10 Youths Trained at HYT’s 10th Community Training Site

Posted on July 28th, 2017

The successful completion of HYT’s 10th ‘One Community at a Time’ training project was celebrated in style, with the opening of an impressive range of buildings and the handing out of certificates to the ten HYT trainees who built them. HYT training manager, Fred Koire, oversaw the eight-month training programme, and the youths at St. Stephen’s primary school, Butaaya, are now equipped to use their newly-acquired masonry skills with HYT and elsewhere.  

St. Stephen's Classroom Door

An HYT certificate opens the door to professional masonry opportunities in Uganda.


St. Stephen’s is a school of 400 or so pupils, in rural Kamuli District, where large numbers of boys drop out to cut sugar cane, while the pregnancy rate among girls remains high. Enhancing infrastructure encourages students to stay at school, and providing staff accommodation means that teachers do not have to walk to work in the rain (or heat!) and are more readily available to support their students. The large and enthusiastic audience at the ceremony included community leaders, local head teachers and the Vice Chairman of Kamuli District, representing the Speaker of Parliament. They were told of the benefits of an environmentally-friendly approach to construction, and encouraged to adopt the interlocking stabilised soil block (ISSB).


St. Stephen's Compound

All HYT buildings, including water tanks, are built using low carbon ISSB technology!


And how better to recommend the technology of East Africa’s future than with the spectacular workmanship of the community’s youth? This particular project gave trainees the chance to demonstrate their artistic flair thanks to the generous support of two Haileybury houses and lower school.


St. Stephen's Staff Block

The community gathers to admire the Lower School staff accommodation.


Lower School’s donation funded the staff house, improving working conditions for teachers and upping the trainees’ experience in all sorts of construction skills, from excavation to completion.


St. Stephen's Water Tank

Special mention goes to OHs Coralie Spearman and Katie Brooking for their expert artistry!


Kipling’s water tank offered trainees the chance to work with specialised curved blocks, and provided the school with 20,000L of water storage! That means more time in class, and less time fetching water from the community borehole.


St. Stephen's Classroom Block

The children are proud of their skilfully constructed and uniquely decorated school.


This year’s Batten Bistro raised enough funding to outfit this double classroom block with doors, windows and security bars, as well as plastering and painting. Trainees were keen to celebrate Haileybury’s contributions with panache, and relished the opportunity to hone their decorative skills across all the buildings.


St. Stephen's Training Team

Quite a team has been assembled here at St. Stephen’s, Butaaya!


The result? Ten trainees have become graduates of HYT’s training programme, empowered to become builders of the future. St. Stephen’s primary school now has three sturdy new structures to enhance its learning environment, helping kids get the most out of their school day. A big HYT thank you goes out to trainers, trainees, and the hugely supportive communities both here in Uganda and back in the UK!  


The Science of ISSB

Posted on June 10th, 2017

ISSB are making attractive, sustainable and affordable buildings for families and communities – so how exactly do they work?


Spacious, stylish and sustainable – find out how we make the blocks that made this!


The Interlocking Stabilised Soil Block – or ISSB, for short – is the technology at the core of what HYT does. It’s a building material that Ugandans use to build robust, attractive and affordable buildings, whilst avoiding the deforestation and high carbon emissions of the conventional burnt brick.

What exactly IS an ISSB? And what makes it an excellent construction material?

The ‘interlocking block’ part of the name is fairly self-explanatory – it’s basically real-life LEGO! This allows for easy quality control on wall thickness, and reduces the amount of expensive mortar required to lay each course.


real-life LEGO

These giant LEGO blocks can even be curved for round structures like water tanks!


However, the ‘stabilised soil’ part of the name isn’t so obvious. What even is soil? And how is it stabilised? The soil referred to here – also known as murram – comes from about 50cm beneath the surface. It’s a mix of sand, silt and clay. It doesn’t contain any of the organic matter in topsoil, so using murram isn’t depriving farmers of their resources. Soil has been used for construction for millennia, and is still used in many parts of the world, from Devon to Delhi. However, there are a few problems with using unadulterated soil for building…


Mixing the Materials

Mixing the materials is a key skill taught to HYT trainees.


Firstly, it is a delicate material that requires skilful design and diligent maintenance. Although soil has good strength once compressed, it is vulnerable to the elements. Most threatening are water, which erodes the surface, and termites, which burrow through. Negating these threats requires competent planning and well-thought-out protection – procedures not to be rushed! Secondly, our tastes have changed over the years – just like most Brits, most Ugandans would rather not live in a mud hut if there’s other options. Burnt bricks and concrete blocks are aspired to because that’s what most people live in, right?


Stylish Ugandan Homes

The ISSB lets homeowners live in style without contributing to devastating deforestation.


ISSB retain many of the environmental advantages of building with just soil, but overcome these two problems – by making soil resilient and attractive. So how does ISSB do this? Well, this is where the ‘stabilised’ part comes in. When we stabilise a soil, this means that we change or add to its chemical composition in order to increase its strength and resilience. There have been many things added (i.e. stabilisers) to soil to stabilise it, such as lime, bitumen – even cheese! ISSB use cement as a stabiliser. The exact amount of cement added depends on the exact type of soil – judging this is one of HYT graduates’ skills after their 9 month training programme. Generally speaking, the amount of cement added to the soil is 5-10% by weight.


Material Stabilisation Diagram

Internal Microstructure of ISSB (cement amount has been exaggerated for clarity)!


The cement stabilises the soil by forming a network of strong crystals (calcium silicate hydrate) which surround the soil particles as the cement sets. The chemical reaction which causes the cement to set needs water – this is why HYT builders add water to the mixture of soil, sand, and cement before making the blocks. Over time, the cement sucks in the water, the setting reaction happens, and a few days later the cement has formed a network of strong crystals surrounding the soil particles. This structure makes the ISSB much stronger and more resilient than if it was just soil.


ISSB Corner Stack

Building in Uganda has turned a corner with the development of the durable yet economical ISSB.


Whilst cement itself has high carbon dioxide emissions from production, because it’s only used in small amounts in ISSB they give a much better environmental performance than burnt bricks. Using cement as a stabiliser avoids the need to fire bricks in a kiln, preventing deforestation for firewood. There’s still several improvements to be made to the technology, but in the meantime, Ugandans will continue using ISSB to build quality buildings for families and communities.


By Alastair Marsh

Postgraduate Researcher in the Department of Architecture and Civil Engineering

University of Bath

Twitter: @AlastairMarsh