Choosing the right sand may seem like a minor detail when working with mortar or render, but the consequences of using the wrong type can be surprisingly serious. From crumbling joints to patchy finishes, incorrect sand selection can cause both structural problems and unsightly results. Find out why choosing the right building sand matters, what can go wrong and how to avoid costly mistakes.
Why the Type of Sand You Use Really Matters
The Hidden Role of Sand in Mortar and Render
Sand is much more than a filler. It forms the bulk of mortar and render mixes, providing body, workability and durability. In mortar, sand binds with cement to create a strong adhesive that holds bricks and blocks together. In render, it provides texture and strength, allowing the surface to resist cracking and weathering.
Why Sand Isn’t One-Size-Fits-All
Different types of sand have different properties. The grain size, shape and purity of sand directly affect how mortar or render performs. Some sands may contain salts or impurities that cause efflorescence, while others may lack the right grain size to provide adequate strength. Choosing the wrong sand for building could compromise the entire structure.
Common Types of Sand and Their Uses
Building Sand (Soft Sand)
Building sand, also known as soft sand, is the go-to choice for bricklaying and general mortar work. It has fine, rounded grains that create a smooth, workable mortar. This makes it ideal for internal and external brickwork, where a clean finish and consistent bonding are required.
Sharp Sand
Sharp sand, often called grit sand, is coarser and angular in texture. It is used where greater strength is needed, such as for floor screeds, paving and external rendering. The angular grains interlock, providing a more stable and durable finish.
Plastering Sand
Plastering sand is a fine, clean sand used specifically for plastering walls. It is free of impurities and graded to create a smooth, crack-resistant finish. Using the wrong sand here can result in a poor surface and compromised durability.
Why Grain Size and Salt Content Matter
Grain size influences the strength and flexibility of mortar and render. Too coarse and the mix can be brittle. Too fine and it may lack structural integrity. Salt content is another key factor. Sands with high salt levels can cause efflorescence – the unsightly white deposits sometimes seen on brickwork. Over time, salts can also lead to deterioration of the mortar.
What Can Go Wrong with the Wrong Sand?
Structural Problems Over Time
Crumbling joints: Using sand with the wrong particle size or impurities can result in weak mortar that crumbles under stress. This not only affects the appearance but can also reduce the overall stability of the structure.
Shrinkage and cracking: Fine sands not suited for external render can cause excessive shrinkage as the mix dries, leading to cracks that let in moisture and compromise durability.
Aesthetic Issues
Patchy finish: Incorrect sand selection often leads to inconsistent finishes, particularly in rendered surfaces where smoothness and colour uniformity are key.
Discolouration and efflorescence: High salt content or incompatible sand types can result in visible white patches or uneven colour on walls and brickwork, detracting from the visual appeal of the project.
Real-Life Mistakes and What They Cost
Render Falling Off Within a Year
A property in Surrey underwent exterior rendering using a generic sand sourced without specification. Within 12 months, large sections of render began to delaminate and fall away. Investigation revealed that the sand used was too fine and contained salts, which caused shrinkage and poor bonding. The homeowner faced an expensive full re-render to correct the issue.
Mortar Cracking in New Build
A local building contractor used unsuitable sand for construction on a new housing development in Redhill. The mortar lacked cohesion, and within a year, widespread cracking appeared in brick joints. Remedial work involved repointing all affected walls, significantly increasing costs and causing project delays.
How to Choose the Right Sand for Your Project
Matching Sand to Application Type
Always match the sand to your project requirements.
- Use building sand for bricklaying and general mortar work.
- Opt for sharp sand where strength and stability are needed, such as for paving or external render.
- For plastering, select a dedicated plastering sand that meets the required standards.
Tips When Buying from Suppliers
Work with reputable suppliers who can provide sand that is consistent and tested. Ask for details about grain size, salt content and suitability for your application. At J&J Franks, we supply high-quality building sand and other aggregates with full traceability, helping you build with confidence.
Testing and Mixing Advice
When in doubt, test small batches before large-scale application. Always follow recommended mix ratios for mortar or render. A little extra care at the start can prevent major problems later.
Pro Tips to Avoid Expensive Errors
Know Your Ratios
Mix ratios should not be guesswork. Follow guidance for the right sand-to-cement ratio to ensure durability and performance. Using too much sand can weaken the mix, while too little affects workability.
Don’t Rely Solely on Builder’s Merchants
While builder’s merchants are a convenient source, not all sands on offer will suit every application. Consult your supplier about suitability rather than choosing on price or availability alone.
Consult Local Experts (Especially in Coastal Areas)
In coastal areas such as Brighton or near Surrey quarries, locally sourced sand may naturally contain higher salt levels unless properly washed. Always check specifications and consult local experts to avoid hidden issues.
It’s Just Sand – Until It’s Not
It is easy to overlook the importance of choosing the right sand for building, but doing so can save time, money and stress. From maintaining structural integrity to achieving a flawless finish, the right sand is an essential part of any construction project. Take the time to select and test the right sand, and your build will stand the test of time.
Building Sand FAQs
Can I use any sand I have lying around?
No. Not all sand is suitable for construction use. Sands from unverified sources may contain impurities or unsuitable grain sizes that can weaken your mortar or render and cause long-term problems.
Is there a difference between building sand and sharp sand?
Yes, there is a difference between sharp and building sand. Building sand, sometimes called soft sand, has finer, smoother grains and is used for bricklaying and internal plastering where a smooth mortar is needed. Sharp sand, on the other hand, has coarse, angular grains that provide strength and grip, making it suitable for paving, screeds and external render.
What’s the best sand for rendering exterior walls?
Sharp sand is generally best for rendering exterior walls. Its angular grains provide strength and durability, helping the render withstand weathering and shrinkage.
