Technical Definitions | ConcreteMaths.com

Concrete and construction terms explained in plain English for 2026 — from C10 to C50 grades, slump, DPM, hardcore and sub-base to BS EN 206, BS 8500, CDM, building control and site measurement terminology.

Use this page as a practical glossary for UK concrete guides, supplier quotes, method statements, planning documents, building control notes and site discussions. Type a term such asslump,C25/30,DPM,sub-base,exposure classorCDM, then filter by category.

Concrete

Concrete is a composite construction material made from cement, water, fine aggregate, coarse aggregate and sometimes admixtures. In UK work it is commonly supplied as ready-mix for slabs, footings, garage bases, driveways, oversites and reinforced structural elements.

Cement

Cement is the binder that reacts with water and hardens around the aggregates. It is not the same as concrete. Common UK descriptions include CEM I, CEM II, CEM III and blended lower-carbon cements used in ready-mix specifications.

Concrete Grade / Strength Class

A strength class such as C25/30 describes characteristic compressive strength. The first number is cylinder strength and the second is cube strength in MPa. Correct grade selection depends on structural load, exposure, cover, finish and project specification.

Slump

Slump measures workability. A low slump mix is stiff and holds shape, while a higher slump is easier to place and compact. Do not add water on site without supplier approval because it can reduce strength and durability.

Exposure Class

An exposure class describes the environment that concrete must resist, including carbonation, chlorides, freeze-thaw cycles or chemical attack. Exposure class affects minimum strength, cement content, water-cement ratio and durability design.

DPM

A damp proof membrane is a sheet barrier used below or within floors to help resist moisture rising into a slab or screed. In domestic work, it is often lapped, taped and connected to damp proof courses at walls.

Hardcore / Sub-base

Hardcore or sub-base is compacted granular material placed below concrete or paving. MOT Type 1 is common for driveways, paths and garage bases because it compacts well and spreads load into the ground.

Formwork / Shuttering

Formwork, often called shuttering on site, is the temporary frame that holds wet concrete to the required size, shape and level until it stiffens. Good formwork helps achieve accurate slab edges and correct finished levels.

BS EN 206

BS EN 206 is the concrete standard covering specification, performance, production and conformity. In the UK it is used together with BS 8500 for national provisions and practical specifying guidance.

BS 8500

BS 8500 is the UK complementary standard to BS EN 206. It helps specifiers choose designated, prescribed and designed concretes for common UK applications, materials and exposure conditions.

Cubic Metre (m³)

A cubic metre is the main unit used for ready-mix concrete orders. For a slab, multiply length × width × depth in metres, then add a sensible waste allowance for uneven ground, spillage and level variations.

CDM

CDM means Construction Design and Management. The CDM Regulations set out duties for clients, designers and contractors to plan, manage and monitor construction health and safety risks.

Technical Terms Should Support, Not Replace, Project Specification

This glossary is written for homeowners, tradespeople and guides. For structural work, unusual ground, retaining walls, reinforced slabs or commercial jobs, always follow the engineer’s design, building control requirements and the concrete supplier’s written specification.

Technical Definitions UKis a practical 2026 glossary for anyone using concrete guides, comparing ready-mix quotes, reading a builder’s estimate or checking a project specification. Construction language can feel confusing because the same job often uses everyday trade words, formal standard terms and supplier shorthand together. A garage base quote might mention C25/30, ST3, mesh, DPM, MOT Type 1, shuttering, pump hire, slump, waste allowance and curing, all in one paragraph. This guide explains those words in plain English so you can understand what is being ordered, measured and priced.

The page is especially useful for UK concrete and groundworks projects such as shed bases, garage floors, domestic driveways, extension footings, oversite slabs, paths, patios, garden rooms, conservatory bases and small retaining structures. It does not turn a homeowner into a structural engineer, but it does help you ask better questions before ordering materials. When you know the difference between cement and concrete, volume and weight, grade and exposure class, sub-base and hardcore, or screed and slab, you are less likely to under-order concrete, choose the wrong mix or miss an important site preparation step.

