Question:

I sometimes get bubbles in the coating after spraying polyurea from my cartridge spray gun. Can you tell me why this happens?

Answer:

The following are pretty much always the cause of bubbles or delamination when applying any pure polyurea product  whether cartridge or proportioner applied:

1. Applying over unprimed aluminum (the polyurea products require it to be primed… PPG has a good product)
2. Applying over fiberglass which hasn’t fully cured and is still off-gassing
3. Off ratio A/B (usually causes large areas of delamination or separation)
   1. You always need to spray 1 – 2 seconds off target to allow the ratio to establish in the mixing tubes (including when you replace the tubes)
   2. The product should always be over 80 degrees when applying (hotter is better) to ensure both sides are flowing properly and evenly
   3. You always need to shake the cartridge before starting application to ensure the sides are not separating
   4. The cartridge always needs to be kept elevated until actually spraying the surface
   5. If the pistons get bent, then the flow can be off
4. Moisture getting into the process (will cause comparatively small bubbles)
   1. Moisture in the air supply
   2. Individual applying the product sweating while spraying
   3. Surface moist (can also cause large areas of delamination)

These recommendations are with respect to our Rhino/Line-X Alternative cartridge products, but can generally be applied to any pure polyurea product which cures in a couple of minutes or less. Polyurea is reactive to water until cured, and any amount of it getting into the process causes issues. This is the most common of all problems which show up after application. Many applicators simply do not take it seriously enough, and you end up with a liner which appears like something erupted from below, or large areas simply detach.