5 PRESERVATION 

BRIEFS 

Preservation of Historic 

Adobe Buildings 

U.S. Department of the Interior 

National Park Service 

Cultural Resources 

Heritage Preservation Services 

Whether built in the 17th century or in the 20th century, 

adobe buildings share common problems of maintenance and 

deterioration. This brief discusses the traditional materials 

and construction of adobe buildings and the causes of adobe 

deterioration. It also makes recommendations for preserving 

historic adobe buildings. By its composition, adobe construction is inclined to deteriorate; however, the buildings can be 

made durable and renewable when properly maintained. 

What is Adobe? 

The adobe, or sun-dried brick, is one of the oldest and most 

common building materials known to man. Traditionally, 

adobe bricks were never kiln fired. Unbaked adobe bricks 

consisted of sand, sometimes gravel, clay, water, and often 

straw or grass mixed together by hand, formed in wooden 

molds, and dried by the sun. Today some commercially 

available adobe-like bricks are frred. These are similar in size 

to unbaked bricks, but have a different texture, color, and 

strength. Similarly some adobe bricks have been stabilized, 

containing cement, asphalt, and/or bituminous materials, but 

these also differ from traditional adobe in their appearance 

and strength. 

Traditional adobe construction techniques in North America have not varied widely for over 31

/2 centuries. Adobe 

SAN XAVIER DEL BAC, TUCSON VICINITY, ARIZONA. Built 

entirely of adobe construction (1783-1797), this is one of the finest 

Spa nish Colonial churches in the United States, ha ving an 

elaborate frontispiece of molded, carved, and painted brick imitating stone. (National Park Service) 

building methods employed in the Southwest in the 16th 

century are still used today. Because adobe bricks are not 

fired in a kiln as are clay bricks, they do not permanently 

harden, but remain unstable-they shrink and swell constantly with their changing water content. Their strength also 

fluctuates with their water content: the higher the water 

content, the lower the strength. 

Adobe will not permanently bond with metal, wood, or 

stone because it exhibits much greater movement than these 

other materials, either separating, cracking, or twisting 

where they interface. Yet, many of these more stable 

building materials such as fired brick, wood, and lime and 

cement mortars are nonetheless used in adobe construction. 

For example, stone may be used for a building's foundation, 

and wood may be used for its roof or its lintels and 

doorways. In the adobe building, these materials are generally held in place by their own weight or by the compressive 

weight of the wall above them. Adobe construction possibilities and variations in design have therefore been somewhat 

limited by the physical constraints of the material. 

Preserving and rehabilitating a deteriorated adobe building 

is most successful when the techniques and methads used for 

restoration and repairs are as similar as possible to the 

techniques used in the original construction. 

Adobe Construction Techniques 

The Brick: The adobe brick is molded from sand and clay 

mixed with water to a plastic consistency. Commonly, straw 

or grass is included as a binder. Although they do not help 

reinforce the bricks or give them added long-term strength, 

straw and grass do help the bricks shrink more uniformly 

while they dry. More important for durability, however, is 

the inherent clay-to-sand ratio found in native soil. The 

prepared mud is placed in wooden forms, tamped, and 

leveled by hand . The bricks are then "turned-out " of the 

mold to dry on a level surface covered with straw or grass 

so that the bricks will not stick. After several days of drying, 

the adobe bricks are ready for air-curing. This consists of 

standing the bricks on end for a period of 4 weeks or longer. 

Mortar: Historically, most adobe walls were composed of 

adobe bricks laid with mud mortar. Such mortar exhibited 

the same properties as the bricks: relatively weak and 

susceptible to the same rate of hygroscopic (moisture absorptive) swelling and shrinking, thermal expansion and contracFor sale by the Superintendent ot Document., U.S. Government PrtntiDI' Oftlce 

Wuhlngton, D.C. 20402 
tion, and deterioration. Consequently, no other material has 

been as successful in bonding adobe bricks. Today, cement 

and lime mortars are commonly used with stabilized adobe 

bricks, but cement mortars are incompatible with unstabilized adobe because the two have different thermal expa"sion 

and contraction rates. Cement mortars thereby accelerate 

the deterioration of adobe bricks since the mortars are 

stronger than the adobe. 

