2011 in Review

The WordPress.com stats helper monkeys prepared a 2011 annual report for this blog.

Here’s an excerpt:

A San Francisco cable car holds 60 people. This blog was viewed about 2,600 times in 2011. If it were a cable car, it would take about 43 trips to carry that many people.

Click here to see the complete report.

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Be Inspired…

Take a four minute break and be inspired.  I received this from Chris Locurto’s blog this morning.

 

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Frozen Lime Mortar

Our team last week installed a repointing test panel on a project in St. Louis. Being the first week of December in the Midwest we knew we were taking a chance with the weather. Question: Are we going to have enough time for the mortar to cure before frost set in? We prepared for winter protection and had the wall and working area at 75F during the installation of the hydraulic lime mortar and left the temperature at that level for five hours after installation.

If you have not seen a frozen surface of a newly installed mortar joint well now you have! As it turns out the weather was below freezing for the critical 4 days after our installation and thus the surface of the mortar froze. I have only received images at this point on the condition so my involvement is somewhat limited as to the severity of the problem. The solution to fix frost bitten mortar is to reinstall the material if the damage is justifiably deep and out of the specification requirement for the joint profile finish. We do have an open stipple finish profile which may come to our rescue, but we must be certain the bond between the mortar and stone has not been jeopardized in any way.

Frost damage on a newly repointed wall with hydraulic lime mortar

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Memberships – Associations

Today’s blog focuses on the importance of industry memberships and associations. I have had the benefit of participating in several industry associations over the years and wanted to tell you about the ones that have helped me the most in my career and education. I have been a member of ASTM since 1992 now almost 20 years. I have witnessed the development of new standards and the revisions of older ones. I have made many friendships throughout the years of my involvement and have grown in knowledge on masonry construction and materials.

I was able to assist in the dinner event that marked the 75 year celebration of Committee C12 on Masonry Mortars in Atlanta back in 2008.  I am currently on the review committee for the Yorkdale Award. I am on the Task Group ASTM C12.03.03 for Restoration Mortars that recently published the new standard ASTM C1713 for Historic Mortars. I attend meetings when I can – they are held twice per year in different cities around the country. I am a voting member of ASTM C12, C7, C15, E36, and E07. I would highly recommend your consideration in joining ASTM as a member for $75 per year it is well worth the money and time invested.

Other associations that I have joined over the years have been the Preservation Trades Network (PTN); The Stone Foundation; The Building Limes Forum (BLF); the Construction Specification Institute (CSI); US/ICOMOS; ICRI; and SWRI. Each membership is targeted toward a specific group of people, so you need to know exactly who your audience is and where you want to build contacts and continue your education. Involvement in these organizations have taught me to be open to new ways of looking at problems and solutions in my industry and have assisted me with the understanding that there are many very knowledgeable people out there ready to answer your questions if you are willing to ask.

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Efflorescence of Masonry

Efflorescence on red brick in the spring

Most investigators agree that efflorescence is caused by multiple factors in combination with the climate and environmental conditions. Views, however, on which factors are the major culprits in causing the problem are not understood or agreed upon between most experts. One thing that most all agree is that efflorescence is a soluble alkali salt, usually sodium and potassium sulfates, but expressed as Na2O and K2O equivalents, that exude from masonry as a solution. Upon drying the solution re-crystallizes as a supersaturated solution on the surface of the masonry causing a unsightly white film, coating or scum that can accumulate.

There are temporary and permanent forms of the condition. The temporary form is often called “new building bloom” and is short-lived, but there are permanent forms as well – disappearing as a result of rain only to reappear again and again for many years.  It is this type of permanent efflorescence that can cause damage to masonry buildings by disintegrating mortar and spalling masonry units.

Some causes of efflorescence can be directed to the contractor and his practices at the jobsite.  For instance, if brick or stone is not covered up and become saturated with water prior to installation; failure to protect unfinished walls from rain; unprotected parapet and or lack of proper flashing; lack of adequate drip edges on sills and cornices; leaky temporary gutters and downspouts; poorly filled mortar joints; chronic damp condition at grade where masonry doesn’t have a chance to dry out quickly after construction.

Brick can have varying levels of alkali salt content as well depending on the clay or shale deposit. Clay and shale deposits vary greatly in the amount of these salts. Some brick manufactures may use barium sulfate to reduce the tendency of efflorescence, but this offers no real guarantee. Generally the denser the brick the harder the unit – the less likely the efflorescence factor.

