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Preserving a Jarrah deck

Taken4ride
Growing in Experience

Preserving a Jarrah deck

Hi all... As said earlier I designed and built a house with a large deck area then moved in 20 years ago. We designed our dream house in the late 80’s, then 1994 bought a property in the NSW Northern Rivers, rehashed original design to include veranda decks around 40% so we could drink in the magnificent views to the border ranges. The house was built by me as owner/builder with contract labour and we took occupancy in 1999. All as designed. Double brick cavity walls to the N and W with timber decking to the NE and E and plain timber boarding to the South. Great.

 

Being from WA we learned to love WA Jarrah. DYK they even used it to build and repair ships.  So when we built the house we ordered Jarrah decking from the local merchant. No problem we were told. It arrived fully wrapped to protect it from the weather. Six months later we laid the deck.  Great. We were surprised at the colour variations but didn’t query it. Roll forward ten years… deck boards splitting, some boards showing rot but not all.  We went back to the suppliers. 

 

Years later I discovered when recoating the deck that I did not have WA Jarrah, just "mixed red hardwoods".  The deck area is not entirely under cover in all areas; one section is heavily exposed to full sun plus the onslaught of heavy weather. Some time back when investigating why some boards seemed not to last, I discovered that a large portion of the boards laid were imported Jarra (note the spelling) from South America.

 

We had received mixed red hardwoods. No wonder there was such a colour variation. The mix we were assured was created around Jarra. Oh yeah. Note the spelling; no ‘H’. Imported from Brazil. Given the mix of species there was an obvious lack compatibility with the deck weatherproofing treatment especially for the Brazilian crap.

So obviously I looked for new suppliers. All east states suppliers without exception said WA Jarrah was exhausted and no longer available. I said bulldust. So I started contacting Jarrah timber mills in our old stomping ground around Pemberton.  Yep… still available. Ordered sufficient to relay the main deck area. It arrived no problem plastic wrapped again. Yep. This time we unwrapped it. All real Jarrah. No knots all straight grained and consistent across every board. We then stacked the jarrah on concrete blocks under the house set well back from weather so that it all could dry out uniformly. Now its all perfect, stable and ready to lay. One characteristic of Jarrah is that it remains stable and equally workable no matter how old it is. Some of the outer boards exposed to light have greyed a little however its all dry and straight. Beautiful.

 

Plan is now to rip the old boards off, cover the bearers with today’s Malthoid equivalent, Camo hidden screw in covered areas and SS bugle head screws in exposed areas.  Sand the lot for uniformity, replace handrails and balustrades with laminated Jarrah boards, seal it all then enjoy the views at our feet and far away all over again.

 

Now the original deck is truly unsafe to toddlers (grandkids) and I am preparing to replace the deck however I am looking for recommendations in regard to what preservation treatment to adopt, both before laying and after.

 

Now Bunnings, east coast version has an issue. Would you believe it we have Jarrah round tables and stools on our deck bought from Bunnings in Midland way back in the ‘80’s. And they were only ever coated (oiled) once.  

 

So it’s become clearly evident now that none of the east coast advisors know a thing about WA Jarrah. All they seem to know is that Jarrah is a colour that comes in a can and is used on lots of timbers to, guess what, make the crappy Jarra or Merbeau etc., look like Jarrah.

 

So how do I get a reputable reference to a product that best suits optimising the natural weather resistance of WA Jarrah while retaining its natural colour and not adding to it.  All key to regaining our dream house before I croak.

 

Anyone got any ideas/suggestions?

 

Re: Preserving a Jarrah deck

An Important secondary question to my first has now become very important.  Fire risk.  Our dream home is rural and with recent fire-storm activity in our hot dry region we are a bit exposed. Yesterday we had dry storms and violent lightning strikes as close as 500 metres away.   One such strike 8km away is still being fought but now "under control".  At Rappville, 50km away, two perished and 15 houses were lost. Its a bit nervy around here right now.

The question has now become "how best to preserve a house with an exposed Jarrah hardwood deck?"

The key drivers behind the question are now deciding whether best to use an oil based penetrating neutral coloured preservative or try and find a water based colour neutral product.    How does one responsibly assess the "Fire Rating" and risk??? Even using a water based product the water evaporates so no preservation there. I'm even contemplating permanent sprinklers over the deck area and under the eves. Cheers.

Re: Preserving a Jarrah deck

Let me tag @Adam_W for you as he also lives in a fire-prone area and no doubt would have put a lot of thought into the topic when building at his new property.

 

Jason

 

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MartyH
Amassing an Audience

Re: Preserving a Jarrah deck

Might not be what you want to hear, but I suspect that if you wanted to be fire conscious you should probably choose a timber-free decking product. Eg https://www.workshop.com.au/t5/Outdoor/Timber-free-deck/m-p/14767#M2079 by @Adam_W 

Taken4ride
Growing in Experience

Re: Preserving a Jarrah deck

Great suggestion... multiple problems; lot of board-gaps. Wind borne flying embers are the biggest risk from any encroaching fire-storm . That's why the first step is to ensure all gutters and downpipes are clear of debris and flushed with water. Then its the detail that between every board there's a gap just perfect to arrest and trap red hot embers. Wind borne embers pass along lines of least resistance, then when trapped in high wind velocity air channels like when passing upward through the board gaps, just where the malthoid bearer strips are located, they burst into flame. Then there's the bearers. They're all dried out 20+ year old timbers. So the whole deck and under-structure becomes a giant strainer. So now I'm thinking along the lines of stripping the old boards, filling and sanding the top of the bearers, sealing them with multiple hardening coats (suggestions invited), finding a non flammable version of malthoid (suggestions invited), hidden screw fixing of all jarrah decking boards, filling all screw holes with putty, then applying multiple coats of Tongue oil over all exposed areas. I've chosen Tongue Oil due to its core polymerization characteristic in that it hardens in contact with air and has a reasonably high >110°C flash point. All this followed by a perimeter installation of pop-up sprinklers as the final touch. Then I should be able to sleep OK after day dreaming on deck. Cheers.

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