Building Foundations: Early adobe building foundations 

varied because of the difference in local building practices 

and availability of materials. Many foundations were large 

and substantially constructed, but others were almost nonexistent. Most often, adobe building foundations were constructed of bricks, fieldstones, or cavity walls (double) 

infilled with rubble stone, tile fragments, or seashells. Adobe 

buildings were rarely constructed over basements or crawlspaces. 

Walls: Since adobe construction was load-bearing with low 

structural strength, adobe walls tended to be massive , and 

seldom rose over 2 stories. In fact, the maximum hejght of 

adobe mission churches in the Southwest was approximately 

35 feet. Often buttresses braced exterior walls for added 

stability. 

In some parts of the Southwest, it was common to place a 

long wooden timber within the last courses of adobe bricks. 

This timber provided a long horizontal bearing plate for the 

roof thereby distributing the weight of the roof along the 

wall. 

Roofs: Early Southwest adobe roofs (17th-mid-19th centuries) tended to be flat with low parapet walls. These roofs 

consisted of logs which supported wooden poles, and which 

in turn supported wooden lathing or layers of twigs covered 

with packed adobe earth. The wood was aspen, mesquite , 

cedar, or whatever was available. Roughly dressed logs 

(called "viXas") or shaped squared timbers were spaced on 

close (2-3 feet or less) centers resting either on the horizontal 

wooden member which topped the adobe wall, or on 

decorated cantilevered blocks, called "corbels," which were 

set into the adobe wall. Traditionally, these vigas often 

projected through the wall facades creating the typical adobe 

Roof Bearing. A roof bearinK timber placed within the adobe walls 

provides even support for the weight of the roof. (Farm Security 

Administration Collection. Library of Congress) 

2 

flat roof, small openings 

brick coping, wood porch 

hip roof, wood trim 

Evolution of Roof Forms. The roofs of early adobe buildings were 

flat, made with mud. with low parapels. Later, brick copings were 

placed on top of parapets and chimneys to protect them from 

ero~'ion, and shed roof porches were added to shelter doors and 

windows. After the railroad reached the Southwest, hip roofs and 

wooden trim began to appear as sawn lumber. shingles. tile , and 

sheet metal became available. (DrawinK by Albert N. Hopper) 

Roof Framing. ViKU logs and savinos are seen in the interior of the 

adobe building. Often the wooden materials that compose the 

traditional flat adobe roof create interesting and pleasing patterns 

on the ceilinKs of the interior rooms. (Photo by Russell Lee. Farm 

Security Administration Collection. Library of Con Kress) 
construction detail copied in the 20th-century revival styles. 

Wooden poles about 2 inches in diameter (called "Ialias") 

were then laid across the top of the vigas. Handsplit planks 

(called "cedros" if cedar and "savinos" if cypress) instead 

of poles were used when available. In some areas, these 

were laid in a herringbone pattern. In the west Texas and 

Tucson areas, saguaro (cactus) ribs were used to span 

between vigas. After railroad transportation arrived in most 

areas, sawn boards and planks, much like roof sheathing, 

became available and was often used in late-l9th- and early20th-century buildings or for repairs to earlier ones. 

Next cedar twigs, plant fibers, or fabric were placed on 

top of the poles or planks. These served as a lathing on 

which the 6 or more inches of adobe earth was compacted. 

If planks were used, twigs were not necessary. A coating of 

adobe mud was then applied overall. The flat roofs were 

sloped somewhat toward drains of hollowed logs (called 

"canales," or "gargolas "), tile, or sheet metal that projected through the parapet walls. 

Gable and hipped roofs became increasingly popular in 

adobe buildings in the 19th and 20th centuries. "Territorial" 

styles and preferences for certain materials developed. For 

example, roof tiles were widely used in southern California. 

Although the railroad brought in some wooden shingles and 

some terra-cotta, sheet metal roofing was the prevalent 

material for roofs in New Mexico. 