Concrete block may in some cases cause temporary efflorescence when the free lime that is liberated in the hydration of the cement carbonates on the surface of the unit. This type of efflorescence is only temporary and usually will wash off in the first rain.

Mortar materials are made from clay and shale and can also pose the ability to deliver salts to the surfaces of finished masonry walls. Portland cement and masonry cements vary greatly in their raw material make up. Cement is derived from limestone or marl of 70-90% total carbonate content, much of which is argillaceous and earthy. Some cement is made with alkali contents over 1% and in the finished product these salts will approximate these same percentages. These cements when used in conjunction with some of the malpractices previously mentioned can cause serious efflorescence.

Most non-hydraulic limes on the other hand are extremely low in soluble salts as well as sulfur content. To give you an idea, most historical limes used in building construction were made from high-calcium limestone averaging over 97% carbonate content. Total alkali content average of 0.1%. Today, most limes are made from Dolomitic limestone with even less than 0.01%. What’s interesting is that often the lime gets the blame for the efflorescence due to its color when in fact it is 10 times less likely to cause the condition than cement or even hydraulic lime. Hydraulic lime (NHL 2, NHL 3.5 and NHL 5) are still widely produced and used in Europe and some parts of the United States and can have alkali contents usually much higher, approximating cement on an average, since these limes are made from impure, siliceous limestone.

The sand aggregate may contribute to the efflorescence if the sand was not washed or if it was dredged from the areas were there might be contamination of sea water. However, most masonry sands are well-graded and have near zero potential for causing any issues related to efflorescence.

In spite of considerable research into the causes of efflorescence and the ways to eliminate it, or at least minimize its occurrence, many of the research findings are conflicting and controversial. Because there are so many different potential causes that this apparent disagreement is not surprising. Although the occurrence of efflorescence cannot be predicted, it is more prone to appear suddenly, like a “disease” in a dry period during cool weather following a sustained rainy period. It does not rear its ugly head in hot dry summer months due to rapid wetting and drying of masonry walls, but in the northern climates of the United States it is apt to occur most often in late fall or early spring after rainy periods and when evaporation is slow and temperatures are relatively low.

Ref. Boynton, Robert, S.; Gutschick, Kenneth,A., Efflorescence of Masonry, Masonry Mortar Technical Notes #4, National Lime Association, Arlington, Virginia, October 1966, Reprinted June 1990

 

 

 

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Repointing in 1/4″ Lifts

As we continue our learning curve on repointing mortar joints in historic masonry buildings we need to sometimes step back and re-evaluate our recommendations based on experience. One of those areas is the repointing mortar in 1/4″ layers -or lifts, usually three separate lifts in a mortar joint that has been cut out to an inch in overall depth. According to the Preservation Brief 2, “Repointing Mortar Joints in Historic Masonry Buildings”,1998 pp.10-11 states:

Single lifts of mortar for repointing are fine so long as the mortar formulation is correct

“Where existing mortar has been removed to a depth of greater than 1 inch, these deeper areas should be filled first, compacting the new mortar in several layers. The back of the entire joint should be filled successively by applying approximately 1/4 inch of mortar, packing it well into the back corners. This application may extend along the wall for several feet. As soon as the mortar has reached thumb-print hardness, another 1/4 inch layer of mortar – approximately the same thickness – may be applied. Several layers will need to fill the joint flush with the outer surface of the masonry. It is important to allow each layer time to harden before the next layer is applied; most of the mortar shrinkage occurs during the hardening process and layering thus minimizes overall shrinkage.”

I do not agree with the 1/4 inch layering for several reasons. First, I believe the potential for cold joints can occur between layers. Second, the possibility of a mason being able to place his thumb back into a 3/8 inch mortar joint cut one inch in depth is not practical. And, third, I do not believe the process adds any benefit for the long-term durability and performance of the new mortar in exchange for the added cost factor to repoint a building three times as compared to one.  That being said, I understand the PB2 authors point to establish methods to minimize shrinkage cracks as the mortar hardens – which this process likely does – if the mortar formulation is not correct, let me explain.

Our experience has been that most shrinkage cracks occur within the first 16 hrs after placement due to three primary reasons: 1) excess water in the mortar material; 2) the incorrect aggregate gradation in the mixture – generally the sand is not coarse enough for the width of the joint – the wider the joint the courser the particles need to be, or; 3) early evaporation of water from the joint causing a flash-set to occur. While we do specify repointing in lifts if the joint depth is greater than 1-1/4 inches.  In this case, place the mortar in 3/4 inch layers, but this is generally not in every location. In most projects there is the occasional deep pocket or void but this is generally not a typical condition everywhere on the building. If you are getting into areas of two inches or more it time to re-lay the brick.

