Good wall plaster in Tanzania is usually a 1:4 cement and sand mix for outside walls and 1:5 or 1:6 for inside walls, applied about 12 to 15 mm thick inside and 15 to 20 mm outside, and kept damp for at least three days afterwards. Most plaster that cracks or sounds hollow fails for one of four reasons: dirty or very fine sand, a mix that is too rich in cement, one thick coat instead of two thinner ones, or no curing at all. Get those right and plaster is one of the cheapest parts of the house to do well.
What mix ratio should I use for plastering?
The mix is measured by volume, usually with a head pan or a gauge box, never by eye. Here is what we use on most of our sites:
| Where | Mix (cement : sand) | Typical thickness | Notes |
|---|---|---|---|
| External walls | 1:4 | 15 to 20 mm in two coats | Faces rain and sun, needs to be denser |
| Internal walls | 1:5 or 1:6 | 12 to 15 mm | Smoother finish, less shrinkage |
| Ceilings and soffits | 1:4 | 6 to 10 mm | Thin coats only, or they fall |
| Wet areas before tiling | 1:4 | 12 to 15 mm | Keep the surface rough so tile adhesive grips |
| Plinth and lower wall outside | 1:3 with waterproofer | 15 to 20 mm | Takes splash-back from rain |
More cement does not mean stronger plaster. A very rich mix shrinks more as it dries and that shrinkage shows up as a web of fine cracks, called crazing. If you want harder plaster outside, a waterproofing additive in the mix does more good than extra bags of cement.
What kind of sand is best for plaster?
Clean, sharp river sand or washed pit sand, sieved to take out stones and roots. Fine beach sand is a bad idea because the salt in it attracts moisture and pushes the paint off later. Sand with a lot of clay or silt is just as bad: it needs more water to work, shrinks more and gives a weak, dusty surface.
A quick test you can do on site: put a handful of sand in a clear bottle of water, shake it and leave it for an hour. If the layer of mud that settles on top is thicker than about a tenth of the sand, ask the supplier for better sand or have it washed. Our guide to building materials prices covers what good sand should cost.
How do you plaster a wall step by step?
- Wait for the blockwork. Give new walls at least a week, ideally two, before plastering so the mortar has shrunk.
- Clean and wet the wall. Brush off dust and mortar lumps, then wet the blocks so they do not suck the water out of the plaster.
- Fix mesh at joints. Where blockwork meets a concrete column or beam, nail a strip of chicken wire or expanded metal mesh across the joint. This one step prevents most of the long straight cracks people see later.
- Fix the screeds. Set small dots of plaster or timber guides at the finished thickness so the plasterer has a level to work to.
- First coat. Throw on the first coat, about 10 mm, and scratch it rough so the next coat grips.
- Second coat. Apply the finishing coat the next day, level it with a straight edge and finish with a wooden or steel float.
- Cure it. Spray or sprinkle water morning and evening for at least three days, longer in the dry season or on walls that face the afternoon sun.
Why does plaster crack or sound hollow?
When you tap a wall and it sounds hollow, the plaster has lost its bond with the blocks. Cracks and hollow patches usually come from:
- No curing. The surface dries too fast and shrinks before it gains strength.
- Too much cement. A rich mix shrinks more and crazes.
- Dirty sand. Clay in the sand weakens the plaster and makes it shrink.
- Dry blocks. The wall sucks the water out of the plaster before it can set.
- One thick coat. A single 25 mm coat sags and pulls away from the wall.
- No mesh at joints. Concrete and blocks move differently, and the crack follows the joint.
Fine hairline crazing is cosmetic and paint usually covers it. A crack wider than about 1 mm, or one that runs diagonally from a window corner, may be structural, and that is a different problem. Our guide to cracks in walls explains how to tell the difference.
How much does plastering cost in Tanzania?
As a rough example in 2026, plastering costs about TSh 7,000 to 13,000 per m² for materials and labour together (about USD 3 to 5), depending on the mix, the thickness and the region. A 15 mm coat of 1:4 plaster uses around a tenth of a 50 kg bag of cement per m². For a typical three-bedroom house with roughly 600 to 800 m² of wall area inside and out, that puts plaster somewhere around TSh 5 to 10 million. Prices are examples only and change by region and season. USD figures use roughly TSh 2,600 per USD.
Should I use skimming or gypsum on top of plaster?
Skim coat (a thin layer of wall putty or gypsum finish) gives the very smooth surface many clients like inside. It is optional. It hides small trowel marks and makes paint look better, but it will not fix plaster that is hollow or badly cracked underneath. Use skim only on internal walls, because most skim products do not like rain. For the paint that goes on top, see our guide to exterior house painting.
Frequently asked questions
How long should plaster cure before painting?
Give cement plaster at least two to four weeks to dry before painting, longer in the rainy season. Paint on damp plaster blisters and peels.
Can I plaster directly on concrete?
Yes, but the concrete must be rough. Smooth columns and beams need hacking or a bonding coat first, or the plaster will fall off.
What is the correct plaster thickness for walls?
About 12 to 15 mm on internal walls and 15 to 20 mm on external walls, in two coats. Anything over 25 mm usually means the blockwork was badly built.
Why is my plaster turning white and powdery?
That is usually efflorescence: salts carried out of the wall by moisture. It points to damp. Read our guide to rising damp to find the cause.
Plastering done properly
Our site teams plaster, cure and finish walls the same way on every job, big or small. Talk to Vika Construction about your building or renovation.
Found this useful? Share it with someone who is building.