Floors: Historically, flooring materials were placed directly 

on the ground with little or no subflooring preparation . 

Flooring materials in adobe buildings have varied from earth 

to adobe brick, fired brick, tile, or flagstone (called "Iajas"), 

to conventional wooden floors. 

Traditional Surface Coatings 

Adobe surfaces are notoriously fragile and need frequent 

maintenance. To protect the exterior and interior surfaces of 

new adobe walls, surface coatings such as mud plaster, lime 

plaster, whitewash, and stucco have been used. Such coatings applied to the exterior of adobe construction have 

retarded surface deterioration by offering a renewable surface to the adobe wall. In the past, these methods have been 

inexpensive and readily available to the adobe owner as a 

solution to periodic maintenance and visual improvement. 

However, recent increases in labor costs and changes in 

cultural and socio-economic values have caused many adobe 

building owners to seek more lasting materials as alternatives 

to these traditional and once-inexpensive surface coatings. 

Mud Plaster: Mud plaster has long been used as a surface 

coating. Like adobe, mud plaster is composed of clay, sand, 

water, and straw or grass, and therefore exhibits sympathetic 

properties to those of the original adobe. The mud plaster 

bonds to the adobe because the two are made of the same 

materials. Although applying mud plaster requires little skill, 

it is a time-consuming and laborious process. Once in place, 

the mud plaster must be smoothed. This is done by hand; 

sometimes deerskins, sheepskins, and small, slightly rounded 

stones are used to smooth the plaster to create a "polished" 

surface . In some areas, pink or ochre pigments are mixed 

into the final layer and "polished." 

Whitewash: Whitewash has been used on earthen buildings 

since before recorded history. Consisting of ground gypsum 

rock, water, and clay, whitewash acts as a sealer, which can 

be either brushed on the adobe wall or applied with large 

pieces of coarse fabric such as burlap. 

Initially, whitewash was considered inexpensive and easy 

to apply . But its impermanence and the cost of annually 

3 

renewing it has made it less popular as a surface coating in 

recent years. 

Lime Plaster: Lime plaster, widely used in the 19th century 

as both an exterior and interior coating, is much harder than 

mud plaster. It is, however, less flexible and cracks easily. It 

consists of lime, sand, and water and is applied in heavy 

coats with trowels or brushes. To make the lime plaster 

adhere to adobe, walls are often scored diagonally with 

hatchets, making grooves about 11 /2 inches deep. The 

grooves are filled with a mixture of lime mortar and small 

chips of stone or broken roof tiles. The wall is then covered 

heavily with the lime plaster. 

Cement Stucco: In the United States, cement stucco came 

into use as an adobe surface coating in the early 20th century 

for the revival styles of Southwest adobe architecture. 

Cement stucco consists of cement, sand, and water and it is 

applied with a trowel in from I to 3 coats over a wire mesh 

nailed to the adobe surface. This material has been very 

popular because it requires little maintenance when applied 

over fired or stabilized adobe brick, and because it can be 

easily painted. 

It should be noted however, that the cement stucco does 

not create a bond with unfrred or un stabilized adobe; it relies 

on the wire mesh and nails to hold it in place. Since nails 

cannot bond with the adobe, a firm surface cannot be 

guaranteed. Even when very long nails are used, moisture 

within the adobe may cause the nails and the wire to rust, 

thus, losing contact with the adobe. 

Other Traditional Surface Coatings: These have included 

items such as paints (oil base, resin, or emulsion), portland 

cement washes, coatings of plant extracts, and even coatings 

of fresh animal blood (mainly for adobe floors). Some of 

these coatings are inexpensive and easy to apply, provide 

temporary surface protection, and are still available to the 

adobe owner. 

Adobe Deterioration 

When preservation or rehabilitation is contemplated for a 

historic adobe building, it is generally because the walls or 

roof of the building have deteriorated in some fashion-walls 

may be cracked, eroded, pitted, bulging, or the roof may be 

sagging. In planning the stabilization and repair of an adobe 

building, it is necessary: 

• To determine the nature of the deterioration 

• To identify and correct the source of the problem causing 

the deterioration 

• To develop rehabilitation and restoration plans that are 

sensitive to the integrity of the historic adobe building 

• To develop a maintenance program once the rehabilitation 

or restoration is completed. 

