To diagnose mortar efflorescence, examine the deposit, potential salt inputs from sand, binder and water, and the moisture pathway allowing material to move. White deposits do not automatically identify contaminated sand. Changing an aggregate before those questions are answered can leave the actual cause untouched.
Tunisia has a specific published example: research on the Antoninus baths at Carthage examined salt alteration using mineralogical and chemical methods.1 This site-specific evidence supports investigating salts rather than attributing every white deposit in Tunisia to one material source.
The framework below proposes a practical investigation for mortar production or a constructed surface. It connects silica sand checks with water, binder, substrate and exposure, without turning a visual observation into a complete laboratory diagnosis.
1. Describe the observation before assigning a cause
Record where the deposit appears: on the mortar, on adjacent masonry, near a joint, at the base or around a water entry point. Note whether it is powdery, crystalline, adherent or accompanied by material loss.
The NPS glossary distinguishes surface efflorescence from salt accumulation beneath the surface, which can have a different damage significance.2 Use these terms to clarify observation, not to diagnose chemical composition by colour alone.
For the proposed inspection, photograph comparable areas with location and scale. Identify when deposits first appeared and any related construction, cleaning or water event. A timeline can reveal a question that a sand certificate cannot answer.
Keep appearance and interpretation separate. “White deposit around this joint” is an observation. “Chloride from the supplied aggregate caused it” is a hypothesis requiring analytical and contextual evidence.
2. Examine the water pathway alongside the salts
A salt investigation needs the moisture context. NPS Preservation Brief 39 describes multiple possible moisture sources, including weather entry, ground moisture, plumbing and water introduced during construction or maintenance.3
In the proposed site review, follow the plausible pathway from entry to the affected area. Inspect relevant joints, drainage, nearby equipment and the substrate condition. Do not assume the visible deposit marks the original point of water entry.
Record differences between sheltered and exposed areas. If the observation changes after wetting and drying, document that sequence rather than compare photographs from unknown conditions.
This does not replace a building assessment. It defines the evidence needed before a material change is selected. A chemically cleaner sand cannot, by itself, close a leak or remove salts already present in a substrate.
3. Identify candidate inputs without choosing the winner first
List the materials and water sources involved in the affected work. Include sand, binder, mixing water, additives, masonry or substrate and relevant external exposure. Keep their delivery or preparation histories identifiable.
The NPS glossary notes that soluble salts can come from different materials and external pathways.2 Therefore, a deposit on a sand-containing mortar does not establish that the sand was the sole source.
For a production investigation, preserve samples from the relevant raw-material lots where available. For existing work, distinguish retained incoming materials from material extracted from the affected surface; these are not equivalent samples.
Create a comparison plan before testing. Ask which result would support or weaken each candidate source. Without that plan, a long list of analytical results can still leave the cause unresolved.
4. Analyse the deposit instead of naming it “saltpetre”
A white appearance can lead to an overly specific informal name. Request identification appropriate to the investigation rather than assuming a particular salt family from visual inspection.
The Carthage research used complementary mineralogical and chemical approaches.1 In a proposed mortar investigation, the laboratory should select methods suited to the sample and question, with clear reporting of what each method establishes.
A surface scrape can characterise the collected deposit but may not describe concentrations deeper in the wall or the original raw material. Define the sample’s location and scope before interpreting the result.
If several phases or ions are identified, keep them distinct. A report that identifies one constituent should not be rewritten as proof that every visible deposit has the same composition. Ask how the measured information relates to the proposed source hypotheses.
5. Distinguish a screening measurement from chemical identification
Electrical conductivity of a prepared extract can be useful as a comparative indicator, but it is not the name of a salt. A value depends on the extraction and measurement conditions as well as the material.
NPS’s salt-investigation methodology uses prepared samples and gradients to help locate salt-affected areas.4 That supports a structured comparison, not a universal threshold for every mortar or sand.
For the proposed laboratory plan, fix the sample mass, extraction conditions, measurement procedure and reporting basis. A result from one extraction should not be compared directly with another made using a different liquid-to-solid ratio.
