Complete Guide to Wall Plastering: Interior and Exterior Step-by-Step

Plastering is one of the most critical finishing works in any construction project in Kenya. Whether you're building a residential home in Nairobi, a commercial property in Mombasa, or a bungalow in Kisumu, proper plastering ensures your walls are smooth, durable, and ready for painting. This comprehensive guide covers everything you need to know about wall plastering work in the Kenyan context.

What is Wall Plastering?

Plastering involves applying a cement-sand mixture to walls and ceilings to create a smooth, uniform surface. It serves dual purposes: protecting the structural elements from environmental damage and providing an aesthetically pleasing finish ready for painting or decoration.

In Kenya, plastering is essential because it protects walls from harsh weather conditions, prevents moisture penetration, and creates a foundation for quality interior finishes. Without proper plastering, your building is vulnerable to dampness, cracking, and premature deterioration.

Materials Required for Plastering in Kenya

Primary Materials

1. Cement

The most commonly used cement types for plastering in Kenya include:

Ordinary Portland Cement (OPC) Grade 32.5: Ideal for general plastering work in residential buildings
Portland Pozzolana Cement (PPC): Suitable for both internal and external plastering
OPC Grade 42.5: Used when higher strength is required

Popular cement brands in Kenya include Blue Triangle, Bamburi, Simba, Savannah, National, and Rhino cement. For standard plastering work, Grade 32.5 cement is sufficient and cost-effective.

2. Sand

Clean river sand or quarry sand is essential for plastering. The sand must be:

Free from silt and organic matter
Properly graded (fine to medium grain size)
Washed to remove impurities

Poor quality sand with high silt content leads to weak plaster that cracks and fails prematurely.

3. Water

Use clean, fresh water free from salts, oils, and organic matter. The water-to-cement ratio significantly affects the plaster quality.

4. Optional Additives

Bonding agents for improved adhesion
Waterproofing compounds for bathrooms and exterior walls
Plasticizers to improve workability

Tools and Equipment

Essential Tools:

Mixing Tools
- Wheelbarrows or mixing pans
- Shovels and hoes
- Electric mixer (for large projects)
Application Tools
- Trowels (finishing trowel and gauging trowel)
- Hawk (for holding plaster)
- Float (wooden or plastic)
- Spirit level
- Plumb bob
- Straight edge (steel rule)
Preparation Tools
- Wire brushes
- Scrapers
- Buckets
- Measuring containers
- Watering can or sprayer
Safety Equipment
- Dust masks
- Gloves
- Safety goggles
- Overalls

Understanding Cement-to-Sand Ratios in Kenya

The ratio of cement to sand determines the strength and workability of your plaster. Here are the standard ratios used in Kenya:

Interior Wall Plastering

Standard Ratio: 1:4 (1 part cement to 4 parts sand)
Smooth Finish: 1:3 (for higher quality finishes)
Economy Option: 1:5 (for non-critical areas, though less durable)
Undercoat (First Coat): 1:5 or 1:6
Finishing Coat (Second Coat): 1:3 or 1:4

Exterior Wall Plastering

Standard Ratio: 1:4
Weather-Resistant: 1:5 or 1:6 (for areas with heavy rainfall)

Ceiling Plastering

Recommended Ratio: 1:4 (provides adequate strength for overhead application)

Plaster Thickness

Total Thickness: 12mm to 20mm
Undercoat: 12mm to 15mm
Finishing Coat: 6mm to 8mm

For most Kenyan residential projects, a two-coat system with a total thickness of 18-20mm is standard practice.

Calculating Material Quantities

Let's calculate materials for plastering a 100 square meter wall with 15mm thickness using a 1:4 ratio:

Step 1: Calculate Wet Volume

Area = 100 m²
Thickness = 0.015 m
Wet Volume = 100 × 0.015 = 1.5 m³

Step 2: Calculate Dry Volume Add 33% for dry volume (bulking of sand and wastage):

Dry Volume = 1.5 × 1.33 = 1.995 m³ ≈ 2 m³

Step 3: Calculate Cement Required For 1:4 ratio (total parts = 1+4 = 5):

Cement Volume = (1/5) × 2 = 0.4 m³
Cement bags = 0.4 ÷ 0.035 = 11.4 bags ≈ 12 bags of 50kg cement

Step 4: Calculate Sand Required

Sand Volume = (4/5) × 2 = 1.6 m³
In cubic feet = 1.6 × 35.29 = 56.5 cft
Approximately 2 tonnes of sand

Step 5: Water Required

Water = 20-25% of dry material weight
Approximately 200-250 liters for this project

Pro Tip: Always add 5-10% extra materials to account for wastage.

