Calcium formate (CAS 544-17-2) is one of the few industrial salts that sells into two markets that never talk to each other. Read the purchase order and you will find it as a chloride-free set accelerator for concrete, mortar and tile adhesive, or as a buffered acidifier in piglet and poultry feed. Both are Ca(HCOO)2, molecular weight 130.11 – and both are made in the same reactor.
The consequence is a specification landscape that confuses first-time buyers: one CAS number, three or four grade names, and certificates that look nearly identical. This guide sets out what the molecule does, how the three commercial grades actually differ, and how to read the numbers – including the single figure that lets you verify a certificate with a titration instead of a chromatograph.
Current specifications for the concrete, feed and industrial grades are on the calcium formate product page.
1. The molecule
| Property | Value | Practical meaning |
|---|---|---|
| Chemical name | Calcium diformate, calcium formate | The calcium salt of formic acid, two formate anions per calcium |
| Formula / MW | C2H2CaO4 / 130.11 | Theoretical calcium content 30.80%; formic acid equivalent 70.75% |
| Appearance | White to off-white crystalline powder | Free-flowing when dry; hygroscopic when exposed |
| Solubility | Freely soluble in water (roughly 16 g/100 mL at 20 deg C) | High solubility is why it is used as a liquid admixture component as well as a powder |
| pH in solution | Close to neutral – the salt of a weak acid and a strong base | Unlike free formic acid, it does not attack equipment or smell in the bag |
| PubChem CID | 10997 | Identity reference |
Two calculated values do most of the work in this product, and both are worth memorising:
| Derived quantity | Calculation | Result |
|---|---|---|
| Theoretical calcium content | 40.078 / 130.11 | 30.80% |
| Calcium at 98% assay | 30.80% x 0.98 | 30.18% – which is exactly where the “min 30.1%” limit sits |
| Formic acid equivalent | 2 x 46.03 / 130.11 | 70.75% – 1 kg calcium formate carries the acid load of 0.71 kg pure formic acid |
2. Manufacturing: two routes, one hidden difference
Route A – direct neutralisation. Formic acid is neutralised with calcium hydroxide or calcium carbonate, the solution is filtered, concentrated, crystallised, centrifuged and dried:
2 HCOOH + Ca(OH)2 -> Ca(HCOO)2 + 2 H2O
This route introduces no chloride. Residual carbonate from an incomplete neutralisation is the usual impurity: it shows up as effervescence when acid is added to a sample, and as a calcium titration below the theoretical value.
Route B – metathesis. Sodium formate is reacted with calcium chloride, and calcium formate is crystallised out of a solution that also contains sodium chloride:
2 NaHCOO + CaCl2 -> Ca(HCOO)2 + 2 NaCl
Route B uses cheaper raw materials, which is why it exists at all. Its weakness is chloride carried into the crystal, in the mother liquor and into the dryer. For feed applications a small chloride residue is tolerable; for reinforced concrete it is a defect, because the whole commercial case for calcium formate over calcium chloride is the absence of chloride. A supplier claiming “chloride-free accelerator grade” should be able to tell you which route the material came from. If they cannot, assume Route B.
3. The three commercial grades
| Parameter | Concrete accelerator | Feed additive | Industrial |
|---|---|---|---|
| Assay | Min 98% | Min 98% | Min 98% |
| Calcium | Min 30.1% | Min 30.1% | Min 30.1% |
| Moisture | Max 0.5% | Max 0.5% | Max 0.5% |
| Arsenic | Max 5 ppm | Max 5 ppm | Usually not specified |
| Particle size | 40-60 mesh as agreed | 60-80 mesh as agreed | 50 mesh |
| Documentation | Chloride declaration, admixture conformity data | Feed-additive registration, GMP+ / FAMI-QS, dioxin statement | Standard COA and SDS |
What genuinely differs, and what does not
Purity does not differ. All three grades are 98% minimum with the same calcium and moisture limits. A “technical grade” quoted at 95% is not a different product line – it is a lower-purity lot, and the balance is moisture and calcium carbonate.
Documentation differs, and it is the real product. A feed-grade lot needs a feed-additive authorisation, a dioxin and heavy-metal statement, and a GMP+ or FAMI-QS chain. A concrete-grade lot needs a chloride declaration and enough consistency data for the admixture producer to keep their conformity mark. The price difference between the three sheets is largely the cost of that paperwork and the segregation it requires.