If a screening result is elevated relative to the agreed reference, use appropriate chemical analysis to answer the source question. A higher conductivity alone does not prove chloride, identify the original input or establish the required remedial treatment.
6. Ask for the aggregate result relevant to the question
An aggregate’s total chemical composition is not the same as its content determined by a specified soluble-salt extraction. Name the quantity required and the method used.
EN 1744-1 concerns chemical analysis of aggregates.5 Its public catalogue establishes the subject; project testing should use the complete adopted method and edition rather than reconstruct a procedure from a short catalogue description.
For the proposed sand comparison, use a representative sample and a laboratory procedure common to reference and candidate. Keep dry-basis results identifiable. If the specification requires a particular soluble constituent, request that result explicitly.
Do not interpret high silica content as proof of low soluble salts. These are separate properties. Equally, do not infer unacceptable material from an isolated result without the relevant application criterion and method.
7. Build a mass comparison across ingredients
A fictional formulation contains 800 kg of dry sand and 200 kg of binder. If the sand contains 100 mg/kg of a measured constituent, its input is 80,000 mg, or 80 g. If the binder contributes 200 mg/kg, its corresponding input is 40 g.
The combined dry-input quantity is therefore 120 g on those stated assumptions. It is not automatically the amount that will migrate to a surface: solubility, reactions and exposure remain separate questions.
If 100 litres of mixing water contain 50 mg/L of the same constituent, they add 5 g. This illustrates why water concentration and solid concentration require different denominators before their contributions can be combined.
Use this proposed balance to compare hypotheses, not predict a visible deposit mass. It can show whether changing one ingredient would significantly alter the measured input. Preserve the analytical definitions so unlike quantities are not added together.
8. Compare formulations by changing one input at a time
For a proposed laboratory investigation, begin with the affected formulation and a controlled reference. If the main hypothesis concerns sand, replace only that input while keeping binder, water, additives and preparation comparable.
A second comparison can examine water; a third can examine binder if the evidence justifies it. Changing all inputs at once may produce a better-looking specimen without identifying which change mattered.
Define wetting, curing and observation conditions before preparing specimens. A specimen dried differently from its reference cannot be treated as a pure raw-material comparison.
Retain both the deposit observation and the relevant measurements. If the changed sand reduces a measured input but deposits remain, investigate the remaining pathways instead of declaring either the certificate or the surface observation irrelevant.
9. Use blanks to detect contributions from the test setup
A laboratory setup can introduce its own background. Containers, water and collection materials belong in the proposed method review when small measured quantities drive the conclusion.
Prepare the appropriate blank under the agreed procedure. If a blank produces a meaningful signal, resolve it before attributing the entire result to the sand. The laboratory should describe how background affects interpretation.
Use the same preparation route for all compared samples. A changed water source or container between batches can create a difference unrelated to the raw material under investigation.
Retained raw material and prepared mortar answer complementary questions. The first helps compare inputs; the second evaluates their behaviour in the defined mixture. Neither should silently substitute for the other.
10. Distinguish cleaning from correcting the mechanism
Removing a visible deposit changes the surface observation. It does not necessarily remove the material source or the water pathway. Keep cleaning, moisture correction and material substitution as separate interventions in the investigation.
NPS moisture guidance emphasises diagnosis before treatment and illustrates the problems of unsuitable interventions on historic materials.3 A proposed response should fit the specific substrate rather than use a generic coating or aggressive cleaning recipe.
Before changing the surface treatment, identify the question to be tested and preserve an untreated comparison where appropriate. Otherwise, cleaning can erase useful evidence before the cause has been established.
For a mortar-production problem, a controlled specimen comparison may be more informative than repeatedly cleaning installed work. For an existing building, the relevant assessment includes the substrate and site conditions. The response follows the evidence, not merely the appearance.
11. Map location and depth when they matter to the diagnosis
A surface sample cannot automatically describe an entire wall. If the source hypothesis concerns rising moisture, external exposure or a particular joint, sample locations should be selected to distinguish those possibilities.
