Repointing and Repairing Grout Lines in Masonry Q&A
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I own one unit in a brick, single story + basement duplex built around 1912. My side was inspected at purchase (1 year 6 mo. ago) and determined to be in good condition. However, there are a few spots that appear to need some mortar repair. I've been told that I could do the tuck-pointing myself. Could you offer some tips? I've also heard that older buildings need a special kind of mortar for tuck-pointing. Can you give me some hints on what this special mortar is and how I can find it?
GC from Denver, Colorado
Tuck-pointing is not exactly the repair you need. Tuck-pointing is a technique using two colors of mortar to give the illusion of a thin grout line in brickwork. One color is carefully matched to the brick and the other is natural (or whatever depending on the aesthetics).
Repointing is the proper term for replacing/repairing the mortar or "grout" between bricks or block. (No problem here... I've goofed up and confused them too!) The basic process involves removing cracked or loose mortar to a depth of at least a half inch, dampen the old work slightly, and press new mortar into the spaces. However, if you want the longest lasting repair, many pros recommend a minimum depth of two times the width of the joint. This minimizes the possibility of the mortar "popping out" of the joint. Soft mortar can be scraped out with a chisel. Hard mortar can be removed with a variety of power tools using small diamond blades, but care must be taken not to damage the brick! Experiment with the tool a bit before starting!
There are special tools you should buy to handle the mortar, such as a hawk and a pointing trowel, that will speed your work and make it easier to do a great looking job. You can even use your fingers in tight spots, though the cement is tough on the hands so I've found wearing nitrile gloves (tougher than latex) offers enough protection!
As far as needing a special mortar, you can use a premixed bagged mortar though "pros" will usually make their own mix. If the original mortar is colored, you can purchase colorant at many home stores. I don't want to rain on anyone's parade, but the premixed products are plenty good for do-it-yourself repair jobs!
It is important to not fill deep joints (1" or more) in one shot to minimize the chance of cracking caused by shrinkage. Apply up to 1/2" thickness, pressing firmly into the joint and allow the mortar to set to firmness (at least few hours), and repeat.
There is some dispute as to whether adding a bonding agent is worthwhile or even desirable. A bonding agent is a chemical that increases the adhesion of the new mortar to the old work plus offers the added benefit of a longer lasting . Though old cement is very hard and nonporous, the mortar will be bonding to the brick primarily, not the old mortar. One downside is that the appearance of the mortar will be somewhat different than untreated mortar. However, these products are unnecessary if you properly repoint the joints, since there is little chance of the new grout failing any more quickly than the original work!
We have a very thorough contributed article that has more information on repairing mortar joints than you'll ever need here:
Hope this is helpful!