posted 16 hours ago
Conrete block is the only widely available masonry unit in the US. Structural bricks, insulated blocks or aerated concrete blocks are rarity, expensive and available from only a few spots resulting in high transportation cost and minimum order quantities.
European houses built from concrete blocks in the 60s stand strong and nothing indicates they will not survive another 200 years. Walls are fire/insect/rodent proof, solid, quiet and easily reinforced to make them earthquake proof. CMU house can be built without any synthetics, as long as it's treated as a true masonry structure and not just a replacement for lumber to be covered with some wood furring, drywall, boards, caulking, etc. (also inviting pests to the created cavities). Because of it, if interior walls are also block then entire interior can be beautifully plastered with lime or clay plasters. Interior masonry walls additionally brace the exterior walls making the structure stronger and reduce flammables to furniture only.
"Distance to combustibles" is not an issue, so building masonry heaters is easy and very compatible with the house.
Maintenance is low.
All of it makes it very permie in my opinion:
-wide availability (also of block factories) reducing transportation
-safe structure that will last a very long time with low or no maintenance
-easy to avoid chemicals as entire house can be naturally and easily finished with mineral materials
The main negative is the interior air quality, because concrete does not want to absorb moisture like adobe, cob, fired clay, porous stones or aerated concrete. It's easily visible when plastering. When we apply plaster to earth block, water is getting sucked quickly, making it difficult to finish it. On concrete it stays wet for quite a long time which makes plastering concrete much easier. I'm assuming that applying thick layer (at least 25 mm/1 inch) of natural breathable plaster would mitigate the air quality problem.
The second challange is how to inulate it naturally. Probably the best would be to build two wythe wall and fill the cavity with perlite, vermiculite or mineral wool. The other option, much more popular, is to attach rigid inulation to the outside and plaster it. Unfortunatelly it usually means using styrofoam which would:
-invite pests (mice love tunelling in styrofoam)
-add a lot of toxic material to the house, despite being hidden, in case of fire it will be nasty and if destroyed by pests, will need to be replaced generating more toxic refuse
Probably there are other rigid insulation panels, but mostly synthetic and if not synthetic then expensive, so the best would be the two wythe wall.
Dry stacked CMU would work the same as mortared provided it has vertical reinforcing. I use 0.5" rebar 32" OC. I'm mortaring and always build wallls at least 16" wide, which doubles the vertical bars.
If I did dry stacked wall I would opt for one bar per block, so 16" OC. I would also add a middle and top bond beam, but for most locations the top one would suffice.
Dry stacked block would be also the easiest building method as compared to other masonry techniques and even more easier than any wood structure construction.
I would not trust SBC as the way to reinforce the wall. I used it once on dry stacked paver wall and it cracked in excessive moisture. Also the SBC would be cement based, further deteriorating interior air quality.
Grouted vertical rebars, solid bond beam and natural breathing plasters would be a way to go.