Blistering appears as bubbles or raised bumps in the paint film, usually caused by moisture or heat trapped underneath. Finding where that moisture is coming from matters more than the blisters themselves, because painting over the problem guarantees it will return.
On exteriors, blistering often points to a leak, poor ventilation, or paint applied before the surface dried fully after washing. We trace the cause before any repainting starts, since fixing the source is what stops the repair from repeating next season.