00 Pre-work: before you depart
Eight tasks to complete before boarding the plane. Construction failures in Bombali are almost entirely preventable — but only if you understand the local context before you arrive.
PW-01
Understand rising damp
Water wicks up from saturated ground into the wall material. The solution is a stone plinth — a base of stone or hard material between the wet ground and the wall above it. This is the single most important concept in this curriculum.
Start: Read about it now
PW-02
Learn the VIP Latrine
Understand what a Ventilated Improved Pit (VIP) latrine is and why the raised variant matters in Bombali's high water table. A standard pit latrine collapses when the water table rises in the rainy season.
Start: Watch a short video on VIP latrines
PW-03
Understand Stabilized Soil Blocks
Local laterite + 5–8% cement + manual press = a compressed block that is stronger than unfired mud and significantly cheaper than fired brick. Watch "Cinva Ram block press" on YouTube.
Start: Watch "Cinva Ram block press" on YouTube
PW-04
Learn the roof overhang standard
Minimum 1-meter overhang protects the wall face from driving rain. Less than 60cm and the wall base erodes within 3 rainy seasons. This number matters — memorize it.
Start: Now
PW-05
Calculate rainwater harvesting potential
Formula: Roof area (m²) × Annual rainfall (m) × 0.8 (efficiency) = litres per year. A 50m² school roof in Bombali yields ~80,000 litres. This is a water supply. Practice the calculation before you arrive.
Start: Practice the calculation
PW-06
Learn to read a site for drainage
Before any construction, identify: where does water flow on this site? Where does it pool? A building placed in a natural drainage path will flood and fail regardless of how well it's built.
Start: Observe your next rain event
PW-07
Research PVC gutter and tank prices in Makeni
Half-round PVC gutter is standard. A 2000L plastic tank is available in Makeni markets for approximately SLL 800,000–1,200,000 (~$40–60 USD). Know this before you price a rainwater system.
Start: 4 weeks out
PW-08
Pack precision tools
A 30m measuring tape, a spirit level, a chalk line, masonry string, and a plumb bob. These are the precision tools that don't exist on most Bombali construction sites and make the difference between walls that are straight and walls that lean.
Start: Buy now
01 Unlearn: assumptions to leave behind
Four assumptions that are common at home and actively harmful in Bombali's high-rainfall, low-resource building context.
Unlearn #1 — "Cement solves everything"
Cement is expensive and imported. A cement-only building strategy is not replicable by the community after you leave. Stabilized Soil Block uses 5–8% cement with local laterite — dramatically cheaper and locally producible.
Unlearn #2 — "This needs a foundation excavation"
In Bombali's shallow laterite soils, the stone plinth approach — building the first 30–50cm of wall in stone or hard laterite blocks — solves rising damp without the cost of a deep poured concrete foundation.
Unlearn #3 — "The roof pitch can be shallow"
In 3,000mm annual rainfall, a low-pitch roof creates standing water and accelerated sheet corrosion. Minimum 30-degree pitch. Teach this standard and do not deviate from it.
Unlearn #4 — "Bigger overhang is wasteful"
1 meter is the minimum. It is not excessive. The 3 rainy seasons a 40cm overhang survives versus the 15 years a 1-meter overhang protects — the math is not close.
What does transfer
Level and plumb discipline, drainage site reading, load calculation principles, materials costing, quality control, record-keeping, safety culture — all directly applicable.
02 Building failure modes
Every failure mode below is preventable. Most are already visible in buildings across Bombali District. Photograph them on Day 1.
| Failure | Cause | Fix |
|---|
| Rising damp erosion |
No stone plinth; wall material wicks moisture from ground |
Build stone plinth 30–50cm above grade before starting wall |
| Mud block collapse (rainy season) |
Overhang <60cm; driving rain hits wall face directly |
Replace roof sheets; extend overhangs to minimum 1m |
| Pit latrine collapse |
High water table saturates pit walls during rainy season |
Raised VIP design: pit above grade, rubble-filled base |
| Roof sheet corrosion |
Low pitch; standing water on sheet surface |
Re-roof at minimum 30° pitch |
| Cracked walls |
No movement joints in long walls; thermal expansion |
Add control joints every 6m in SSB walls |
03 Stabilized Soil Blocks (SSB)
The most viable skill transfer for construction in Bombali. Local laterite + 5–8% cement + water → compressed in a manual Cinva Ram press → cured 28 days → load-bearing wall block.
Cheaper than fired brick. Stronger than unfired mud. Locally producible from materials underfoot. The press is the capital investment; once built or purchased, the community can produce blocks indefinitely from local soil without external supply chains.
