STRENGTHENING OF STONE MASONRY ARCH BRIDGES THREE ...

Common Problems
In rare cases, a stone can crack all the way through during the thawing process,
rendering it unstable. The best cure for this condition is selecting the proper stone, and
paying close attention to proper installation details and techniques that assure water can
drain out of and away from the stone.
Plant Growth
Those in the North are probably familiar with the sight of ivy climbing a stone or brick
wall. If left unchecked, climbing plants such as ivy can root in the joints of stonework
and cause structural problems. If they stay rooted in the ground, they are mainly
harmless and can be cleared off easily.
Fig. 4.7 – Stone masonry affected by plant grouth
Other types of growth, like algae and lichen, can have more permanent effects on the
appearance of your stone. Because algae and lichen do not require soil for nourishment,
they can spread over the entire surface of the stone, forming large patches.
In the short run, plants and organic growth may not seriously damage stone; however,
restoration of stone structures involves careful cleaning and removal of both organics
and pollutants.
Human Traffic
On pavers and steps, one of the most noticeable weathering effects is human traffic.
Walking on stone surfaces can scratch the surface when hard materials, such as pebbles
in the sole of a shoe, are dragged over it. In outdoor settings these scratches are less
noticeable, while in delicate interiors they may be unsightly.
Leonardo da Vinci Program 35