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Archive for Monday, August 24, 2009

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Make it a point to repoint mortar joints

August 24, 2009

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If the mortar on your wall, chimney or patio is cracked and crumbling away, it is time to grab a trowel, mix up some mortar and re-point your way into a rewarding home repair project.

Step 1: Use a cold chisel and a hammer to clean out the mortar joint to be repaired. Place the chisel next to the brick or stone and angle it toward the center of the joint before striking it with the hammer. Clear the area to a depth at least twice that of the mortar joint width. Brush away any loose material before proceeding.

Step 2: Mix clean drinkable water into the dry mortar mix. Never use chemical additives when mixing mortar for re-pointing. Mix mortar in small batches, mixing only what you can use in a half-hour. Finished mortar should be a butterlike consistency that smooths nicely when the bottom of a trowel is run over it. For most projects, a premixed type N mortar, typically one part Portland cement, one part hydrated lime and six parts sand, will work fine. Unfortunately, using a cement based mortar on older structures will cause irreparable damage. If the structure is more than 75 years old, consult a preservation specialist to determine the correct mortar mixture.

Step 3: Mist the brick or stone area to be re-pointed. Place a lump of prepared mortar on a plastering hawk or on the bottom of a flat trowel. Use the edge of the hawk or trowel to protect the brick or stone edge as you carefully press a thin layer of mortar into the joint using a narrow tuck-pointing trowel. Fill the joint with one quarter-inch of mortar at a time. Press it firmly into the joint and mist the area as needed to keep it moist but not wet.

Step 4: Once the joint is filled, flush with the brick or stone surface, allowing it to set until a print is formed when you press your thumb into the mortar. This process may take anywhere from 30 minutes to 24 hours.

Step 5: When the mortar is thumbprint firm, use a jointing tool or dowel rod to rub the surface to smooth a shine. Lightly brush the surface with a stiff bristle brush to give the new mortar a weathered look.

Step 6: Wipe away any excess mortar from the brick or stone area and clean your tools immediately with cold water. Keep the mortar joints moist for at least a day to facilitate curing and reduce shrinking.

When the mortar is completely set, use a mixture of muriatic acid and water along with a stiff bristle brush to clean away any remaining mortar residue from the face of the brick or stone.

Comments

Darin Wade 4 years, 6 months ago

whats wrong is that there is too much pressure of air in the house during the winter hot and cold combines and causes the mortar to crack..

the problem is unbalanced air pressure associated with

temputure fluxuation.

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tbaker 4 years, 7 months ago

I read your post and really appreciate the time you took to prepare it. It's thorough, succinct, helpful and timely with winter coming on. Thank you.

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