Methods for Constructing True Gothic Architecture
What makes architecture truly Gothic? To be authentically Gothic, a building must fulfill two primary goals.
It must embody the main Gothic elements in a Gothic aesthetic. These main elements are the pointed arch, the large tracery windows, the ribbed vault, and the ornate decoration. In larger churches the flying buttresses would be included in this.
The structure and the aesthetics are one and the same thing. All of the main elements of Gothic architecture are major structural elements when built in masonry (i.e. stone, brick, etc.) For a building to be truly Gothic, it must rely on these Gothic elements to hold up the building. The pointed arches must be structural masonry arches that actually distribute the weight of the upper parts down to the ground. The tracery of the windows actually support the glass work inside them. The shape of the ribbed vault, composed of masonry components, really does hold itself up and makes the lofty interior space.
Building Gothic in the Modern World
One may easily ask if it is even possible to build Gothic today. Has not the ability to construct such magnificent edifices been lost to the shadows of time? The skills and trades needed; they must be nonexistent. No one knows the secrets of the early Gothic master builders. Time and again it is said that true Gothic structures have not been built for hundreds of years. Whether or not one should use it, it is impossible.
(The Carmelite Monks work on construction during their allotted work times. See their Horarium here.)
These notions could not be further from the truth. Even in the past 50 years not only churches, but magnificent cathedrals have been built in the true Gothic style. A few examples would be the magnificent Liverpool Cathedral in England, completed in 1978, or the National Cathedral in Washington D.C., completed in 1990. The skills to build Gothic are by no means lost. On the contrary modern technology gives the ability to build Gothic with an ease and strength unknown in the medieval age.
Essential Medieval Methods
There are a number of methods and points of Gothic architecture that are essential and, if not followed, will result either in the loss of the Gothic aesthetic or the complete failure of the building.
Deeply Profiled Features
The layers upon layers of profiles in a Gothic church, the hoods, cornices, copings, plinths, gablelets, etc. are essential both to the look of Gothic and to the longevity of the building. All of these water shedding courses constantly send water away from the wall. In this, as in most Gothic elements, the aesthetic is not divorced from the practical, but the two are joined into one.
Water management is built into the very fabric of the building. Rather than relying on waterproofing materials which have a very short lifespan in the Gothic idea of time, Gothic architecture uses a proliferation of projecting courses and moldings to constantly shed water away from openings and walls, preserving the buildings for centuries. The look this creates is so very different from the flat facades of modern architecture which must rely on many different waterproofing agents to work short term, and will fail in the long term.
In Gothic, the structure and the architectural beauty are the same thing. Gravity itself is what keeps these seemingly weightless creations standing for centuries. In the end it is simply stone stacked upon stone, utilizing the high compressive strength of stone to its advantage. This kind of structure will last indefinitely, as long as its supports and foundations do not move, for there is nothing to fail except the gradual dissolving of the materials, and stone does not dissolve quickly.
Construction of the Ribbed Vault
The ribbed vaulting, though at first glance one of the most incredible and seemingly miraculous elements of Gothic, is in the end fairly easy. However there are a few key points that must be followed in order to ensure it will last.
The buttresses must be sized sufficiently to prevent the walls from moving. A pointed arch is a very strong shape. However if the abutments upon which it presses move out, the arch will flatten, eventually causing the arch to collapse. The medieval method applied a rule of proportions to the size of the buttress. The base unit was the span of the vault (the inside width of the building). The wall should be 1/10th of the vault span. The buttress thickness is determined as 1/3rd to 1/2th the span of the vault. This enabled the buttress to be large enough to counteract the thrusts of the vault without risk of movement.
Tas de Charge
The area where the vault comes down into the walls is crucial. Following a structure known as “tas-de-charge”, this begins at the capitals that top the columns, before the vault begins to spring out. The gradually separating ribs of the vault are worked out of single blocks of stone for each course. The mortar joints of each stone are kept in the horizontal plane up to the point where the ribs are fully separated from each other, which is frequently about halfway up the vault. This method greatly reduces the span of the vaulting as each course is “corbelling” out past the previous one.
The final full stone, upon which a beveled bed is worked to receive the first independent voussoir (rib stone), is the skewback (or springer) of the vault because its top face is skewed and the vault springs forth from it. Now when the thrust of the vaults travel down the voussoirs, they pass through the mortar joints from voussoir to voussoir, since they are perpendicular to the direction of the thrust. However the bottom face of the skewback is not perpendicular to the thrust, so that when the thrust reaches that point it attempts to push the skewback sideways out of the wall. All of the thrust of the vaults is then attempting to slide the skewback out of its position.