General Advice: There are several principles that when 

followed generally result in a relatively stable and permanent 

adobe resource. 

I. Whenever possible, secure the services or advice of a 

professional architect or other preservationist proficient 

in adobe preservation and stabilization. Although this 

may be more costly than to " do-it-yourself," it will 

probably be less expensive in the long run. Working with 

a deteriorated adobe building is a complex and difficult 

process. Irreversible damage may be done by well-meaning but inexperienced .. restorationists." Moreover, 

professional assistance may be required to interpret local 

code requirements. 

2. Never begin restoration or repairs until the problems that 
Deteriorated Adobe Building. By virtue of it.1 fraKile nature . the 

adohe huildinK must he restored hy thorouKh. systematic . and 

professional measures that will insure its future survival. (Technical Preservation Service.1 Division) 

have been causing the deterioration of the adobe have 

been found, analyzed, and solved. For instance, sagging 

or bulging walls may be the result of a problem called 

"rising damp" and/or excessive roof loads. Because 

adobe deterioration is almost always the end product of a 

combination of problems, it takes a trained professional 

to analyze the deterioration, identify the source or sources 

of deterioration, and halt the deterioration before full 

restoration begins. 

3. Repair or replace adobe building materials with the same 

types of materials used originally and use the same 

construction techniques. Usually the best and the safest 

procedure is to use traditional building materials. Repair 

or replace deteriorated adobe bricks with similar adobe 

bricks. Repair or replace rotted wooden ·Iintels with 

similar wooden lintels. The problems created by introducing dissimilar replacement matetials may cause problems 

far exceeding those which deteriorated the adobe in the 

first place . 

Sources of Deterioration 

The following are some common signs and sources of adobe 

deterioration and some common solutions. It should be 

cautioned again , however, that adobe deterioration is often 

the end-product of more than one of these problems. The 

remedying of only one of these will not necessarily arrest 

deterioration if others are left untreated. 

Structural Damage: There are several common structural 

problems in adobe buildings, and while the results of these 

problems are easy to see, their causes are not. Many of 

these problems originate from improper design or construction, insufficient foundations, weak or inadequate materials, 

or the effects of external forces such as wind, water, snow, 

or earthquakes. In any case the services of a soils engineer 

and/or structural engineer knowledgeable in adobe construction may be necessary to evaluate these problems. Solutions 

may involve repairing foundations, realigning leaning and 

bulging walls, buttressing walls, inserting new window and 

door lintels, and repairing or replacing badly deteriorated 

roof structures. 

There are many tell-tale signs of structural problems in 

adobe buildings, the most common being cracks in walls, 

foundations, and roofs. In adobe, cracks are generally quite 

visible, but their causes may be difficult to diagnose . Some 

cracking is normal, such as the short hairline cracks that are 

caused as the adobe shrinks and continues to dry out. More 

4 

Structural Damage and Cracking. SaKKinK . hulKinK. and crackinK 

of wa ll.1 and roo/l are .liKns of seriou.1 prohlem.1 in the adohe 

huildinK. It is always advisahle to secure professional services in 

the repair of such prohlems. (National Park Service) 

extensive cracking, however, usually indicates serious structural problems. In any case, cracks, like all structural 

problems, should be examined by a professional who can 

make recommendations for their repair. 

Water Related Problems: Generally , adobe buildings deteriorate because of moisture, either excessive rainwater or 

ground water. Successful stabilization, restoration, and the 

ultimate survival of an adobe building depends upon how 

effectively a structure sheds water. The importance in 

keeping an adobe building free from excessive moisture 

cannot be overestimated. The erosive action of rainwater 

and the subsequent drying out of adobe roofs, parapet walls, 

and wall surfaces can cause furrows, cracks, deep fissures, 

and pitted surfaces to form . Rain saturated adobe loses its 

cohesive strength and sloughs off forming rounded corners 

and parapets. If left unattended, rainwater damage can 

eventually destroy adobe walls and roofs, causing their 

continued deterioration and ultimate collapse. Standing rainwater that accumulates at foundation level and rain splash 

may cause "coving" (the hollowing-out of the wall just 

above grade level). 

