What’s the Difference Between Mortar and Cement? Unveiling the Masonry Myths
Mortar and cement are often used interchangeably, but that’s incorrect. Cement is a key ingredient in mortar, providing the binding properties, while mortar is the mixture used to bind building blocks together; it also adds flexibility and helps accommodate minor movements in the structure.
Understanding the Foundation: Cement
Cement, in its simplest definition, is a binder, a substance that sets and hardens independently, and also binds other materials together. It’s the glue that holds much of our built environment together. This binding process, known as hydration, occurs through a chemical reaction with water.
- Types of Cement: Portland cement, the most common type, gets its name from its resemblance to Portland stone. Other types include masonry cement, used specifically for mortar mixes, and specialized cements for unique applications like rapid setting or high-strength needs.
- Production Process: Cement production is a complex process involving heating limestone with other materials like clay and shale to extremely high temperatures. The resulting product, clinker, is then ground into a fine powder, creating cement.
- Cement Composition: Cement is primarily composed of calcium silicates, aluminates, and ferrites. These compounds react with water to form hydrated compounds that interlock and provide strength.
Mortar: The Binding Force in Masonry
Mortar is a mixture of cement, fine aggregate (usually sand), and water. Its primary function is to bind bricks, stones, blocks, or other masonry units together in a structure. It also fills irregular gaps between these units, distributes the load evenly, provides a weather-resistant seal, and allows for some movement without cracking.
- Mortar Components: The key ingredients in mortar are:
- Cement (the binder)
- Fine aggregate (sand)
- Water
- Sometimes, lime is added for workability and flexibility.
- Mortar Types: Mortar is classified into different types based on its compressive strength and performance characteristics. Common designations are Type M, S, N, O, and K, with Type M being the strongest and Type K the weakest. The choice of mortar type depends on the specific application and the building’s structural requirements.
- Functions of Mortar:
- Binds masonry units together.
- Seals joints against water penetration.
- Compensates for variations in masonry unit sizes.
- Provides an aesthetically pleasing finish.
Key Differences: Cement vs. Mortar
| Feature | Cement | Mortar |
|---|---|---|
| Definition | Binder used to hold other materials together. | Mixture of cement, sand, and water used to bind masonry units. |
| Composition | Primarily calcium silicates, aluminates, and ferrites. | Cement, fine aggregate (sand), water, and sometimes lime. |
| Function | Ingredient that provides binding capability. | Binds masonry units, seals joints, and distributes load. |
| Use | Used in concrete, mortar, and other construction materials. | Used to bond bricks, stones, blocks, etc. |
| Strength | Higher compressive strength when used pure. | Compressive strength depends on the mortar type and cement content. |
| Workability | Not workable in its pure form. | More workable due to the addition of sand and lime. |
Common Mistakes and Misconceptions
One of the most common mistakes is using pure cement as mortar. This can lead to cracking and failure due to cement’s inherent rigidity. Another misconception is that stronger mortar is always better. In some cases, a weaker mortar can allow for more movement and prevent damage to the masonry units themselves. Choosing the correct mortar type for the specific application is crucial for long-term structural integrity. Furthermore, incorrect mixing ratios can severely compromise mortar strength and durability.
Frequently Asked Questions About Cement and Mortar
1. Can I Use Cement Instead of Mortar?
Absolutely not. Cement is an ingredient in mortar, but it is not a replacement for it. Using cement alone will create a rigid, inflexible bond that is prone to cracking and failure. Mortar’s sand content is critical for creating the necessary workability and flexibility.
2. What is the Role of Sand in Mortar?
Sand acts as a filler in mortar, increasing its bulk and reducing shrinkage. It also improves the workability of the mortar, making it easier to spread and bond to masonry units. The sand’s grading (particle size distribution) also affects the mortar’s strength and appearance.
3. What is Lime Mortar and How Does it Differ From Cement Mortar?
Lime mortar uses lime as the primary binder instead of cement. Lime mortar is more flexible and breathable than cement mortar, allowing for better moisture management in older buildings. However, it is significantly weaker and requires specialized knowledge to work with properly.
4. How Do I Choose the Right Mortar Type for My Project?
The choice of mortar type depends on several factors, including the type of masonry units being used, the building’s age, the local climate, and the structural requirements. Consult a qualified mason or structural engineer to determine the most appropriate mortar for your specific project. Consider the expected compressive strength and exposure conditions.
5. What is the Shelf Life of Cement and Mortar?
Cement has a shelf life of approximately 6-12 months when stored properly in a dry location. Mortar mix (pre-blended dry mortar) also has a similar shelf life. Once water is added, the hydration process begins, and the mortar must be used within a few hours.
6. How Do I Mix Mortar Correctly?
Mixing mortar correctly involves following the manufacturer’s instructions carefully. Generally, it involves adding water to the dry mix gradually while mixing thoroughly until you achieve a smooth, workable consistency. Avoid adding too much water, as this can weaken the mortar. Use a mortar mixer for larger projects.
7. Can I Add Pigments to Mortar?
Yes, pigments can be added to mortar to achieve a desired color. However, it’s important to use only pigments specifically designed for mortar and to follow the manufacturer’s instructions carefully. Adding too much pigment can weaken the mortar.
8. How Important is Curing Mortar?
Curing is essential for mortar to achieve its full strength and durability. Curing involves keeping the mortar moist for several days after it’s applied. This allows the cement to hydrate properly and develop its full strength.
9. What are Some Common Mortar Problems and How Can They Be Avoided?
Common mortar problems include cracking, crumbling, and staining. These problems can be avoided by using the correct mortar type, mixing the mortar properly, curing it adequately, and ensuring proper drainage around the masonry.
10. Can I Repair Old Mortar Joints Myself?
Repointing old mortar joints (replacing damaged mortar) can be a DIY project, but it requires careful preparation and execution. If you are not comfortable working with mortar or if the damage is extensive, it’s best to hire a professional mason. Matching the existing mortar is critical for both appearance and compatibility.
11. What is Tuckpointing?
Tuckpointing is a technique used to enhance the appearance of brickwork by applying a thin ribbon of contrasting mortar over existing joints. It is often used on older buildings to create a more defined and aesthetically pleasing look.
12. Is it Possible to Use Pre-Mixed Mortar?
Yes, pre-mixed mortar is available and can be convenient for small projects. However, it is generally more expensive than mixing your own mortar. Ensure that the pre-mixed mortar is the appropriate type for your project.