On Sun, 31 Oct 2004 13:26:04 +0000, robsut
wrote:

I have a cedar wood framed greenhouse which is approx 40 years old and
which is now showing it's age! The main frame is in good condition and
the timber is solid. All that is need of is no more than a good clean
and a preservative applied. The problem is that on the roof glazing bars
and the surrounding frame, water has started to penetrate into the wood
making it soft and causing moss to grow under the glass. Over the next
few weeks if it is dry, I hope to remove the glass from the frame a
section at a time, remove the old putty and thoroughly clean the rails
and then put the glass back in.
Before I put the glass back in, I have a few questions: -
1. Treatment of the wood - I would like as to treat the wood which has
become soft so as to stop any more damage being caused. What would be
the best product to do this with bearing in mind the wood is/will be damp?
2. What should I put the glass back in with - linseed oil putty,
mastic/silicone or the glazing tapes I have seen?
3. Once the glass has been refitted, what is the best way of sealing the
exterior joint between the glass and the glazing rails - linseed oil
putty or mastic/silicone sealant?
Thanks for your help.

Hi,

Best to treat the wood when dry, anything water soluble that can soak
into the damp wood will most likely be able to leach out again, and
could get onto the plants underneath.

Removing the glass and covering the roof with a tarp with plenty of
ventilation at the sides would help the wood to dry out.

If the wood can be treated dry, Cuprinol Green can be used though it
does stain the wood a bit. If this is a problem they also do a clear
version.

If the wood really must be treated damp there is very little that will
do it, try a search on octoborate/glycol preservatives.

Problem with linseed putty is the oil can soak into the wood and the
putty dries out. Sometimes cedar greenhouses had no sealing round the
glass as the panes overlap like tiles and leaks inside shouldn't be
much of a problem.

If the greenhouse gets a lot of muck from overhanging trees then
sealing between the glass and the rails with a UV resistant
polyurethane could be the best way to go. Silicone may not adhere to
damp wood so well.

To prevent new growth of moss and algae try fixing a strip of zinc
along the apex of the roof, a goog on "moss zinc" will give some
details.

If the rails are getting damage from the sun then some microporous
wood stain like Sadoling will help protect them.

cheers,
Pete.