Ground water (water below ground level) might be present 

because of a spring, a high water table, improper drainage , 

seasonal water fluctuations, excessive plant watering, or 

changes in grade on either side of the wall. Ground water 

rises through capillary action into the wall and causes the 

adobe to erode, bulge , and cove. Coving is also caused by 

spalling during the freeze-thaw cycles. As water rises from 

the ground into the wall, the bond between the clay particles 

in the adobe brick breaks down . In addition, dissolved 

minerals or salts brought up from the soil by the water can 

be deposited on or near the surface of the wall as the 

moisture evaporates. If these deposits become heavily concentrated, they too can deteriorate the adobe fabric . As the 

adobe dries out , shrinkage cracks usually appear; loose 

sections of adobe bricks and mud plaster may crumble . 

A water-tight roof with proper drainage is the best 

protection against rainfall erosion. Adobe wall and roof 

surfaces properly maintained with traditional tiles or surface 

coatings generally resist the destructive effects of rainwater. 

Roof drains should be in good repair and sufficient to carry 

rainwater run-off from the roof. In an effort to halt the 

destructive effects of rainwater, 19th-century builders often 

capped parapet walls with fired bricks. These bricks were 

harder and better suited to weather the erosive action of 

rainwater; however, the addition of a brick cap to an existing 

parapet wall creates a drastic change in a structure's 

appearance and fabric. The use of traditional lime mortar 
with the fired brick is advised because it is more water-tight 

and compatible with the harder brick. 

Rainwater that has accumulated at adobe foundations 

should be diverted away from the building. This may be 

done by regrading, by building gravel-filled trenches or 

brick, tile, or stone drip gutters, or by any technique that 

will effectively remove the standing rainwater. Regrading is 

perhaps the best solution because defective gutters and 

trenches may in effect collect and hold water at the base of 

the wall or foundation. 

In repairing "coving," the damage caused by rain splash, 

adobe bricks stabilized with soil cement might be considered. 

On the other hand, concrete patches, cement stucco, and 

curb-like buttresses against the coving usually have a negative effect because moisture may be attracted and trapped 

behind the concrete. 

Cement stucco and cement patches have the potential for 

specific kinds of water related adobe deterioration. The 

thermal expansion coefficient of cement stucco is 3 to 10 

times greater than that of adobe resulting in cracking of the 

stucco. Cracks allow both liquid water and vapor to penetrate the adobe beneath , and the stucco prevents the wall 

from drying. 

As the moisture content of the adobe increases, there is a 

point at which the adobe will become soft like putty . When 

the wall becomes totally saturated, the adobe mud will flow 

as a liquid. This varies with the sand, clay , and silt content 

of the adobe. 

If the adobe becomes so wet that the c lay reaches its 

plastic limit, or if the adobe is exposed to a freeze-thaw 

action, serious damage can result. Under the weight of the 

roof, the wet adobe may deform or bulge. Since the 

deterioration is hidden from view by the cement stucco, 

damage may go undetected for some time. Traditional adobe 

construction techniques and materials should therefore, be 

used to repair or rebuild parts of the wall~. 

The destructive effects of moisture on adobe buildings 

may be substantially halted by several remedies. 

I. Shrubs, trees, and other foundation plantings may be 

causing physical damage. Their roots may be growing 

into the adobe, and/or they may be trapping excessive 

moisture in their roots and conducting it into walls. Their 

removal might be considered to halt this process. 

2. Level ground immediately adjacent to the walls may be 

causing poor drainage. Regrading cO!lld be considered so 

that the ground slopes away from the building, eliminating 

rainwater pools. 

