Anchor Hole Cleaning

Why anchor holes need cleaning

Drilling a hole in concrete or masonry leaves dust packed against its walls and in the bottom. A chemical anchor holds by the resin bonding to the wall of the hole, so dust left behind sits between the resin and the concrete. Hobson's article on concrete anchoring lists chemical anchors as sensitive to poor hole cleaning; spin-in capsules are less sensitive because the resin mixes with the remaining dust.

Hobson's chemical stud and internal thread anchor data sheets say to clean the hole following the chemical maker's instructions and, as a minimum, to follow the AEFAC (Australian Engineered Fasteners and Anchors Council) certified installer method. Each XCHEM PRO resin data sheet shows its own cleaning sequence, and a chemical anchor only reaches the values in its ETA or data sheet when it is installed that way. Hobson's steps for mechanical anchors, such as drop-in anchors, also start with blowing the dust out of the hole.

Blow, brush, blow: the hole cleaning method

The AEFAC certified installer method, as set out on Hobson's chemical stud and internal thread anchor data sheets, is the minimum for those anchors. The XCHEM PRO resin sheets show their own steps, with compressed air and a drill-driven brush, and refer you to the ETA for full installation (see the table below). The stud sheet minimum is:

1. Blow the hole out from the bottom, 3 times, with a hand pump (holes up to 20mm diameter) or compressed air at 6 bar or more.
2. Brush the hole from the bottom, 3 times, with the correct wire brush (brush diameter at least the hole diameter), turning the brush as you pull it out.
3. Blow the hole out from the bottom again, 3 times, with the hand pump or compressed air.
4. Then inject the resin and set the stud or rod as the resin maker's instructions say.

Which brush for which hole and anchor

Mungo labels its brushes with two numbers: the hole diameter, then the brush diameter. Mungo's MIT-SP data sheet pairs a 10mm hole with a 12mm brush (article 1690040, our 10 / 12) and a 16mm sleeve hole with an 18mm brush (1690043, our 16 / 18). The MIT-BS-H1 and MIT-BN-H1 hand brushes give a range of holes before the slash, for example 14-18 / 20 for 14 to 18mm holes with a 20mm brush.

The brush diameter for each anchor is on its data sheet. The table below takes it from Hobson's chemical stud anchor sheet (260605DS, which also covers the long rod kits), the internal thread anchor sheets and the Mungo MIT-SP sheet, and matches it to the Mungo brushes with that brush diameter. For the M20 internal thread anchor (34mm hole) the sheet gives a 36mm brush; the nearest in the range is 35 / 37, so check with us.

The HEC steel power brushes (10 to 24) and nylon hand brushes (8, 10 and 22) are labelled with one number. Hobson publishes no data sheet saying whether it is the hole or the brush diameter, so check the brush against the brush size on your anchor's or resin's data sheet; the brush must be at least as wide as the hole. The anchor sheets call for a wire brush, so treat the nylon brushes as the exception (see steel or nylon below).

For the M12 internal thread anchor (22mm hole) the sheet asks for a 26mm brush, so the table points to the Mungo 24 / 26 brush even though Mungo labels it for a 24mm hole.

Hole cleaning brushes and tools we carry

Every brush, adaptor, extension and blow-out tool on this page. Mungo brush sizes are hole / brush diameter; HEC sizes are as Hobson labels them.

Hand pump or compressed air?

Hobson's chemical stud and internal thread anchor sheets allow a hand pump for holes up to 20mm diameter as the AEFAC minimum. For larger holes they call for compressed air at a minimum of 6 bar. The XCHEM PRO resin sheets show compressed air (an air blow gun), so where you use one of those resins follow its sheet and ETA. Always blow from the bottom of the hole so the dust comes out rather than being pushed around.

The HEC blow-out pump holds 840ml. The Mungo MIT-AP-D1 is a metal compressed air blow-out tool with a 1/4 inch internal thread for the air line fitting, for holes too big for a hand pump or for a lot of holes.

Power brushes, SDS-plus adaptors and extensions

Power brushes fit a drill through an SDS-plus brush adaptor, and a 300mm brush extension adds reach when the hole is deeper than the brush. Hobson lists both the HEC and the Mungo adaptors and extensions in size M6; use the adaptor and extension of the same brand as the brushes. On the stud sheets' AEFAC minimum, a hand or power brush both work the same way: from the bottom of the hole, 3 passes, with a brush at least as wide as the hole. The XCHEM PRO resin sheets show the brush driven by a drill, so with those resins use a power brush and follow the sheet and its ETA.

Steel or nylon brush?

Hobson's chemical stud and internal thread anchor sheets call for a wire brush, and the Mungo MIT-SP sheet lists steel brushes for its installation data. Use a steel brush unless the resin or anchor maker's instructions name a nylon one. Mungo also makes a nylon hand brush (MIT-BN-H1, 10-16 / 20) and a steel and nylon RB-H brush in 28, and HEC makes nylon hand brushes with a wooden handle.

Anchor hole cleaning gear in Adelaide

Allmat supplies hole cleaning brushes, blow-out pumps, chemical anchor resin, studs, guns and nozzles to builders, concreters and steel fixers across Adelaide and South Australia. Add the brushes to a quote with the resin and studs, and we will price the lot.

Questions