Why microcracks appear in polycarbonate: A practical analysis from NovaTeplitsa

Polycarbonate has earned the trust of farmers and private farm owners as the ideal material for greenhouses. Its advantages are obvious: high transparency, exceptional strength (200 times stronger than glass), lightweight, and excellent thermal insulation properties. However, over time, some owners notice a fine network of cracks, known as "spiderweb," on the material's surface.

In this article, NovaTeplitsa experts, drawing on their many years of experience working with polycarbonate, will examine in detail why microcracks occur, how they affect a greenhouse, and, most importantly, how to avoid them.

What are microcracks and why are they dangerous?

Microcracks are small surface damages on a polycarbonate sheet. They are initially barely noticeable, but can deepen over time.

The danger lies not only in the aesthetic defect. Due to microcracks:

1. Light transmittance decreases: The material becomes cloudy, and the plants in the greenhouse do not receive critical sunlight.
2. Thermal insulation deteriorates: In cellular polycarbonate, cracks can lead to depressurization of the cells, allowing moisture and dirt to enter them.
3. Strength decreases: The leaf becomes brittle and more vulnerable to mechanical stress such as hail or strong wind.

Understanding the reasons is the first step to durable and efficient greenhouse.

Reason #1: Lack of or poor quality UV protection

This is the most common and serious cause. Polycarbonate, by its chemical nature, is vulnerable to ultraviolet radiation. Without proper protection, sunlight destroys the polymer chains, making the material brittle and yellow.

How does this work: Qualitative polycarbonate for greenhouses It has a coextruded UV protective layer. This isn't just a simple coating, but a 30-60 micron thick layer "fused" into the sheet surface during production.

Risk factor: There's a lot of cheap, no-name polycarbonate on the market, or so-called "lightweight" (eco) sheets. These sheets either lack a protective layer, or have a minimal thickness (10-15 microns), or are applied unevenly. This material begins to deteriorate within 2-3 years of use.

Comparison table: High-quality and inexpensive polycarbonate

Feature / Parameter	High-quality certified polycarbonate	Cheap "eco" or "no-name" polycarbonate
UV protective layer	Coextrusion, 30-60 microns	None or < 20 microns, spray applied
Raw materials	100% virgin polycarbonate	Addition of secondary raw materials (recycled PC)
Manufacturer's warranty	10-15 years (real, documentary)	Absent, or 1-3 years (conditional)
Result in 3-5 years	Maintains transparency and strength	It turns yellow, becomes brittle, and becomes covered with microcracks.

Expert advice: NovaTeplitsa always recommends requesting certificates of conformity from the seller and checking the markings on the sheet's protective film. These clearly indicate which side of the sheet contains the UV layer (this side should be on the outside of the greenhouse) and the manufacturer's warranty period.

Reason #2: Installation errors and “internal stress”

Even the most expensive premium polycarbonate can be ruined by improper installation. The main enemy is neglect. thermal expansion material. This is not just a recommendation, but a law of physics.

Technical data: Polycarbonate has a significant coefficient of linear thermal expansion—approximately 0.065 mm/m°C. This means that a 6-meter sheet can expand by 1.95 cm in length when exposed to a temperature difference of 50°C (for example, from -10°C in winter to +40°C in the sun in summer).

Errors that lead to cracks:

1. Rigid mount: The sheets are screwed directly to the frame. When the polycarbonate expands, it pushes against the fasteners, creating enormous internal stress. It is at these points that cracking begins.
2. Incorrect holes: The holes for the screws are drilled “butt-to-toe” (less than 2-3 mm of reserve).
3. Using regular screws: Lack of sealing and cushioning.

The right solution (Installation technology):

• Using special thermal washersThey have a foot that limits the pressure and a soft EPDM seal that cushions and seals the connection.
• Drill holes 2-3 mm wider than the screw shank diameter. This allows the sheet metal to "play" for free thermal movement.

Reason #3: Exceeding the minimum bending radius

This problem is typical for arched greenhousesEach polycarbonate sheet (especially cellular) has a clear technical specification – the minimum allowable bending radius.

For example, for a sheet 4 mm thick this is approximately 0.7 m, for 6 mm – 1.05 m, for 8 mm – 1.4 m. (Data may vary depending on the manufacturer).

If the sheet is bent more during installation (that is, the arch is made steeper than permitted), it will develop constant critical internal stress. Add to this UV radiation and temperature fluctuations, and the appearance of microcracks is only a matter of time.

Reason #4: Chemical incompatibility

Despite its strength, polycarbonate is chemically sensitive to certain substances. Contact with these substances causes clouding and cracking.

What should be strictly avoided:

• Aggressive detergents: Contains ammonia, solvents, alkalis, chlorine.
• Some sealants: Especially vinegar-based sealants (silicones with a strong vinegar smell). They release an acid that destroys the polymer.
• PVC profiles: Some low-quality PVC profiles or seals release plasticizers over time, which chemically “attack” the polycarbonate, making it brittle.

Professional approach: For sealing, use only neutral silicones (odorless), and for sealing, use EPDM rubber profiles or specialized polycarbonate profiles.

Conclusions of NovaTeplitsa experts

The appearance of microcracks in polycarbonate is almost always the result of one of three factors or a combination of them:

1. Saving on materials (purchase of a sheet without UV protection or from unknown raw materials).
2. Unprofessional installation (ignoring thermal expansion).
3. Design errors (the arch bend is too steep).

To ensure your greenhouse lasts for decades without losing its transparency or strength, follow these three simple rules:

• Buy certified materials from reliable suppliers who provide a full package of documents and an official guarantee.
• Trust installation to professionals who understand technical tolerances and use the correct components (thermal washers, neutral sealants, EPDM gaskets).
• Take proper care of your greenhouse, wash it only with a clean soapy solution without abrasives or harsh chemicals.

Need a consultation on choosing polycarbonate or an estimate for your greenhouse project? Contact the specialists at NovaTeplitsa. We guarantee not only the quality of the materials but also the correct installation, ensuring the longevity of your harvest.