For 2026, UK construction search intent has become more guide-driven. Users want fast answers for “how many cubic metres of concrete do I need”, “what grade concrete for a garage base”, “what does C30 concrete mean”, “what is a DPM”, “what is Type 1 sub-base” and “what is BS 8500”. This page links those definitions to useful articles so readers can move from understanding a term to estimating a real quantity, cost or specification.

Term: Cement; Plain English Meaning: The powder binder that reacts with water and helps concrete harden.; Where You See It: Bags, ready-mix specs, mortar mixes
Term: Concrete; Plain English Meaning: Hardened construction material made from cement, water, sand and aggregate.; Where You See It: Slabs, footings, bases, foundations
Term: Mortar; Plain English Meaning: Workable mix used to bed and joint bricks or blocks.; Where You See It: Bricklaying, blockwork, pointing
Term: Aggregate; Plain English Meaning: Stone or gravel particles that form the bulk of concrete.; Where You See It: Ready-mix, ballast, sub-base
Term: Fine Aggregate; Plain English Meaning: Sand-sized aggregate in concrete or mortar.; Where You See It: Mortar, screed, concrete mixes
Term: Coarse Aggregate; Plain English Meaning: Larger stone aggregate, often 10mm or 20mm in concrete.; Where You See It: Ready-mix and site-mix concrete
Term: Slump; Plain English Meaning: A measure of concrete workability and flow.; Where You See It: Ready-mix delivery tickets
Term: Curing; Plain English Meaning: Keeping concrete moist and protected while strength develops.; Where You See It: Slabs, floors, driveways
Term: Admixture; Plain English Meaning: Chemical added to modify setting time, workability or durability.; Where You See It: Ready-mix specifications
Term: Water-Cement Ratio; Plain English Meaning: The relationship between water and cement content, important for strength and durability.; Where You See It: Designed concrete, exposure classes

Concrete gradeis one of the most searched construction terms in the UK because it appears on ready-mix quotes, engineer notes and articles. Under BS EN 206, concrete strength classes use notation such asC20/25,C25/30orC30/37. The first number refers to cylinder strength in MPa, and the second refers to cube strength in MPa. UK domestic users often hear the cube number because UK testing has traditionally used cubes, but suppliers and standards often present both values.

C10/15is generally a low-strength blinding or non-structural mix.C15/20can be used for light bedding, kerbs and simple non-structural work where suitable.C20/25is common for domestic slabs, paths and lighter footings.C25/30is widely used for garage bases, driveways and reinforced domestic concrete when design conditions allow.C30/37and above are used where higher structural performance, durability or loading is needed. Higher strength does not automatically mean “better” for every job; the correct mix must match the application, exposure, reinforcement and finish.

In many UK quotes you may also see old or trade-friendly labels such asGEN,ST,RCorPAV. These are designated concrete categories commonly used for practical ordering. For example, a domestic garage base may be described by some suppliers as C25/30 or ST3, while reinforced structural work may be ordered under an RC designation. Because names vary by supplier, always confirm the exact strength class, slump, aggregate size, exposure requirements and delivery method before booking.

Term: Sub-base; Meaning: Compacted granular layer below concrete, paving or asphalt.; Why It Matters: Supports loads and reduces settlement risk.
Term: MOT Type 1; Meaning: Well-graded crushed aggregate commonly used as sub-base.; Why It Matters: Compacts firmly for driveways and slabs.
Term: Hardcore; Meaning: General term for broken stone, rubble or granular fill below slabs.; Why It Matters: Needs suitable grading and compaction.
Term: Excavation; Meaning: Digging out soil to required depth and formation level.; Why It Matters: Controls base depth and finished level.
Term: Formation Level; Meaning: The prepared ground level before sub-base or concrete is placed.; Why It Matters: Wrong formation can cause incorrect slab thickness.
Term: Compaction; Meaning: Mechanically consolidating fill or sub-base.; Why It Matters: Prevents future settlement and cracking.
Term: Blinding; Meaning: Thin concrete or sand layer used to create a clean working surface.; Why It Matters: Protects membranes and helps level preparation.
Term: Footing; Meaning: Concrete base that transfers wall or column loads into the ground.; Why It Matters: Critical for extensions, walls and foundations.
Term: Strip Foundation; Meaning: Continuous concrete footing under load-bearing walls.; Why It Matters: Common in domestic extensions and masonry walls.
Term: Pad Foundation; Meaning: Isolated foundation supporting a point load, post or column.; Why It Matters: Used for posts, steel columns and framed structures.

