Translation of Granite Fracture Repair Technology

1. Common Causes of Granite Fractures and Core Repair Requirements

(1) Main Causes of Granite Fractures

• External Impact: Bumps and collisions during transportation, improper force application during installation (such as excessive single-point load-bearing), and heavy object impacts during daily use (such as hard objects falling on kitchen countertops) are the most direct causes of granite fractures. Although granite has high hardness, it is quite brittle. When the local area bears external force exceeding its flexural strength, it is prone to developing penetrating cracks or complete fractures.
• Temperature Stress: Granite has a low thermal expansion coefficient (approximately 5-8×10⁻⁶/℃). However, under extreme temperature changes (such as outdoor granite experiencing alternating summer exposure and heavy rain, or kitchen countertops being exposed to long-term high-temperature radiation near stoves), internal stress will be generated inside the stone due to uneven temperature. When the stress exceeds the tensile strength of the stone, cracks will gradually form and even lead to fractures.
• Structural Deformation: If the installation foundation of granite (such as walls, cabinets) settles or deforms, or the fixing method is improper (such as failing to reserve expansion joints), long-term uneven stress will cause the accumulation of internal stress in the stone, eventually leading to fractures.
• Material Defects: Some granites have natural cracks, interlayers, or loose structures. Under the inducement of external factors, these defects will become “breakthrough points” for fractures, significantly increasing the probability of fractures.

(2) Core Repair Requirements

• In Terms of Appearance: After repair, the glue marks should be as integrated as possible with the color and texture of the granite, avoiding obvious color differences or glue lines. Especially for decorative surfaces (such as countertops, wall surfaces), the visual effect is a key evaluation indicator.
• In Terms of Performance: The glue should have hardness, strength (flexural, compressive), weather resistance (outdoor use requires resistance to high and low temperatures, ultraviolet rays), and chemical resistance (kitchen countertops require resistance to oil stains, acid, and alkali corrosion) similar to those of granite. This ensures that the stone can bear the use load for a long time after repair and avoids secondary fractures.

2. Types and Characteristics of Glues Suitable for Fractured Granite

(1) Epoxy Resin Glue: The “First Choice” for Granite Repair

Core Characteristics

• High Bonding Strength: The shear strength of epoxy glue on stone can reach 15-25MPa, and the tensile strength can reach 10-20MPa, far exceeding the tensile strength of granite itself (approximately 5-10MPa). After repair, the strength of the fracture surface can even exceed that of the stone itself, effectively avoiding secondary fractures.
• Good Hardness Matching: After curing, the Shore hardness of epoxy glue can reach D75-D85, which is close to the hardness of granite (Mohs hardness 6-7). After repair, the surface is not prone to scratches or dents, maintaining the wear resistance of the stone.
• Excellent Weather Resistance and Chemical Resistance: It has a wide temperature resistance range (-50℃ to 150℃). When used outdoors, it can resist ultraviolet aging (epoxy glue with anti-UV additives should be selected). At the same time, it is resistant to oil stains, acids, and alkalis (such as vinegar, soy sauce, and detergents commonly used in kitchens), making it suitable for long-term use.
• Strong Color Adjustability: By adding color powders (such as titanium dioxide, iron oxide red powder, carbon black) or stone-specific pigments that match the color of granite, a high degree of integration between the glue and the stone color can be achieved, which is especially suitable for the repair of dark granite (such as Black Galaxy, China Black).

Applicable Scenarios

• Indoor and outdoor load-bearing stones: Such as kitchen countertops, floor granite tiles, outdoor landscape stones (stone monuments, steps).
• Scenarios with high requirements for strength and durability: Such as stone wall surfaces in commercial spaces, repair of large granite sculptures.

(2) Unsaturated Polyester Glue: The “Economical Choice” with Low Cost

Core Characteristics

• Fast Curing Speed: At room temperature (25℃), the gel time of polyester glue is approximately 10-30 minutes, and the complete curing time is approximately 2-4 hours, which is suitable for scenarios requiring rapid repair (such as temporary seam filling).
• Low Cost: The price of raw materials is lower than that of epoxy resin, and the cost per unit dosage is approximately 60%-80% of that of epoxy glue, making it suitable for batch repair or scenarios with low-cost requirements.
• Obvious Limitations: Poor weather resistance, easy to age, yellow, and crack when used outdoors for a long time; weak chemical resistance, easy to be corroded by strong acids and alkalis; low hardness (Shore hardness D60-D70), the repaired surface is easy to wear, and the bonding strength (shear strength 8-15MPa) is lower than that of epoxy glue, so it is not suitable for load-bearing or long-term use scenarios.

