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Dutchman patching a timber

Started by canopy, December 22, 2020, 09:23:58 PM

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canopy

I have some 8x8 posts with end splitting that will be exposed to weather. I want the cracks sealed up to keep water out and for better visual appearance. Would a dutchman wood patch be a good solution for this? I've used dutchmen with good results on furniture applications and there are wood glues like Titebond III that are waterproof. If a good solution, how would one go about dimensioning patches to hold the stresses well enough?



 

Brad_bb

Being outside brings in a whole different element.  Can you be more specific about how they will be treated?  Will they get wet from rain?  Are they walnut (not sure from the pic)? Are they structural?  If they never get wet and aren't exposed to direct sunlight, you could epoxy.  Dutchmans are typically done on end grain.  If no wet and no sun, you could fill the checks with wood and epoxy.  

Now if you are just talking about the void in the upper right of the upper timber, that you could make some large dowels and bore two holes or whatever it takes, and glue the dowels in with urethane glue (like Gorilla glue).  Urethane glue is the best to use in outdoor conditions for that kind of timber repair.  Make the dowels from the same wood preferably, or just use walnut.
Anything someone can design, I can sure figure out how to fix!
If I say it\\\\\\\'s going to take so long, multiply that by at least 3!

canopy

Posts will be under an overhang but will get sun and any driving rain, hence why I said 'exposed to weather'. Not structural, not that it should matter as a proper glue joint should strengthen the timber. Bottom is fastened to concrete slab with timberlinx and a plexiglass moisture barrier. The posts are teak and will be finished with a danish type oil. I don't get why one would want a urethane glue or epoxy versus the excellent glue I noted for use with a dutchman and produces a stronger bond than the wood it joins together. The idea is each dutchman starts at the bottom of the post and runs up the side of the post past where the splits end just like any other normal usage of a dutchman.

kantuckid

Since your wood is teak and your on another continent, etc.,  I'd suggest reading the excellent Titebond glues website for what glues tropical teak well? Also,finishes such as WATCO's teak oil are blended for dense tropical woods, whereas Danish oil not so much. Danish oilis in fact an indoor finish for the most part used on furniture. 
Arguing over what glue w/o much more tech knowledge is counter-productive IMO. 
I'd leave them as they are and use them, then if it got lots worse9 as in it gets on yer nerves too much after time :D) maybe I'd fill the voids with a colored epoxy. 
For now I build whatever your doing and ditch the patches idea and Danish Oil too. Cracks in wood are a normal thing and patches are often ugly enough compared to ala naturale.
Kan=Kansas;tuck=Kentucky;kid=what I'm not

canopy

There are also danish type oils made specifically for outdoor use and that is what I have used for years. Though it must be said the durability is not ideal as gable fascia getting full sun and rain needs resanded and refinished in some spots yearly so I do appreciate the tip about Watco. It's important a breathable finish is used to prevent the oil in the teak from getting trapped behind the finish and bubbling.

I have spoken with the titebond manufacturer about gluing teak years ago and they say it is important to glue within 24 hours of cutting otherwise the oils will come to the surface and make it difficult for the glue joint to hold. Doing that I have always had good results. So I have to wonder if a filler of epoxy might do nothing to hold the cracks tight since it may not have a proper surface to bond with.

Cracks in timbers indoors are common and I don't mind. But at the base of a post getting repeated rain wicked deep inside the timber is a valid concern I think. There is an old adage that wood lasts forever--you just have to keep it perfectly wet or perfectly dry. It's the repeated wet dry cycles that are the problem.

I disagree dutchman patches are ugly. Nothing looks worse than a bead of wood filler. A dutchman is hardly noticeable to the casual observer and that's usually the whole reason people go to the trouble of making them. On close inspection a dutchman adds just more texture to the organic appearance of wood and the workmanship can be appreciated like good wood joinery.

kantuckid

Seems that you've answered all your own questions.   :D
Danish oil is whatever is in it as not a hard and fast formula but rather it's a traditional woodworkers combo of linseed or tung oil with a varnish and solvent in typically a 1/3-1/3-1/3 sort of mix that can use spar varnish but usually not thought of as outdoors given the lack of UV inhibitors and other goodies that make wood last outdoors.
I didn't say I'd add a bead of wood filler but I would lean toward no patch at all and replace the entire beam if it wasn't up to the job. 
 


Kan=Kansas;tuck=Kentucky;kid=what I'm not

canopy

> usually not thought of as outdoors given the lack of UV inhibitors and other goodies that make wood last outdoors

Sure, but the type I use is specifically intended for outdoor use and is water repellent, has UV protection and fungicides.

> I didn't say I'd add a bead of wood filler

Yes, but a bead of epoxy would surely look like a bead of wood filler and might not able to hold the cracks tight.

> replace the entire beam if it wasn't up to the job

True, and surely that's what 99.9% of people do. But I find myself frequently needing to salvage lower grade timbers to see if there is a way to make them work. If not might have to settle for a totally different material like concrete or steel which again, most people wouldn't mind doing. But I see promise in these 8x8's and want to get the most out of them that I can.

> Seems that you've answered all your own questions

Actually none of my questions have been answered. What I want to know is if a dutchman would be suitable for the job and how to dimension them to hold. I also appreciate suggestions of any other good techniques.

everythingwood

Not being familiar with that term I had to look up what a Dutchman patch was and I saw two examples.  One was a rectangular patch which is intended to cover the whole defect, the other was a dovetail key to span and strengthen the defect.  I have no experience with the former but have used the latter (dovetail key) plenty of times on large slabs.

Personally I see no reason why dovetail keys could not be used to stabilize the posts.  Done properly they provide a mechanical fix that is not reliant on any type of glue.  Of course, I would still glue or epoxy them into place with an adhesive that is appropriate for the wood.  

Question:  If you apply heavy clamping pressure can you close the gaps at all?  If not, they probably aren't weakening the post to any large degree.  If you can, then it is a structural issue  (of course you noted that they will not be used in a structural use).  

If the posts were mine, and I could close the cracks I would do so with several large clamps then cut a few  dovetail keys to span the cracks and epoxy them in place.  I would then fill the remaining cracks with epoxy for good measure then level the patch and epoxy and finish as usual.  As for size, I'm sure there are some engineering equations that could help design the dovetail keys but I am not aware of them.  I would go big... use a 1:8 ratio on the dovetails and make them at least one inch thick.  cut the dovetail key and use it as a pattern to mark the beam then drill and chisel a mortise for the key.  I would probably epoxy the key(s) in place first then release the clamps prior to filling the cracks with epoxy.

As for aesthetics, while I'm not sure I would like a large rectangular patch, In my opinion the dovetail style are very attractive.  I know I am not alone in this since I see many slab-type table tops with dovetail keys where they aren't really necessary.  I think it's gotten to the point that if a customer sees a crack they expect to see a dovetail key "fixing" it.

Just my two cents.    

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