Sleeper retaining wall

maklahoma

Hi all

I am building a retaining wall of new oak sleepers. The sleepers are 2400x200x100mm and are lying on their 200mm side. I have stacked 4-6 on top of each other (staggered the joints of course). I fixed them to each other with 150mm stainless steel timberlock screws (at least 6 per 2400mm sleeper). On the top course of sleepers I would like to hide the screws more than by just countersinking the heads. I was planning on countersinking the head deeply and covering them with a short oak dowel plug (see schematic drawing attached). My question to you guys is, how deep would you make the hole for the 18mm diameter dowel plugs? I would like to have them just as deep as necessary, because drilling the 18mm holes will be quite some work...

Please let me know what you think!

hogweed

I would think 2-3 cms would be enough with a tin layer of woodglue on the dowel. Or could you just use some woodfiller on top of the screw head? If you mix it with some sawdust from the sleepers that would give you a colour match. 

maklahoma

Thanks for your comment. I have not had very positive experience with woodfiller, especially with regards to longevity. 2-3 cm for the dowels sounds reasonable in terms of stability. I hope that my (cheapish) 18mm auger will be up to the task...

Dave Humby

Have you got, or can you make, any access at the rear of the sleepers? If you have you could drill at a 45 degree angle to fix the top two sleepers together. That way you would have no screw heads to worry about aesthetically. This is how I built mine albeit with reclaimed railway sleepers. 

Nollie

I wouldn’t think you need to make them very deep at all, as they are not structural, just aesthetic. Have a look at decorative metal studs too, which, if spaced evenly, might finish it off nicely as well as hide the screw holes. My top layer isn’t screwed through from the top to the under layer at all, just screwed together with some flat metal plates or L brackets on the corners, all on the inner vertical face. Their own weight largely keeps them in place, I find, but mine are three sleepers tall at the most and only for raised flower beds. If you are trying to retain a slope your superior engineering approach is probably wise!

maklahoma

Thanks Dave and Nollie for your suggestions. Unfortunately I can only access some sleepers from the back, but not all of them. That would of course have been the "neatest" finish with no visible traces of the screws on the top course whatsoever.

The L brackets are probably a tad less solid than I would want. As my "wall" is 6 sleepers high at the highest position and will also serve as bench in summer garden parties (at least that is what I imagine), I want to rather overengineer.

Nollie

And you don’t want to sit on knobbly studs! Sounds as if you have all the bases covered, maklahoma. The only other thing I can think of is that the dowels, whatever depth you decide on, might end up a bit raised or pop out, as they will be a different wood to your sleepers, probably and might expand at a different rate. Perhaps don’t make them too tight a fit and glue them in with a flexible adhesive, to give you room for expansion? That’s being super picky though and they may not be a problem at all.

hogweed

Or if you still have access to the 'inside', you can get these pre-drilled metal strips (I have them in my garage holding the roof trusses on to the walls), which you could screw down the inside for three or 4 sleeper depths. That would be more than sturdy enough I would think to hold your top sleeper in place. . 

Lizzie27

How are your friends going to sit on a wall six sleepers high?  The mind boggles!

Fairygirl

They're each 100mm deep - so 600mm in total.  2 feet in old money. That's about right for a seat - maybe a little high, but not excessively high   
I don't think your 'plug' covers need to be more than 1 or 2 cm at most. As said - they're aesthetic only. Just make sure they're in tight, so that no glue is needed, in case you need to access the screws in future.