Applicable Scenarios

• Indoor non-load-bearing stones: Such as decorative granite ornaments, seam filling in non-load-bearing areas of background walls.
• Temporary repair or low-cost projects: Such as simple repair of kitchen countertops in rental houses.

(3) Acrylate Glue: The “Niche Choice” for Rapid Emergency Repair

Core Characteristics

• Extremely Fast Curing Speed: It can achieve initial fixation in a short time, which is suitable for emergency repair (such as temporary fixation of fractured stones during installation).
• Prominent Limitations: Low bonding strength (shear strength 5-10MPa), low hardness (Shore hardness D50-D60), poor weather resistance (easy to age and discolor), the repair effect is difficult to maintain for a long time, and the color adjustability is poor, making it easy to have obvious glue marks.

Applicable Scenarios

• Emergency temporary repair: Such as temporary fixation of fractured stones during transportation to gain time for subsequent professional repair.
• Non-decorative and non-load-bearing parts: Such as crack repair in hidden parts of granite furniture.

(4) Comparison Table of Core Performances of the Three Types of Glues

3. Professional Operation Process for Granite Fracture Repair

(1) Preliminary Preparation: Tool and Material List

Core Materials

• Two-component epoxy resin glue (select transparent or color-adjustable type according to the stone color; it is recommended to choose “stone-specific epoxy glue”, such as the stone glue series of brands like Henkel and Loctite).
• Color matching agent: Stone-specific color powder or color paste (consistent with the color of granite; it is recommended to test the color difference on a small piece of stone first).
• Cleaning agent: Anhydrous ethanol, acetone (used to clean oil stains and dust on the fracture surface).
• Filler (optional): Quartz powder, talc powder (if there are large gaps on the fracture surface, fillers similar to the stone color can be added to enhance strength and reduce the amount of glue used).

Tools

• Cleaning tools: Lint-free cloth, cotton swabs, sandpaper (800-grit, 1200-grit, 2000-grit, used to polish the fracture surface).
• Glue application tools: Plastic scrapers, syringes (needle diameter 0.5-1mm, used for glue application in narrow gaps), gloves (to prevent glue from sticking to hands).
• Fixing tools: G-clamps, F-clamps, tape (masking tape, to avoid damaging the stone surface), foam pads (used to buffer the fixing pressure).
• Post-treatment tools: Utility knife (to clean excess glue), polishing pads (wool wheels, sponge wheels, used for surface polishing), polishing agent (stone-specific polishing paste).

(2) Key Operation Steps (Taking Epoxy Glue as an Example)

Step 1: Cleaning and Treatment of the Fracture Surface – “No Impurities Is the Prerequisite for Firm Bonding”

• Dip a lint-free cloth in anhydrous ethanol or acetone, and wipe the fracture surface repeatedly to remove impurities such as oil stains, dust, and water stains on the surface (impurities will seriously reduce the bonding strength of the glue and lead to repair failure).
• If there are burrs, protrusions, or unevenness on the fracture surface, gently polish it with 800-grit sandpaper to form a rough “matte surface” on the fracture surface (increasing the contact area between the glue and the stone and improving the bonding strength).
• After polishing, clean the fracture surface again with anhydrous ethanol to ensure no dust remains, then let it dry (approximately 10-15 minutes, to prevent moisture from affecting the curing of the glue).

Step 2: Glue Preparation and Color Matching – “Consistent Color Is the Key to Aesthetics”

• According to the ratio specified in the epoxy glue instruction manual (usually epoxy resin: curing agent = 2:1 or 3:1; the ratio must be strictly followed, as improper ratio will lead to incomplete curing of the glue or reduced strength), mix the two components in a clean container.
• Add an appropriate amount of color powder (it is recommended to add a small amount multiple times), and stir thoroughly with a scraper until the color of the glue is consistent with the surface color of the granite.
• Take a small amount of the prepared glue and apply it to the hidden part of the granite (such as the back of the fractured part). After curing (approximately 2 hours; heating can accelerate curing), compare the color difference. If the color difference is obvious, adjust the amount of color powder and repeat the test until the colors match.

