Verification
Sampling and In-Situ Strength Checks for Liquid Screed
Verifying screed strength on site involves a combination of sampling at placement and in-situ checks, referenced against the compressive strength class specified.
Need strength verification on a specified screed?
We can discuss sampling and testing arrangements for liquid screed projects across Exeter and the South West.
Or call our landline on 01392 237700
Every liquid screed is specified with a compressive and flexural strength class under BS EN 13813, but strength is not something that can be judged by eye once the floor has cured. Where verification is required, it is carried out through sampling taken during placement and, where appropriate, in-situ checks on the finished floor.
Sampling typically involves taking representative samples of the screed as it is pumped, which are then cured and tested under controlled conditions to confirm they meet the declared strength class. This gives traceable evidence that the material delivered to site matched its specification.
In-situ checks on the finished slab are a further layer of verification, useful where there is a specific concern about a localised area or where sampling records are incomplete. Both approaches should be considered at specification stage if strength verification is a project requirement.
Sampling during placement
The most reliable way to verify that a liquid screed meets its declared strength class is to take samples as it is being placed, in line with the relevant standard test methods. These samples are cured under controlled conditions matching the standard before being tested for compressive and flexural strength.
Because the samples are taken directly from the batch being pumped into the building, this method gives the most representative record of the material actually installed, which is valuable where strength verification forms part of a contractual requirement.
Checking the finished floor
Where sampling records are unavailable, or where there is a specific concern about a defined area of floor, in-situ checks can be carried out on the cured screed itself. These provide useful supplementary evidence but should be interpreted carefully, since in-situ conditions differ from laboratory-cured samples.
Any in-situ checks should be assessed against the strength class specified for the project rather than a general assumption of adequacy, and results should be documented clearly so they can be referred back to later if required.
Keeping a defensible testing paper trail
Each cube or prism taken at placement should carry a label linking it to the bay poured and the date cast, so a strength result can be traced back to a specific area rather than the floor as a whole.
A curing tank log noting storage temperature alongside the lab certificate for each sample closes the gap between a test result and proof that it was obtained under the standard's conditions.
Where strength verification meets site protection
Cube or prism samples taken at placement are only useful if the poured bay they represent survives to be tested; scaffold feet, stacked boards or early foot traffic can crack a bay before its 28-day result is even due.
Where a sample location sits near a doorway or plant room, flagging that area for extra protection avoids losing the one bay the verification record depends on.
Formulation choice and its effect on sampling results
Cementitious and calcium sulfate samples gain strength at different rates, so a cube test scheduled for a cementitious curing age can under-read an anhydrite sample tested too soon, or vice versa.
Recording which formulation each sample represents, alongside the finish it was cast to receive, stops a strength result being judged against the wrong curing timeline.
Reference points for sampling & strength checks
| Strength classes referenced | CA (calcium sulfate) / CT (cementitious) classes under BS EN 13813 |
|---|
Sampling & Strength Checks — the points that decide it
- Strength class (e.g. CA or CT class under BS EN 13813) should be defined at specification stage
- Samples taken during placement give the most representative record of material as installed
- Sample curing and testing should follow the relevant standard test method
- In-situ testing on the cured floor can supplement or substitute for sampling where records are absent
- Test frequency should reflect floor area and the significance of the application
- Results should be referenced back against the design strength class, not a generic benchmark
- Records of sampling and results should be retained as part of project documentation
Sampling & Strength Checks — your questions
Need strength verification on a specified screed?
We can discuss sampling and testing arrangements for liquid screed projects across Exeter and the South West.
Or call our landline on 01392 237700
In short
Verifying screed strength on site involves a combination of sampling at placement and in-situ checks, referenced against the compressive strength class specified.
Need strength verification on a specified screed?
We can discuss sampling and testing arrangements for liquid screed projects across Exeter and the South West.