Particle size differs by application, not by grade name. Coarse material (40-60 mesh) dissolves more slowly, which spreads the accelerator’s heat release over the first hours rather than spiking it in the mixer. Fine material (60-80 mesh) disperses faster in a premix and stays suspended in a feed line. A 50 mesh industrial powder is a general-purpose compromise.
Why 30.1% calcium is a free acceptance test
Because the theoretical calcium content of the pure salt is 30.80%, a 30.1% floor is simply 98% assay expressed in calcium terms. That makes it testable with an EDTA titration in any plant laboratory. If a delivered lot titrates below 30.1%, one of three things has happened: the assay is genuinely under 98%, the lot has absorbed moisture beyond specification, or carbonate filler is present. You do not need the full assay method to know that something is wrong – and you do not need to trust the supplier’s number to check it.
4. Calcium formate as a concrete accelerator
The mechanism
Calcium formate accelerates the hydration of tricalcium silicate (C3S), the phase that governs early strength. It does this in two ways: it raises the calcium ion concentration in the pore solution, which shortens the induction period before calcium silicate hydrate begins to precipitate, and the formate anion reacts with tricalcium aluminate (C3A) to form calcium formate-bearing AFm phases. The net effect is a higher early heat of hydration and faster strength development at 1 and 3 days, with the long-term strength essentially unaffected at normal doses.
It is used at roughly 0.5-2% of cement weight, depending on the accelerator effect required, the cement type and the ambient temperature. Because the effect is thermal as well as chemical, dosage is usually set by trial pour rather than by calculation: the same dose that gives 20% extra 1-day strength at 5 deg C can be excessive at 25 deg C.
Why not just use calcium chloride
Calcium chloride is cheaper, more soluble and a more powerful accelerator per kilogram. It is also a chloride source, and chloride ions break down the passivating oxide film on reinforcing steel and initiate pitting corrosion. Most concrete standards cap acid-soluble chloride content in reinforced concrete, and many forbid chloride-based accelerators outright in prestressed elements, in marine exposure classes and in repair mortar applied over existing rebar.
That regulatory boundary is the entire commercial case for calcium formate. It is not a better accelerator – it is the accelerator you are allowed to use. The buying decision is therefore a cost-per-unit-of-early-strength calculation against a chloride limit, and it should always be compared at equal early strength, not at equal tonnage.
What to watch in the field
Three interactions dominate complaints. First, calcium formate works against retarders: a mix containing a strong retarder (gluconate, tartrate, sucrose) may need the retarder reduced rather than the accelerator increased. Second, high doses increase the risk of efflorescence as formate migrates to the surface with water. Third, in dry-mix mortars the powder’s particle size controls how quickly the mix stiffens after water addition, so switching mesh mid-project changes the working time.
5. Calcium formate as a feed acidifier
What the 70.75% figure is for
Formulations are written in terms of formic acid, but formulators prefer to buy a salt. The conversion is fixed: calcium formate delivers 70.75% of its weight as formic acid equivalent, so 1.41 kg of calcium formate replaces 1.00 kg of pure formic acid on a molar basis. Any quotation that does not make this conversion is not comparable with one that does.
Why the salt rather than the acid
Free formic acid is corrosive to feed mill equipment, volatile in the bag, and reduces palatability at effective doses. Calcium formate is a dry, near-neutral powder that dissociates in the stomach and releases the acid where it is wanted. The practical benefits claimed in feed use follow from lowering gastric pH: suppression of acid-intolerant pathogens, better pepsin activity, and improved digestibility of protein in young animals.
Because it is buffered, calcium formate can be dosed higher than free acid without a palatability penalty, and it also contributes calcium – which is either useful or a nuisance depending on the mineral balance of the formulation.
Regulatory position
Calcium formate is authorised as a feed additive in the EU under the number E238, for use in all animal species. Other markets maintain their own feed-additive catalogues. Inclusion rates are typically in the range of 0.5-2% of the complete feed, with higher levels in weaning diets – always within the national maximum, and always checked against the calcium and formic acid contribution to the rest of the premix.
Feed claims are regulated separately from chemistry. Statements about gut health or performance must match the authorised claim for the additive in the destination market; this article deliberately describes the chemistry and the specification instead.
