HELP/MFAQ: WriteyPaint 5-Year Warranty:

All WriteyPaints must be applied on a surface that is 100% sealed (example: drywall that is properly primed and painted).
• Guaranteed to always erase for 5 years
• Warranty is voided if too thin of a coat is applied 
• Warranty is voided if WriteyPaint is applied in an unideal environment.

Please see Paint FAQ for more details