Why do I need to polish the glass before applying a sealant or coating?

A glass sealant bonds to bare, contamination-free glass. If old sealant, mineral deposits, or an oily film is present, the new product will not bond correctly and will haze or fail early. Polish the glass first with a product such as Soft99 Glaco Compound, Bilt Hamber Re-View, or CarPro Ceriglass until the surface becomes hydrophilic (water sheets flat with no beading), which confirms the glass is clean and ready for coating.

How long does a glass sealant last, and what causes it to fail?

Duration depends on the product and how you use the car. Soft99 Glaco Ultra delivers up to 9 months; Soft99 Glaco DX approximately 4 to 6 months. The primary failure mechanism on a windscreen is running wiper blades across dry glass, which physically abrades the sealant layer with each pass. Side and rear glass without wipers lasts significantly longer under the same sealant. Using screenwash before operating the wipers is the single most effective maintenance habit.

What is the correct technique for applying a glass sealant to a windscreen?

Put the wipers into service mode to lift the blades off the glass. Apply the sealant in large circles across one half of the screen at a time, finishing with a single up-and-down pass to level it. After the product has cured, clear the edges with a straight wipe first, do an initial wipe to take the bulk off, then flip to a clean non-linting glass cloth for the final buff. Leave the glass sealant for at least 12 hours before the car gets wet.

Can I apply a new glass sealant over an existing one without stripping it?

For non-ceramic glass sealants, yes. The new product cross-links with the existing layer, and no stripping is needed. Check the glass feels smooth after washing: if it is rough, clay or polish first; if smooth, apply directly. Allow 10 to 15 minutes before buffing off, though this window varies with temperature and humidity. Avoid heavy all-purpose cleaners within 24 to 36 hours of any glass coating application.

What causes wiper judder after applying a glass sealant?

Two distinct causes. First, a fresh hydrophobic sealant removes the thin water film that normally lubricates the wiper blade against bare glass, increasing direct rubber-to-glass contact and causing chatter. Second, over-layering sealants without stripping the old ones creates microscopic surface roughness that the blade drags across. Always rule out dirty or perished wiper blades first, as grease and cracked rubber are the more common cause of judder and streaking.