How to Remove Hardened Concrete from a Mixer Drum

Hardened concrete in a mixer drum costs payload on every trip, buries the fins that do the mixing, and, left long enough, ends with someone inside the drum swinging a chipping hammer. This guide covers 3 ways to remove hardened concrete from a mixer drum: chipping it out, staying ahead of it with water, and dissolving it so it rinses off. You get the routine for each, a comparison on downtime, labor, and drum wear, and what to order for the build-up you have.

How build-up forms in a mixer drum and what it costs

Every load leaves some concrete on the fins, blades, and shell. If it is not rinsed out before it sets, it cures in place, and the next load sticks to it. Build-up grows in layers, and it gets harder to take off every day it stays.

The cost shows up in 3 places:

• Weight. Cured concrete in the drum rides along on every trip. For example, assume 7 cubic feet of build-up and normal-weight concrete at 150 pounds per cubic foot (both are assumptions for the example, not measurements). At those figures the build-up weighs 1,050 pounds (7 times 150) and is a little more than a quarter of a cubic yard (7 of the 27 cubic feet in a yard). On a truck that loads to its weight limit, that is concrete it cannot deliver.
• Mixing. As the fins are buried, the drum mixes less evenly and discharges more slowly.
• Capacity. A drum lined with hardened concrete holds less than its rated volume.

The signs are easy to track: the empty truck weighs more on the scale than it used to, the drum takes longer to discharge, and the fins look rounded or buried through the hatch.

3 ways to remove hardened concrete from a mixer drum

Many yards combine the 3 routines below.

Chipping it out

Chipping is the fallback when build-up has gotten ahead of everything else. Someone climbs into the drum with a chipping hammer and breaks the deposit off the fins and shell a piece at a time, and the truck stays out of service until the job is done. Chipping works on any thickness of deposit, but it is slow, heavy work, and the hammer does not stop at the concrete: strikes that miss land on the fins and shell.

The acid-free wait-and-rinse routine

The cheapest concrete to remove is concrete that has not cured. A thorough rinse at the end of every load, with the drum turning so water reaches the fins and the head, takes fresh concrete out before it sets. Some yards add a soak while any leftover paste is still fresh, to keep that residue from setting on the steel: fill the drum partway with water, wait, turn the drum, and rinse again. Others charge the drum with coarse aggregate and water and turn it to scour out fresh residue.

These are general practices for concrete that has not cured yet. Once it has, a hose or a wash-bay pressure washer will not take it off the steel, and an aggregate scour at most wears down the thinnest film. This routine keeps a clean drum clean; it does not bring a neglected one back.

The dissolver routine

A concrete dissolver (buyers also call it a cement dissolver) goes onto the cured build-up, stays there until the build-up softens, and the softened material pressure-washes off. Heavy deposits take a repeat application, and the build-up comes off with a rinse instead of a chipping hammer. Slide Off, Slide Off+, and Blaster all work this way; the What to order section below covers which one fits your drums.

How the 3 routines compare:

Routine	Downtime	Labor	Drum wear
Chipping	The truck is out of service for the whole job, and the job grows with the deposit.	Heavy manual work inside the drum, a piece at a time.	Hammer contact on fins, blades, and shell. Missed strikes mark the steel.
Acid-free wait-and-rinse	A rinse after every load, plus a soak or scour cycle while residue is still fresh. Little help once concrete has cured.	Low per load, but only if the rinse happens after every load.	Little from water; an aggregate scour is abrasive by design. Build-up that gets past the rinse keeps growing.
Dissolver routine	Wash-bay time to apply, let it work, and rinse, plus a repeat pass on heavy deposits. No chipping job.	An operator with a sprayer or foamer and a pressure washer, in the PPE the SDS calls for.	No hammer contact. Follow the surface notes: Slide Off and Slide Off+ list steel, painted steel, rubber, and plastics, and Slide Off+ carries corrosion inhibitors; Blaster lists steel and rubber and says to test painted and aluminum surfaces first.

