Inspect the gutters to determine which areas need to be repaired. Keep an eye out for cracks and pinholes. Be careful when looking at the joints and folds. Look out for corrosion. Water penetration into the attic is also a sign that there are leaks. Look at interior plaster to determine which areas need repair.
Clean the gutters so that they are free of debris and dirt.
Lay the waterproof membrane over the hidden gutters. Make sure there is enough material to go beyond the edges. This extra membrane is trimmed away later.
Roll the membrane up and apply the water-based adhesive to the old gutters with an emulsion roller. Lay the membrane onto the wet adhesive. Smooth over the membrane with a soft bristle broom to get rid of any air bubbles or wrinkles. Do not stretch the membrane, as it can tear.
Trim away any extra membrane along the edges of the gutter with a pair of very sharp shears.
Paint some contact adhesive along the edge of the membrane and the edge of the gutter. The contact adhesive will grab the membrane immediately so be careful when sticking the edges down.