The Densifying and Sealing of Concrete, Explained

Concrete is a wonderfully durable material when correctly made and treated, but its porosity and strength vary, and where a floor has to look good, be durable and stay stain-proof, it needs specific treatment. Here's how densifying and sealing actually works, and where each step fits.

Two starting points: hard-troweled or diamond-ground

A shiny, non-slip, easily cleaned concrete floor can be achieved by more than one route. The first distinction is between:

Properly hard, smooth concrete, achieved with a dry-shake hardener such as Samson MBFT, which only needs regular washing to maintain its finish.
Diamond-ground concrete, where exposed aggregate is the desired look. Diamond grinding removes the durable surface skin and exposes entrapped air bubbles, leaving a surface that's usually dusty and porous and needs chemical densification to restore its integrity.

Where MBFT has been correctly used, subsequent regular washing of an Densifier HC-treated surface gives a satin finish, which can then be optionally treated with a stain-repellent sealer depending on the intended use of the floor.

Densifying, filling and sealing

For a diamond-ground floor, the entrapped air and pin holes should first be filled with a pre-polymered cementitious filler: Samson P3 Primer works well for this. To restore durability and stop dusting, a penetrating reactive silicate is needed: Samson Densifier HC is formulated for exactly this.

Densifying and filling reduce dusting and porosity, but the pores of the concrete remain absorbent and therefore easily stained. A liquid repellency treatment and a suitable membrane are needed for shine and non-slip properties when wet: Samson Siloxane Solution or MM Sealer Buffable provide this.

Diamond grinding itself requires various coarseness of pads, moving from initial rough grinding through to fine grinding and shining.

Critical processes to follow

Vacuum all dust off before applying the densifier by brush or a microfibre applicator.
On the first densifier application (after rough grinding), even coverage matters. If further grinding will follow, the unreacted densifier need not be washed off, but on a second application, all unreacted chemical must be washed off, since unreacted densifier that isn't removed leaves a crystalline residue and a scratched appearance.
Only attempt the final liquid repellency treatment once the floor is thoroughly dry, otherwise you risk streaking and cloudiness in the sealer.
Apply the final sealer thinly and smoothly with a suitable fibre mop; rollers and sheepskin applicators leave lines of over-application at the edges.
Allow the final sealer to become completely touch dry, then shine it to a satin finish with a buffing pad. High-speed (1000 rpm) burnishing equipment can achieve a high shine if that's the desired result.

Tips that get overlooked

MM Sealer Buffable is a solvent-carried pure acrylic that thickens quickly if left open, so the best results come from working wet-to-wet quickly with a thin application. Densifier washes off equipment with water; MM Sealer Buffable applicators need air-drying thinners or Samson Stripper A. Fire hazard warnings must be followed and flame-proof equipment used, and the work area kept well ventilated.

Next step

Browse our densifiers & sealers range or request on-site technical advice for your specific floor.