When most people buy a quartz sink, they only focus on appearance and price, rarely stopping to think: How is a quartz sink with its warm texture, hardness, and wear resistance actually made? As a core component used daily in the kitchen, its production process directly determines its lifespan and user experience.

In this first article of the "Quartz Sink Manufacturing Process" series, I'll take you inside the factory and break down the entire production process from start to finish. This article focuses on the first half of the process – from material pouring to initial forming – covering key steps such as pouring, curing, cutting, polishing, and hole punching, giving you real insight into how a high-quality sink is born.

Step 1: Material Pouring – The "Starting Point of Life" for a Sink

The production of a quartz sink begins with material pouring. It sounds simple, but this is actually the most critical step in the entire process, having the greatest impact on the quality of the finished product.

What are the raw materials?

The main raw materials for a quartz sink are natural quartz sand (about 85%-93%), high-performance resin (about 7%-15%), plus a small amount of pigments and additives. These materials are mixed evenly according to strict formulas to form a flowable mixture.

The core difference between different brands and price points lies in this formula – the purity of the quartz sand, particle size distribution, resin quality, and pigment stability. Each factor affects the final product's hardness, stain resistance, and weather resistance.

The role of fiberglass molds

The mixed slurry needs to be injected into fiberglass molds for shaping. Why fiberglass? This material has an extremely smooth surface, releases easily from molds, is corrosion-resistant, and has excellent dimensional stability. It's highly suitable for products like quartz sinks that demand high surface smoothness and dimensional precision.

Molds typically consist of an upper mold and a lower mold. The lower mold determines the internal shape of the sink (the concave basin area), while the upper mold forms the exterior and edges of the sink. During pouring, the mixed slurry is evenly injected into the closed mold cavity.

Key process point: Vacuum vibration pressing

Pouring isn't just "pouring it in" and being done. To ensure the finished product has no air pockets and uniform density, vacuum vibration pressing is required during pouring – applying vibration and pressure simultaneously in a high-vacuum environment to expel air from the mixture, allowing the material to densely fill every corner of the mold.

If this step isn't done properly, visible bubbles and pinholes will appear in the finished product, directly affecting the sink's strength and water resistance. Good brands repeatedly fine-tune the parameters in this stage, and some even use multi-stage vibration pressing to ensure density consistency across all batches.

Step 2: Oven Curing – 2 Hours at 80°C

After pouring is complete and the mold is closed, the sink is far from "solidified" and needs to go into an oven for high-temperature curing.

Why is an oven needed?

The resin in the quartz mixture cures very slowly at room temperature and has insufficient strength. Heating accelerates the resin's cross-linking reaction, allowing the quartz particles and resin to form a strong, integrated whole. This process is professionally called thermal curing.

Temperature and time: 80°C for 2 hours

Based on experience, 80°C for 2 hours is the ideal curing parameter. At this temperature, the resin neither decomposes or discolors due to overheating, nor does it cure incompletely due to insufficient heat.

• Too low (e.g., 60°C): Longer curing time, reduced production efficiency, and potential issues with insufficient surface hardness.

• Too high (e.g., above 100°C): May cause resin aging and discoloration, or even generate internal stress that leads to cracking during later use.

During the 2-hour baking process, the material inside the mold gradually transforms from a flowing slurry into a hard solid. Temperature uniformity inside the oven is critical – good factories use circulating hot air ovens to ensure the temperature difference at any point on the mold is no more than ±3°C.

Secondary shaping: Correction after cooling

After being removed from the oven, the sink is still warm and requires secondary shaping. Why? Because during high-temperature curing, the material undergoes slight thermal expansion and contraction. Additionally, when the constraints of the mold are released, the sink's edges may experience minor deformation.

Secondary shaping is typically done by placing the semi-finished sink on a dedicated shaping fixture and allowing it to cool naturally to room temperature (or using air cooling), stabilizing the sink's shape. Some factories perform an initial dimensional inspection at this stage – pieces that exceed deformation limits are either reworked or scrapped.

Doing this step well ensures precise dimensions during subsequent cutting and hole punching. Doing it poorly leads to increasing deviations the further you process.

