Treated lumber is bad, bad, bad. Use any thing but that. Even paint wont help as the pressure treated lumber will bleed for a couple years. I used metal frames for the top. I know thats not suitable for decorative pergola. any lumber thats not treated is fine but will not last as long is the draw back.

Adam - I had big problems with CCA treated pine when I first went into growing brom's and consequently was asked by our bromeliad society to write an article for out society newsletter part of which I attach below In the hope it may help you:

USING TIMBER WHICH HAS BEEN TREATED WITH PRODUCTS
CONTAINING COPPER

By Neville Wood
2007

I
have been asked to write this article about the problems I encountered when I
built my shade house from timber treated with products containing copper.
Hopefully it will save other members especially the newer members from falling
into the same traps that I did.

When
I first became interested in growing broms I decided to renovate an old shade
house that I had grown orchids in many years before. Originally I had built the
shade house framework from galvanised pipe which I thought would last forever.
However, I underestimated the effects of salt air on steel (even galvanised
steel) and living only one street back from the ocean, after a couple of years
corrosion soon became apparent. By the time I was ready to start growing broms,
the framework needed totally rebuilding and I decided to use CCA treated pine
for the framework as it was guaranteed to withstand weather and insect damage
for 20-30 years, plus it was easy to work with.

With
my shade house finally renovated, I began collecting bromeliads from various
places and watched my collection slowly grow until finally the shade house was
housing a reasonable collection which I was quite proud of. All went well until
one day I noticed one of my Neoregelias had rotted in the centre of the cup. I
didn’t worry too much as I had extras of that variety and accepted that
everyone lost a plant or two occasionally. A week or two went by and I noticed
another had leaves which were starting to die and looked like a severe case of
sunburn. Again I didn’t worry too much as we had a very hot summer at that time
and I thought maybe it was a case of too much sun as I only use 50% shade
cloth.

After
a few weeks we had two or three thunder storms with very heavy rain and when I
next went to the shade house (probably a week later) I had at least one dozen
very sick plants showing advanced rot at the base of the leaves. On removing
the outside leaves I found the rot had travelled right through all the layers
of the leaves beneath making the plant impossible to save.

On
examining my other plants, all appeared healthy with none showing any signs of
rot. The other thing that puzzled me was that all of the affected plants were
in a straight line on the same bench. In my previous job I had been taught to
always “look up and down and all around” when assessing the scene of an
accident and remembering this I immediately looked up. The possible cause of my
problem was staring me right in the eye, because one of the roof timbers was in
a straight line directly above the line of damaged plants. It didn’t take too
much guessing to realise that something had dripped onto the plants from the
timber above and caused the damage, but what had it been?

I
moved the plants from immediately below the timber and months went by with no
further problems. It was many months later when I purchased a copy of
“Bromeliads for the Contemporary Garden” by Andrew Steens (This is also in our
library) and I read a section on problems on page 186, it was mentioned that
bromeliads should never be planted in shade-houses constructed of timber
treated with copper or boron based preservatives as these chemicals can leach
out of the timber and onto the plants causing serious damage. I now knew the
damage was caused by copper leaching from the overhead timbers in my shade
house and this was further re-enforced when I read an article in our Newslink
warning of the same problems.

WARNING:
Years ago, the regulations weren't as strict as they are now and the strength of the chemicals used were much stronger than they are now so don’t make the mistake of assuming that because treated timber is old, the toxins will no longer be active. I have CCA treated pine logs as garden edging
and they have been in place for at least thirty years. In one garden I have a
number of Aechmea recurvata and if a leaf comes in contact with the treated
pine edging, the leaf will start to die due to chemical burns, so the toxins are still very much
active after all that time.

WHAT
ABOUT “WAX WOOD”?

I
enquired about a new treated timber product called “Wax Wood” and was informed
that although the chemicals used are different to those used in the CCA
treatment, the major chemical used is still copper. The chemicals together with
wax are pumped into the timber under pressure at the same time and although the
external surface of the timber has a wax coating, assurances can’t be given
that a certain amount of copper still isn’t present.

PAINTING

I
have read where acrylic paint can be used successfully, but on discussing this
with a sales rep. from a large paint company, I was advised that the paint used
should be oil based.

He
went on to say that acrylic paint can be painted over a damp surface i.e.
brickwork, fibro etc. and the surface will dry from the inside out. This means
the moisture trapped beneath can pass through the acrylic paint to the outside.
He didn’t see why the same wouldn’t occur with the copper in treated timber
products. Oil based paints on the other hand would offer much better protection
and he suggested an oil based primer first, followed by an oil based undercoat
and two coats of an oil based enamel. Admittedly this method would be more
expensive and time consuming than using a couple of coats of acrylic paint but
I think the protection it offers would make it worthwhile.

It’s
also possible that an oil based primer followed by an oil based undercoat may
seal the timber sufficiently so that it could then be covered with a couple of
coats of acrylic paint. Whatever method you choose, make sure all cracks are
properly sealed with the primer and undercoat before the finishing coats are
applied. If you decide on a new structure using treated timber which has been
painted, remember to paint any cut ends or cut outs before assembling to ensure
that all surfaces are adequately sealed.

Like
CCA treated timber products, “Wax Wood” can also be painted as described above
to prevent leaching of chemicals.

Note
also that any fasteners used such as nails, screws, bolts etc. must be hot
dipped galvanised, otherwise the chemicals will cause them to rust right through
in a year or two.

I
hope this helps.

All
the best, Nev.

I have asked for quotes on the construction of a new shadehouse, but the builder has come back saying treated timber might be the only option as jarrah and other hardwood is hard to source. Needless to say, if I can't have hardwood I will be going with steel!

Adam I have seen people use treated pine posts and slipped PVC pipe over them.
The other option as in Nev's post is to paint them.

My galvanized frame is still in great shape after 16 years. I touch it up ever couple years and its fine. Commercial greenhouse are all steel or galvanized frames here.

My frames are steel also.

Hi everyone - Please don't get me wrong; I never meant to infer that timber was better than steel (After all I worked in the Steel Works for thirty years), but where I live near the sea, after three years my steel framed shade house started to rust (even though it was galvanised) and timber was the only other option when it needed eventual replacement.

I've since been told there's a new product on the market now made from re-cycled plastic which can be used in place of timber. It comes in the usual building sizes of 3" x2" and 4" x 2" and is naturally rot and Termite proof. It can be nailed, screwed or bolted and worked with the usual carpenter's tools such as drills and hand saws etc. So probably worth finding out about, but I don't know how it compares price wise with timber or steel.

All the best, Nev.