Advice on paint defects
In damp weather, a small quantity of water vapour is absorbed into the paint structure and is then evaporated again in dry conditions (osmosis). This process is normal and does not harm a well constructed finishing process. However, poor processing of the primers will leave hygroscopic/water soluble substances (salts) behind as contaminants. These cause a local concentration of a salt water solution which lift the paint film into water blisters. Blisters can occur in many sizes, patterns and frequency and can form between individual layers or beneath the entire film build. In dry weather most blisters will temporarily recede.
- The surface to be painted (filler, bare metal etc) was not cleaned thoroughly. Contamination from salt residue, eg dirty sanding water or hand sweat, was left on the surface under or between coats. The blister pattern may indicate the cause (beading = wipe marks, prints = finger or hand prints).
- Wet sanding operations (particularly with polyester based products) without sufficient time to allow water to evaporate before application of top-coats.
How to avoid
- Thoroughly clean the areas to be painted with clean water. Change sanding and cleaning water regularly, especially in winter when vehicle paintwork in for repair is covered in salt. Consider changing to dry sand operations to avoid water absorption when sanding. Finally (depending on the substrate) clean the area with Glasurit Cleaner 700-1 and Glasurit Wax and Grease Remove 541-5 or Glasurit Panel Cleaner 360-4. 2] Allow sufficient time for water to evaporate when wet sanding (circa 2 hours at 20ºC). Dry sand where possible especially with polyester based products.
Sand down and remove the paint layers back to a sound substrate. Be prepared to strip the areas back to bare metal where necessary. Refinish with the correct choice of primers fillers and top-coats.