Building components · Substructure & Ground
Blinding Layer
Explains why a layer that carries no load is nevertheless a distinct element, and what is lost when it is omitted.
Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.
Overview
What a blinding is
A blinding is a thin layer placed over a prepared surface with two purposes: to stop that surface deteriorating, and to give the next operation something clean and regular to work on. It is usually a weak concrete or a fine granular layer.
It is a working element rather than a structural one. Nothing above relies on it to carry load, but several things above rely on the surface it creates — reinforcement positioning, membrane laying and setting out all become harder without it.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a sub-base. A sub-base is a load-spreading layer with a structural job; a blinding protects and levels, and carries nothing.
- It is not a separation layer. A separation layer keeps two materials apart for chemical or physical reasons; a blinding creates a working surface, and may or may not separate anything.
- It is not structural concrete, even when it is made of concrete, and the distinction matters because it is not designed or reinforced as though it were.
Terminology
Common names and aliases
These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.
- blinding
- blinding concrete
- sand blinding
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- The condition of the surface it is placed on, since a blinding covers a formation rather than repairing it.
- How soon it follows the operation that exposed the surface beneath.
- The regularity it achieves, because the layers laid on it inherit its irregularities.
- Whether what is laid over it — a membrane in particular — needs a surface free of sharp material.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
A blinding is commonly the thing that stops a formation softening between exposure and the next operation.
Its practical value is largely in what it makes possible: laying membranes, positioning reinforcement and setting out all become straightforward on a blinded surface.
Irregularity in a blinding is inherited by the layers above, including any membrane laid directly on it.
Materials
Commonly formed from
Material families this element is commonly realised in. This states common practice only — it is not a statement that any of these materials suits this component in a particular building, which depends on the whole assembly and on qualified review.
Assemblies
Building systems this element is met in
The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.
Where it is met
Application contexts
Building contexts where this element is commonly encountered. Association is not recommendation: appearing here does not mean the component suits every instance of that context, or any particular one.
- Basement
- Ground Floor
- Substructure
Clarifications
Commonly misunderstood
- That a blinding is structural. It is not designed to carry load, and treating it as though it were misreads its purpose.
- That it is optional cosmetic work. Where a membrane or reinforcement is laid over a formation, the blinding is what makes that practical.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- What is the blinding here intended to achieve — protection, a laying surface, or both?
- Does anything laid over it require a particular surface condition?
- How soon after the formation is exposed will the blinding be placed?
- Is the blinding thickness and regularity adequate for the operation that follows it?
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this element involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this element comes up.
What this entry does not do
- No thickness, mix, strength or tolerance is stated here, and a blinding is not designed as a structural layer.
- Whether a blinding is required, and what it should be, follows from the design of the elements above it.
Substructure & Ground Elements
The prepared surfaces, layers and buried members between undisturbed ground and the first structure above it.
Browse all substructure & ground entries →