Step-by-Step Plastering Process

Part 1: Preparation Work (Critical for Success)

1. Surface Preparation

Clean the wall thoroughly:

Remove dust, dirt, loose particles, and debris using wire brushes
Scrape off any oil, grease, or paint
Remove projecting mortar from joints
Check for hollows, bumps, or uneven surfaces

2. Joint Raking

Rake mortar joints to a depth of 10-12mm using a scraper or chisel
This provides a key for the plaster to grip
Horizontal and vertical joints should be properly raked

3. Surface Dampening

Wet the wall thoroughly 2-3 hours before plastering
This prevents the wall from absorbing water from the fresh plaster too quickly
Re-dampen just before application if the surface dries out

4. Application of Bonding Agent (Optional but Recommended)

For smooth surfaces or dense blocks:

Apply cement slurry (cement + water mixture) or commercial bonding liquid
This improves adhesion and reduces the risk of de-bonding

5. Fixing Reference Points and Screeds

Use a plumb bob to check wall verticality
Fix plaster dots (reference points) at regular intervals
Install screeds (vertical strips of plaster) spaced 1-1.5 meters apart
Screeds act as guides to maintain uniform thickness

Part 2: Mixing the Plaster

Dry Mixing Method (Most Common in Kenya):

Measure materials accurately using a headpan or bucket
- For 1:4 ratio: 1 headpan cement to 4 headpans sand
Mix cement and sand thoroughly when dry
- Turn the mixture at least 3 times to ensure uniformity
- The color should be consistent throughout
Add water gradually
- Create a crater in the center of the dry mix
- Pour water slowly while mixing
- Continue adding water until you achieve a workable consistency
- The mix should be thick but spreadable (like toothpaste)

Machine Mixing (For Large Projects):

Add sand first, then cement, then water
Mix for at least 5 minutes to ensure homogeneity
Use within 30-45 minutes of mixing

Important: Never use plaster that has begun to set. If it stiffens, discard it rather than adding more water, as this weakens the plaster significantly.

Part 3: Applying the Undercoat (First Coat)

1. Application Technique

Load plaster onto the hawk
Using the trowel, apply plaster from bottom to top
Press firmly to ensure good contact with the wall
Apply at an angle of about 45 degrees
Work in vertical strips between screeds

2. Leveling

Use a straight edge or wooden float to level the surface
Move the straight edge in a zigzag upward motion
Fill any depressions with additional plaster
Remove excess plaster

3. Scratching

While the plaster is still wet but firm, scratch the surface using a comb or wire brush
Create horizontal grooves about 3mm deep
This provides a key for the finishing coat

4. Curing

Keep the undercoat moist for at least 7 days
Spray with water 2-3 times daily
Protect from direct sunlight and rain
Allow 7-10 days before applying the finishing coat

Part 4: Applying the Finishing Coat (Second Coat)

1. Preparation

Dampen the undercoat thoroughly before application
Ensure the undercoat is completely dry (7-10 days minimum)

2. Application

Mix a finer batch using 1:3 or 1:4 ratio
Apply a thin coat (6-8mm) using a steel trowel
Work in small sections for better control
Apply with upward strokes

3. Floating

Use a wooden float to spread and level the plaster
Work in circular motions
This brings the finer particles to the surface

4. Troweling (Final Finish)

After the plaster begins to set (wait 1-2 hours)
Wet the trowel slightly
Polish the surface with firm, sweeping strokes
Continue until you achieve a smooth, even finish
For walls that will be painted, a smooth finish is essential

5. Curing the Finish Coat

Cure for at least 14-21 days before painting
Spray with water regularly for the first week
Proper curing prevents cracks and ensures maximum strength

Interior vs. Exterior Plastering: Key Differences

Interior Plastering

Characteristics:

Focus on smooth finish for aesthetic appeal
Less exposure to weather elements
Standard ratio: 1:3 to 1:4
Can use finer finishes like gypsum for the final coat

Special Considerations:

Bedrooms and living areas require the smoothest finish
Kitchens and bathrooms need moisture-resistant plaster
Consider adding waterproofing compounds in wet areas

Exterior Plastering

Characteristics:

Must withstand rain, sun, and temperature variations
Requires weather-resistant mix (1:4 to 1:6 ratio)
Thicker application for better protection
More emphasis on durability than aesthetic finish

Special Considerations:

Add waterproofing compounds in the mix
Ensure proper curing to prevent cracking from thermal expansion
Finish should be slightly rough to provide better key for paint
Apply external waterproofing treatments after plastering

Weather Considerations in Kenya:

Coastal regions (Mombasa, Kilifi): Use stronger mixes due to high humidity and salt air
Nairobi and Highlands: Standard mixes work well
Arid areas (Northern Kenya): Focus on proper curing to prevent rapid drying

Common Plastering Defects and How to Avoid Them

1. Cracking

Causes:

Excessive cement in the mix
Rapid drying due to insufficient curing
Thermal expansion and contraction
Too thick application in one coat
Structural movement

