Core drilling slurry is concrete fines suspended in water, and it is the part of the job most likely to cause a complaint, a blocked drain or a fine. The volume is small, but handling rules are not optional, and the cheapest plan is decided before the first hole.

How much you are actually making

Hole	Slurry, roughly	Handling
50 mm × 100 mm	1-2 litres	Bucket
100 mm × 200 mm	6-10 litres	Tray
150 mm × 300 mm	20-30 litres	Drum or wet vacuum
200 mm × 400 mm	50-70 litres	Plan disposal before drilling

Containment that works

1. Ring the hole with a putty dam or a vacuum collar so water leaves with the bit, not across the floor.
2. Run a wet vacuum continuously instead of mopping at the end; mopping spreads the fines.
3. For overhead work use a collar plus shroud and a hose to a bucket. It is not optional.
4. Line the tray with a filter bag where local rules require solids separation.

Settle, separate, dispose

Let the bucket stand for a few hours: solids settle and clear water sits on top. Decant the clear water, which in most jurisdictions may go to sanitary sewer with approval but never to storm drains, and put the solids in a skip as construction waste. Never pour slurry into a storm drain, a garden or a watercourse: it sets like weak concrete and it is the fastest route to a fine.

Recycling water

• Settled water can feed the next hole through a pump and filter, halving water use on multi-hole jobs.
• Keep a separate clean container for the final flush so the hole does not finish with fines.
• Clean the vacuum and collar at the end of the day; set slurry in a vacuum means replacement, not cleaning.
• Label containers so the next trade does not tip them into a drain.

Paperwork

The volume math nobody does until the tank overflows

Slurry looks like a small stream and behaves like a large volume. Estimating it before the first hole decides whether you need a bucket, a settling tank or a vacuum truck.

Hole	Concrete removed	Water used	Slurry to handle
50 mm x 150 mm	0.3 l	2-4 l	3-5 l
100 mm x 300 mm	2.4 l	15-25 l	18-28 l
200 mm x 300 mm	9.4 l	40-60 l	50-70 l
300 mm x 400 mm	28 l	90-140 l	120-170 l

The removed concrete is trivial; the water is the problem. A single 200 mm hole can fill a standard wet vacuum twice, which is why containment has to be sized to the hole and not to the hose.

Separation in three stages

• Stage one, at the hole: collar dam and vacuum capture. Everything that leaves the hole is caught before it reaches a floor joint or a lift shaft.
• Stage two, in a settling container: a 100-200 litre drum or a lined skip, where solids drop and clear water rises. Two hours of settling turns a drum of slurry into sludge at the bottom and water on top.
• Stage three, before any drain: a filter bag or a geotextile sock. If the water is still visibly cloudy after settling, it is not ready for a drain.
• Solids go to a skip as controlled waste. Slurry solids set like weak concrete and block drains permanently if they get there.
• Label the containers. An unlabelled drum of grey water on a site will be poured down a drain by someone who does not know better.

The settling container is the cheapest piece of equipment on the job and the one that decides whether disposal is legal. Skips and drums are fine; a hose into the site drain is not, and the fine is usually larger than the whole drilling contract.

Where the water can legally go

Discharge rules vary by jurisdiction, but the logic is consistent: water that has passed through a settling stage and a filter, with pH near neutral and no visible solids, may go to a foul sewer with consent; water with cementitious solids may not go to surface water or storm drainage anywhere.

• Foul sewer discharge usually needs prior consent from the local water authority and a pH check, not just a verbal OK from the site manager.
• Water recycling is viable for coring: settled water can feed the rig again for non-critical cuts, cutting fresh water demand by half.
• Never discharge into a soakaway, ditch, river or storm drain. Cementitious fines set in the pipe and the pollution is traced back to the site.
• Keep the discharge record: volume, date, destination and consent reference. That is what an inspector asks for.

What the client actually sees

Slurry handling is judged by what is visible at the end of the day, not by the method statement. Four things on site decide whether the job reads as professional or as a mess that will not be repeated.

• A dry, clean working area: the drill zone is wiped and the hose is stored, not trailing across a finished floor.
• No stains on adjacent surfaces: a ring on a wall or a mark across a threshold costs more to remove than the slurry cost to collect.
• Contained drums, labelled and sealed: an open drum of grey water in a car park is the image the client remembers.
• A written disposal record: destination, volume and date, handed over with the close-out. It is what lets a facilities manager sign without checking.

None of this is heavy equipment. It is one drum with a lid, one hose that gets wound up, and one line in the handover document — the three things most often missing when slurry becomes a complaint.

Ask the site manager where slurry is allowed before you start, write it into the method statement, and photograph the containment. Where the site runs waste transfer notes, put slurry solids on them. Asking costs nothing and is the only defence when a drain blocks three floors down.