A chemically reactive release agent. Rather than acting only as a barrier film, it reacts with free lime in the fresh concrete to form a thin soap at the interface, which releases cleanly and consistently and produces noticeably fewer blemishes, less staining and better colour uniformity than a neat oil. For architectural and visible concrete the difference is easily visible in the finished pour and is worth the higher material cost.

It causes exactly the defects it was meant to prevent. Excess agent retards the cement at the surface, producing dusting, softness and colour variation, and pooled material trapped against the form face generates blowholes and pinholing. Over-application is the most common cause of poor concrete surfaces attributed to release agents. Apply a thin, even film, and wipe back any run or pool before the concrete is placed.

By low-pressure sprayer with a fine nozzle, which gives the thin, even coverage the product is designed to deliver. Brushes and rollers tend to leave heavy patches and dry areas in equal measure, and flooding the form guarantees over-application. Work systematically across the whole form face including corners and returns, since a missed area will stick and tear, then check for and remove pooling at the base.

Yes. Steel forms need a product with rust inhibition, since bare steel left coated between pours will corrode and mark the next surface. Timber and phenolic-faced plywood absorb release agent at different rates, so coverage and reapplication differ, and new plywood is typically more absorbent than a face that has been used several times. Plastic and GRP forms have their own requirements. Match the product to the face you actually have.

Yes, and it must be dealt with. Any residue left on the struck concrete surface acts as a bond breaker, which is its function, and will compromise renders, screeds, tile adhesives, paints and bonded repairs applied later. Where the face is to be coated or bonded, plan for surface preparation to remove the residue, and tell the following trade what was used rather than leaving them to discover it.

Yes. Water-based emulsions and vegetable ester based products offer substantially lower volatile organic compound content than solvent-carried mineral oils, and are increasingly specified on environmentally sensitive sites, in enclosed areas and where site or client requirements demand them. They generally need a little more care over application conditions and drying time, particularly in cold or damp weather, but perform comparably when used correctly.

Long enough for any carrier to flash off and short enough that the film is not contaminated or washed away. In practice that usually means the same working day, ahead of reinforcement fixing where possible so that steel is not coated. Protect treated forms from rain, which will strip or dilute the film, and from dust and site traffic. If forms stand for an extended period or get wet, inspect and reapply.