How Can We Prevent Our Masonry From Crumbling?

Badly done pointing job using portland cement.

To prevent spalling, the formation of salts and water penetration, the most important thing is often what you do not do.

Applying a moisture barrier like a non-breathable paint or mastic coating can trap water that causes the formation of salts and accelerates the deterioration. If you must re-point the mortar joints, use a compatible mortar between the joints that allows the stone and brick to expand and contract and that does not block in moisture. Portland Cement rich mortars can be very destructive because they set up very hard and they form salts once the moisture does penetrate. Other preventative measures can be through wall flashing or a wall cap, like a lead clad copper flashing over the top of a parapet to prevent water from penetrating directly down into the wall. Other causes such as movement in the foundation or seismic cracks may require structural repairs.

 Does the Mortar Really Make a Difference?

At Preservation Trades Company we often argue that it is better to use a scientifically designed mortar such as Jahn Restoration mortar, because it will perform better.

Why conduct an expensive mortar analysis and match the original mortar, if the original mortar didn't work very well to begin with? Why not make it work better?

Once, lime mortar was the traditional mortar of choice. But you could build a brick or stone wall only so high before it would have to be left to set and dry. It would take years to build a foundation with lime putty mortar. With natural cement lime one could build faster and cheaper. But natural cement still takes a long time to cure—sometimes as long as one year. And, after World War II there was simply not enough natural cement to build all the buildings and runways. So the switch was made to Portland cement. But Portland cement is fired at a much higher temperature and causes the formation of salts (tricalcium silicates) that cause the stone and brick to spall. Portland cement-rich mortars are what destroy most historic buildings.

Some Portland cement in the mix is fine, as long as the mortar is designed to allow the salts to escape. If it is too hard or too dense, it will spall the surrounding substrate. Jahn Mortar began importing historic mortars from Europe about 20 years ago. Jahn mortar is very good and contains a small amount of Portland cement. Because Portland cement is rich in pozzolan (super dry clay), the mortar hardens and cures correctly. Jahn mortars are scientifically designed mortars that are made to match the substrate. These scientifically designed mortars are used in buildings throughout Europe.

There are good lime putty and mortars on the market, such as those made by historic mason Jimmy Price. However, like the Rosendale natural cement, they must be mixed in the field. We also use Keim (German) stucco and mineral paints. Jahn mortar is always our first choice.

 What Can We Do To Stop The Leaks?

Spalled stone from bad parapet flashing.

Most of our clients call us when a leak develops in the wall. Usually this happens after they have tried to repair it a number of times.

In most cases the water is penetrating at a failed flashing point between a parapet wall and a roof or at some transition point between a roof system and a wall. Also, in most cases, to correct the problem a roofer climbs up on the roof and applies a mastic (tar) sealant to the flashing point. This may stop the leak for a few months or even a few seasons, but once the mastic sealant pulls loose from the stone or brick it forms a funnel. Because it sticks to the metal flashing, it will create a perfect water catching basin and direct it straight into the wall.

In most historic structures the wall has a cavity in the middle. It may be filled with rubble but the water will run down between the inner and outer veneer where it will strike a window header or tie stone that penetrates the wall.

At this point it pools and runs straight to the inside causing the plaster to bubble up and fall off just above the window opening or it will run down the jambs and cause the plaster to fall of at the ends of the sill. When this happens it always looks like the windows are the culprit or the wall above the windows is leaking. Always look first at the roof above the windows. In most cases water runs down hill. Use standard historic methods to repair your flashing. If done correctly it will last for another 50 or even 80 years. Avoid applying any mastic or sealants. They may have been developed by NASA and they may work great in outer space, but we have never once seen them last more then a few short seasons here on Earth. Copper, lead and stainless steel flashings work great if they are installed correctly.

Open and cracked mortar joints can also allow water to penetrate into the walls. Stone absorbs water so, if you have a stone parapet cap, it could absorb water much like a sponge. And then, once it absorbs all it can hold, it pours out into the wall cavity below and runs in at the first place it finds where there is a shelf that penetrates the wall.

 Why Are Our Stones & Bricks Crumbling?

Your brick, stone and mortar have tiny fissures or cracks where water or moisture can penetrate.

In the case of natural stone these tiny cracks can be the result of how the stone is mined, how it lies in the ground and from what level of the mine it is extracted.

The cracks may be the result of the composition of the stone or the way that the stone is formed in the earth. In the case of brick they can be caused by surface erosion, the expansion of the mortar joint and the way that the brick was originally made. One thing you can count on is that sooner or later water will penetrate your brick and stone one way or the other. Once moisture penetrates the stone or brick it can form salts and or freeze. If it freezes it can expand inside the crack and cause the crack to expand.

Once the water or moisture penetrates into the stone or brick it causes the natural salts to form. The salt crystals expand and cause the brick or stone to spall. Salt that form inside the stone or brick is called subflorescence. Once the subflorescence reaches the surface it appears as a white powder or effloresces. This surface salt, which is calcium carbonate, does not taste like salt but it is a form of salt, and it cannot be stopped until you prevent the water or moisture from penetrating into the substrate.

 Why Are Our Stained Glass Windows Bulging?

Stained glass windows are composed of a matrix of lead glass, steel and putty.

The putty surrounds each glass and lead came panel and the putty usually surrounds each individual piece of glass. If your stained glass panels are older than 50 years (and most are), then the putty has most likely dried out and cracked. Once that happens it absorbs moisture and it expands. When the surrounding putty hardens and expands, it put pressure on the glass and causes it to bulge.

