Why pressure washing can void your roof tile warranty
Choosing the right maintenance method for your roof is more than just an aesthetic decision; it is a legal and structural one. Many homeowners are surprised to learn that using a high-pressure jet wash can immediately invalidate the manufacturer’s warranty on their roof tiles.
Here is why pressure washing is considered a “destructive” cleaning method by tile manufacturers:
1. Removal of the Protective Surface Layer
Most modern roof tiles, especially concrete and clay varieties, are manufactured with a specific protective coating or “fire-glazed” finish. This layer is designed to shed water and reflect UV rays.
- The Risk: High-pressure water acts as an abrasive, similar to sandpaper. It can strip away this top layer, leaving the tile porous.
- The Warranty Impact: Manufacturers guarantee their tiles based on the integrity of this coating. Once it is removed, the tile is no longer performing as engineered, and the warranty is voided.
2. Erosion of the “Fine” Aggregates
Concrete tiles are made of a mixture of cement, sand, and pigment.
- The Risk: Pressure washing can blast away the “fines” (the smallest particles of sand and cement) from the surface. This creates a pitted, rough texture.
- The Result: A pitted surface provides a much larger surface area for moss and lichen to anchor into, often leading to faster and more aggressive regrowth than before the clean.
3. Structural Damage: “Nail Sickness” and Displacement
Roofing systems are designed to shed water downward via gravity. They are not designed to withstand water being forced upward or sideways at 2000+ PSI.
- Fixing Failure: Intense pressure can rattle tiles, loosening the nails or clips that hold them in place. This is often referred to as “nail sickness” when fixings become compromised.
- Membrane Damage: Water forced under the laps of the tiles can soak the underlying wooden battens and the breathable membrane. If this moisture is trapped, it leads to rot that the manufacturer will not cover, as it was caused by “external misuse.”
4. The Freeze-Thaw Consequence
By making the tiles more porous through pressure washing, you allow them to absorb more water.
- The Risk: In the winter, this absorbed water freezes and expands (frost weathering).
- The Damage: This causes “spalling,” where the face of the tile literally pops off. Because this damage was induced by an unapproved cleaning method (pressure washing), the manufacturer will deny any claims for tile failure.
The Approved Alternative: Manual Scraping and Biocide
To keep your warranty intact, most manufacturers and professional roof cleaning Birmingham specialists recommend a low-pressure or manual approach.
Manual scraping removes the bulk of the moss without mechanical force. Following this with a professional biocide treatment kills the spores at a molecular level without the need for high-pressure water. This ensures your roof stays clean, your tiles stay intact, and your warranty remains fully valid.