SSB vs. alternatives
| Material | Cost / block | Strength | Local production | Cement required |
|---|
| Burned brick | High (fuel cost) | High | Possible | None |
| Cement block | Very high | Very high | Yes | High |
| Unfired mud block | Near zero | Low | Yes | None |
| SSB (laterite + 5–8% cement) | Low | Medium-high | Yes | Low |
The 5% rule
Test your laterite before committing to a mix ratio. Some laterite soils require up to 8% cement; others stabilize well at 5%. Press 5 test blocks at each ratio, cure for 7 days, and run a scratch test and drop test before full production. The investment in testing saves wasted cement.
04 Rainwater harvesting
A 3-week team can install a complete rainwater harvesting system on a school with an existing metal roof. All materials are available in Makeni. The intervention is primarily labour and knowledge, not imported equipment.
The first-flush diverter is critical — it diverts the first 20 litres of each rainfall (which carries dust, bird waste, and roof debris) before allowing water to fill the storage tank. Without it, tank water quality degrades rapidly. Build it from standard PVC fittings available in Makeni.
Materials for a school guttering system (50m² roof)
| Component | Quantity | Local source | Approx cost |
|---|
| Half-round PVC gutter | 20m | Makeni hardware | SLL 200,000 |
| PVC downpipe | 4m | Makeni hardware | SLL 60,000 |
| First-flush diverter | 1 | Build from PVC fittings | SLL 30,000 |
| 2000L plastic tank | 1 | Makeni market | SLL 800,000–1,200,000 |
| Gutter brackets | 12 | Makeni hardware | SLL 60,000 |
Gutter fall — the critical detail
Install gutter with a minimum fall of 1:200 toward the downpipe (5mm drop per 1m of run). A level gutter pools water and creates a breeding site for mosquitoes. Use your spirit level and chalk line to set the correct slope before fixing any bracket.
05 VIP Latrine
The Raised VIP (Ventilated Improved Pit) design for high water table areas. The pit is above grade — built from rubble-filled walls rather than dug into the ground. This solves the rainy season collapse problem that makes conventional pit latrines unviable in much of Bombali District.
Superstructure: local fired brick or SSB. Vent pipe: 150mm PVC, painted black to create thermal updraft that draws odour out of the pit and up through the pipe. Fly screen on vent pipe top: flies enter the dark pit interior, are drawn toward the light at the pipe top, cannot exit through the screen, and die. This is the "VIP" mechanism — not a euphemism, but a functional description of the odour and fly control system.
Girls' school latrine — non-negotiable design feature
A girls' school latrine requires a locking door from the inside. This is the single most important design feature for keeping girls in school past puberty. A latrine without an internal lock is effectively unusable by adolescent girls and women. Do not build without it.
06 The stone plinth
The foundation intervention that costs almost nothing and extends wall life by decades. The concept is simple: break the physical connection between wet ground and the wall material above it.
Method: Collect hard laterite stones, broken fired bricks, or any durable non-porous material from the site. Build the first 30–50cm of the wall in this material — mortared with a strong sand-cement mix — before starting mud blocks, SSB, or any other wall material. This creates a capillary break between the saturated ground and the wall above.
This technique is standard practice in traditional building in drier climates and in good-quality masonry worldwide. It is largely absent in Bombali because it was never formally introduced to local building practice, not because local builders lack the skill to execute it once shown.
Demonstrate before explaining
On Day 4, build a 30cm section of plinth in front of the community. Show the material, show the mortar, show the height. Then explain why. Physical demonstration followed by explanation is more effective than explanation alone in a context where most participants have no prior exposure to the concept.
07 21-day schedule
PreWeek −4
Pre-departure preparation
- Research VIP latrines — understand the raised design and vent pipe mechanism
- Learn SSB — watch the Cinva Ram video, understand the 5–8% cement ratio
- Buy measuring tape, spirit level, chalk line, plumb bob
- Calculate rainwater potential for one school from satellite image (Google Maps)
Wk 1Day 1
Building survey
Walk every building. Photograph: overhangs, rising damp stains (look for dark tide marks on lower walls), pit latrine conditions, roof pitch and sheet condition. Map the failures. Do not touch anything today.
Wk 1Day 2
Community meeting — present the evidence
Present the photographs to the community. Ask: which failure is causing the most harm right now? This is not a rhetorical question — their answer shapes the entire program.
Wk 1Day 3
Site selection — community decides
Select the site for the first intervention, agreed by the community. Conduct a full drainage observation: where does water flow? Where does it pool? Record in field notebook.
