The architecture of the California missions was influenced by several factors, those being the limitations in the construction materials that were on hand, an overall lack of skilled labor, and a desire on the part of the founding priests to emulate notable structures in their Spanish homeland. While no two mission complexes are identical, they all employed the same basic building style.
Site selection and layout
Although the missions were considered temporary ventures by the Spanish hierarchy, the development of an individual settlement was not simply a matter of "priestly whim." The founding of a mission followed longstanding rules and procedures; the paperwork involved required months, sometimes years of correspondence, and demanded the attention of virtually every level of the bureaucracy. Once empowered to erect a mission in a given area, the men assigned to it chose a specific site that featured a good water supply, plenty of wood for fires and building material, and ample fields for grazing herds and raising crops. The padres blessed the site, and with the aid of their military escort fashioned temporary shelters out of tree limbs or driven stakes, roofed with thatch or reeds. It was these simple huts that would ultimately give way to the stone and adobe buildings which exist to this day.
The first priority when beginning a settlement was the location and construction of the church (iglesia). The majority of mission sanctuaries were oriented on a roughly east–west axis to take the best advantage of the sun's position for interior illumination; the exact alignment depended on the geographic features of the particular site. Once the spot for the church was selected, its position would be marked and the remainder of the mission complex would be laid out. The priests' quarters, refectory, convento, workshops, kitchens, soldiers' and servants' living quarters, storerooms, and other ancillary chambers were usually grouped around a walled, open court or patio (often in the form of a quadrangle) inside which religious celebrations and other festive events often took place. The cuadrángulo was rarely a perfect square because the Fathers had no surveying instruments at their disposal and simply measured off all dimensions by foot. In the event of an attack by hostile forces, the mission's inhabitants could take refuge within the quadrangle.
The basic, common elements found in all of the Alta California missions can be summarized as follows:
Arched corridors; Curved, pedimented gables; Terraced bell towers (with domes and lanterns) or bell walls (pierced belfries); Wide, projecting eaves; Broad, undecorated wall surfaces; and Low, sloping tile roofs.
The Alta California missions as a whole do not incorporate the same variety or elaborateness of detail in their design exhibited in the structures erected by Spanish settlers in Arizona, Texas, and Mexico during the same nevertheless, they "...stand as concrete reminders of Spanish occupation and admirable examples of buildings conceived in the style and manner appropriate to the country in which they were built." Some fanciful accounts regarding the construction of the missions claimed that tunnels were incorporated into the design of the garden, to be used as a means of emergency egress in the event of attack; however, no historical evidence (written or physical) has ever been uncovered to support these wild assertions.
Building materials
The scarcity of imported materials, together with a lack of skilled laborers, compelled the Fathers to employ simple building materials and methods in the construction of mission structures. Since importing the quantity of materials necessary for a large mission complex was impossible, the padres had to gather the materials they needed from the land around them. Five basic materials were used in constructing the permanent mission structures: adobe, timber, stone, brick, and tile. Adobes (mud bricks) were made from a combination of earth and water, with chaff, straw, or manure added to bind the mixture together. Occasionally pieces of bricks or shells were placed in the mix to improve the cohesiveness. The soil used may have been clay, loam, or sandy or gravelly earth. The making of the bricks was a simple process, derived from methods originally developed in Spain and Mexico. A convenient, level spot was chosen near the intended building site and close to a suitable water supply (usually a spring or creek). The ground was dug up and soaked with water, whereupon bare-legged workers would stomp the wet earth and binders into a homogeneous consistency fit for carrying to, and placing in, the brick molds.
The mixture was compressed into the wooden formas, which were arranged in rows, and leveled by hand to the top of the frame. From time to time, a worker would leave an imprint of his hand or foot on the surface of a wet brick, or perhaps a literate workman would inscribe his name and the date on the face. When the forms were filled, the bricks were left in the sun to dry. Great care was taken to expose the bricks on all sides, in order to ensure uniform drying and prevent cracking. Once dry, the bricks were stacked in rows to await their use. California adobes measured , were thick, and weighed , making them convenient to carry and easy to handle during the construction process.