Prevention:

Use correct cement-to-sand ratios
Cure properly for 7-14 days minimum
Apply in thin coats (maximum 15mm per coat)
Ensure structural stability before plastering

Fix:

Fill hairline cracks with diluted cement paste
For wide cracks, rake out and re-plaster the section

2. De-bonding (Plaster Separating from Wall)

Causes:

Dirty or oily surface
Dry substrate that absorbs water too quickly
Excessively thick single coat
Poor quality materials

Prevention:

Clean surface thoroughly before plastering
Dampen wall adequately
Use bonding agents on smooth surfaces
Apply in two coats rather than one thick coat

Fix:

Remove loose plaster completely
Clean and prepare surface properly
Re-plaster the affected area

3. Efflorescence (White Powder Patches)

Causes:

Soluble salts in cement, sand, bricks, or water
Moisture movement through the wall
Poor waterproofing

Prevention:

Use high-quality, salt-free materials
Ensure proper waterproofing
Avoid plastering during rainy season
Use clean water

Fix:

Brush off white deposits when dry
Seal the surface with specialized sealers
Address moisture source

4. Blistering and Bulging

Causes:

Late slaking of lime particles (if lime is used)
Poor mixing
Moisture behind the plaster
Application on damp surface

Prevention:

Mix materials thoroughly
Ensure wall is dry before plastering
Address any water leakage issues
Use properly slaked materials

Fix:

Remove affected areas completely
Fix moisture source
Re-plaster after surface dries

5. Popping

Causes:

Presence of contaminants (burnt lime, organic matter)
Poor quality materials
Presence of foreign particles

Prevention:

Use clean, screened sand
Source materials from reputable suppliers
Inspect materials before use

Fix:

Remove affected areas
Re-plaster with quality materials

6. Uneven Surface

Causes:

Unskilled application
Inadequate use of screeds and levels
Inconsistent thickness
Poor quality tools

Prevention:

Hire experienced fundis (masons)
Use proper screeds and guides
Check level regularly during application
Use quality tools

Fix:

Sand down high spots (minor issues)
Apply skim coat for overall leveling
For major unevenness, remove and re-plaster

7. Flaking and Peeling

Causes:

Too much water in mix
Application on damp surface
Poor surface preparation
Inferior materials

Prevention:

Use correct water-to-cement ratio
Ensure surface is properly prepared
Use quality materials
Allow adequate drying time between coats

Fix:

Scrape off loose material
Prime the surface
Re-plaster affected areas

Cost Breakdown for Plastering in Kenya (2025)

Material Costs (Approximate)

Cement:

50kg bag of OPC Grade 32.5: KES 700-900
50kg bag of PPC: KES 750-950

Sand:

River sand per tonne: KES 1,500-2,500 (varies by region)
Lorry load (7-10 tonnes): KES 12,000-25,000

Water:

Usually minimal cost if piped water available

For 100 m² Interior Plastering (1:4 ratio, 15mm thickness):

Cement: 12 bags × KES 800 = KES 9,600
Sand: 2 tonnes × KES 2,000 = KES 4,000
Total Materials: KES 13,600

Labour Costs

Labour rates vary significantly across Kenya:

By Region (2025 estimates):

Nairobi: KES 300-450 per m²
Coastal Region: KES 280-400 per m²
Western Kenya: KES 250-350 per m²

For a 4-Bedroom House:

Total plastering cost: KES 150,000-300,000
Duration: 2-5 weeks
Materials: 80-100 bags of cement
Sand: 4-5 lorry loads

Fundi (Mason) Daily Rates:

Experienced mason: KES 1,200-2,000 per day
Helper/laborer: KES 600-1,000 per day

Total Cost Estimate (100 m²):

Materials: KES 13,600
Labour: KES 30,000-40,000
Total: KES 43,600-53,600

Note: Prices vary based on location, material quality, and project complexity. Always get multiple quotes.

Tips for Hiring Fundis in Kenya

Finding reliable fundis (masons) is crucial for quality plastering work:

1. Ask for Recommendations

Consult neighbors who recently completed construction
Ask at local hardware stores
Use verified platforms like Find a Fundi, Fundi Link, or Fundis App

2. Check Experience and Portfolio

Request to see previous plastering projects
Ask for references from past clients
Look for fundis with at least 3-5 years experience

3. Verify Skills

Ask about different plastering techniques
Discuss cement-to-sand ratios and curing processes
A knowledgeable fundi will explain the process clearly

4. Get Written Quotations

Obtain at least 3 different quotes
Ensure quotes include materials and labor breakdown
Clarify payment terms and project timeline

5. Agree on Quality Standards

Discuss expected finish quality
Set milestones for payment
Agree on curing periods and inspection points

6. Supervision is Key

Visit the site regularly during plastering
Check plumb and level frequently
Ensure proper curing is being done

