ISSB Excels in Strength Tests

Posted on August 26th, 2019

HYT is well underway with our training project in the world’s second largest refugee settlement, Bidi Bidi. A total of 18 South Sudanese and 10 Ugandan youths are undergoing intensive training thanks to an ongoing partnership with Mercy Corps.

HYT Trainees
Day 1 of training in Bidi Bidi in partnership with Mercy Corps.

Planning Permission

In Uganda’s extreme north an environmental crisis is following its ongoing humanitarian counterpart. Trees are becoming scarce, the lack of forest cover is increasing the area’s vulnerability to climate change; exposing it to desertification and soil degradation.

In February 2019, HYT arrived in Yumbe with a viable alternative to the environmentally devastating burnt brick. Interlocking Stabilised Soil Blocks (ISSB) require no firewood in their production, far less concrete during construction and no transportation costs. Our innovative construction practices were met with cautious curiosity.

Introducing the benefits of ISSB to the District, UNHCR and Mercy Corps Partners.

The District Engineer, Settlement Commandant and UNHCR are responsible for construction, quality control and strategy within the settlement. They have the monster task of coordinating the effort to bring the refugee’s standard of living to an acceptable level.

HYT is thrilled that our training has 10 female participants in Bidi Bidi.
With the pressure on HYT to showcase ISSB technology, we had ISSB master Philip Yiga overseeing the project.

Passing the First Test

28 days after the first block was pressed, a sample was taken to Teclab Kampala, an independent material testing lab. According to UNBS(2011) the Uganda standard (US849), states that blocks must achieve 2.5 Mega Pascals (MPa) for dry compressive strength to be used in construction. Our ISSB blocks averaged 5.1MPa, this is the equivalent force of 0.51kg pressing on every squared millimetre of the blocks surface!

Blocks are weighed and measured before being crushed.

Not only have our blocks far surpassed the required strength, they have saved 16.4 tons of firewood that would have been used in an equivalent structure made out of burnt brick!

The first round of testing was a great success.
Specialized machines compress the blocks

This is a huge moment for HYT, in an epicentre of Uganda’s international aid and development activity we have irrefutably displayed the power of ISSB technology. International aid should not be spent on environmentally destructive practises when there is an affordable, safe and sustainable option available. HYT is gearing up to help NGO’s and government bodies make the switch to safeguard the environment for future generations.

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Winners of the Ashden International Award for Sustainable Buildings 2017.

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Water we doing?

Posted on May 21st, 2019

In 2018 HYT built 33 ISSB water tanks in schools across Uganda, with a total capacity of 650,000 litres. Access to stored rainwater increase the time students spend learning in the classroom, by removing the need to fetch water from boreholes – an endeavour involving heavy jerrycans and multiple kilometre journeys.

Primary school children posing in front of a brand new ISSB water tank.

Plastic water tanks

Most water tanks in Uganda are made of plastic, and although they are easy to install, they do suffer from some key flaws. The main issue with plastic tanks is their longevity, damage is easily done to the main body and is difficult and expensive to repair. Unfortunately most of the damage is caused by people vandalising the tanks, often using knives or screwdrivers to pierce the tank.

A typical plastic tank found in many Ugandan schools.

Another disadvantage with using plastic water tanks is the transport costs and associated environmental impact. The vehicles used to transport a tank to its destination will produce pollution and increase the carbon footprint of the tank.

ISSB water tanks

Affordable, durable and environmentally friendly. The ISSB water tank is probably HYT’s most competitive product.

HYT builds water tanks out of ISSBs, this produces strong and durable structures. As the tanks are made from compressed blocks that are very difficult to pierce or damage, and can easily be repaired with some mortar. Additionally, since the blocks are produced on site, the transport costs are minimised, further reducing the environmental impact of tank construction.

A team of HYT masons can build two water tanks a month, with each tank taking a total of two weeks to complete.

As the water tanks are cylindrical, HYT uses curved blocks created with a different press. Construction begins with the foundation of the tank, this consists of a shallow circular trench in which a four-block high ring is built. This ring is then filled with concrete to form a flat base for the tank. At this stage a hose pipe is put through the base, this is used to filter out sediment which drifts to the base of the tank, ensuring the water provided is clean.

HYT masons use a wooden plank to flatten the concrete on the foundation of a tank.

Now the main body of the tank is built. The main cylinder consists of 16 slightly smaller rings of blocks. Unlike regular ISSB buildings, water tanks require mortar between each of the blocks to ensure the tank is watertight.

Once the main body of the tank is completed, wire mesh is attached to the outside and inside of the cylinder. The purpose of this mesh is twofold: it increases the durability and strength of the blocks in addition to providing a surface for the plaster to adhere to. Next the inside of the tank is plastered with a mix of mortar and a waterproofing agent. Then small rocks and mortar are used to make a bowl-like shape in the base of the tank. This is done to reduce the pressure around the rim of the base, as the weight of water in a full tank is 20,000 kilograms.

The bowl-like shape around the rim of a tank, made from small rocks and mortar.

At this point the tank is almost complete, a hole is drilled in the front to fit the tap and a roof is added and connected to gutters on the building. Finally the tank is plastered and painted, and the HYT masons will move onto their next project.

Rainwater harvesting Projects
HYT rainwater harvesting tank addresses multiple SDG’s

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Winners of the Ashden International Award for Sustainable Buildings 2017.

Watch our exciting video, or check out our work at