Facilities for milling lumber were almost non-existent: workers used stone axes and crude saws to shape the wood, and often used logs which only had their bark stripped from them. These methods gave mission structures their distinctive appearance. Timber was used to reinforce walls, as vigas (beams) to support roofs, and as forms for door and window openings and arches. Since most of the settlements were located in valleys or coastal plains almost totally devoid of suitably large trees, the padres were in most cases limited to pine, alder, poplar, cypress and juniper trees for use in their construction efforts. Indians used wooden carrettas, drawn by oxen, to haul timber from as much as forty miles away (as was the case at Mission San Miguel Arcángel). At Mission San Luis Rey, however, the ingenious Father Lasuén instructed his neophyte workers to float logs downriver from Palomar Mountain to the mission site. The lack of good-sized timber forced the men to design mission buildings that were long and narrow. For example, the widest inside dimensions of any of the mission buildings (at San Carlos, Santa Clara, and Santa Cruz) is : the narrowest, at Mission Soledad, spans . The longest structure, at Mission Santa Barbara, stretches . Stone (piedra) was used as a construction material whenever possible. In the absence of skilled stonemasons, the inexperienced builders resorted to the use of sandstone; though easier to cut, it was not as weather-resistant as that which would have been used by skilled artisans. To bind the stones together, the priests and Indians followed the (Mexican) Pre-Columbian technique of using mud mortar, since mortar made from lime was unavailable to them. Colored stones and pebbles were added to the mud mixture, giving it "a beautiful and interesting texture."
Ladrillos (conventional bricks) were manufactured in much the same manner as adobes, with one important difference: after forming and initial drying, the bricks were fired in outdoor kilns to ensure a much greater endurance than could be achieved through merely sun-drying them. Common bricks typically measured ten inches (250 mm) square and were thick. Square paving bricks were equal in thickness to the common variety, but ranged from across. Many of the structures erected with this type of brick remained standing long after their adobe counterparts had been reduced to rubble.
The earliest structures had roofs of thatch or earth supported by flat poles. Tejas (roof tiles) were utilized in later construction (beginning around 1790) to replace the flammable thatch. The semicircular tiles consisted of clay molded over a section of a log was which well-sanded to prevent the clay from sticking. According to the accounts of Father Estévan Tapís of Mission Santa Barbara, some thirty-two Native American males were required to make 500 tiles each day, while the women carried sand and straw to the pits. The mixture was first worked in pits under the hoofs of animals, then placed on a flat board and fashioned to the correct thickness. Sheets of clay were then placed over the logs and cut the desired to size: they ranged in length from , and tapered from in width. After trimming, the tiles were dried in the sun, then placed in ovens and burned until they took on a reddish-brown coloring. The quality of the tiles varied greatly among the missions due to differences in soil types from one site to another. Legend has it that the first tiles were made at Mission San Luis Obispo, but Father Maynard Geiger (the Franciscan historian and biographer of Junípero Serra) claims that Mission San Antonio de Padua was actually the first to use them. Aside from their obvious advantage over straw roofs in terms of fire retardance, the impermeable surface also protected the adobe walls below from the damaging effects of rain. The original tiles were secured with a dab of adobe and were held in place because of their shape, being tapered at the upper end so they could not slide off one another.
Construction methods
The earliest projects had a layer of streambed stones arranged as a foundation, upon which the adobes were placed. Later, stone and masonry were used for foundation courses, which greatly added to the bearing capacity of the brickwork. Aside from superficial leveling, no other ground preparation was done before construction started. There is some evidence to indicate that the initial structures at some of the outposts were produced by setting wooden posts close together and filling the interstitial spaces with clay. At completion, the building would be covered with a thatched roof and wall surfaces would be coated with whitewash to keep the clay exterior from eroding. This type of construction is known as "wattle and daub" (jacal to the natives) and eventually gave way to the use of adobe, stone, or ladrillos. Even though many of the adobe structures were ultimately replaced with ones of piedra or brick, adobe was still employed extensively and was the principal material used in building the missions as there was an almost universal lack of readily-available stone. The adobes were laid in courses and cemented together with wet clay. Due to the low bearing strength of adobe and the lack of skilled brick masons (albañils), walls made of mud bricks had to be fairly thick. The width of a wall depended mostly on its height: low walls were commonly two feet thick, while the highest (up to thirty-five feet) required as much as six feet of material to support them.
Timbers were set into the upper courses of most walls to stiffen them. Massive exterior buttresses were also employed to fortify wall sections, but this method of reinforcement required the inclusion of pilasters on the inside of the building to resist the lateral thrust of the buttresses and prevent the collapse of the wall. Pilasters and buttresses were often composed of more durable baked brick, even when the walls they supported were adobe. When the walls got too high for workers on the ground to reach the top, simple wood scaffolding was erected from whatever lumber was available. Many times posts were temporarily cemented into the walls to support catwalks. When the wall was completed, the posts were removed and the voids filled with adobe, or were sometimes sawed off flush with the surface of the wall.