The dissolver routine, step by step

The middle 5 steps, from the PPE to the rinse, follow the product pages and the resources page’s handling notes. Emptying the drum first, rinsing from the top down, and the check before the next load are general wash-bay practice. Read the label and the SDS before use, and wear the PPE the SDS calls for. Have everything at the wash bay before you start: the product, water for mixing if it is a concentrate, a sprayer or foamer, and a pressure washer.

• Empty and rinse the drum. Wash out the loose material first. The dissolver goes on cured build-up; fresh concrete comes out with water.
• Put on the PPE. Slide Off and Slide Off+ call for gloves and eye protection. Blaster calls for acid-rated gloves, eye protection, and a face shield.
• Mix, if the product needs it. Slide Off is used as supplied, no mixing. Slide Off+ and Blaster are diluted 5:1, five parts water to one part concentrate, with the product added to the water, never the reverse. A 55-gallon drum of either makes 330 gallons of use solution.
• Apply it to the build-up. Spray or brush Slide Off or diluted Blaster onto the cured concrete. Put Slide Off+ on with a foamer or sprayer so it clings to vertical and overhead steel, which inside a drum is most of the surface.
• Let it work. Leave it on until the build-up softens and loosens. Do not let Slide Off+ or Blaster dry on the surface.
• Rinse. Pressure-wash the softened material away, working from the top down. Repeat on heavy deposits.
• Check before the next load. Look at the fins and shell through the hatch and treat any deposit that is left, so the next load does not bond to it.

Keeping the drum clean between treatments

The wait-and-rinse routine and the dissolver routine work together. Rinse after every load so the drum only ever carries a thin deposit, and put the dissolver on a schedule instead of waiting for the fins to disappear. The rinse step on all 3 product pages ends with “Repeat on heavy deposits,” so the thinner the build-up when you treat it, the fewer passes it takes. Whether you go by the calendar or by the signs listed at the top of this guide, treat before the deposit needs chipping.

Beyond the drum, all 3 product pages list chutes, hoppers, discharge steel, and concrete pump equipment and hoses; each page lists the product’s other uses. In a precast or block plant, the dissolver does the same job on forms and mixers. For the outside of the truck, Dynamic Green Degreaser is the fleet wash at 40:1 to 50:1, and Phos Clean takes the cement dust and rust stains off the cab; its page says to test first.

What to order

For a drum on a regular cleaning schedule, order Slide Off, an acid-based dissolver that is pre-blended and used as supplied, or Slide Off+, a foaming 5:1 concentrate of acids, surfactants, wetting agents, foaming agents, and corrosion inhibitors whose foam clings to fins, blades, and vertical steel. For a drum that has gone too long between cleanings, start with Blaster, a hydrochloric acid (muriatic acid) concentrate diluted 5:1 and the strongest cement dissolver in the line, then keep the drum clean with Slide Off or Slide Off+. All 3 are in the Concrete category.

Each ships in a 55-gallon drum or a tote: 330 gallons for Slide Off, 275 gallons for Slide Off+ and Blaster. At 5:1, a tote of Slide Off+ or Blaster makes 1,650 gallons of use solution. Drum and tote prices are on the product pages and exclude freight and any applicable taxes; freight is calculated at checkout on the pallet count.

Orders ship from Granite City, Illinois; drums ship 4 to a pallet, and each tote takes a pallet position of its own. A Safety Data Sheet ships with every order, and the technical data sheet is available on request. Tote quantities, standing orders, and fleet programs can be quoted by phone from the Kirkwood sales office.

Not sure which one fits your drums? Fleets and plants can request a free sample of any Slide Off product before the first drum and test it on their own build-up. Tell us what you are cleaning and where it ships, and the Kirkwood sales office will confirm the product and ship the sample with its Safety Data Sheet and use directions. If your drums already carry heavy build-up, call 314-266-4600 and describe it.