Question 1

What is thermal shock in concrete?

Accepted Answer

Thermal shock occurs when concrete is exposed to rapid and extreme temperature changes (e.g., steam cleaning a cold floor or hot industrial spills). The rapid expansion and contraction cause surface crazing, cracking, and delamination. In environments prone to thermal shock (like food processing plants), we use heavy-duty polyurethane (PU) concrete screeds which have a thermal expansion coefficient similar to concrete, allowing them to expand and contract without failing.

Question 2

How deep should concrete cover be over rebar?

Accepted Answer

The 'cover depth' is critical for protecting steel rebar from carbonation and chloride attack. British Standards (BS 8500) typically recommend a minimum cover of 25mm to 50mm, depending on exposure conditions (e.g., marine environments require deeper cover). If the cover is too shallow, environmental agents reach the steel quickly, causing premature corrosion. In repairs, if we cannot achieve the original cover depth, we use specialized coatings or extra-dense repair mortars to provide equivalent protection.

Question 3

What is Alkali-Silica Reaction (ASR)?

Accepted Answer

Often called 'concrete cancer,' Alkali-Silica Reaction (ASR) is a chemical reaction between alkalis in the cement paste and reactive silica found in certain types of aggregate. This reaction produces a gel that swells when it absorbs moisture, exerting tremendous pressure from inside the concrete and causing extensive 'map cracking.' Unlike simple corrosion, ASR affects the concrete matrix itself. While it cannot be reversed, its effects can be managed by limiting moisture ingress using specialized waterproofing and breathability strategies.

Question 4

What is 'laitance' and why remove it?

Accepted Answer

Laitance is a weak, milky layer of cement fines, water and the finest aggregate particles that rises to the surface of fresh concrete. It forms through bleeding — as heavier aggregate settles, mix water carries the lightest cement particles upward — and it is made worse by over-wet mixes, over-troweling, over-vibration and poor finishing. Once the concrete has hardened, that surface layer stays behind as a soft, dusty, porous skin with very little structural strength of its own, only loosely bonded to the sound concrete beneath. That is why it matters so much in repair and waterproofing: if you apply a coating, a resin floor, a tanking slurry or a repair mortar directly over laitance, the new material bonds beautifully to the laitance — and then the laitance peels away from the slab, taking your expensive system with it. It is one of the single most common causes of coating and screed failure. You can often detect laitance by scratching the surface (it powders and dusts), by a change in colour and sheen, or by a simple pull-off test that shears within the surface layer rather than in the substrate. Removing it means mechanical preparation to cut back through the weak skin and expose the sound aggregate beneath: diamond grinding for thin removal on smooth floors, shot blasting (captive abrasive blasting) for larger areas, or scabbling and grit blasting where more aggressive removal is needed. Acid etching is sometimes used on domestic work but is far less reliable and is generally avoided on commercial projects. The goal is a clean, open, sound surface at the right concrete surface profile (CSP) for the system being applied. MPS Concrete Solutions removes laitance by grinding and shot blasting as standard surface preparation before every flooring, coating and waterproofing installation, because the bond to the substrate — not the product itself — is what determines how long the finished system lasts.

Question 5

What is Flowable Micro-concrete?

Accepted Answer

Flowable micro-concrete is a specialized, high-strength repair material designed to be poured or pumped into formwork. It has high fluidity, allowing it to self-compact and fill complex voids or areas around congested reinforcement where traditional hand-applied mortars cannot reach. It is often used for large structural repairs, such as column jacketing or deep deck repairs, providing a finish that matches the original concrete's strength and density.

What is thermal shock in concrete?