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Why We're Moving to Pre-Cast Hemp Blocks

March 2026 · Joe D'Alo · 5 min read

For more than two decades, I've been building with hempcrete the traditional way: mixing hemp hurds and lime binder on site, packing it around a timber frame in lifts, and waiting for it to cure. It works. It produces beautiful, high-performance walls. But the industry is evolving, and so are we.

We're now transitioning to pre-cast hemp blocks as our primary installation method, and I want to explain why. This isn't a compromise. It's an upgrade.

What is cast-in-situ hempcrete?

Cast-in-situ (or manual cast) hempcrete is the original method. You mix the hemp and lime on site, then pack it around a structural timber frame in layers, typically 300mm lifts. Each lift needs time to settle and begin curing before the next is added. The process is labour-intensive, weather-dependent, and requires experienced hands to get consistent density and coverage.

Done well, it produces exceptional results. Our 50+ completed projects are testament to that. But it has real limitations on a modern construction schedule.

What are pre-cast hemp blocks?

Pre-cast hemp blocks are hempcrete compressed and cured in a controlled factory environment before arriving on site. They come in standardised dimensions, consistent density, and are ready to install immediately. Think of them as the natural building equivalent of a high-performance masonry block, but carbon-negative, breathable, and thermally superior.

The blocks are installed around the same structural timber frame, mortared with a lime-based mix, and finished with lime or clay solid plaster in the same way as cast-in-situ walls. The end result is visually and functionally identical. The process to get there is significantly better.

Why blocks are better

Consistent quality

Factory production means every block is mixed, compressed, and cured under controlled conditions. Density is uniform. There's no variation caused by weather, site conditions, or the fatigue that comes with a long day of manual packing. For clients, this means a more predictable, reliable outcome.

Faster construction

Cast-in-situ hempcrete requires the wall to be built in stages, with curing time between lifts. Pre-cast blocks can be installed at full wall height in a single day. This reduces the construction programme significantly, which matters for clients managing budgets and move-in dates.

Less weather dependency

Mixing and packing hempcrete on site in cold or wet conditions is problematic. The lime binder needs warmth to cure properly. Pre-cast blocks have already done their curing. Installation can proceed in a much wider range of conditions.

Reduced site waste

On-site mixing generates waste from over-batching, spillage, and off-cuts. Pre-cast blocks arrive in the exact quantities needed, with minimal waste. For a material we care deeply about, that matters.

What stays the same

The performance characteristics that make hempcrete exceptional don't change. Pre-cast hemp blocks are still carbon-negative. They still regulate humidity passively. They still provide excellent thermal mass and insulation. They're still finished with lime or clay solid plaster. The wall breathes, performs, and improves with age in exactly the same way.

The structural timber frame remains. The lime solid plaster finish remains. The philosophy remains. We're just building smarter.

The construction process in images

What this means for your project

If you're considering a hempcrete home or extension, pre-cast blocks mean a tighter programme, more predictable costs, and the same exceptional performance you'd expect from SANA. We're still doing the work. We're just doing it better.

If you have questions about hemp blocks, the installation process, or how this affects your specific project, get in touch. I'm happy to walk you through it.