Oak dowels: what size?

[Roundtuit]

Hi.  I'm building a retaining wall for a raised patio out of oak sleepers, screw-fixing each course as I go (only 3 high, laid flat, so 300mm). To fix the top course and lock the whole thing together I was planning on drilling some 20mm holes through all 3 courses and knocking 20mm oak dowels in.  Just looking at ordering some dowels, and it's struck me that a 20mm dowel (taking into consideration manufacturing tolerances) might be too big for a 20mm hole.  I could get 3/4 inch (19.05mm) dowels which would go in, and hopefully swell to fit tight?  I've bought 20mm drill bit, so would rather buy dowels to suit if possible.  What would you do?

 

cheers

[ProDave]

I suspect the dowels will need to be quite a bit smaller than the hole or you will never get them in.

[jamieled]

Assuming the sleepers are green, then they should shrink around your pegs to get a good fit as they dry out.

In post and beam framing it would be normal to use tapered pegs rather than a consistent diameter. These can be whacked in reasonably tight, then trimmed.

[Miek]

I would use steel rod. I don't think you will drive a wooden dowel through 3 sleepers unless it's loose, and that defeats the point. You can hide the steel with a wooden plug afterwards.

[Jeremy Harris]

40 minutes ago, Miek said:

I would use steel rod. I don't think you will drive a wooden dowel through 3 sleepers unless it's loose, and that defeats the point. You can hide the steel with a wooden plug afterwards.

 

 

Me too.  We held an oak sleeper wall together with stainless steel rebar, driven into slightly undersized holes.  Worked a treat.  The chap that built our wall this way reckoned that it had to be stainless, as oak will attack ordinary steel fairly quickly.

[jfb]

you can always shave a bigger peg down but not the other way round!

[Roundtuit]

Thanks all; some interesting thoughts.  I think I'd better experiment with a few methods using off-cuts before I go nuclear with the drill....

[SiBee]

For three sleepers high screwed together per layer; rather than dowels what about using something like the timber fix screws? These are flanged so the head  could be a feature or drive them in further and they can be recessed. Plug the hole if you wish.

Thats how I have done them. Never corroded either. I used an impact driver and  clearance hole.

[Roundtuit]

2 minutes ago, SiBee said:

For three sleepers high screwed together per layer; rather than dowels what about using something like the timber fix screws? These are flanged so the head  could be a feature or drive them in further and they can be recessed. Plug the hole if you wish.

Thats how I have done them. Never corroded either. I used an impact driver and  clearance hole.

 

Thanks, I was just thinking the same.  I've got some 140mm stainless Spax timber screws I was planning to recess ~25mm into the second course to fix it; I'll see how it goes!

[Temp]

Mine is only two courses high but retains stones and gravel. I just counter sunk the heads and used plenty of screws to hold them together. Timberlok sleeper screws are pretty tough. Plenty strong enough to hold sleepers together but i found they were prone to shearing if I didn't drill pilot holes. Mine are proper hardwood reclaimed sleepers. I had to drill top sleeper, insert screw, hammer head to make a mark on the sleeper below, then move the top sleeper so I could drill hole in the lower one.