It is then imperative to make the skewback solid stone all the way back into the wall. Some Gothic churches attempted to fill this space with rubble and concrete, but the results were disastrous as the materials did not have the compressive strength to take the forces at work in that area, causing the skewback to slide out and the vaults to collapse. The high compressive strength of many stones is very advantageous in this regard. For example the Kansas Silverdale limestone the Carmelite Monks use has a compressive strength of over 6500 psi, twice that of ordinary concrete.
The buttresses then must be robust enough to be able to take the thrust coming out through the skewback and divert it down. Pinnacles are placed on top of the buttress to add weight, making it impossible for the thrust of the vaults to move anything out.
When flying buttresses are utilized they must connect into the walls at two key points, at the level of the skewback to hold it in place, and at the top of the wall to support the roof and take any wind loads.
Masonry Construction
Gothic buildings are created primarily out of stone, a material that does not rust, rot, or break down easily. Following the Gothic principles the lofty heights and spans can be accomplished in this one material. The truth of this can be seen in the countless Gothic buildings that have stood the test of time.
Lime Mortar
Lime mortar is essential to the longevity of these large masonry buildings
In the 1800s Portland cement was discovered. It quickly grew to popularity because it would cure rapidly and become extremely hard. However in recent decades it has been found that this hardness can do more harm than good. Many old buildings that were repointed with the Portland mortar have had a rapid increase in the rate of deterioration. This mortar is so hard it will spall and break apart the edges of all but the strongest stones. It also does not flex or breathe, forcing any movement to happen within the stones themselves. As time went on it became standard practice to introduce control joints into the buildings to try and make up for this lack of flexibility.
The medieval builders looked at the mortar joint as a sacrificial layer. The lime mortar they utilized is far weaker than the stone acting as a cushion that absorbs the movement of the building. It also breathes , allowing any moisture trapped in the walls to escape, rather than collect inside the stones and cause possible freeze/thaw damage. When used in a vault, it gives a certain amount of elasticity to the vault and helps to prevent cracking. It even self heals to a certain extent as the free lime in the mortar recrystallizes in cracks.
Modern Advancements
“In matters purely mechanical, the Christian architect should gladly avail himself of those improvements and increased facilities that are suggested from time to time. The steam engine is a most valuable power for sawing, raising, and cleansing stone, timber, and other materials. … It is only when mechanical invention intrudes on the confines of art, and tends to subvert the principles which it would advance, that it becomes objectionable.” -Augustus Pugin
Modern technology has brought a host of improvements to the construction of Gothic. For indeed Gothic architecture is not bound by the methods by which it is constructed, but rather by the end result. Here are but a few of the advancements that the modern builder has at his disposal.
Engineered Wall Structure
There have been new improvements on the rubble wall structure. In the medieval method the two faces of the wall were constructed of cut stone and the core between was filled with rubble (typically a mixture of broken stone, mortar, gravel, and almost anything else at hand. This type of composite wall would be impossible to engineer as there is no concept of what strength such a mixed core could have. In the 20th century builders used brick as the core of the rubble wall, such as in the Liverpool Cathedral and Washington National Cathedral. Today a reinforced concrete block core is used. While following in the same mindset of the medieval builders this easily engineered core brings with it many enhanced abilities, such as a vigorous protection against earthquakes, so long the bane of masonry structures. In fact, such a Gothic building has been described as a “sumo wrestler”, able to take on whatever is thrown at it.
The Invention of Stainless Steel
Iron has historically been used in Gothic as a reinforcement for spires and pinnacles, such as Frieburg, as well as a remedial cure for the lack of proper buttressing or foundations, such as in Amiens and Sainte-Chapelle. However iron has the propensity to rust, expanding up to five times its original size. This leads to a phenomenon known as rust jacking, where the masonry containing the reinforcement is split apart from the inside. Many techniques were devised in an attempt to circumvent this issue, such as the coating of the iron ties in lead or tar, which
were only effective insofar as they completely encompassed the iron.
Stainless steel was invented in the early 1900s. Virtually rust free and available in a wide variety of strengths it practically eliminates the issue of rust jacking and the fears of using metal as a reinforcement in the stone.