3. The installation of footing drains may be considered. 

Trenches about 2 to 2V2 feet wide and ~everal feet deep 

are dug around the adobe building at the base of the walls 

or at the foundation if there is any. If the soil is weak, it 

may be necessary to slope the sides of the trench to 

prevent cave-in of the trench and subsequent damage to 

the wall. The walls and bottom of the trench should be 

lined with a polyethylene vapor barrier to prevent the 

collected water from saturating the surrounding soil and 

adobe wall. Clay tile. or plastic pipe. which drain to a 

sump or to an open gutter, are then laid in the bottom of 

the trench. The trench is filled with gravel to within 6 

inches of grade . The remaining excavation is then filled to 

grade with porous soil. 

A Word of Caution: Plant removal. reumdinu . or trenchinu 

may he potential/y de.ltructive to archeolouical remains 

a.I.l"Ociated with historic adohe huildinu .lite.l. An\' di.lturhance of the uround should, therefore. he undertaken with 

prudence and careful planninu. 

Once anyone or all of these solutions has effectively 

minimized the problems of rising ground water, the coving 

and deterioration of the walls can be corrected by patching 

the area with new adobe mud and by applying traditional 

surface coatings. It should be remembered, however, that 

unless the capillary action is stopped effectively, thi\ erosive 

condition will certainly continue. Most important. surface 

coatings and patching only repair the effects of ground water 

and wind erosion, they cannot cure the cause. 

Coving. Salt.1 depo.lited hy ri lin~ ~mund water can evaporate and 

caa .le Ipallin~ of the adohe hrick.1 at th e ha.le of the wall. a 

.leriou.1 condition called "covin~." Covjn~ can al.w he cau.led 

and/or exacerhated hy the em.lion of rain splash. (National Park 

Service) 

RAI NWATER SPLASH 

GROU~D WATER 

RISI~G DA\1P 

Water, Wind, Animal, Insect, and Vegetation Damage. Most deterioration of adohe hui/din~ 1 can he directly correla ted with the 

pre.lence of either exce.l.live rainwater. ~ro and"·a ter . or both. 

Succe .llful adohe .lIahilizalion and re .l{()ralion depend.1 upon 

keepinK the adohe hui/dinK moi.lture free. repaired. and well 

maintained. (DrawinK hy David W. Look. AlA. ha.led on sketches 

hyAlhert N. Hopper) 

5 
Wind Erosion: Wind-blown sand has often been cited as a 

factor in adobe fabric erosion. Evidence of wind erosion is 

often difficult to isolate because the results are similar to 

water erosion; however, furrowing caused by wind is usuall y 

more obvious at the upper half of the wall and at the 

corners, while coving from rainsplash and ground water is 

usually at the lower third of the wall . 

Maintenance is the key to mitigating the destructive effects 

of wind erosion . Wind damage on adobe walls and roof 

surfaces should be repaired with new adobe mud . Any 

traditional surface coating may be applied to protect against 

any possible future destructive effects. If high wind is a 

continuing problem, a wind screen or breaker might be built, 

using fencing or trees. Care should be taken to plant tree s 

far enough away from the structure so that the roots will not 

destroy the foundaticn or trap moisture. 

Vegetation, Insects, and Vermin: Vegetation and pests are 

natural phenomena that can accelerate adobe deterioration. 

Seeds deposited by the wind or by animals may germinate in 

adobe walls or roofs as they would in any soil. The action of 

roots may break down adobe bricks or cause moisture 

retention which will harm the structure. Animals, birds, and 

insects often live in adobe structures, burrowing and nesting 

in walls or in foundations. These pests undermine and 

destroy the structural soundness of the adobe building. The 

possibility of termite infestation should not be overlooked 

since termites can travel through adobe walls as they do 

through natural soil. Wood members (lintels, floors, window 

and door shutters, and roof members) are all vulnerable to 

termite attack and destruction. 

