Using Crackit: Cracking

When cracks appear

Reaction starts as soon as water hits the powder. Inside a confined hole the mix expands, hardens, and pushes against the walls. Most jobs show first cracks between 3 and 20 hours, depending on temperature. Gaps widen over the following day or two.

How long until you see cracks

The mix begins expanding the moment water is added. Packed into a bore, it swells against the walls and starts splitting the surrounding material. First hairline cracks often show within 45 minutes in warm conditions; cooler rock takes longer.

Material temperature drives the timeline — hotter stone or concrete reacts faster. At around 30°C, expect meaningful cracking in 6–8 hours. In cold weather, allow extra time. Gap width can reach 10–30 mm (⅜″–1⅛″) over several days where free faces allow movement.

Let Crackit work to full depth before prying pieces out — pulling too early reduces the leverage the expansion creates.

While you wait:

1. No tamping or caps needed — leave holes as poured.
2. Cover with tarpaulin if rain is expected before cracks appear.
3. Light surface misting after cracks start can open gaps faster.
4. Only fine cracks showing? Run a little water along the crack line to encourage further expansion.

Slowing the reaction on hot days

Higher temperatures speed everything up. Reaction inhibitor sachets (20 g each, supplied with cartons) can be pre-dissolved in the mixing water before adding powder — this reduces blow-out risk. Use the table below for dosing:

Removing the broken material

When gaps reach roughly 3–5 cm, start secondary breaking with a hand hammer, hydraulic breaker, or excavator ripper. Again — wait for full-depth cracking before forcing pieces apart.

Before you break it apart:

1. Wear safety glasses during all secondary breaking.
2. Crack width can keep growing to 10–30 mm over days — patience pays off on thick sections.