Answers to common UK concrete, cement, aggregate, slab, foundation, reinforcement, quantity and specification questions — built for homeowners, builders, students, DIY users and early-stage project planners in 2026.
concretemaths.com/ FAQs — What This Page Covers
This FAQ guide answers the most common questions people ask when using concretemaths.com/ guides and UK construction guides. The goal is simple: help you estimate quantities, understand terminology and avoid common ordering mistakes before you speak to a supplier, contractor, structural engineer or Building Control officer.
Concrete, mortar, screed, aggregates and reinforcement all depend on context. A simple garden slab may only need a practical volume working, while a structural foundation or reinforced slab may need a specification written to the relevant standards. That is why this page separates quick DIY quantity questions from structural specification questions. It also explains where our guides can help and where professional design is required.
Quick Rule
Use concretemaths.com/ to estimate quantities, compare materials and understand the basics. For structural design, load-bearing foundations, reinforced concrete, retaining structures, basements, commercial work or unusual ground conditions, always involve a competent professional and follow Building Regulations.
Guide Questions
Find out which guide to use for slabs, bags, tonnes, sharp sand, cement, ballast, foundations and ready-mix concrete.
Specification Questions
Understand concrete grades, exposure classes, BS 8500, reinforcement standards and when a formal engineer specification is needed.
Safety Questions
Learn why wet concrete, cement dust, silica dust, heavy bags and manual handling need proper PPE and control measures.
Most Common ConcreteMaths Questions — Quick Reference
Use this table to choose the right page. If you are estimating materials, start with the quantity guide. If you are specifying concrete, start with the grade or standards guide.
- User Question: How much concrete do I need?; Best Page / Resource: Concrete Slab Guide UK; Key measurement: Length × width × depth; Important Note: Add wastage; order ready-mix in m³.
- User Question: How many bags of cement do I need?; Best Page / Resource: Cement Bags Guide UK; Key measurement: Concrete/mortar volume + mix ratio; Important Note: 25kg cement bags are common in UK retail.
- User Question: How much sharp sand do I need?; Best Page / Resource: Sharp Sand Guide; Key measurement: Area, depth and compaction; Important Note: Useful for screed, bedding and laying work.
- User Question: How do I convert m³ to tonnes?; Best Page / Resource: m³ to Tonnes conversion guide; Key measurement: Volume × material density; Important Note: Density changes by material and moisture content.
- User Question: What concrete grade should I use?; Best Page / Resource: Concrete Grade Guides; Key measurement: Use, load, exposure and ground conditions; Important Note: Structural work may require engineer specification.
- User Question: How deep should foundations be?; Best Page / Resource: Foundation Depth Guide; Key measurement: Soil type, load, trees and frost risk; Important Note: Building Control and engineer measurement may be required.
Guide FAQs: Volumes, Bags, Tonnes & Bulk Loads
The most common concretemaths.com/ questions are quantity questions. Users usually know the job they want to build but need help converting it into a material order. The important point is that guides estimate practical quantities; they do not automatically confirm that the material specification is structurally suitable.
Concrete volume questions
Concrete volume is normally measured in cubic metres in the UK. For a rectangular slab, footing or base, multiply length by width by depth using metres. For example, a 4m × 3m slab at 100mm depth is 4 × 3 × 0.10 = 1.2m³ before wastage. A small percentage allowance is usually sensible because excavations are rarely perfect, sub-bases may vary, and concrete should not be ordered short.
Bagged concrete questions
Bagged concrete is convenient for small repairs, post holes and very small slabs, but it becomes expensive and labour-intensive at larger volumes. Once your project approaches roughly half a cubic metre or more, it is usually worth comparing bagged concrete against ready-mix or small-load delivery. Bags also vary by product yield, so always check the manufacturer’s stated litres per bag rather than assuming every bag produces the same volume.
Bulk bag questions
UK aggregate and sand bulk bags are commonly sold as large builder’s bags, often around 800–850kg depending on supplier, product, moisture and packaging. They are not always a full metric tonne. That matters because a guide result of 1.0 tonne may require more than one bulk bag if the bag is 850kg, and a guide result of 1.7 tonnes may require two bulk bags or a loose-load quote.
Do Not Confuse Volume With Weight
One cubic metre is a volume. One tonne is a weight. Sand, gravel, MOT Type 1, topsoil and concrete have different densities, so the same m³ volume will not produce the same tonne weight.
