Release agents and admixtures for concrete: which to choose and when

If you want to separate the pour from the formwork without damaging the surface, you need a release agent; if you want to change how the mix behaves (more workable, less shrinkage, better adhesion, less water loss), you need an admixture. They are two different products and do not replace one another. In the collection, release agents have coverage rates of about 1 litre per 50-100 m² of formwork, while admixtures are dosed as a percentage of the cement weight, for example between 5 and 15%, as stated on the product data sheet.

The types

• Ready-to-use release agents: applied as supplied to clean formwork, by spray, brush or roller. One example is the Sformoil Ferro for formwork.
• Emulsifiable release agents: diluted with water before use, according to the technical data sheet.
• Plasticising admixtures: make the mix flow more easily without adding water, such as the Fluimax 2HS.
• Expansive admixtures: added at the mixing stage to counteract shrinkage, such as the Kimitech AD.
• Synthetic and polymer resins: added to mortars to improve adhesion and waterproofing, for example the Kimitech B2.
• Evaporation retarders: form a film that slows the water loss of the fresh pour, such as the Antievaporante W.
• Premixed cement mortars: mixed only with the stated amount of water; the coverage is given in kilograms per square metre per centimetre of thickness.

How to choose by job

The features to look at

• Consumption and coverage: for release agents it is expressed in litres per square metre, from 1 litre per 50 m² to 1 litre per 100 m². The higher the coverage, the less product is needed for the same formwork. For admixtures it is a percentage of the cement weight; for mortars it is 12-19 kg/m² per centimetre of thickness.
• Method of application: spray, brush, roller. Spraying is faster on large formwork; brush and roller are for corners and small pieces.
• Pack: from the 5 kg bucket or the 17.5 kg tin to the 20 kg pail, up to 20-25 kg bags, 19 litre pails and 208 litre drums. Choose according to the site's consumption.
• Consistency and density: liquid products have a density of about 1.04-1.1 g/cm³. It is needed to convert litres and kilograms when dosing.
• Technical data sheet: the dosage, the moment at which to add the product and compatibility with the cement must be read on the data sheet of the individual product.

Common mistakes

• Applying too much release agent. It must be applied as a thin, even film: excess leaves stains and can spoil the adhesion of plaster and paint.
• Contaminating the reinforcement. Release agent on the reinforcing bars reduces bond with the concrete: protect the bars or apply the product before positioning them.
• Applying release agent on dirty formwork. Clean the formwork of residues and dust first.
• Adding water instead of a plasticiser. More water makes the mix more fluid but weaker.
• Dosing admixtures by eye. Too little does not work and too much changes the mix unpredictably: follow the data sheet and use graduated containers.

Frequently asked questions

What is the difference between a release agent and an admixture?

The release agent is applied to the formwork and stops the pour from sticking. The admixture is mixed into the concrete and changes its characteristics. They can be used together on the same site.

How much release agent is needed?

It depends on the product: in the collection the coverage ranges from 1 litre per 50 m² to 1 litre per 100 m². Check the data sheet of the product you choose.

Is the admixture added to the water or to the mix?

Normally to the mixing water or directly in the mixer, stirring until the mix is uniform. The exact moment is given in the technical data sheet.

Is protective equipment needed to apply them?

Yes: gloves and goggles. Always read the label and the safety data sheet of the product.

You will find all the products in the Release Agents and Admixtures for Concrete and Mortar collection: to choose the right one for your pour, ask the AMES technicians for a quote or advice.