We build timber framed pergolas. These pergolas are exposed to the elemenets. Typically we use Western Red Cedar and so the exposed wood holds up quite well. The wood surfaces within the joinery are of concern to me. What flashing techniques are available to protect these wood to wood connections?

I plan to use copper flashing for aesthetic reasons and for longevity.

While reviewing other postings I have seen reference to using a Borate Paste in exposed joints as a preservative. Is this commercially available or home mixed?

In an effort to revive this post, I am submitting it again.

I am interested in preserving the inside wood to wood surfaces of timber frame joinery in timbers exposed to the elements.

Are there any ideas out there?

Hello Jonathan,

Would you consider bedding the joint with a bedding compound? Shipwrights use dolphinite, but it canrun out in the first months with heat if the joint isn't especially tight. It tacks up harded over time. Shipwrights also use a mixture of turps, bees wax, and pine tar. I can't find my recipe right now, but if your'e interested I can keep looking.
I also bed all my nonvisual joints in tar, such as post bottoms to bracket. Shipwrights call it bear ____, if you want to talk the lingo.

My experience with red cedar, and it's much wetter up here, is the wood holds up well if you can prevent water from entering any end grain. There's always Anchor Seal for that. Unfortunately, it runs like crazy on visual stuff, but once it's dry it's fairly stable. And you can recoat when it's tacky but not completely dry.

Best of luck.

Zach

Thank you Zach,

I agree, its the end grain that I am trying to protect.

Does Dolphinite have wood-preservative qualities? What about the other recipes?

I have heard of using Borate as a preservative but am wondering if any one has experience with it.

My first thought was to use a flashing to cover the joint and prevent water intrusion in the first place. Does any one have experience flashing timber framed joinery?

Thanks.

Jonathan,

The Borates will not hold up to continued saturation. They are best for situations where there may be occaisional water incursion. Your copper flashing does not sound like a bad idea. One thing to consider in flashing will be how to retard water entry while providing plenty of areas for the water to exit - i.e. gooping up the whole joint may enchance, not retard decay.

Wish I had a better answer for you,

Andy

Drilling small weeping holes would help alleviate some of the moisture, but not all. Just a thought....

Thank you all for the good ideas and facts.

It seems to me that if I can put a flashing on the upper entries to a joint and extend these down below the lower entry to a joint while leaving the lowest entry open, any water that enters will have a ready avenue of escape. I think that good ventilation will be a key factor.

Now what I can't figure out is how to attach the upper edge of the flashing material to the wood above the joint without water running down between the wood and flashing.

Is there a technique for letting in the flashing material into the wood surface with bedding compound to seal the upper edge?

Thanks,

I'm not sure of your exact application but in retro flash situations (window & door heads, etc.) I normally cut a shallow, upward angled kerf into the wood, tuck the flashing into it & seal with caulk.

Hi Scott,

You can see the application on our website:

www.PacificPergola.com

The pergolas you see do not have flashing.

Thanks.

Hi Jonathan,

Does the Dolphinite and other bedding compounds have preservative qualities?

Of course, and water displacement, too. I just watched a couple shipwrights slather dolphinite under the fir sponsons on a fine old wood boat. If it's good enough for the ocean...

I don't know if you finish your wood with oil. If so, oil first, then assembly with enough dolphinite to ooze out. If natural, you might consider masking right up to the line with good blue or green masking tape.

My supplier for marine stuff like dolphinite is Fisheries Supply in Seattle 1-800-426-6930. John Hastill is my sales rep. It shouldn't be hard to find a tub in Oregon, or Fisheries will deliver.

As for mixing oil, pine tar, etc. That's more of a heavy oil you could lather on, and yes it prevents moisture and rot, but could really throw your finish for a loop, as it's very contagious.

There's something reassuring about keeping moisture away from the inside out.

One other thought: frame in yellow cedar, as it's infinitely more rot resistant and much funner to work. I could look into a supplier from up this way, since mine just changed hands.

Best,

Zach