Step 3: Glue Application and Positioning Fixation – “Uniform Glue Application + Stable Fixation”

• Use a scraper or syringe to evenly apply the prepared glue to one of the fracture surfaces. The thickness of the glue application should be controlled at 0.1-0.3mm (excessive thickness will lead to excessive glue overflow and increase the difficulty of subsequent cleaning; insufficient thickness may result in incomplete bonding).
• If there are gaps on the fracture surface (width > 0.5mm), a small amount of quartz powder (with particle size matching the gap width) can be added to the glue, stirred evenly, and then applied to fill the gaps and enhance strength.
• Accurately align the two fracture surfaces (ensure the stone texture is aligned to avoid misalignment affecting the appearance), gently press for 1-2 minutes to expel the air between the fracture surfaces (air residue will form bubbles, reducing the bonding strength and affecting the appearance).
• Fix the butted stone with G-clamps or F-clamps. The fixing pressure should be uniform (it is recommended to place a foam pad between the clamp and the stone surface to avoid damaging the stone surface). The pressure should be such that there are no obvious gaps on the fracture surface and a small amount of glue overflows (the overflowing glue can be cleaned up later; if no glue overflows, there may be insufficient glue application).
• Check whether the stone butt joint is flat and whether the texture is aligned. If there is misalignment, adjust it in time, then keep it in a fixed state and place it in a cool and ventilated place for curing (epoxy glue takes 24 hours to fully cure; avoid moving or vibrating during this period).

Step 4: Post-Treatment – “Glue Removal + Polishing + Buffing, Restoring the Stone Texture”

• After the glue is fully cured, remove the fixing clamps, and gently scrape off the excess glue overflowing on the stone surface with a utility knife (scrape along the tangent direction of the stone surface to avoid scratching the stone).
• Gently polish the glue mark with 800-grit sandpaper to remove the residual glue line, then use 1200-grit and 2000-grit sandpaper for fine polishing in sequence to keep the repaired area flat with the stone surface (when polishing, wet the surface with water to reduce dust and prevent the sandpaper from scratching the stone).
• Dip a sponge wheel in stone-specific polishing paste and polish the repaired area (control the rotation speed at 1500-2000 rpm) until the gloss of the repaired area is consistent with that of the stone itself and there are no obvious polishing marks.
• Finally, wipe the polished surface with a lint-free cloth to remove the residual polishing paste and complete the repair.

4. Post-Repair Maintenance and Solutions to Common Problems

(1) Key Points of Post-Repair Maintenance

Curing Period Maintenance

Daily Use Maintenance

• Indoor Countertops (Such as Kitchens): Avoid placing high-temperature objects for a long time (such as pots just taken out of the stove; it is recommended to use heat insulation pads). Clean regularly with neutral detergents (such as detergent), and avoid direct contact with strong acids and alkalis (such as hydrochloric acid, oxalic acid).
• Outdoor Stones: Rinse regularly with clean water to remove surface dust and dirt. Apply a stone protective agent (such as silane-based protective agent) once a year to enhance the weather resistance and stain resistance of the stone.
• Avoid Secondary Damage: When moving or cleaning the stone, avoid strongly impacting or scratching the repaired area. If slight cracks are found in the repaired area, fill them with glue in time to prevent the cracks from expanding.

(2) Common Problems and Solutions

Color Difference in the Repaired Area

• Cause: Improper amount of color powder, insufficient color testing between the glue and the stone, incomplete polishing and buffing.
• Solution: If the color difference is slight, it can be improved by re-polishing (increasing the amount of polishing paste and extending the polishing time); if the color difference is obvious, carefully scrape off the original glue with a utility knife, re-prepare glue with matching color, and re-repair according to the process.

Secondary Fracture of the Repaired Stone

• Cause: Wrong glue selection (such as using polyester glue to repair load-bearing stones), incomplete cleaning of the fracture surface, insufficient fixing pressure, or insufficient curing time.
• Solution: Scrape off the glue at the fracture, re-clean the fracture surface, replace with high-strength epoxy glue, and ensure uniform fixing pressure and sufficient curing time (at least 24 hours).