>>> JRhodes <[log in to unmask]> 30/07/99 5:35:35 >>>
wrote:
"Could the shading effect actually be beneficial in moderating the
temperature swings?"

I worry about the whole biodeterioration argument.
Vines do macro-damage - opening the joints.
The sucker pads do micro-damage - attaching to the surface and plucking it when removed.
Lichen does micro-damage - plucking the surface of stones when removed.
Lichen can also do more substantial damage via the effect of the organic acids gradually dissolving the stone below.

However, the effect of vines in providing insulation to the surface could be enormously beneficial, particularly for materials which suffer from moisture and thermal expansion problems such as clay-rich sandstone.  An evergreen vine like ivy will provide sufficient surface cover to reduce surface temperature variation (particularly in summer) and to reduce significantly the amount of surface wetting to the masonry.

On this basis, there is the distinct possibility that the ivy might prolong the life of susceptible masonry materials, whilst actually forcing the wall apart due to growth through joints.

What to do?  Trellis screens with a gap for regular maintenance sounds pretty slick to me!

Shall we start the "ivy saves buildings" push?

Cheers

david