Standards & Compliance FAQs
concretemaths.com/ pages often mention UK standards and Building Regulations because concrete work sits between practical site estimating and formal structural design. For normal estimating, a guide can help you understand quantities. For compliance, the relevant designer, contractor, engineer or Building Control body must confirm the final detail.
The UK concrete specification route is commonly linked to BS EN 206 and BS 8500. BS 8500 provides UK-specific provisions and guidance for specifying concrete, including exposure, constituent materials and specification methods. For building work in England, GOV.UK Approved Documents provide guidance on ways to meet Building Regulations, and Approved Document A covers structural elements such as foundations, walls, floors, roofs and chimneys.
BS 8500 / BS EN 206
Used for concrete specification, performance, production and UK national provisions. Relevant when specifying designed, prescribed or designated concrete.
Approved Document A
Relevant to structural elements including foundations, floors, walls and roofs. Useful for understanding building-control context.
Approved Document C
Relevant to site preparation, unsuitable material, sub-soil drainage and moisture resistance, including damp-related construction details.
Does concretemaths.com/ replace Building Control?
No. concretemaths.com/ is a working and guidance website. It helps estimate quantities, compare options and understand terms before you order materials or discuss your project. It does not approve building work, issue structural design checks, replace a trial pit, replace a concrete specification, or provide legal compliance sign-off.
Do I need a structural engineer?
You may need a structural engineer where the work affects load-bearing elements, foundations, steel beams, retaining walls, reinforced concrete, basements, unusual ground, large openings, piled foundations, commercial buildings or any structure where failure would be serious. For simple non-structural landscaping or small DIY jobs, a guide may be enough for quantities, but that does not make the work structurally approved.
Popular FAQ Categories on concretemaths.com/
These are the sections users most often need when planning a UK concrete or building-materials project.
Slabs & Bases
Questions about concrete slab depth, shed bases, garage bases, patio slabs, sub-base, DPM, mesh, joints and curing.
Cement & Mortar
Questions about 25kg cement bags, mortar mix ratios, bricklaying, pointing, render and concrete made with ballast.
Aggregates & Sand
Questions about sharp sand, building sand, ballast, MOT Type 1, gravel, bulk bags, tonnes and compaction.
Foundations
Questions about strip foundations, trench fill, soil type, tree influence, frost depth and Building Regulations approval.
Concrete Grades
Questions about C10/12, C15/20, C20/25, C25/30, C30/37, C40/50, exposure classes and designed mixes.
Downloads
Questions about checklists, printable quantity sheets, project notes, specification reminders and downloadable resources.
Safety FAQs: Cement, Concrete Dust & Manual Handling
Concrete and cement products are familiar materials, but they still require care. Wet cement-based products can damage skin, cement and concrete dust can irritate airways, and dry cutting or chasing can create respirable crystalline silica dust. Manual handling also matters because cement bags, aggregate bags and wet concrete are heavy.
At a minimum, use suitable gloves, eye protection, long sleeves, sturdy footwear, dust controls and washing facilities. Do not kneel in wet concrete, do not allow cement slurry to sit inside gloves or boots, and avoid dry sweeping dusty material where wet control or extraction is more appropriate.
Wet Cement Can Burn Skin
Cement-based products such as concrete and mortar can cause dermatitis and burns. Treat cement safety as a real site risk, not just a comfort issue.
Common safety questions
- Can I mix concrete by hand?Yes for small quantities, but use PPE and avoid overloading yourself with heavy mixing and lifting.
- Is concrete dust dangerous?Dust can be hazardous, especially where silica-containing material is cut, ground or broken without controls.
- Should I wear gloves?Yes. Use suitable waterproof/protective gloves and keep cement slurry away from skin.
- Can I wash concrete down drains?Avoid discharging cement washout into drains or watercourses. Dispose of waste responsibly.
concretemaths.com/ Is for Estimating — Not Structural Sign-Off
Use the guides and guides for planning, ordering and understanding materials. For load-bearing structures, foundations, reinforcement, commercial projects or Building Regulations approval, always use a competent designer, engineer, supplier specification and Building Control process.
concretemaths.com/ FAQs
Common questions about our guides, UK concrete quantities, material conversions, standards, safety and project planning in 2026.