Historic Masonry Re-pointing: Repair or Ruination?

Specific Inspection Topics Exterior Inspections
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Far too often, as I inspect a home, I must endure the agony of watching a well meaning but ignorant mason destroy old historic masonry. Richmond, Virginia has thousands of beautiful solid masonry row houses with ornate brickwork. Many of these lovely buildings are in desperate need of re-pointing, but if I had my way no one would be able to lay a tool to them without a clear understanding of what to do and how to do it. Not only does an improper job look horrifying, but it actually accelerates future deterioration! That changes the event from a cosmetic pity to a catastrophe.

There are many things that can be done in a number of ways, but there is truly only one way to re-point old masonry. If you know a mason, be sure that he receives a copy of this article for the sake of every colonial mason that ever “raised the cotton”.

Rule # 1: Match the existing mortar color. That makes sense, but so few masons actually do it. It seems there are those that could care less and use gray mortar and those that care a bit and use Riverton C-81 (an off the shelf wheat colored mortar).

Have the sand delivered to the job ahead of time. Ship a coffee can of that sand along with several samples of the mortar to be matched to Riverton Corp1111 Riverton Rd. Front Royal, VA 22630 or call 800-558-8887to make arrangements. Riverton produces over 800 colors of masonry and their lab will bag and ship the exact mix needed to match your project.

Rule # 2: Remove enough old mortar to guarantee the new work will stay. A thin layer of new mortar will break loose in a season or two due to freeze and thaw action.

Rule # 3: Moisten your work area. Cement curing is intended to be a chemical process and not an evaporative or absorption process. If you apply wet mortar to a bone dry and thirsty surface, the water will be drawn from the mortar far too quickly which weakens the mortar and compromises the bond between mortar and brick. I used to literally soak tomorrow’s work area before I called it a day.

Rule # 4: Don’t make your mortar too soupy. Wet mortar applied to a damp surface makes for a smeared mess. Believe it or not, I used to actually mix my mortar to the consistency of stone mortar which when carefully applied to a damp surface worked and tooled perfectly. Mix your mortar to a consistency that only clumps when squeezed. This consistency actually is less likely to give up its moisture through absorption of dry adjacent materials.

Rule # 5: Don’t return the mortar joint to the front face of the brick! There are both cosmetic and technical reasons for not doing this and we will cover them both.

Over time the face edges of a brick wear and round. If you point to the surface of the face of the brick the mortar joint will appear to be twice its original thickness. Nothing looks worse than a fat mortar joint.

More importantly, if you bring the mortar out to the face of the brick, the new cement laden mortar will act as a dam trapping moisture in the lower portion of the brick which will accelerate spalling caused by seasonal freeze and thaw. This is also why it is so critical to match your materials softness. If the brick is soft and porous you must do your best to make the mortar equally soft and porous to promote drying and avoid future spalling.

So then, how should we form the new joint? Use a trowel and “tuck pointer” of “slicker” and push the mortar into the joint only to the beginning taper of the weathered edge of the brick. Now, strike or tool the joint with the “tuck pointer” or “slicker”. This process takes considerably more time which needs to be taken into account when pricing a large project. But, to do otherwise is bordering on criminal. The damage is irreparable and permanent.

Rule # 6: Brush the work with a genuine horse hair brush. You must brush the work because this also, like the tooling, brings cement to the surface to form a nice weather seal. Genuine hair is soft and won’t drag out material.

Rule # 7: Cure your work. I can’t emphasize this step enough. You’ve just applied damp mortar to a system that has been in place and practically bone dry for decades. As stated earlier, cement is supposed to cure chemically over a period of approximately and ideally 28 days. As soon as your work is set, keep it wet for days if at all possible.

Rule # 8: Avoid harsh chemical cleaners. If a mason is careful and uses the stone consistency mortar process he can avoid the need to clean the masonry all together. If cleaning is necessary use the mildest product available and designed for your specific application.

If a mason follows these steps he will preserve the beauty and life of old masonry for generations to come. Also, he will begin to receive telephone calls from historical societies across the country. I did and it didn’t take very long. My first proper point up project was in a sleepy little town in the foothills of the Appalachian Mountains called Bluemont, Virginia. Within weeks I received calls from historical societies regarding work in Georgetown (Washington, DC) and Baltimore, Maryland. I have no idea how either of those people found me.

Michael G. Bryan
President
MGB Inspection Service, Inc
MGB Publications, Inc.
Founder www.inpsectorsreference.com

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Hi to all,

Michael, thanks, very interesting article.

A couple of years ago I went out to a small presentation at one of New Hampshires historic buildings that was undergoing restoration.

The guest speaker for the evening was a master mason from the area who specialises in restoration, I gotta tell you he was fascinating, he requently re-grinds old mortar to mix into new mortar, with old mortars containg fiber materials such as straw and cow dung! he also went through the various mixes and their uses, and the importance of getting replacement mortars of the correct strength based on the brick/block/or stone being used.

For those interested in old buildings he hasdone much of the masonry work at this historic site:

http://www.strawberybanke.org/

Regards

Gerry

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I have read that old mortar was much softer and allowed for expansion and contraction of bricks. From what I gather softer mortar (less lime) is better in historical brick work. Any thoughts on that?

Thanks.

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Actually, lime mortar behaves as a coagulant. It will crack and break lose just like any mortar. The beauty of lime mortar is that it is “self healing” (The poper term for this phenomenon is “Autogenous healing”). Over time the lime will migrate with water and refill cracks. It is a similar process to stalactite and stelagmite formulation.

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Michael,
Great post. I love the old houses and there are a great many in Pensacola. This was at the turn of the century a hugh lumber producing town and many of the old homes are still standing today and in use. Many are used as offices for lawyers, interior designers and other professionals but a good many are still residences and kept to their original glory. I have inspected homes over 100 years old with the original cypress siding and still in pristene condition with the usual weathering but as hard as iron. The one thing I run into a lot is the mortar was at times made with beach sand because it was and is so plentiful. You can rub it out of the joints with your finger. I appreciate your post as it appears to defy conventional wisdom on restoring original brickwork. I have several books on renovation and restoration work and most refer to cleaning the brick with muratic acid prior to beginning the work or restoring and even so far as saying to avoid any moisture on the brick prior to repointing. I am asked all the time why the concrete slabs around here always crack shortly after they are poured. My standard response is that the ground was not properly prepped. It is as dry as a chip and they pour the concrete and move on. I can remember when I was a kid the old timers would wet the ground for a couple of days prior to pouring and then use burlap sack soaked in water to keep the concrete wet to properly cure. Those old slabs are still around today without a single crack and as smooth as glass.

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Doug, did you know that in the old days many smart builders used to actually practice a water cure or earth cure process with concrete. That is, they would literally submerge or bury concrete to slow the cure. Concrete is pretty interesting. Under ideal conditions, it should take approx 28 days to reach a 90% cure and 100 years to reach a full cure. In other words, the half llife of perfect concrete would be approximately 100 years.

Poured or formed concrete should be kept wet for as long as possible to reduce dramatic shrinkage cracks.

Again, most of the cracks we see in chimney caps are from improperly cured mortar. You can’t heap up mortar like that and expect it to not crack if you don’t properly cure it.

http://www.geocities.com/samshank/curing.html