Q: What is the correct method for total repointing?
A: Correct total repointing requires removing the joint to a depth of approximately 2-1/2 times its width and then using a compatible mortar in relation to the final p.s.i. and both the liquid and vapor transmission rate as that of the remaining joint and brick. High lime content pointing mortar is compatible with the soft and absorptive nature of historic brick which rely on their “fired skin” to protect themselves and the building from rain intrusion. If high concentrations of Portland cement were in the repointing mortar instead of lime, when moisture in the brick were to expand and contract during freeze/thaw cycles, often the unyielding mortar forces the softer face of the brick to exfoliate thus leaving a vulnerable unburned “salmon” center of the brick exposed to the elements.
Blocks from the World Trade Center Memorial and the construction site of the new World Trade Center sits a half acre patch grass dedicated to raising awareness of the Great Irish Famine. This memorial was under construction on September 11, 2001 when the Twin Towers fell. The memorial saved that day, simply because of the direction the wind was blowing. The plume of dust blew from 1 World Trade Center in just a way that it didn’t touch a single stone, all of which were donated from each county throughout Ireland. Even a 19th century cottage was disassembled in the County of Mayo and re-laid in Manhattan using a lime mortar that was determined to most closely match that of the original. The memorial was dedicated in 2002 by former New York mayor Ed Koch.
A team from LimeWorks.us recently visited the site and put together a collection of images seen below. The names carved in the stones represent the counties of Ireland. St. Astier Natural Hydraulic Lime was used throughout the memorial walls and cottage, supplied by LimeWorks.us. The structure has been holding up very well and we are very proud to have been part of this important piece of built heritage.
Bricks can hollow back quite profusely in some cases. What are some of the causes?
Don’t forget vermin. Accelerated wetting and drying cycles near the bottom of the brick building cause an increase in the decay of the soft bricks. However, where there is water and calcium rich lime mortar there can be ants and bugs nesting in and behind the wythe. Masonry Bees are found in some parts of the country and will burrow. Sparrows and Starlings will take the calcium bits from lime mortar and like a cuttle bone use the grains for digestion. Some very deep holes in the brickwork are from wood peckers who sense the presence of the bugs and they hone in on certain areas in an attempt to get to them. Here’s one example that may have been caused by a combination of water and animals.
When people talk about “green” construction, I often wonder what the environmental benefit of the construction is. Is it new construction? If so what is the environmental impact? I would hope that a perfectly good existing building wasn’t torn down to make way for supposed progress.
It is my belief that the greenest building is the one that is already standing and most likely played a role in a community’s development. It could be an old department store, manufacturing warehouse or barn. Sometimes plans call for only the façade of a building to be saved which helps keep the architectural integrity of a community intact. This can be a positive compromise because the more useful modernized building can be built and yet some historic fabric is retained to tell the story and retain the flavor of what the building was in its local context.
In the end, as long as something is retained for adaptive reuse, whether it is for aesthetics or the entire structure, there is a measure of success in reducing a “green” construction project’s carbon footprint.
In most instances, a building that has been saved from the wrecking ball is old. What does old really mean? Well that’s pretty subjective but I would like to think of old in the context of US building history as being pre 1930, or roughly 80 years and older. When an old building is going to be adaptively reused one way or another then appropriate materials should be used to fix what is broken with compatible repair materials. Using in-kind repairs will further promote the legacy and overall usefulness of a building for years to come while lowering its impact on the environment.
Old buildings are usually very strong and often made of brick and stone that has proven to stand the test of time. However it’s the mortar that binds those materials together and meant to be sacrificial. Mortar should fail first not irreplaceable historic masonry units. The embodied energy to replace a masonry unit is much greater than the mortar. Therefore, it is imperative that a suitable replacement mortar be used to mend what is failing and the mortar be weaker and slightly more permeable than the surrounding masonry units.
In the case of masonry mortar, lime is typically the binder in these old buildings and should be regarded as key to the dynamic that has allowed the building to be in service so long. Often the original mortar is still in place, proving its superiority and therefore should be replaced in-kind. The use of modern day Portland cement based mortars, which are stronger and denser when placed over the top of lime based mortars, are less sympathetic to the historic masonry and can trap moisture causing further damage to the historic fabric. The historic masonry units and adjacent historic elements can best be kept in conservation with the use of the right lime mortar. The correct Natural Hydraulic Lime (NHL) mortars when used where they are appropriate can become a compatible repair materials that is sympathetic to the working dynamics of an historic masonry building. Secondly, NHL mortars remain reversible without damage to the building unlike the alternative which is the too over-used hard, brittle and dense Portland cement based mortars which are known to cause irreversible damage in conjunction with historic masonry fabric.
Building on last week’s FAQ Friday, the use of lime paints doesn’t have to stop with use on the exterior of a building. Lime paints are great for use on interior walls by themselves or used as a pre-hydrated and dispersed pigmenting agent that can be mixed with Ecologic™ Mortar, NHL, or a combination of the two when formulating your own colored plasters.
There are many benefits of using lime paint on internal walls but there sometimes needs to be some preparation involved to make sure that the lime paint or plaster will adhere to the substrate. Often times I hear that someone will want a colored plaster finish on their interior walls but they do not know if lime paint will adhere. The simplest way to check is to spritz some water on the wall. If there is no absorption of the water, the wall is either too smooth or not porous enough. We need some suction. One way to achieve this is to apply a base coat of Takcoat™.
Takcoat™. was discussed in detail in a previous FAQ Friday So to keep it short I will just say that it is a VOC free, transitional lime and sand prepared plaster material that can be applied to smooth painted or unpainted surfaces. Once Takcoat™. is cured then adequate suction and mechanical key is provided for Lime Paint and lime plaster to adhere to the wall surface. There are ranges of different lime finishes that can be applied to the wall ranging from a rough open pore surface texture to an incredibly smooth polished Venetian or Tadelakt finishing style. The finish is dependent on the client’s wishes and the skill level of the craftsperson.
In my opinion, craft skill level is fundamentally dependent on the tools a craftsperson has at their disposal. One important tool to have when formulating different plasters is pigmentation. The lime paints we sell at LimeWorks.us come in a variety of colors that can be used as integral pigments mixed into plaster formulations or on their own as a decorating top coat. Having a good pigmentation methodology gives a craftsperson more options during the planning stages of a project. A good pigmentation methodology also makes reproduction of the mockups on to the entire application easier once a decision has been made on a certain color since the consistency of our products makes this a smooth process.
Lime paint comes as a dry powder consisting of a high calcium lime paint base and dispersed pigments if the paint is a colored one. Dilution of the lime paint with water to make a quart, gallon or 5-gallon unit will further breakdown the pigment and further slake the hi-cal lime. When a known volume of paint has been made it can be used in Ecologic™ Mortar formulations or gauged into lime plaster for color.
So whether you know what style of plaster finish you want to achieve or you would rather let your imagination run wild and experiment, just contact us and we will be able to help you develop your plaster system to ensure a successful project.