Cubic metreis the key unit for ready-mix concrete. A common mistake is to measure length and width in metres but depth in millimetres, then forget to convert the depth. For example, a 100mm slab uses 0.1m as the depth in the formula. The basic volume formula is length × width × depth. For irregular shapes, split the area into rectangles or triangles, work out each part separately and add the totals. Then add a waste allowance, usually 5–10% for domestic work depending on ground accuracy, formwork quality and pour complexity.

Linear metreis used for items measured by length, such as trench footings, edging, drainage runs, shuttering boards or reinforcement bars.Square metreis used for surface area, such as slabs, membranes, paving, insulation boards and mesh coverage.Tonneis commonly used for aggregates, ballast, sand, MOT Type 1 and disposal. Because different materials have different bulk densities, one cubic metre does not always equal one tonne. Crushed aggregate, sharp sand, ballast and concrete all convert differently.

Waste allowanceis the extra percentage added to a determined quantity to cover practical site variation. Ready-mix concrete is expensive to under-order because a second delivery may involve a short-load charge, delayed finishing and a cold joint. Over-ordering also costs money and creates disposal issues. A guide should therefore estimate a realistic volume, then show an adjusted quantity including waste. For small slabs, even 0.1m³ can matter; for driveways and garage bases, depth variation can change the final order by several hundred pounds.

Term: Ready-Mix; Definition: Concrete batched by a supplier and delivered to site by mixer truck or volumetric vehicle.; Buyer Tip: Best for accurate larger pours and consistent quality.
Term: Volumetric Concrete; Definition: Concrete mixed on site from materials carried separately on the lorry.; Buyer Tip: Useful where exact final quantity is uncertain.
Term: Transit Mixer; Definition: Rotating drum vehicle carrying pre-batched concrete from the plant.; Buyer Tip: Plan access, unloading time and washout area.
Term: Short Load; Definition: Small ready-mix order below supplier minimum or efficient load size.; Buyer Tip: Ask for short-load fees before booking.
Term: Waiting Time; Definition: Extra charge if the truck is kept on site too long.; Buyer Tip: Have labour, resources and formwork ready before arrival.
Term: Line Pump; Definition: Concrete pump using hoses to place concrete away from the truck.; Buyer Tip: Useful for rear gardens, tight access and long carries.
Term: Boom Pump; Definition: Pump with articulated boom for higher or longer-reach placements.; Buyer Tip: Often used for commercial or difficult access work.
Term: Washout; Definition: Safe area for cleaning concrete chutes, resources or pump lines.; Buyer Tip: Never allow cement washout into drains or watercourses.

BS EN 206is the main European concrete standard used in the UK for specification, performance, production and conformity. It defines many of the terms used on delivery tickets and concrete specifications, including strength classes, exposure classes and conformity requirements.BS 8500is the UK complementary standard used alongside it. For practical UK projects, this is important because national exposure conditions, materials and designated concrete options are addressed through BS 8500 guidance.

Building Regulationsare legal requirements for building work. For structural matters in England, Approved Document A gives guidance connected with loads, ground movement, foundations, walls, floors and structural stability. A simple shed slab may not need the same oversight as an extension foundation, but once work supports a building, affects structure or involves retaining ground, building control and professional design can become important. Scotland, Wales and Northern Ireland have their own building control systems and approved guidance, so always check the local route.

