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Re: tuckpointing

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Neil:
 
I would recommend the following, based on NJ/PA experience (that's a big qualifier in itself):
 
Stucco - get rid of it
Mortar - follow Nels excellent suggestions and refer to the website he already gave. As far as brick "dust" goes, my standard solution is to repoint with a soft mortar and leave the "dust" in place. Typically, this is sand. If it is confined, in my opinion it has plenty of strength, so the pointing is to ensure confinement. Of course, seismic resistance is nil.
 
As far as FRP for lateral resistance, if this is for wind, the brick should be able to accommodate it. If for seismic I would recommend a separate structural system.
 
Hope you (and everyone on the list) had a great fourth.
 
Regards,
 
----- Original Message -----
From: Neil Moore
Sent: Wednesday, July 05, 2006 10:54 PM
Subject: RE: tuckpointing

Nels:

The discussion of old brick buildings is very timely for us.   We are presently rehabilitating an 1853 brick building that has undergone severe differential settlement.  (The front of the building was founded over an old creek bed with the remainder of the building on rock)  In 1932, there was a major reconstruction of the distressed area, but the settlement continued.   Sometime in the last 20 years, someone installed a stucco coating on the exterior walls.   Parts of this has cracked and/or crazed, indicating that the settlement will go on forever if we don't fix THAT problem.   Apparently this was to seal the walls.
 
But upon removing some wood paneling in the interior, we found copious brick dust, like maybe the brick termites were at work.   We also found some wetness to the brick as well as whole bricks missing in the 16" wall.   The grout appears to be somewhat soft which from reading Nels' reference, maybe a good thing.
 
The building's brick foundation goes down about five to six feet to good material, but the interior is rubble fill with the water table sometimes at the surface.   In 1932, a contractor installed a 6" unreinforced concrete foundation wall inside the existing brick foundation wall.  This "new" wall only supports the 1st floor joists.
 
The owner is anxious to complete the project, but I don't know what to do about the ugly stucco at this point.  We've been discussing using FRP on each side of the walls to take out of plane loads.  (2001 CBC) 

Neil Moore, SE, SECB
neil moore and associates
shingle springs, california


distressed structures investigations





At 03:19 PM 7/5/2006, Nels Roselund wrote:
Bruce,
 
The purpose of tuckpointing is to restore the masonry to its condition when it was built by removing deteriorated mortar and replacing it with new mortar packed into head and bed joints.  Tuckpointing can?t make it better than new.  Tensile strength should be ignored; pointing won?t improve or worsen it ? it is zero.  Compressive strength is the important property of old masonry [it is good at carrying gravity loads], and tuck pointing may be counted on to restore it.  Shear strength was generally ample if the building was not built in earthquake country, and pointing will restore it.  Unreinforced masonry structures that are hundreds ? even thousands ? of years old are still standing and in use; to continue, they require only regular periodic observation, maintenance and repair [mainly repointing of deteriorated mortar joints, maybe 2 or 3 times per century].
 
To someone unfamiliar with old URM buildings, and used to modern masonry, almost any old mortar will seem to be in very poor condition, soft enough to be eroded from the joints with a finger ? but it is probably O.K..  Except for damage caused by periodic wetting and drying, mortar is nearly inert and undamaged by the passage of time.  To determine the quality of mortar to be matched by the tuckpointing mortar, match what you find in the joints in a protected location [under a roof or eaves, or near a reentrant corner.  Expect to find that It is unlike modern mortar; it is usually much softer than the masonry units.  Resist the urge to replace old mortar with a harder material.  With passage of time, after pointing with a modern mortar, changes of temperature and atmospheric humidity will slowly lead to damage to the old bricks by the hard modern mortar.
 
A good guide for tuck pointing is Preservation Briefs 2, Repointing Mortar Joints in Historic Masonry Buildings from http://www.cr.nps.gov/hps/tps/briefs/brief02.htm
 
Nels Roselund
, SE
South San Gabriel, CA
njineer(--nospam--at)att.net

From:
Bruce Holcomb [ mailto:bholcomb(--nospam--at)brpae.com]
Sent: Wednesday, July 05, 2006 1:30 PM
To: seaint(--nospam--at)seaint.org
Subject: tuckpointing
 
How does tuckpointing affect mortar tensile, compressive and shear strengths?  This is for 3-wythe brick walls in two separate buildings? one is about 80 years old, the other is 120 years old.  Any thoughts on mortar tensile, compressive and shear strength of these old buildings?
 
 
Bruce D. Holcomb, PE, SE
Butler, Rosenbury & Partners
www.brpae.com