Not all bulging is bad. Some stained glass windows tend to bulge slightly when they are installed and they stay that way forever. Others tend to continue to bulge until the pressure cracks the glass and the panel comes out of the frame. When this happens they need to be straightened and set back into the frame. If wire ties and putty have come loose they will need to be replaced. Just because your stained glass windows are bulged and cracked does not mean that they need to have a protective covering installed or that they need to be re-camed or re-leaded. Recaming a stained glass panel is very expensive and, unless the lead is corroded beyond repair, they do not need to be recamed.

 Do We Need A Protective Covering Over Our Stained Glass Windows?

Installing a protective covering is often a false economy. Protective covering can cause more problems then it cures.

Often an unsuspecting property committee can be duped into installing a plastic covering. If there is a threat of vandalism the bullet resistant plastic covering is an easy sell. What most churches need protection from is not vandalism but rather plastic salesmen. Once you agree to install the plastic covering the necessary restoration and maintenance of the windows is usually minimized or completely overlooked.

Over time the plastic coating can become brittle, hazed and clouded.

Once the plastic covering is installed the property committee is often led to believe that everything is taken care of and they do not need to worry about the stained glass windows. A lot of the restoration work that we do now is the direct result of a poorly installed plastic of glass covering that was installed years ago. Usually the plastic is not properly seated and sealed. Plastic expands and contracts a lot more than glass. The perimeter of the plastic covering pulls loose from the sealant and water leaks into the space between the stained glass and the plastic. It runs down onto the sill and causes the wood to rot. Sooner or later the painted wood frame surfaces that are covered by the protective covering need to be repainted. When this happens the covering will need to be removed. Whatever thermal savings you gained by installing a protective covering will be lost when you have to take it down to repaint the wood or steel frames.

The type of covering you choose to use and how it is installed is very important. How it is vented is also important. If it condensates then you will have problems with rusted or rotted frames. If your windows open there may be problems with designing a covering that can be ventilated. If you are concerned about vandalism or thermal heat loss, it is a good idea to look closely at all the alternatives before you install a protective covering.

 How Can We Clean Our Historic Building?

You have to be very careful if you decide to clean your historic building.

High-pressure water and sand blasting with abrasive mediums like baking soda or sand can be very destructive.

Sand can remove the glazed surface from the brick, and baking soda can force salts into the stone that will later cause the stone to spall. Even large amounts of low-pressure water can soak the stone or brick long enough to create destructive salts to form beneath the surface of the stone. Some chemicals can be very destructive to the historic fabric as well as harmful to the environment.

It is a good idea to figure out what is making your building look so grimy and dirty and then test different methods and materials in small areas. We have had a lot of success with architectural biocides when it comes to removing biological growth. We have had a lot of success with a method that uses a gentle micro abrasive vortex with a high volume of air and low-pressure water. Great care must be taken if you plan to clean your building, because it can cause more problems than it solves; however a thick, non- breathable coating of grime from years and years of sulfite deposits can cause the stone or brick to spall.

 How Can We Save Money?

There are several ways that you can save money.

The first and most important thing to do is to understand what is wrong with your historic building and what needs to be done to correct the problem.

If you think the first thing you need to do is hire an architect you may be wrong. If you are building a new building, you definitely need an architect right from the start. If you are restoring an old building, you need a detective. What you want to avoid is the expensive historic condition survey, mortar analysis and any work that does not identify and quantify the activities that may be necessary to correct the problems. Once you have a plan you can call in the specialists and apply their trade where it is needed.

 How Do We Figure Out What Is Wrong & How Do We Fix It?

In most cases an experienced historic restoration contractor can investigate the problems and give you a “not-to-exceed” cost to fix the problem based on the worst-case scenario.

This is the service we provide. If the contractor has never done the work before then why hire him to tell you what it costs? Sometimes we have to simulate the conditions to predict the cost, but we usually come pretty close. The worst thing you can do is to hire an architect to draw up a set of specifications and drawings (that you may or may not need) and put the work out to bid. Taking the low bid or bids from inexperienced contractors can lead to disaster and huge cost overruns.

The worst place to be is stuck with a contractor who has the upper hand because he is already on the job and you have to pay him to do additional work. Your reputable project manager who is experienced in historic restoration should be able to do the discovery work that is necessary to uncover the extent of the problem, He should also be able to tell you what your options are as far as the available historic methods and materials and how much it will cost. And he should be able to tell you what resources are available (craftsmen) and how much they cost per hour. If you know how long it takes to do the work, how much the labor costs and what the materials cost, you should be pretty close to knowing the total cost.

Does It Cost More To Restore It Or Replace it?

Properly done, restoration cost less then replacement.

Often the flashing at the parapets and chimney can be replaced leaving the main roof intact. This costs much less than total replacement and often lasts longer then a new roof with the less substantial composition. We can restore steel casement windows in place for about the same cost as a new aluminum window frame, and it will last much longer than the new aluminum frame.

Dale Waters is a recognized authority on stained glass and masonry restoration. His book, How to Restore and Protect Stained Glass Windows, has been cited by Preservation Forum, which is published by the National Trust for Historic Preservation. Finding plastic to be unreliable for protective coverings when a protective covering is necessary, Waters was the first to return to glass for the protection of stained glass windows. Glass has proven to be the covering of choice by most clients because of its pleasing aesthetic qualities, long life span, easy maintenance and comparative low initial cost.

Waters is a strong proponent of using Jahn restoration mortar—a mortar developed by Cathedral Stone, Inc. — which has virtually revolutionized stone repair and restoration. Dale Waters and Preservation Trades Co. have completed several hundred historic and sacred property restorations, ranging from small rural chapels to massive urban cathedrals.

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