Curved dry stacked wall

Hi,
Just wondering if anyone has built a curved dry stacked wall. Following Rob Roy's book (Earth-Sheltered Houses: How to Build an Affordable Underground Home) am thinking of building a similar sheltered earth cylinical shaped house set into the slope of some land I have on the side of a mountain. I'm concerned though that the fibres of the surface bonding cement will not bridge the gap between the outer edges of adjacent blocks (of the curved wall) and this will reduce the strength of the surface bonding. I can find quite a lot of information online of square dry stacked homes but none (outside Rob Roy's book) on houses with dry stacked curved walls. This makes me worried that I'm embarking on a doomed venture. Does anybody know of any examples that I've missed? Thanks heaps in advance. Nigel.

Hi Nigel
You can tell an original 'blackhouse' around here because the corners are curved rather than straight. The stone walls would originally have been dry stacked with rubble in between. So a curved wall as such is not a new thing - far from it!

Lewis blackhouse with curved walls

source

Nigel Hughes wrote: I'm concerned though that the fibres of the surface bonding cement will not bridge the gap between the outer edges of adjacent blocks (of the curved wall) and this will reduce the strength of the surface bonding.

I'm confused - so are you looking to build a house using a dry stacked technique or something different?

Sorry, should have been more specific. I'm wanting to build the walls out of dry stacked (rectangular) concrete blocks- to meet building design regulations (so it is a cylinder rather than a dome). That is, it will have an (earth covered) flat roof.

Nigel,,

I don't have good experience with surface bonding cement touching the soil. I built a small underground container and it started cracking after a few years in Midwest climate.
I can not imagine it would work on a curved but jagged surface.
Have you considered building the bermed wall straight?
If you use regular concrete blocks you could keep the curvature and reinforce them with vertical rebar and then grout solid. It would be actually better to do it for entire wall.
I assume that dry stacking is chosen, because it's easier and faster than levelling each block on the mortar bed. Having verical reinforcement would keep laying easy but at the same time it would ensure strong wall, especially if topped with a bond beam) and would allow keeping it curved. It would be an order of magnitude better that relying on SBC, which I consider easy, but weak and not lasting solution.

Thank you Cristobal, I hadn't heard of surface binding cracking before, so it's good to know that this can happen. And yes I was erring towards core filling with rebar and concrete, even though Rob Roy (in the store mentioned book) said he got away with just filling them with sand. Was thinking of doing the curved wall because a straight wall would need extra reinforcing column to enable it to hold back the dirt. A circular wall that was inherently strong just seemed a simpler safer option.
I've also read that the irregularities in the block shape/size can make it difficult to get dry stacking walls straight. Did you find this with your underground dry stacked room?

What I have built was a small compartment in the ground maybe 100x80x60 cm. I have used concrete pavers and then plastered it with SBC outside and inside. My experience with concrete block indicates that they are quite precise in dimensions. If they have not uniform height you can alleviate it by rotating block in the next course to cancel out the height differences.
I think that in your case - curved wall with grouted rebars would be the best. I would also patch the resulting wedge shaped vertical joints with some fine aggregate concrete.
How are you planning to finish the interior?

Thanks again Cristobal for your reply. I was just thinking of attaching the plumbing and electrical conduit on the (visible) inside surface of the wall. Apparently it can be done quite neatly with a retro look. Was reading last night that attaching things to surface bonded walls is not easy (and a reason ICF walls are preferred over dry stacking CMUs). Do you have any thoughts/experience you are willing to share in this regard?

For electrical I have used chaser and cut grooves in the compressed earth blocks. I got used Bosch in UK on ebay, 110 V as wall chasing is normal practice in Europe, because it's normal to plaster walls afterwards.
For pipes I hid them in the slab and because of that I made them with 316 welded stainless. It matters a lot how you lay out all plumbing. Try to put everything in one corner of the house: mechanical room, bathroom and then kitchen with the kitchen sink on the bathroom wall. If pipes are good looking (not plastic) then you can leave them exposed close to the floor.
If you grout the blocks then you don't have to worry about SBC and you could use lime plaster. It just looks gorgeous and adheres to concrete very well. It would improve air quality in the concrete house - lime is permeable to water  so the plaster can breathe as opposite to concrete.
If you have any questions, please ask. I went through entire cycle of building masonry home (and smaller buildings)..

I built my house basement starting 40 years ago with dry laid concrete block, surface bonded for initial stability before grouting, appearance and some water resistance. I used vertical rebar about 2' on center and a bond beam at the top and filled all cores with concrete. It has lasted without issue since then, and even had a pickup-sized dump truck full of gravel slide down a bank into it near the exposed end of the wall during backfilling. I saw the wall deflect several inches, and return to vertical when we pulled the (emptied - by hand :O ) truck off the wall.

A curved dry-laid block wall with cores filled and rebar at appropriate intervals should last as good as forever. I would knock out bits of block web in one or more rows horizontally to lay rebar in, for added strength; this is what I have done in later additions. #3 rebar is easy to handle without special tools and will hold a block wall together fine. I agree with grouting the exposed wedges for a smoothish base for surface bond, and waterproofing and insulation outside that. Depending on the width of the gaps, it might be worthwhile cutting a lot of slivers of brick or other masonry to minimize the amount of grout needed. A large blob of grout is going to want to sag.

In the world of landscaping and building retaining walls there are a few different shaped concrete blocks which are designed for dry stacking but they are specifically designed for curved walls.  These blocks have grooves and notches that interlock at the ends and on the outside edges and in the case of the retaining wall that I built, I filled all the holes with small gravel.   Filling the holes with mortar and rebar would be incredibly strong.
Check out landscaping or retaining wall blocks to consider your options.   I should note that each extra row of blocks with the interlocking front edge results in a setback of each row of about a half to one full inch.
The big problem comes in where you would have a corner of two intersecting walls.  There is no easy way I know of to allow the corners to meet smoothly.  So if building an enclosed stand alone structure, you almost have to build a dome or a cone shape.  

Nigel, what dimensions are we looking at for this structure?
Thickness of blocks, Wall height, diameter of the room.
Height of soil against the wall.
How are you creating the roof structure?

For a curved wall, I would use standard 8" thick block. There is no advantage in going thicker for any residential scale structure, and thinner starts to be trickier to align and fill cores with concrete.