How to prime a concrete pump line: grout runs done properly

If you want one habit that prevents more blockages than any other, learn how to prime a concrete pump line properly. A dry line strips the grout out of the first concrete through it — the paste soaks into the pipe wall and the rubber, and by the far end you're pumping bare rock with no lubrication. That's not bad luck. That's a blockage you ordered yourself.

Why the grout run matters

Concrete travels on its paste. The grout run coats the inside of the whole line before the real mix arrives, so the first cube slides instead of scouring. Longer run, more surface to coat, more prime. Old rubber drinks more than new steel. Cold mornings drink more than warm ones. Skimp on any of it and the far end of the line finds out first.

Ways to prime

Wet the line first — water through the run before anything else. Then the grout: order a slurry run on the first agi, use a primer bag if that's your system, or mix your own — cement and water, sloppy, no rock. A short residential run might only need a bag or two mixed wet. A long run around a house and up a level needs proper grout, and more of it than you think. Nobody has ever blocked a line by priming too generously.

Order the grout with the load and it turns up when the concrete does. Rely on she'll-be-right and you're mixing cement in a wheelbarrow at 6:45 while the agi driver watches his drum spin and the builder watches you.

Pump it like you mean it to work

First strokes slow. Watch the gauge, listen to the pump, let the prime walk the run rather than sprint it. This is also peak hose-whip territory — the air ahead of the prime has to come out the end somewhere, so the end hose stays down and the boys stay clear until concrete is flowing clean and solid.

Where the prime goes

Not in the pour. Ever. Prime slurry and the lean first mix have no place in a structural slab, a footing, or anything with an engineer's name on it. The linehand catches it — barrow, bucket, waste spot agreed with the builder before the pour, back on the truck if it has to be. Sort that agreement at setup, not with a barrow overflowing and forty metres of concrete coming behind it.

Restarts are re-primes in disguise

A long wait between loads, a blockage cleared, a line moved and re-joined — the coating you laid down at 6am isn't there any more. Treat the restart with the same respect: slow strokes, eyes on the gauge, everyone off the end hose.

Priming costs you a few dollars of cement and ten minutes. Not priming costs you a blocked line, a cooked load, a filthy builder and an afternoon of bashing clamps. It's the cheapest insurance in the industry. The blokes who wrote the Operators Club field manuals learned that the hard way so you don't have to.