English Heritage has published a very useful explanation of the use of resin repairs in the Timber edition, pg. 311- 318, of the Practical Building Conservation series. Anyone interested in learning more about the use of this technique should refer to this information.
Sufficient time has now elapsed since the first use of epoxy resin for the repair of structural timber-frames, non-structural timbers and joinery items such as windows. We are now starting to see the consequences of the use of the use of the product, especially externally.
It seems that the resin itself can survive remarkably well. However, we are now seeing that it can encourage further decay due to the inherent non-breathable characteristic of the product. This can lead to creating a hidden habitat for beetles, especially death-watch beetle. We are also now starting to see decay around the edge of the resin. Some examples are shown in the photos here.
The dilemma is what to now do about it. In theory, it might be possible to remove the resin with minimal damage to the historic timber-frame. A decision would need to be made as to what alternative option could be used. If an attempt is made to remove it, even if only for an exploratory look, then it should only be done with great care and in a less obvious location.
There is, as yet, no consensus of opinion on the life expectancy of resin repairs nor on what to do to a building that has already been repaired using the product. It is a considerable uncertainty and dilemma for the years ahead.