Step 3: Trimming the Bottom, Trimming the Edges, and Drilling the Overflow Hole – From "Blank" to "Rough Shape"

After oven curing, the sink can be understood as a "blank" – the general shape is there, but the bottom is uneven, the edges have flash, and there are no drainage or overflow holes yet. This step accomplishes three basic machining operations: trimming the bottom, trimming the edges, and drilling the overflow hole.

Trimming the bottom

"Trimming the bottom" means cutting away the excess material on the bottom of the sink. During pouring and curing, a thin layer of material or gate residue may form on the sink's bottom. This needs to be leveled using a lathe or CNC cutting equipment to reveal a flat basin bottom.

After trimming the bottom, the sink's depth dimension is determined. The precision of this step directly affects whether the sink sits level after installation – if the bottom is uneven, gaps may appear when installing an under-mount sink, potentially causing the sink to wobble.

Trimming the edges

The four edges of the sink also need trimming. During mold pouring, material can overflow from the mold gaps, forming flash (burrs). Trimming the edges uses high-speed rotating diamond saw blades or water jets to cut away the excess flash along the sink's outer contour, making the outer edges neat and dimensionally precise.

Good edge trimming requires smooth edges, no chipping, and good perpendicularity on all four sides. Inferior products often cut corners (literally and figuratively) at this step, resulting in uneven edges or even wavy cuts.

Drilling the overflow hole

The overflow hole is a small hole near the top of the sink's side wall, connected to an overflow channel. When a user forgets to turn off the faucet, the water level rises to the overflow hole and automatically drains out, preventing flooding.

A specialized drill bit is used to drill the overflow hole, with the hole diameter typically between 20-30mm. Positional accuracy is very important – if it's too low (it won't serve its overflow function), or too high (it may compromise the edge strength of the sink). Overflow systems with multiple holes (e.g., double or triple holes) require all holes to be drilled in one operation with single positioning to ensure coaxiality and proper spacing.

Step 4: Polishing the Four Edge Burrs – Achieving a "Non-Cutting" Finish

After edge trimming, the four edges of the sink are dimensionally correct, but the edge cross-sections are typically sharp and rough – touching them can easily cut your skin. The task of this step is to polish the four edge burrs, with a simple, direct goal: non-cutting.

How to polish?

Use hand-held pneumatic sanders or automatic edge polishing machines, equipped with various grits of sandpaper or diamond grinding wheels, polishing progressively from coarse to fine:

• Coarse grinding (60-80 grit): Quickly removes burrs and large saw marks left from edge trimming.

• Medium grinding (120-180 grit): Smooths out coarse grinding marks and begins to round the edges.

• Fine grinding (240-320 grit): Gives the edges a delicate, non-scratchy feel.

During polishing, care must be taken to ensure natural edge transitions – you need to remove the sharp corners without turning right angles into rounded ones (unless a rounded edge is the intended design). Experienced craftsmen repeatedly test with their hands until the edges feel smooth with no prickly sensations.

Why is this step important?

Polishing the four edge burrs affects not only safety (installers and users frequently contact the edges) but also the quality of subsequent surface treatments. If the edges have burrs or irregularities, subsequent coating applications (spray coatings or non-stick coatings) may suffer from poor adhesion or peeling.

Additionally, this step is an intuitive indicator distinguishing cheap products from high-quality ones. A quartz sink costing a few hundred yuan often has edges that are hastily polished or not polished at all – they feel prickly to the touch. A product costing two or three thousand yuan has edges that are smoothly and comfortably rounded – the details show the quality.

Step 5: Punching the Circular Overflow Channel – Opening the Overflow Passage

The overflow hole has been drilled, but the overflow channel is not yet open. The overflow design of a quartz sink typically involves drilling a small hole on the inside of the basin wall, connected via an internal channel to the drain connection on the outside of the basin wall. This step is "punching the circular overflow" – opening this channel completely.

How to punch?

A specialized punch (a conical or cylindrical diamond tool) is inserted into the overflow hole opening and rotated under pressure, following the preset channel direction to punch through to the drain connection on the sink's outer wall.

The resulting channel must be circular – this is the origin of the term "circular punching." A circular channel offers the least water flow resistance, is less prone to clogging, and provides better sealing.

