Plaster Cement Mix Ratio Guide: How Much Do You Need?

Plaster mix ratios explained, cement quantity per square metre, and a worked example for plastering a typical house.

Plastering is one of the stages where getting the cement to sand ratio right actually matters, both for finish quality and for how much cement you need to budget for. Here's a clear breakdown of plaster mix ratios, how much cement they use, and how to estimate quantity for your job.

Common plaster mix ratios in Kenya

Mix ratio (cement:sand)	Typical use
1:3	External plastering, areas exposed to weather
1:4	Internal plastering, standard walls
1:5	Internal plastering on smooth, well prepared surfaces
1:6	Ceiling plastering, lightly loaded finishes

A richer mix (more cement relative to sand) gives a stronger, more weather resistant finish, which is why external walls typically use a 1:3 or 1:4 ratio while internal work can use a leaner 1:5 or 1:6 mix.

How much cement per square metre of plaster?

Mix ratio	Thickness	Approx. cement per m²
1:4	12mm	~4.5 kg (roughly 11 m² per bag)
1:4	15mm	~5.6 kg (roughly 9 m² per bag)
1:6	12mm	~3.2 kg (roughly 15 m² per bag)

Figures are approximate and assume standard block or brick surfaces with reasonable evenness. Rougher surfaces or thicker application increase consumption.

Worked example: plastering a 100 m² house (both sides)

For a house with roughly 100 m² of wall surface plastered internally and externally, at a standard 1:4 ratio and 12mm thickness, expect a combined internal and external plaster area of around 180 to 220 m², which typically uses in the range of 20 to 25 bags of cement.

What affects plaster cement consumption

Surface flatness: uneven blockwork requires thicker application in places, increasing overall consumption
Plaster thickness: even a few extra millimetres across a whole house adds up quickly
Number of coats: some finishes require a scratch coat plus a finishing coat, effectively doubling material for that section
Wastage: allow 5 to 10% extra for spillage and rework, particularly for less experienced crews

Choosing the right cement grade for plastering

Standard 32.5N or 32.5R cement is the appropriate grade for almost all plastering work. There's no benefit to using a higher strength 42.5N cement for plaster, since plastering doesn't carry structural load. Using it would simply increase cost without improving the finish.

Get help estimating your plastering job

If you have your wall area or house plan, our technical desk can calculate cement quantity for your specific job and recommend the right grade and bag order.

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Figures are indicative estimates for planning purposes only. Confirm quantities against your site's specific conditions before ordering.