Wk 1Day 4
Stone plinth demonstration
Find stone material on site. Build a 30cm demonstration section in front of the local masons. Show the technique, then have them replicate it. Watch for mortar consistency and height.
Leave behind: the demonstration section as a permanent physical reference
Wk 1Day 5
SSB demonstration — first 20 blocks
Mix soil, measure cement proportion at 5%, press 20 blocks. Set to cure. Community members observe the mixing ratio, the pressing technique, and the curing process. These 20 blocks are Day 15's building material.
Wk 1Day 6
Rest — market walk
Walk the market. Price materials: PVC gutter, downpipe, gutter brackets, tanks. Find the local mason community — who is currently building and where? Build the relationships that make Weeks 2 and 3 work.
Wk 1Day 7
Plan Weeks 2–3 with community and masons
The community and local masons decide the build sequence. Your role is to facilitate the planning conversation, not to set the agenda. A plan they own is executed; a plan you set is abandoned.
Wk 2Day 8
SSB production day — 100 blocks
Local team presses 100 blocks. You check quality — press each block by hand, inspect edges, verify mix ratio is correct. They run the production; you quality-check at the output.
Wk 2Day 9
Rainwater guttering site survey
Measure roof, plan gutter layout, write materials list. Calculate gutter fall and downpipe position. Mark bracket positions on the fascia with a chalk line.
Wk 2Day 10
Gutter materials procurement
Go to Makeni hardware stores together with the community committee member responsible for materials. Teach the purchasing decisions: what to check for quality, how to negotiate, what alternatives exist.
Wk 2Day 11
Gutter installation
Community team installs. You supervise level and fall — minimum 1:200 slope toward downpipe. Use spirit level and chalk line throughout. Do not allow any bracket to be fixed without checking the slope.
Wk 2Day 12
First-flush diverter construction and installation
Build the first-flush diverter from PVC fittings. Show the community why it exists — demonstrate the principle with dirty water. Install on the downpipe. Connect to tank.
Leave behind: written first-flush diverter maintenance note with the school committee
Wk 2Day 13
VIP latrine site marking
Choose site (uphill from water sources, minimum 30m from any well), mark layout, begin rubble-fill base construction. Confirm internal locking door provision in the design.
Wk 2Day 14
Community day
Organized by the host community. Attend, participate, listen. Do not bring work.
Wk 3Day 15
VIP latrine walls — SSB blocks now 10 days cured
SSB blocks (pressed on Day 5 and Day 8) are now 10 days cured. Local mason leads the wall construction. You check plumb and level at each course. Do not lay a block for them; correct and observe.
Wk 3Day 16
VIP vent pipe installation
Install 150mm PVC vent pipe. Paint black — every coat. Attach fly screen to pipe top with wire. Show community the mechanism: dark pit → fly toward light → screen traps fly. This is the science of the VIP.
Wk 3Day 17
Roof overhang extension
On the most critically underserved building, extend overhangs using additional timber and corrugated sheet. Teach the 1-meter rule with a tape measure in hand. Show where the rain would land at 60cm vs. 1m.
Wk 3Day 18
Documentation in Krio
Local mason writes the SSB mix recipe and pressing procedure in Krio. This is their document, not yours. You assist with formatting if needed but the content and language are theirs.
Leave behind: laminated SSB production guide in Krio with the mason
Wk 3Day 19
Teach the builders
Present the full curriculum to all local masons and the school or community committee. Cover: stone plinth, SSB production, roof pitch, 1-meter overhang rule, rainwater harvesting, VIP latrine design.
Wk 3Day 20
Commitment ceremony
Local masons and community committee commit to using the stone plinth and 1-meter overhang standard in all future construction. Public commitments in a community setting are kept at a measurably higher rate than private ones.
Wk 3Day 21
Depart — tools stay
Leave spirit level, measuring tape, and chalk line with the lead mason. Confirm WhatsApp contact. Depart.
Leave behind: spirit level, 30m measuring tape, chalk line, masonry string
08 Success metrics
30 Days
- SSB blocks in production independently
- Rainwater tank in use and water quality acceptable
- VIP latrine functional and in use
- Stone plinth technique used on at least one additional structure
90 Days
- Local masons teaching SSB technique to others
- Girls' school latrine with locking door operational
- Community committee tracking rainwater tank levels
12 Months
- SSB used in a community-initiated building project (not program-funded)
- Zero new rising damp failures in buildings with stone plinths
- Rainwater system supplying dry-season water needs