Common problems

If the punch goes off-center, the channel is not circular, or the inner wall of the channel is rough, it can lead to:

• Slow overflow drainage – water spills over the sink edge before draining out

• Easy accumulation of dirt and bacteria

• Poor sealing when installing overflow fittings, with potential for leaks

Good factories use positioning fixtures at this step to ensure the punch's angle and depth are precisely controlled. After punching, they blow high-pressure air through the channel to check for smooth passage.

Step 6: Opening the Faucet Hole – Reserving the Mounting Location

Most quartz sinks come with a reserved faucet mounting hole. Although many users now choose deck-mounted faucets (the faucet is mounted on the countertop, not occupying the sink), some sink models still use sink-mounted installation – meaning the faucet is fixed directly to the sink's edge.

Hole location

The faucet hole is typically opened at the center of the sink's rear rim or in one corner of the side rim (depending on the design). The standard hole diameter is 32-35mm, suitable for the bases of the vast majority of kitchen faucets.

Drilling process

A diamond hole saw combined with a water-cooled drill press is used to drill the circular hole in one go. Because quartz has very high hardness (Mohs hardness of 6-7, second only to tempered glass and diamond), ordinary drill bits can't penetrate it at all. While the diamond hole saw rotates continuously, water must be constantly sprayed for cooling, preventing localized overheating that could cause resin decomposition or micro-cracks.

Special requirements

If the user needs to install a water filter faucet or soap dispenser, two or even three holes may be required. These need to be done together during this faucet hole opening step, with spacing that conforms to industry standards (typically 100-120mm center to center).

After opening the hole, the hole edge needs to be chamfered (ground into a small arc) to prevent hand injuries or cuts to the water supply hose. This step is easily overlooked but directly reflects the level of workmanship.

Step 7: Polishing Out Air Bubbles – Polish If Bubbles Exist, Skip If Not

During the pouring and curing process of a quartz sink, despite vacuum vibration pressing, tiny air bubbles may still remain inside the material or on the surface. These bubbles become exposed during subsequent cutting and polishing, forming pinhole-sized pits or porosity.

Why polish out bubbles?

• Aesthetic issues: Exposed bubbles create small pits that trap dirt, affecting visual quality.

• Waterproofing issues: If a bubble penetrates the surface layer, water or oil may seep inside, leading to discoloration or mold growth over time.

• Hygiene issues: Tiny pits are breeding grounds for bacteria and are hard to clean.

How to inspect and handle?

This step is performed on demand – workers or quality inspectors carefully examine the entire surface of the sink under strong light (especially corners, edges, areas around holes, and other stress-concentrated zones), locating points where bubbles are exposed.

• If bubbles exist: Use a small hand-held polisher with a fine grinding head (such as a conical diamond grinding pin) to grind away the material around the bubble, exposing fresh, dense quartz layer. After grinding, the area needs to be filled with resin paste of the same color, then sanded smooth to match the surrounding surface.

• If no bubbles exist: Skip this step and proceed to the next process (fine surface polishing, applying protective coating, etc.).

The deeper significance of this step

"Polish if bubbles exist, skip if not" may seem casual, but it actually embodies the principle of quality control: don't do unnecessary work, but problems must be addressed. Good factories record the bubble rate for each batch and use that data to optimize the vacuum vibration pressing parameters during pouring, reducing bubble formation at the source. Poor factories often turn a blind eye to bubbles – after all, spraying a layer of dark protective paint can hide them – but after a few months of use when the paint wears off, the bubbles will be exposed.

Summary: Seven Steps in the First Half Lay the Quality Foundation

The seven steps above are the key processes in taking a quartz sink from raw material to initial forming:

For a quartz sink to be durable, good-looking, and functional, none of these seven steps can be done carelessly. In the next article, I will continue introducing the subsequent processes: fine surface polishing, applying nano protective coating, installing accessories, quality inspection and packaging – so stay tuned!

If you're currently using a quartz sink at home, why not check it against this article – Are the sink's edges prickly to the touch? Are there small pinholes in the basin bottom? Is the overflow hole unobstructed? These are all useful tips for judging quality. Feel free to share your user experience in the comments section!