically takes 3–5 months before volume production. • Tooling investment. The mould is a significant one-time investment, made once per model and size. • Economic batch size. SMC moulding is economically suited
to programmes of roughly 20,000–50,000 parts per year. Below that range, mould amortisation dominates unit cost. The practical consequence for buyers is a two-route supply model. Where an existing model fits the project, production can start from standing tools immediately (the route also used for private-label supply of existing models). Where a new size or geometry is required, the project should be planned as a tooling programme — drawings and forecast volumes first, mould investment second — rather than as a simple purchase order. Homietek's published supply terms follow exactly this distinction: wholesale from stock and private label on existing models, and custom tooling & production for new geometries.
6. Application to Shower Trays and Basin Tops In shower trays, the mould-defined process permits very low finished profiles — for reference, Homietek's Serie L tray family is moulded at a 26 mm profile across 30 size variants from 800 × 700 mm to 1800 × 900 mm — with the drain position and fall to drain formed in the tool rather than machined afterwards. Thin profiles reduce step-over height for accessibility-led design while the closedmould process keeps the large, flat section dimensionally stable. In basin tops, the same process supports integrated-bowl designs with consistent bowl depth and wall thickness; Homietek's Serie KG family, for example, is moulded with a 460 mm bowl depth and 145 mm overall height across five widths from 600 to 1200 mm, in single- and three-tap-hole variants. In both product families, colour is compounded into the material rather than applied as a surface coating, so the visible surface is the structural material itself.
7. Limitations and Trade-offs A balanced assessment requires stating the material's constraints: • Cost position. SMC requires substantial press capacity and precision tooling, and its raw material cost is higher than commodity plastics; small production runs are uneconomic for the reasons set out in Section 5.
• Design is mould-bound. Once a tool is cut, geometry changes require tool modification or a new tool. Design flexibility after tooling is limited, and product development must therefore be front-loaded. • Surface character. Mould replication is faithful but the moulded surface can show texture variation that makes SMC less suited to applications demanding optical-grade gloss. • Process emissions. SMC production involves volatile organic compounds at the sheet-production and moulding stages, which must be managed at the production site with appropriate ventilation and process controls. • Machining. The cured composite is hard and strong; cutting and secondary machining require appropriate tooling and equipment.
8. Quality Control Points in Production Manufacturer quality control for SMC sanitary ware concentrates on: 1. Incoming sheet control — sheet weight per unit area and charge weight (typically held within ±0.1 kg of target), sheet maturation state, and paste viscosity windows for both impregnation and moulding. 2. In-process control — press parameters (temperature, pressure, closing speed, cure time) held to the validated window for each tool. 3. Part inspection — dimensional checks against the tooldefined geometry (footprint, drain position, profile height), surface inspection for the cosmetic face, and completeness of cure. 4. Batch traceability — parts traceable to sheet batch and production shift, so any field issue can be isolated to a defined production population.
9. Conclusion SMC compression moulding offers sanitary-ware manufacturers a route to large, thin, dimensionally stable parts with an integral
cosmetic surface and short, repeatable production cycles. Its constraints — tooling investment, mould-bound geometry and an economic volume threshold — are the mirror image of its strengths, and they shape how buyers should engage: existing models for speed and private label, tooling programmes for genuinely new geometries. Specified with those economics understood, SMC is a durable and well-proven material platform for shower trays and basin tops.
References • EN 14527:2016, Shower trays for domestic purposes — European standard for shower tray requirements and test methods. • ASTM D2583, Standard Test Method for Indentation
Hardness of Rigid Plastics by Means of a Barcol Impressor. • ISO 62, Plastics — Determination of water absorption. • Industry design guidance on sheet moulding compound (SMC) and bulk moulding compound (BMC) materials and compression moulding practice, composites industry association publications.
About the author: Jerry Wong is Manager at Homietek New Material Technology Co., Ltd., a manufacturer of SMC shower trays (Serie L, Serie U, Serie TS) and Serie KG basin tops supplying trade and project buyers. Product documentation: https://shower.homietek.com