Tensioned Stone
The 20th century saw a great deal of development in the realm of reinforced masonry. However this was primarily focused on concrete. In more recent years these same technologies have been applied to stone, with sometimes remarkable results. One excellent example is the tensioning of stone elements by means of stainless steel all thread rods to pull together several stone pieces. This has the advantage of taking a tensile load applied to the stone and turning it into a compressive load, giving the stone an excellent ability to resist wind and seismic loads. It has been used to advantage in the spires of the Sagrada Familia in Barcelona, as well as in a number of smaller spires and pinnacles of recent construction.
Seismic Reinforcement of Masonry
There has been much research in recent decades on how to preserve historical buildings from the threat of earthquakes. Masonry buildings are by nature stable, relying on gravity to hold themselves together. However when the ground upon which they rely is in turmoil, they quickly lose their ability to stand.
Many different techniques have been attempted with varying degrees of success. Reinforced concrete walls have stood up well to earthquakes, the reinforcement giving a necessary amount of elasticity to the building. However this same method when applied to vaults does not fare as well. Vaults again rely on gravity to hold themselves together. They have little strength when the walls spread out, or when force is applied from underneath. To rectify this frequently a reinforced concrete cap is poured over the topside of the vault stones. This however would lock in the vault rigidly and frequently cause the vault below to crack up because of this rigidity. It adds a great deal of weight to the vault, requiring larger buttresses. It also tended to create moisture collection problems in the webstones and ceiling decoration as the moisture from the warmer interior, unable to penetrate the concrete cap, would condensate on the cooler ceiling.
Italy has had many opportunities to test different systems in real life scenarios over the earthquakes of the past decade. Recently an innovative new technology has yielded excellent results there and is now making its way into the United States. This is FRCM, or fiber reinforced cementitious matrix. The system utilizes a carbon fiber mesh that is bonded to the back of the vault with a specially formulated mortar. It is extremely breathable, eliminating the moisture issues of the concrete cap. Less than 1” thick, it is extremely lightweight. The carbon fiber mesh acts as a net tying the stones together without locking them rigidly. This allows for normal expansion and contraction, preventing cracking, and also has excellent seismic performance. The vault acts as a hom*ogenous whole, fluidly absorbing an earthquake’s vibrations.
Modern Engineering
Modern engineering has brought innumerable insights and clarity to Gothic construction. Rule of thumb calculations and simple laws of proportions have been tested and verified. Dynamic loads out of the control of the medieval builders can now be taken into account and planned for in ways that simple proportional laws could not.
Cranes and Stone Handling
The use of modern equipment to speed up the actual construction cannot be underestimated. When one considers the labor that was involved in Medieval Europe simply to hoist a stone in place it is easy to see how much easier Gothic architecture is today than ever before.
Powered cranes of all sorts have revolutionized the world of material handling. Tower cranes, bridge cranes, mobile cranes, scaffold mounted cranes, forklifts; the list goes on and on. Now even stones weighing tens of tons can be effortlessly lifted and placed precisely into position.
The invention of hydraulic scaffolding has eliminated the veritable forest of supports that typically made up the scaffolding of a Gothic worksite. Now scaffold platforms can safely and effortlessly climb up the sides of the building as construction progresses.
Stone Carving
The advancement in stone carving may be the most revolutionary. Diamond tipped saw blades and milling bits cut and shape the stone at blistering speeds compared to older methods. CNC machines automate a significant amount of the detail work, and also allow the talents of modern man to be used in the construction of such glorious edifices. When one considers an ornate piece that used to take a month now only takes two days, the gain in productivity is enormous. This allows for even more ornate decoration in churches as the time required to make each piece is decreased.
Experience
And the greatest advantage of the modern builder is the wealth of knowledge handed down from those men who have built Gothic before him. Though textbooks may be lacking, the Gothic builder left his mark in the buildings he constructed. In every Gothic building there is a wealth of information in what works and what does not. In the collapses of Beauvais, the reinforcements of Strasbourg and Ulm, the fire of Notre Dame Paris, and innumerable other examples, the lessons are clear in what can be changed to improve and avoid the mistakes of the past. This alone is one of the greatest gifts the Gothic builders of history have left to this day, rivaling the structures they have bequeathed to us, the gift of the ability to make this uplifting architecture a part of our very own culture and world.