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The Lime Cycle

Lime has been used for thousands of years for building construction as an ingredient in mortar and plasters and limewash. The conversion process by which the material claims its name is from the lime cycle. It is described in most books as a clock face with the corresponding chemical reactions and changes to limestone that take place as it goes through the various cycles.

The Lime Cycle

At the noon position on the clock face we have limestone [calcium carbonate – CaCO3]. As we move around the clock-face toward the three o’clock position we introduce heat. The heat needed to convert limestone to quicklime [calcium oxide – CaO] is 1,650F.  At that temperature the CO2 is driven off, water is vaporized into a gas at a much earlier stage in the firing process at 212F. From the three o’clock position moving toward the six o’clock position we introduce water to the quicklime.

This converts the quicklime into lime putty while giving off an exothermic reaction causing the water to boil in a process called lime slaking. The lime putty [calcium hydroxide – Ca(OH)2] settles down into a consistency of thick Philadelphia cream cheese before its ready for use. The quicklime naturally takes the amount of water it needs and drains off the rest, so in a sense you over soak the quicklime during slaking and the material finds its natural balance as it settles down into a putty under the water – a process that generally takes 60 to 90 days to complete if left undisturbed.

Moving now from the six o’clock position to the nine o’clock position we introduce sand, and mix the lime mortar or plaster into a cohesive mixture usually in a volumetric ratio of 1 part lime putty to 2.5 parts sand. We end up at the nine o’clock position with our mixture ready for installation.

From the nine o’clock position back to the noon position we introduce water to the walls [by spray misting] in a series of wetting and drying cycles to encourage carbonation.  Carbonation is defined as the process by which lime cures – or converts, back to limestone from which it originated. We suggest a minimum of nine (9) wetting and drying cycles to initiate this process after installation. And that’s it!  That is the process of the Lime Cycle. We take limestone apart using fire, mix it back up with water and sand and we have lime-stone mortar in the end – a very durable long-lasting material.

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The Peter H. Brink Award for Individual Achievement

Pamela Bates received the 2011 the Peter H. Brink Award for Individual Achievement from the National Trust for Historic Preservation – announced in the Preservation Magazine November/December  page 46. I was inspired to read her commitment to the Lowell’s Boat Shop in Massachusetts, the oldest continuously operating boat shop in the country founded in 1793.

Lowell's Boat Shop

Through its different ownerships and threats by big developers – for the prime waterfront property, the building survived after Bates assembled a coalition called Lowell’s Maritime Foundation which purchased the landmark. The nonprofit took ownership in 2007 and has operated Lowell’s ever since.

What I think is most dynamic about the preservation plan is it includes building wooden boats, a well-kept secret, in a working museum setting. People can actually go there and watch boat building in progress.  I believe the best museums are the working museums – full of life, just like the old days when business was booming in the 1700s.

Today, I acknowledge Pamela Bates for her inspiration, patience, and preservation energy. Congratulations Ms. Pamela Bates and to the National Trust for selecting a great candidate for the Peter H. Brink Award for Preservation.  I hope to someday visit this property in the future and hope you will too.

Lowell’s Boat Shop: http://www.lowellsboatshop.com/pages/pressmedia.html

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Mortar Analysis – Limitations

Mortar analysis can be done various ways with several different approaches to identify the original mortar ingredients of a formulation. However, there are limitations and replacement mortar specifications should not be based solely on laboratory analysis. Analysis requires interpretation, and there are important factors which affect the condition and performance of the mortar that cannot be established through laboratory analysis. These may include: the original water content, rate of curing, weather conditions during original construction, the method of mixing and placing the mortar, and the cleanliness and condition of the sand (Pres. Brief 2 pg. 2).

Mortar can be evaluated by simple wet-chemistry of using hydrochloric acid and water to dissolve out the binder components (calcium carbonate) leaving only the sand particles behind. The ratio of binder to sand can be determined by drying the sample first then weighing it before and after the wet-chemistry process. The problem occurs when calcium carbonate is part of the sand component which would give you a false reading of the ratio. There is also x-ray diffraction, and petrographic analysis by microscope, as well as thin-section technology, where small samples of mortar are cut into very thin sections and dies are injected into the sample showing the different components of the mortar. In addition, ASTM C1324 is a test method to determine components of hardened mortar samples.