CDM Regulationsare health and safety rules for construction projects in Great Britain. They apply more widely than many homeowners realise. Even domestic projects have duties, although some responsibilities transfer to designers and contractors. CDM terms such as client, contractor, designer, principal designer, principal contractor, risk assessment, method statement and construction phase plan appear in more formal projects, supplier paperwork and commercial work. Understanding them helps you separate technical material terms from legal safety duties.

Term: Screed; Meaning: A finishing or levelling layer placed over concrete or insulation.; Common UK Project: Floors, underfloor heating, garages
Term: Rebar; Meaning: Steel reinforcement bar used to improve tensile performance.; Common UK Project: Foundations, retaining walls, structural slabs
Term: Mesh; Meaning: Welded steel reinforcement sheet placed in slabs.; Common UK Project: Garage bases, driveways, floors
Term: Spacer; Meaning: Plastic or concrete support holding reinforcement at the correct level.; Common UK Project: Reinforced concrete placement
Term: Cover; Meaning: Concrete depth between reinforcement and outside surface.; Common UK Project: Durability and fire resistance
Term: DPC; Meaning: Damp proof course within a wall to resist rising damp.; Common UK Project: Brickwork and blockwork
Term: DPM; Meaning: Damp proof membrane sheet used in floor build-ups.; Common UK Project: Slabs, extensions, garages
Term: Insulation; Meaning: Thermal layer used below or above concrete in floors.; Common UK Project: Extensions and habitable rooms
Term: Expansion Joint; Meaning: Joint that allows movement and reduces cracking risk.; Common UK Project: Driveways, floors, external slabs
Term: Control Joint; Meaning: Deliberate joint or saw cut that guides shrinkage cracking.; Common UK Project: Concrete slabs and pavements

When a builder, supplier or engineer uses a technical term, do not treat it as decoration. Each word normally affects price, performance or risk. If a garage base quote says150mm C25/30 concrete on compacted Type 1 with DPM and mesh, the sentence gives you thickness, strength, ground preparation, moisture control and reinforcement information. If another quote only says “concrete base”, it is not automatically cheaper in a meaningful way; it may simply be less detailed. A technical glossary helps you compare like with like.

For guides, definitions also prevent measurement mistakes. Depth is not the same as area. Concrete grade is not the same as slump. Hardcore depth is not the same as concrete thickness. A metre cube is not the same as a tonne. Reinforcement mesh is not included in a basic concrete volume working unless the page specifically prices it. Waste allowance is not a hidden profit margin; it is a practical adjustment for the difference between neat drawings and real site conditions.

For suppliers, clear terms reduce order errors. Before ordering ready-mix, confirm the volume in cubic metres, the strength class or designated concrete, the required slump/workability, aggregate size, access restrictions, whether a pump is needed, unloading time allowed, waiting charges, cancellation rules and whether additives such as retarders or fibres are included. In hot or cold weather, ask about curing and placement recommendations. For reinforced or structural work, never guess the mix; use the design specification.

For homeowners, the biggest benefit is confidence. You do not need to memorise every British Standard clause, but you should understand the words that directly affect your job. If you can explain your slab size, depth, sub-base, DPM, finish, access and intended load, a supplier or contractor can price more accurately. If you only ask “how much is concrete”, the answer may ignore the actual site conditions that drive cost.

