However, many years of research and on site experience have shown that this method is not completely effective, even with paints, with which it is traditionally used.
The moisture vapour permeable (sometimes referred to as microporous) finishes attempt to deal with the problem in a different manner by allowing resin to filter through the finish without blistering or peeling of the finish, hence full protection is maintained.
In the short term, resin exudation tends to look unsightly, but within a year or so the excess resin becomes exhausted and exudation ceases. The initial resin should be cleaned from the timber using a lint free cloth dampened with cellulose thinners or methylated spirits.
Any loose or rusty nails, screws, etc. should be replaced with galvanised or non-ferrous fixings, which will not corrode, even if exposed to the weather.
Wherever possible it is preferable to use lost head nails, but if this is impractical, nails should be punched home, and remaining holes filled with a suitable woodfiller.
Although this is not generally apparent to the naked eye, greying of exposed timber is a tell-tale sign that this is occurring. If these fibres are not removed by thorough sanding prior to coating under the stresses of weather they can detach from the main body of the timber taking the coating with them.
However, research has shown that even after only 2-3 weeks, and before any real colour change is seen, damage may already been done to these fibres and sanding is therefore recommended prior to coating.
You will need to use either a proprietary fungicidal wash or a solution of one part bleach to two parts water. This needs to be scrubbed onto the surface and allowed to ‘work’ for a minimum of 20 minutes before scrubbing off and rinsing with clean water. Allow to fully dry before redecoration.