Specification
Writing a liquid screed specification clause
How the individual elements covered across this section — depth, strength class, surface regularity, joints and edge detailing — come together into one written clause.
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Most of the specification questions covered elsewhere in this section — depth, strength class, surface regularity, joints, edge insulation — eventually need to be pulled together into a single written clause that an installer can price and build from. A specification scattered across separate notes and verbal instructions is far more likely to produce gaps or contradictions than one coherent document.
This page sets out a structure for that document: the order the information typically needs to appear in, and the level of detail that makes a clause genuinely usable rather than just a formality attached to a drawing package.
It is intended as a practical checklist for architects, specifiers and self-builders assembling their own specification, drawing on the more detailed guidance on each individual element found elsewhere in this section.
A workable structure for the clause
A clear specification clause typically moves from general to specific: material and standard (for example, a CT cementitious liquid screed to BS EN 13813), build-up type (bonded, unbonded or floating), depth and tolerance, strength class, surface regularity class, then joint and edge detailing requirements, finishing with any underfloor heating coordination notes. Working through the elements in this order tends to surface gaps — for example, realising strength class has been stated without a depth to match it — before the document is finalised rather than after.
Where a project has multiple zones with different requirements, repeating this structure per zone, referenced against a floor plan, is clearer than trying to capture every variation in a single paragraph of prose.
Avoiding the most common gaps
The most frequent weaknesses in specification clauses we see are: strength class and depth stated without reference to each other, surface regularity omitted entirely despite a sensitive floor finish being planned, and joint layout left as a general note rather than a defined plan. Underfloor heating coordination — particularly minimum pipe cover — is also commonly left implicit rather than stated as its own requirement.
Checking a draft clause against each of the individual topics covered across this specification section is a reasonable way to catch these gaps before the document goes out to tender or to an installer for pricing.
Where damp-proofing sits in the finished clause
The membrane type and its position relative to the insulation should be named in the same document as the screed depth, since assuming groundworks has it covered is a common source of gaps.
A clause that specifies screed depth and strength but stays silent on damp-proofing has left one of the floor's most consequential decisions to chance.
Writing a spec clause — the points that decide it
- 1A usable clause states build-up type, depth (with tolerance), strength class, and surface regularity class together, not scattered across separate documents.
- 2Reference the relevant standards explicitly (BS 8204, BS EN 13813) so classifications are unambiguous.
- 3Include joint layout and edge insulation requirements, ideally cross-referenced to a marked-up plan.
- 4State any underfloor heating coordination requirements, including minimum pipe cover, if relevant.
- 5Note pre-pour inspection or datum-check requirements so verification is built into the process, not an afterthought.
- 6Keep wording specific and testable throughout — avoid subjective terms like 'suitable', 'adequate' or 'as required' without a defined standard behind them.
- 7Review the clause against the actual room-by-room loading and finishes intended, not a generic template copied from another project.
Need help drafting your specification?
Send us your project details and we will help pull together a complete, workable screed specification clause.
Or call our landline on 01392 237700
Writing a spec clause — your questions
In short
How the individual elements covered across this section — depth, strength class, surface regularity, joints and edge detailing — come together into one written clause.
Need help drafting your specification?
Send us your project details and we will help pull together a complete, workable screed specification clause.