6. Industrial and other uses
| Application | Function |
|---|---|
| Leather processing | Deliming and bating auxiliary; buffers the pelt during enzyme treatment without the aggressiveness of a strong acid |
| Drilling and workover fluids | Formate brine component – high density with low corrosion and no chloride |
| Dry-mix mortar and grout | Setting accelerator in tile adhesives, self-levelling compounds and repair mortars |
| De-icing blends | Component in non-chloride de-icers and in blended products where a calcium source is wanted |
| Chemical synthesis | Intermediate to formate esters and oxalate chemistry |
7. Comparing calcium formate with the alternatives
| Product | CAS | Accelerator strength | Chloride | Where it wins |
|---|---|---|---|---|
| Calcium formate | 544-17-2 | Moderate | None | Reinforced and prestressed concrete, repair mortars, chloride-capped specifications |
| Calcium chloride | 10043-52-4 | Strong | High | Plain concrete, cold-weather set acceleration where chlorides are permitted, and cost per unit of acceleration |
| Calcium nitrate | 10124-37-5 | Moderate | None | Non-chloride acceleration plus a corrosion-inhibiting nitrate ion; higher cost |
| Sodium formate | 141-53-7 | Mild | None | Where sodium rather than calcium is wanted, and in de-icing |
| Sodium gluconate | 527-07-1 | Retarder, not accelerator | None | Opposite effect – used to extend working time and reduce water demand |
Within our catalogue, the chloride-based comparison is set out on the calcium chloride 94% and calcium chloride 74% flakes pages, and the retarder side of the balance on the sodium gluconate page.
8. Buying guide
- Which grade, and on which document? Ask for the COA template before the price. If the certificate has no arsenic line, you are being offered industrial grade for a feed or construction job.
- Which manufacturing route? Ask directly whether the material is neutralisation-grade or metathesis-grade. The answer decides chloride content.
- Particle size and its distribution. “50 mesh” alone is not enough – ask for the passing percentage and the fines content.
- Moisture and packaging. 0.5% max in 25 kg PE-lined bags, or jumbo bags for concrete plants. Material consolidated in a humid container will arrive caked.
- Lot-to-lot consistency. Ask for three consecutive COAs, not one. Assay drift between lots shows up as a drifting set time on site.
- Documentation package. Feed registration and GMP+ / FAMI-QS for feed; chloride declaration and admixture conformity data for concrete.
9. Safety and handling
Calcium formate is a low-hazard solid: not flammable, not classified for transport, and not a sensitiser. Dust is irritating to eyes and the respiratory tract, so bag dumps should be vented and operators should wear goggles and a dust mask. It is not corrosive in solution, which is one of its advantages over free formic acid.
Store dry and sealed below 30 deg C. The material is hygroscopic; opened bags should be resealed and stacks should not sit directly on a concrete floor, which wicks moisture. Under those conditions the shelf life is normally two years.
10. FAQ
Is calcium formate the same as calcium diformate?
Yes – both names describe CAS 544-17-2, Ca(HCOO)2.
Can calcium formate replace calcium chloride one-for-one?
No. Calcium formate is a weaker accelerator per kilogram, so a higher dose is needed to reach the same early strength. The comparison must be made at equal early strength, and the dose ceiling is set by efflorescence risk and by the mix’s retarder balance.
Is calcium formate chloride-free?
Calcium formate contains no chloride by formula, but the metathesis manufacturing route can leave a chloride residue. For reinforced concrete, ask for a chloride declaration rather than relying on the name of the chemical.
How much formic acid does calcium formate contain?
70.75% by weight, calculated as 2 x 46.03 / 130.11. One kilogram of calcium formate is equivalent to about 0.71 kg of pure formic acid.
Why is the calcium content specified at 30.1%?
Because 98% assay corresponds to 30.18% calcium. The 30.1% floor is a convenient, titratable cross-check on purity.
Is calcium formate allowed in organic feed production?
Feed-additive authorisation and organic certification are separate questions, and organic rules differ by market. Confirm against the certification standard of the destination market rather than the additive authorisation alone.
References and further reading
- Formula, molecular weight and PubChem CID 10997 – verified against the PubChem record for CAS 544-17-2.
- Calcium content, calcium-at-98%-assay and formic acid equivalent – calculated from atomic weights, working shown in section 1.
- Specification limits as quoted on the current product certificate for each grade.
- Related reading: calcium chloride 94%, sodium gluconate in construction, sodium formate.
Disclaimer. This article is a technical and commercial overview. It does not replace the batch certificate of analysis, the safety data sheet, the admixture standard of your market, or the feed-additive regulation of the destination country. Dose figures are starting points for trials.
For a current COA on any of the three grades, a 1 kg sample, or pricing on 25 kg and jumbo-bag quantities, contact PolyBlueChem.
Related reading.