Quality Control Checklist

Before, during, and after plastering, use this checklist:

Before Plastering:

[ ] Surface is clean and free from dust/oil
[ ] Joints are properly raked
[ ] Wall is adequately dampened
[ ] Materials are of good quality
[ ] Mixing ratios are correct
[ ] Tools are ready and in good condition

During Plastering:

[ ] Proper thickness is maintained
[ ] Surface is level and plumb
[ ] No hollow sounds when tapped (indicates de-bonding)
[ ] Screeds are properly aligned
[ ] Mix consistency is correct
[ ] Work is progressing according to schedule

After Plastering:

[ ] Surface is smooth and uniform
[ ] No visible cracks or defects
[ ] Regular curing is being done
[ ] Adequate drying time before painting (14-21 days)
[ ] Final inspection confirms quality

Special Plastering Techniques

1. Rough Cast Finish (Tyrolean Finish)

Popular for exterior walls
Creates textured, decorative surface
Applied by throwing mortar onto the wall
Weather-resistant and hides minor imperfections

2. Floating Coat

Intermediate finish between rough and smooth
Uses wooden float for texture
Common for exterior walls before painting

3. Smooth Trowel Finish

Standard for interior walls
Creates mirror-smooth surface
Achieved by final troweling when plaster is semi-dry
Best for modern painted finishes

4. Textured Finishes

Created using special tools or techniques
Popular in decorative work
Can be done with standard plaster or special compounds

Environmental Considerations

Sustainable Plastering Practices in Kenya

Water Conservation
- Reuse water where possible during curing
- Use spray bottles instead of hoses
- Harvest rainwater for plastering work
Material Efficiency
- Calculate exact quantities to minimize wastage
- Store cement properly to prevent spoilage
- Reuse clean leftover sand
Timing
- Plan plastering during moderate weather
- Avoid hot, dry periods that require excessive watering
- Don't plaster during heavy rains
Local Sourcing
- Buy materials from local suppliers to reduce transport costs
- Use locally available sand types
- Support Kenyan cement manufacturers

Frequently Asked Questions

Q: How long should I wait before painting plastered walls? A: Wait at least 14-21 days for the plaster to cure completely. Painting too early traps moisture and causes paint failure.

Q: Can I plaster during the rainy season? A: It's possible but not ideal. Protect freshly plastered walls from direct rain, and ensure adequate drying time. The dry season is preferable.

Q: What's the difference between cement plaster and gypsum plaster? A: Cement plaster is more durable and water-resistant, ideal for exterior and wet areas. Gypsum plaster provides a smoother finish but is suitable only for dry interior areas.

Q: How do I fix a cracked plaster wall? A: For hairline cracks, apply flexible filler. For wider cracks, rake out the crack, clean it, dampen, and fill with fresh plaster. For extensive cracking, consult a professional.

Q: Should I use bonding agents? A: Yes, especially on smooth surfaces like concrete or when plastering over painted walls. Bonding agents significantly improve adhesion.

Q: What's the best cement brand for plastering in Kenya? A: Blue Triangle, Bamburi, Simba, and Savannah are all reputable brands. Choose Grade 32.5 OPC or PPC for standard plastering work.

Q: How can I tell if my fundi is doing good work? A: Check for uniform thickness, level surfaces, proper curing, and no hollow sounds when tapping the wall. A quality job shows attention to detail at every stage.

Q: Is machine plastering better than manual plastering? A: Machine plastering is faster and more consistent for large projects. Manual plastering allows more control and is sufficient for residential projects.

Conclusion

Quality plastering is the foundation of beautiful, durable walls in any Kenyan construction project. By understanding the correct cement-to-sand ratios, following proper application techniques, ensuring adequate curing, and avoiding common defects, you can achieve professional results whether you're doing it yourself or supervising fundis.

Remember these key takeaways:

Preparation is 50% of the job - Clean, damp, and properly prepared surfaces are crucial
Use correct ratios - 1:4 for most applications, adjusted based on specific needs
Apply in two coats - Undercoat and finishing coat for best results
Cure properly - Minimum 7 days for undercoat, 14-21 days before painting
Hire experienced fundis - Quality workmanship makes all the difference
Use quality materials - Don't compromise on cement and sand quality
Plan for weather - Time your plastering work appropriately

Whether you're building in Nairobi, Mombasa, Kisumu, Eldoret, or anywhere else in Kenya, these principles remain constant. Quality plastering protects your investment and creates the perfect canvas for your interior and exterior finishes.

For more construction guides and tips specific to the Kenyan market, visit makaobora.com.

Disclaimer: Costs and rates mentioned are approximate estimates based on 2024-2025 market conditions and vary by location, material quality, and project specifications. Always obtain multiple quotations and consult with qualified professionals for your specific project.