Term: Air Entrained Concrete; Definition: Concrete containing tiny controlled air bubbles to improve freeze-thaw resistance.; Practical Example: External driveways, yards and paving exposed to frost.
Term: Ballast; Definition: A mixed aggregate containing sand and stone, commonly used for site-mixed concrete.; Practical Example: Small DIY concrete pours and fence posts.
Term: Batching; Definition: Measuring concrete ingredients by weight or volume before mixing.; Practical Example: Ready-mix plants and site-mixed concrete.
Term: Cold Joint; Definition: A weak or visible joint formed when fresh concrete is placed against concrete that has already started to set.; Practical Example: Delayed second delivery during a slab pour.
Term: Compressive Strength; Definition: The ability of hardened concrete to resist crushing loads.; Practical Example: Grade selection such as C25/30 or C30/37.
Term: Concrete Cover; Definition: The depth of concrete protecting reinforcement from corrosion, fire and exposure.; Practical Example: Reinforced slabs, beams and foundations.
Term: Expansion Joint Filler; Definition: Compressible material placed in a joint to allow movement.; Practical Example: Concrete against walls, kerbs and existing slabs.
Term: Fibre Concrete; Definition: Concrete containing fibres to help control plastic shrinkage and improve toughness.; Practical Example: Garage slabs, industrial floors and external paving.
Term: Float Finish; Definition: A surface finish created with a hand or power float after placing concrete.; Practical Example: Garage floors, workshops and utility slabs.
Term: Power Float; Definition: A machine used to finish large concrete floor surfaces.; Practical Example: Commercial floors and smooth garage slabs.
Term: Retarder; Definition: Admixture that slows setting time, often useful in warm weather or longer deliveries.; Practical Example: Large pours, hot weather and complex placement.
Term: Sulfate Resistance; Definition: Concrete durability property for ground containing sulfates or aggressive chemicals.; Practical Example: Foundations in certain clay soils or made ground.

Do not confuse grade with thickness.A stronger grade does not fix an under-designed slab. For example, a 75mm slab may still be too thin for a garage floor even if the concrete is a higher strength class. Thickness, sub-base quality, reinforcement, joint layout and curing all work together. When guides ask for depth, they are working out volume, not proving the slab design.

Do not confuse sub-base with concrete.A slab build-up might include 150mm compacted MOT Type 1 and 100mm concrete, but those are separate layers. Sub-base is usually ordered by tonne or bulk bag, while ready-mix concrete is ordered by cubic metre. If you enter the total excavation depth into a concrete guide, you may over-order concrete because the sub-base thickness should not be counted as concrete.

Do not confuse “waterproof” with “damp resistant”.A DPM helps resist moisture in a floor build-up, but it must be detailed correctly. Punctures, poor laps, missing tape, rough hardcore and unconnected wall details can all reduce performance. For basements, retaining walls or wet ground, specialist waterproofing design may be required rather than a simple domestic DPM approach.

Do not use old trade names without confirmation.Some suppliers still use familiar terms such as ST2, ST3, GEN1, GEN3 or RC mixes, while standards and specifications may use C20/25, C25/30 or C30/37. These terms can overlap in everyday use but should not be treated as universal substitutes. Ask the supplier to confirm the exact strength class, designated concrete, exposure class and slump on the quote or delivery ticket.

Do not assume every concrete job needs the same finish.A tamped finish can provide grip outdoors, a floated finish can suit a garage or workshop, and a power-floated finish may be appropriate for larger internal floors. Finish affects labour, timing, weather protection and sometimes the required mix. If the finish is not written into the quote, two prices may not include the same level of workmanship.

A good UK concrete quote should make the technical terms visible. For ready-mix, look for the concrete strength class or designation, volume in cubic metres, slump or workability, aggregate size, delivery address, truck type, unloading method, waiting time allowance and VAT treatment. For groundworks, look for excavation depth, disposal, sub-base type, compaction, DPM, reinforcement, formwork, concrete thickness, finish and curing. If those details are missing, the price may still be usable as a rough estimate, but it is harder to compare against another contractor.

For a garage base, a strong quote may say something like: excavate to formation, install compacted MOT Type 1 sub-base, lay DPM, install A142 mesh on spacers, pour 150mm C25/30 concrete and finish to falls. That one sentence includes at least eight technical terms, each with cost and quality implications. If another quote simply says “garage base supplied and fitted”, ask what is included before choosing based on price alone.

For a driveway, check whether the quote includes excavation, waste removal, sub-base, edge restraints, concrete grade, air entrainment, reinforcement or fibres, joints, finish and curing protection. For footings, check width, depth, trench conditions, spoil removal, concrete grade, building control inspection timing and whether the price allows for difficult ground. Clear definitions help prevent disputes because both customer and contractor understand the same scope.