Blistering Over Ochre. If a coat of oil paint is applied over a heavy coat of ochre priming which has dried hard and flinty, it will often cause it to blister badly when exposed to the heat of the sun. This result is due to the paint not penetrating into the hard surface, thus leaving an excess of oil on the ochre coat. Where ochre is mixed dry with oil, it is impossible to thoroughly incorporate the two and when applied will sometimes raise up in small blisters: the under part will be found dry and the paint can be powdered. This is caused by the dry ochre lying on the surface, absorbing all of the oil and leaving nothing to satisfy the wood, consequently, the heat of the sun will soon pull it away. This is more noticeable after another coat of paint has been applied over the priming.
To successfully repaint blistered work, the character of each kind of blister must be understood; study the cause of the trouble and repaint the surface accordingly. If water or dampness is the cause, the paint for retouching should be mixed with a full oil reduction to satisfy the bare wood; if from fat oil, it must be mixed with sufficient turpentine to penetrate the surface which this oil leaves; if from fatty or non-drying oil, the surface must be first washed with turpentine to remove the grease, then touched up with paint mixed with part turpentine to assist in penetrating to a good depth.
For ochres and like surfaces, the same directions apply for touching up as for a peeled surface. On old work where the paint has blistered from an excess of oil, retouch with paint mixed half flat. This will penetrate through the old paint and give a good foundation. After the work on the foregoing has been touched up, the entire building can be given a coat of paint: this will even up fairly well, but the spots caused by the blisters will show to a certain extent.
Roof. Do not paint damp shingles. Allow time for rain, dew or frost to dry off and the roof to become thoroughly
