Brick and Mortar

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Brick and Mortar

Mortar
Repairs
References

Historic brick—17th–19th century

♦  Softer brick that needs to breath
♦  Necessitates softer mortar
♦  Many variations

Modern brick—mid-20th century

♦  Harder brick that does not need to breathe as much
♦  Harder mortar is more acceptable

Mortar

Definition—material that distributes the load of the brick or masonry, functions as “an expansion joint and vapor membrane around masonry blocks or brick. The mortar must be weaker and more permeable than brick.”1

Replacement/repair of mortar

  • ♦  Matching the ingredients in the original mortar can avoid further damage to the bricks.
  • ♦  Laboratory testing can determine original mortar ingredients.
    • ◊  Samples can be mailed to two companies outside of Virginia.
      • −  Be cautious of any lab results – lime or oyster shells that are used as an aggregate in Fredericksburg, will be dissolved by testing process and assumed to be a binder. Leading to a whiter lime mortar.
    • ◊  Matched on-site by Eurotech (see link below).
  • ♦  Common ingredients in historic mortar
    • ◊  Lime
    • ◊  Aggregate:
        • −  Sand (various kinds)
        • −  Oyster shells
    • ◊  Small amounts of brick dust (hydraulic properties)

Do not use Portland cement on historic brick

  • ♦  Too strong, it will not allow the brick to expand.
  • ♦  Spalling will occur (when the face of the brick pops off) and eventually deteriorate the brick.
  • ♦  Forces moisture to move through brick (rather than the mortar).
  • ♦  Mortar, on historic brick, needs to expand and contract; Portland cement does not allow that to happen.

“A basic principle of historic masonry is that mortar must always be softer than the units it touches.” 2

Color matching of mortar. An experienced mason who is familiar with historic brick will be able to create a close color match.

  • ♦  This color can also be affected by the ingredients (e.g., sand, brick dust).

Repairs

Fix the cause of the problem not just the symptom.

  • ♦  Water running over from a gutter? Causing damage at gutter as well as splash back on ground below?
  • ♦  Leaks in downspouts?
  • ♦  Splash back from a road or sidewalk (or gutter located above)?
  • ♦  Rising damp from poor drainage under the building?
  • ♦  How is water getting away from the building?
    • ◊  Downspouts
    • ◊  Sump pump drainage
  • ♦  All surfaces within six feet of the foundation should be sloped away from house at least a ¼” per foot.
  • ♦  Are gutters properly sloped?

Address these problems as well or you will find yourself redoing the repairs soon.

Replacement of mortar:

  • ♦  Facing mortar is not meant to last 100s of years—brick is.
  • ♦  If removing the remaining mortar, it must be done very carefully.
    • ◊  Mechanical methods in unskilled hands can result in damage to historic brick.
    • ◊  Angle grinders and saws should be avoided.
  • ♦  Is the mortar neatly placed and not sloppily spread over the joint?
  • ♦  A variety of mortar finishes or strikes can be applied. Flush, weathered, etc. Discuss this with your mason before starting the project.
  • ♦  What does the joint look like now?

Brick sealants:

  • ♦  A non-breathable sealant is not appropriate for historic brick, it needs to expand and contract as a part of its function in your house’s system.
  • ♦  Even a 100-percent breathable water repellent option is not necessary if restorations are done correctly.
  • ♦  Be wary of salesmen that offer a “sealant” and assume it is the best thing for your historic home.
    • ◊  Your house is unique. Historic brick does not function the same way as modern brick.
  • ♦  Not all brick surfaces need a sealant of any type, and it should be carefully considered before applying. (See Preservation Brief #1 below.)
  • ♦  Sealants can cause moisture to travel up walls, could cause rotting of joists.
  • ♦  If your brick has been sandblasted previously, it will need special consideration.
    • ◊  Consult an experienced building preservationist.

Other brick coatings:

  • ♦  Not all brick was intended to be exposed. Often softer historic brick had a lime-based whitewash to protect it. By removing this whitewash, you are exposing a weaker surface to the elements.
  • ♦  Painting brick—Painting brick, much like the use of clear sealants, can inhibit the natural expansion and contraction process of the brick. Paint also conceals problems that may exist underneath. Cracks, rising damp, moisture issues can all be concealed by a painted exterior.

Never sandblast!

  • ♦  The Secretary of Interior Standards calls for non-abrasive methods to remove paint from brick. Sandblasting and abrasive methods removes the protective coating on bricks from when they are originally fired. Once this coating is gone, they are much more susceptible to environmental factors and degrade much faster.
  • ♦  To avoid any potential damage with paint removal, allow paint to fail naturally and use a colored limewash to fill in the gaps until it has all been removed.

References

NPS Preservation Brief 1 – Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings by Robert C. Mack, FAIA, and Anne E. Grimmer
https://www.nps.gov/tps/how-to-preserve/briefs/1-cleaning-water-repellent.htm

NPS Preservation Brief  2—Repointing Mortar Joints in Historic Masonry Buildings by Robert C. Mack, FAIA, and John P. Speweik
http://www.nps.gov/tps/how-to-preserve/briefs/2-repoint-mortar-joints.htm

See also Brief 6—Abrasive Cleaners, 15—Concrete, 38—Graffiti, 42—Cast Stone
http://www.nps.gov/tps/how-to-preserve/briefs.htm

Preservation Brief 6—Dangers of Abrasive Cleaning to Historic Buildings by Anne E. Grimmer
http://www.nps.gov/tps/how-to-preserve/briefs/6-dangers-abrasive-cleaning.htm

NPS Preservation Brief 39—Controlling Unwanted Moisture in Historic Buildings by Sharon C. Park, AIA
http://www.nps.gov/tps/how-to-preserve/briefs/39-control-unwanted-moisture.htm

Striking and Pointing Brickwork—DIYData.com
http://www.diydata.com/techniques/brickwork/pointing/pointing.php

Eurotech—Historic Masonry Restoration Information
http://eurotechusops.com/historic-masonry-restoration/

1 Excerpt from, Repairing & Maintaining Historic Brick in the Butte Area, Alex Brown & Kelly Speer.

2 Quote from, A Handbook and Resource Guide for Owners of Virginia’s Historic Houses, Camille Agricola Bowman, Virginia Department of Historic Resources