Sand particle shape from an analysis - Historic Scotland

The most useful information that can come from a laboratory analysis is the identification of the sand by gradation and color. This allows the color and the texture of the mortar to be matched with some accuracy because sand is the largest ingredient by volume.

A simple non-technical evaluation of the masonry units and the mortar can provide information concerning the relative strength and permeability of each-critical factors in selecting the repointing mortar – while visual analysis of the historic mortar compared to the new replacement repointing mortar can be made. It’s important to match the un-weathered portions of the historic mortar in case the building will be cleaned in the future, or cleaning should be taken into account before the sample is matched.

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Repointing – Lime Putty Mortar Placement

Lime putty mortar repointing, ca. 1850 after cement ribbon joints were removed

As I sit and write this blog I realize I am writing about style and approach to a specific task that many of you have been doing for many years. So I will start with this disclaimer – I will share my experiences with you on many successful repointing projects that involved lime putty mortar and most required no washing after wards except an occasional vinegar quick rinse to remove the white film from red brick units. I have made mistakes along the way and worked over the years to attempt to figure out what is the best practice approach to this task of mortar replacement called repointing.

Repointing, unlike tuckpointing, requires the full preparation of the joints to a depth of 2 to 2-1/2 times the width as discussed in yesterdays post. The American version of tuckpointing is only a skim coating of cement-based mortar over the top of existing mortar joints without the removal process (Chicago). The British version of tuckpointing is where a mortar joint is actually made to the same color as the units and a grapevine line is established in the center of the joint and tucked with a different color and mixture of mortar – true tuckpointing. This true tuckpointing is remarkably difficult to learn but in the end it makes brickwork appear straighter and rubble stonework look like it was laid up in ashlar units.

Mixing lime putty mortar is straight forward. You mix the putty into the sand placing the sand in the wheelbarrow first. Create a hole in the sand for the putty and place the putty into the hole and start to twist and knead the material together. What is interesting is that you do not need additional water during the mixing process; there is enough water in the lime putty to give you a good brown-sugar consistency for repointing. If you are laying brick you can add a small amount of water to create a spreadable mortar. A good repointing mortar should not be able to be spread with a trowel, if it is, than you have too much water in the mixture. If this occurs all is not lost, simply set the material aside on a dry sheet of plywood and allow the excess water to run off (be absorbed into the wood) until you get the desired consistency. This may take several days.

Pre-soaking the joints with water prior to mortar placement

Pre-soak the wall with water. Be sure to get the water between the units and back into the existing original mortar joints. I have had projects where the water pre-soaking process never made it back into the joints – the sprayer was held too far away from the wall surface and while the unit faces received water the joints remained dry – especially the tighter joints. To ensure that you are getting the water back into the joints run the sprayers right on the walls and into the joints filling them with water. Allow the water to absorb into the wall materials and become Saturated Surface Dry (SSD) – no standing water to the touch, no drips, no glistening or shining if viewed from an angle – usually takes 8 to 10 minutes depending on the rate of absorption. You are now ready to start placing the mortar material.

It is most important that your repointing tools fit between the masonry units to enable you to compress the mortar back to the original material. If your repointing tools are too wide you will stain the face of the masonry as you attempt to get the material back into the joint and you will not get the necessary compression required for a good job. You may need to alter your tools by using a bench grinder to create thinner repointing tools. Most big box stores only carry 3/8 inch size even though ¼ inch sizes are available. Work from a hawk. If you are right-handed, work from right to left, on a slight angle, leading with the tip of the repointing tool. Overfill the mortar joints past the surface of the masonry units at least ¼ inch. Allow to dry and become thumbprint hard. Scrap away the excess mortar using a margin trowel and follow the contours of the masonry edges if required. Match the mortar joint profile of the original work. Stipple brush finish the joints by beating the faces with a churn brush – opening up the surfaces to expose the aggregate and create a texture that will encourage prompt evaporation of water and rapid carbonation as the mortar cures.

Protect the mortar for the first 24 hours after placement from wind driven rain and direct sunlight. Keep the material moist – spraying the entire wall with water three times per day for the first three days after application. The material carbonates as it goes through wetting and drying cycles – a minimum of at least nine (9) cycles. Do not allow the mortar to dry out too quickly. Repointing into hot or warm masonry units (south elevation) during summer months is not recommended. The masonry units simply will draw out the water from the mortar to quickly as the temperature rises reducing the chances for proper curing and carbonation to take place.

Repointing tools are available at: http://ushg.macusa.net/heritagedetail1.1.php?Current_Name=Restoration%20Pointing%20Iron

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