Exposed concrete and polished concrete are not the same material finish. They are different treatments of the same material, each producing a different surface quality, a different light behavior, and a different maintenance relationship. Choosing between them — and knowing where each belongs in a contemporary residence — is a design decision made in the material specification phase.
In MÉTODO, both finishes appear in our projects. The section and the program determine which belongs where.
As-Cast Exposed Concrete: What It Shows
As-cast concrete is the surface that comes off the formwork. It is the most direct and unmediated expression of the material. What it shows:
- Formwork marks: The grain or texture of the form facing material impressed into the paste surface. Plywood produces a smooth surface with grain marks. Rough-sawn lumber produces a heavily textured surface. Foam or fabric produces even smoother results.
- Tie holes: Small circular voids or plugged holes where the tie rods that held the formwork in position were threaded. Their pattern is designed (in MÉTODO's work) or accidental (in most other concrete construction).
- Pour lines: Faint horizontal lines where successive lifts of concrete met. If the pour was continuous and well-executed, these may be barely visible. If the pour paused for more than 45 minutes, a cold joint may be visible.
- Aggregate character: In well-vibrated concrete, aggregate contacts the form face and is visible in section at the surface. The aggregate size, color, and distribution affect the visual texture.
- Bleed water marks: Horizontal staining where water rose to the surface during curing. Visible in poorly specified or poorly placed concrete. Minimized by low water-cement ratio and proper consolidation.
As-cast concrete at its best is a record of making. It communicates construction — not as a flaw but as content.
Polished Concrete: What the Process Reveals
Polished concrete begins after the concrete has achieved full compressive strength (28 days minimum). The process:
- Grinding (16 to 30 grit): Removes the surface paste and exposes aggregate. This step reveals the coarse aggregate distribution and any subsurface voids.
- Honing (50 to 400 grit): Progressive refinement removes the grinding marks from the previous step and smooths the surface.
- Polishing (800 to 1500 grit): Further refinement produces a sheen. Above 800 grit, the surface begins to reflect light.
- Densifier treatment: A lithium or sodium silicate densifier is applied between grinding steps to harden the surface paste and reduce porosity.
- Guard or sealer: A final topical guard or penetrating sealer is applied to prevent staining.
The result is a surface that is fundamentally different from as-cast concrete. It is flat, reveals aggregate, reflects light, and does not show formwork marks — because the formwork surface has been removed. It is a different material expression, not a superior one.
Application Logic: Where Each Finish Belongs
As-cast exposed concrete is appropriate for:
- Vertical surfaces (walls, columns) at living distance where the formwork record is part of the architecture.
- Ceiling undersides where the slab soffit is the finish and where grinding is not practical.
- Exterior walls where the material's honesty is the facade language.
- Feature elements — fireplaces, stairs, kitchen islands — where the making process is the focal content.
Polished or honed concrete is appropriate for:
- Floor surfaces, where cleanability matters and micro-texture accumulates dust and debris.
- Kitchen countertops, where a sealed, smooth surface is more hygienic.
- Bathroom walls and floors in wet areas, where a sealed surface is essential.
- Surfaces that receive direct sunlight at a raking angle — a polished floor handles raking light more elegantly than a textured surface, which can appear rough under harsh direct light.
The two finishes can coexist in the same room. A concrete wall with as-cast formwork texture, a polished concrete floor, and a concrete ceiling with as-cast slab soffit create three distinct material expressions that together constitute the complete material argument of the space.
Light Behavior: The Critical Difference
The most significant practical difference between as-cast and polished concrete is how they respond to light.
As-cast texture diffracts light. Under diffuse lighting (overcast sky, indirect artificial light), as-cast concrete reads evenly. Under directional light (raking sun, a spotlight), every surface variation casts a micro-shadow, and the texture becomes dramatic. La sombra antes que la luz — the shadow before the light — is literally visible on a well-textured concrete wall in afternoon sun.
Polished concrete reflects light. At lower polish levels (honed at 400 grit), it diffuses light softly. At higher polish levels (800 to 1500 grit), it creates a specular reflection — the ceiling above, the window, or the light source is visible as a reflection in the floor. This can be a spatial asset or a distraction, depending on the room's light quality and the position of occupants.
In a contemporary residence, we typically specify honed concrete floors at 400 grit — enough to reveal aggregate and produce soft light diffusion without mirror reflectivity. For walls, as-cast is the default unless surface quality requirements make grinding a necessity.
Maintenance Requirements for Each Finish
Both finishes require maintenance, but different types:
As-cast wall concrete: Apply penetrating silane or siloxane sealer after curing. Reapply every 7 to 10 years. Clean with neutral pH cleaner. Avoid acid cleaners (vinegar, tile cleaners) which attack the cement paste. Stains absorbed into unsealed concrete may not be fully removable.
Polished floor concrete: Reapply densifier guard every 2 to 5 years depending on traffic. Clean with pH-neutral floor cleaner. Scratches in the top 1 to 2 mm can be re-polished to remove them — a maintenance operation that wood or stone cannot offer. High-gloss finishes show heel marks and dust more than honed finishes.
The choice between the two finishes should include a maintenance conversation with the client. Polished concrete floors require periodic professional re-polishing in high-traffic areas. As-cast walls require minimal maintenance if sealed correctly at installation.
Próximos pasos
Concrete finish specification is a design development decision, not a finish selection that can be deferred to the end of design. The structural slab or wall designed for grinding has different tolerances and curing requirements than one designed for as-cast exposure.
Conoce el método de MÉTODO — how we approach concrete surface specification and material detail in our residential projects.