How to Repoint Brick with an Angle Grinder (Step by Step)

Crumbling mortar joints don't fix themselves. Repointing — raking out the old, deteriorated mortar and packing in fresh — is what keeps a brick wall structurally sound and watertight. The good news: with an angle grinder and the right attachment, the hardest part of the job goes from days of chiseling to hours of controlled grinding. Here's the full process, the way masons do it.

What You'll Need

• Angle grinder (4-1/2" or 5", corded or cordless) with a 5/8"-11 spindle
• Carbide mortar rake matched to your joint width (1/4", 5/16", 3/8" or 1/2") — for lime and soft-to-medium cement mortar
• Dust shroud + HEPA vacuum — grinding mortar releases crystalline silica (see safety below)
• Pointing trowel and hawk, jointer, masonry brush, mortar mix matched to the original (type N or O for most older brick; type K/lime mortar for historic walls)
• Safety glasses, P100 respirator, gloves, hearing protection

Step 1: Assess the Joints and the Mortar

Scrape a joint with a screwdriver. If mortar powders out or comes loose in chunks, it's due. Check how deep the deterioration goes — you'll want to remove mortar to a depth of about 2 to 2.5 times the joint width (typically 3/4" to 1"), or until you hit sound mortar.

Match your new mortar to the old. Hard modern mortar (type S) on soft historic brick traps moisture and spalls the brick face. When in doubt on pre-1930 masonry, use a softer lime-based mix.

Step 2: Rake Out the Old Mortar

This is where the mortar rake earns its keep. Thread it onto the grinder spindle (5/8"-11 — no adapter needed on DeWalt, Makita, Milwaukee or Bosch grinders), set the guard and dust shroud, and work the horizontal bed joints first:

• Pick a rake width slightly narrower than the joint, so carbide never touches brick.
• Let the tool's weight do the work — steady passes along the joint, 3/4" to 1" deep.
• Do the short vertical head joints second, grinder braced with both hands.
• Stop at sound mortar. You don't need to hollow out the wall — just reach clean, solid material.

A carbide rake removes lime and soft cement mortar quickly without the blade wander you get from a cutting disc. For very hard Portland-cement joints, a diamond tuck point blade is the better match.

Step 3: Clean the Joints

Vacuum the raked joints, then brush them out. Any dust left in the joint weakens the bond of the new mortar. Lightly mist the joints with water before repointing — dry brick sucks the moisture out of fresh mortar before it can cure.

Step 4: Pack the New Mortar

Mix mortar to a stiff, "snowball" consistency. Load the hawk, press mortar off the trowel edge into the joint in layers of about 1/4", compacting each layer before the next. Fill bed joints first, then head joints — the reverse of how you raked.

Step 5: Tool and Brush the Joints

When the mortar is thumbprint-hard, strike it with the jointer to match the original profile (concave is most common). Once it has stiffened further, sweep diagonally with a dry brush to remove crumbs and blend the new work in. Keep the wall damp for 2–3 days in hot weather so the mortar cures instead of drying out.

Safety: Silica Dust Is the Real Hazard

Grinding mortar produces respirable crystalline silica. For professionals, OSHA's silica rule effectively requires a shrouded grinder with HEPA extraction for this task — and on a DIY job your lungs deserve the same setup. At minimum: dust shroud, HEPA vac, P100 respirator, and never dry-grind indoors without extraction.

Common Mistakes to Avoid

• Using a cutting disc instead of a rake: discs wander and nick the brick arrises. Rakes and tuck point blades are made to stay in the joint.
• Too shallow: a 1/4" skim of new mortar over bad joints fails within a couple of seasons.
• Mortar too hard: stronger is not better — the mortar should always be softer than the brick.
• Repointing in frost or direct summer sun: aim for 40–90°F and shade the fresh work.

The Right Tool for the Job

The PRODIAMANT carbide grout cutter ("Mortar Mole") was built exactly for this: three tungsten carbide edges, a full 1" working depth, four widths from 1/4" to 1/2", and a 5/8"-11 thread that spins onto any standard U.S. angle grinder. It ships from U.S. stock in 24 hours — and if you're doing a whole wall, 5+ wheels are automatically 10% off.

Related guides: How to remove old mortar joints (tuckpointing basics) · Angle grinder safety: 10 rules