QUESTION
I am building a small bridge to go over our garden pond. I have used treated
outdoor timber to build the frame, and planks of garden decking for the walkway.
The treatment used on the timber frame and decking has left the wood with a greenish
tinge. I am now a bit worried as someone has just told me that the run off from
this type of treated timber will most likely kill off the fish and other wildlife
when it gets in to the pond. Is this true?, and what can I do about it? If this
is the case, is there a wood seal or varnish that I can apply to seal the wood
and stop the chemical treatment leaching into the pond?
ANSWER
The greenish tinge you mention is most probably due to the fact that the timber
has been tanalised so that it does not rot. This should not cause any problems.
One of the bigger dangers to fish is Lime leaching in from unwashed patio slabs
or concrete e.g. a Waterfall, with G4 sealer especially formulated from concrete.
If you would feel happier sealing the bridge, use Cuprinol decking seal which
is a quick drying sealant – this will protect the wood and as it contains
a fungicide to prevent Algae from growing it should stop any slippery areas
on this bridge. Should you do this make sure none of it splashes into the pond
itself.