The NPS methodology describes salt gradients as an investigation tool.4 For a proposed assessment, keep location, depth and preparation attached to each result. Do not average them into one figure before examining the pattern.
Higher values in one zone can guide the next observation, but do not alone prove the pathway. Compare with moisture information and the construction history. Several mechanisms can coexist.
Use sampling appropriate to the material and site. On heritage work, the investigation needs to respect the fabric being assessed. The aim is to resolve a diagnostic question with relevant evidence, not simply collect the largest number of specimens.
12. Set a material decision that the evidence can support
A useful investigation can end in different decisions: retain the sand, change a preparation step, qualify another lot, revise another ingredient or address water entry. A predetermined sand replacement prevents that range of findings from being considered fairly.
For the proposed acceptance rule, state the measured aggregate requirement and the controlled application comparison. A lower soluble-input result is relevant, but its practical effect should be assessed within the mixture and exposure actually intended.
If the candidate meets the raw-material criterion but the surface result remains unacceptable, investigate the system further. Do not promise an efflorescence-free mortar solely from the sand certificate.
For Tunisian projects, the silica sand page helps describe the material requirement. A strong enquiry separates sand quality, complete formulation and moisture pathway, using laboratory evidence to decide which change is justified.
13. Compare extracted concentrations on the correct basis
Consider a fictional extraction producing 20 mg/L of a constituent in 0.5 litres of liquid from 0.1 kg of dry sample. The extracted amount is 10 mg; on that stated sample basis it is 100 mg/kg.
A second extraction at 10 mg/L using one litre from the same sample mass also represents 10 mg, or 100 mg/kg. The liquid concentrations differ while the calculated amount per dry sample is equal.
These examples are not standard test instructions. They demonstrate why concentration, extract volume and sample mass must accompany a comparative result. Any calculation should follow the laboratory’s adopted method, including relevant corrections and the distinction between extracted and total content.
14. Keep the diagnostic conclusion narrower than the hypothesis
A finding that a candidate sand contains less of a specified soluble constituent supports that comparison. A controlled mortar trial with fewer deposits supports the defined trial result. Neither alone identifies every source in installed work.
Write the conclusion in those measurable terms, then state which decision follows. This preserves the value of the analysis without overstating its reach.
The most useful supplier discussion is consequently precise: which constituent, which method, which preparation and which formulation trial? That chain helps identify a material improvement while leaving the rest of the investigation visible.
15. Read material and specimen results together
A proposed table can collect the sand reference, analytical result using the common method, other ingredients held constant, preparation conditions and deposit observation for each variant. Keep original values visible rather than replace them with a general judgement such as “better quality”.
Consider three possible outcomes. The candidate has a lower measured content and the specimen shows less deposit under controlled conditions: the observations fit the hypothesis, but transfer to installed work still requires its context. The candidate has a lower content without a visible difference: investigate whether the controlled constituent is relevant or another contribution dominates. Finally, deposits decrease without an analytical difference in the chosen parameter: examine preparation, another constituent or test variation rather than rewrite the chemical result.
These outcomes lead to different next steps. They prevent declaring a winner from one favourable number. The comparison makes a purchasing decision explainable, particularly when price or supply conditions change.
16. Check whether material quantities use a dry or wet basis
In a fictional example, a 1 kg wet sample containing 5% water has 0.95 kg of dry material. If it contains 95 mg of a measured constituent, that corresponds to 95 mg/kg of wet sample but 100 mg/kg of dry material. The two values describe the same sample with different denominators.
This calculation is not an analytical procedure. It shows why the basis must be named before comparison. A dry specification cannot be compared directly with a wet certificate without appropriate conversion and measurement information. Preserve the water content used in the calculation rather than assume a typical value.
Apply the same discipline to a formulation balance. Wet sand dosing and dry sand quantity can differ; the corresponding water belongs in the actual preparation balance. Identify the masses used so the controlled comparison remains interpretable. This avoids seeking a salt difference in a trial whose preparation states were not equivalent.