Is it safe on all fabrics?
Fabricadabra is designed for soft tops and interior fabrics without altering their look or feel, but care should always be taken to apply a consistent and even coverage of product - any high spots or drops/runs may look different.
How often should I reapply?
Every few months, or sooner if water repellency fades. On garaged cars a few coats of sealant may last years, but normally 3-6 months is to be expected. It depends on wear/use and how much sunlight the fabric is exposed to.
Do I need to prep the surface first?
Yes, clean and dry the fabric thoroughly before applying. Otherwise you could be sealing contaminants in - inconsistent finishes are often because invisible contamination is preventing the product soaking into the fabric evenly. Even if you can't see it, contamination may still be there in the form of natural grease from skin, fabric conditioners on clothes, hand cream, suntan lotion etc.
Can it be layered for extra protection?
Yes, multiple coats will boost durability and increase water repellency - up to a point. Tightly woven fabrics will perform better than loosely woven or high pile materials. The smoother your fabric is, the easier it will be to protect. Very rough materials may resist application entirely.
What if no product is absorbed at all into the fabric?
Some fabrics are completely water repellent by nature, say 100% polyester. These will not absorb any coatings, although sealants may still sit on top of the fibres or add additional protection.