It is important to rid adobe structures immediately of all 

plant, animal, and insect pests and to take preventive 

measures against their return . Seedlings should be removed 

from the adobe as soon as they are discovered . Large plants 

should be removed carefully so that their root systems will 

not dislodge adobe material. Pest control involving the use 

of chemicals should be examined carefully in order to assess 

the immediate and longlasting effects of the chemicals on the 

adobe building. Professional advice in this area is important 

not only because chemicals may be transported into the 

walls by capillary action and have a damaging effect on the 

adobe fabric , but also for reasons of human and environmental safety. 

Material Incompatibilities: As adobe buildings are continually swelling and shrinking, it is likely that repair work has 

already been carried out sometime during the life of the 

building. Philosophies regarding adobe preseJ:.vation have 

changed, and so have restoration and rehabilitatiml techniques. Techniques acceptable only 10 years ago are no 

longer considered appropriate. Until recently , adobe bricks 

have been repointed with portland cement; deteriorated 

wooden lintels and doors have been replaced with steel ones; 

and adobe walls have been sprayed with plastic or latex 

surface coatings. The hygroscopic nature of adobe has 

rendered these techniques ineffective and, most important, 

destructive . The high strength of portland cement mortar 

and stucco has caused the weaker adobe brick to crack and 

crumble during the differential expansion of these incompatible materials. Steel lintels are much more rigid than adobe. 

When the building expands, the adobe walls twist because 

they are more flexible than the steel. Plastic and latex wall 

coatings have been used to seal the surface, keeping it from 

expanding with the rest of the brick. Portions of the wall 

have consequently broken off. In some instances, incompatible materials can be removed from the building without 

subsequently damaging the structure. Other times, this is not 

possible. Professional advice is therefore recommended . 

6 

Repairing and Maintaining the Historic Adobe Building 

Once the adobe deterioration and any resulting structural 

damage is repaired , the restoration of the adobe building can 

proceed. Careful attention should be given to replace, repair, 

and/or reproduce all damaged materials with traditional or 

original materials. 

Patching and Repairing Adobe Brick: In patching and 

replacing adobe brick , every reasonable effort should be 

made to find clay with a texture and color similar to the 

original fabric. When an individual adobe brick has partially 

disintegrated, it may be patched in place . The deteriorated 

material may be scraped out and replaced with appropriate 

adobe mud . Often fragments of the original adobe brick have 

been ground up, mixed with water, and reused to patch the 

eroded area. However, some professionals advise against the 

reuse of material which has spalled off because it frequently 

contains a high concentration of salts. 

If a substantial amount of the brick has been d~stroyed or 

spalled , commercially made adobe bricks and half-bricks can 

be obtained , or they may be made at the site or nearby . 

Generally these are 3 or 4 inches thick , and ideally they are 

composed of unstabilized adobe (that is, without any chemical additives). The deteriorated adobe bricks should be 

scraped out to insert the new bricks. If most of the brick is 

not deteriorated , then the deteriorated portion may be 

replaced with a half-brick. It may be necessary to cut back 

into undeteriorated portions of the brick to achieve a flush 

fit of the new or half-bricks. Spray (do not soak) the new 

brick and surrounding area lightly with water to facilitate a 

better bond . Too much moisture can cause swelling. Always 

use traditional adobe mud mortar. 

When entire bricks or sections of the brick walls have to 

be replaced , caution should be exercised when buying readymade bricks. Many are now manufactured using stabilizing 

agents (portland cement, lime, or emulsified asphalt) in their 

composition . While the inclusion of these agents in new 

adobe bricks is a technical advancement in their durability , 

they will prove incompatible with the fabric of the historic 

. \ \ ' . 

. l', 

Cement Mortar Incompatibility. Th e strunKer and less flexible 

cement mortar has caused the softer adobe bricks to crumble thus 

leavinK a " honeycomb" of cement mortar joints. (National Park 

S ervice ) 
adobe building. Concrete blocks and cinderblocks are likewise tempting solutions to extensive adobe brick replacement; but, like commercially stabilized adobe bricks. they 

are not compatible with older and more unstable adobe 

bricks. However, concrete blocks have been used for interior 

partitions successfully. 

Patching and Replacing Mortar: In repamng loose and 

deteriorated adobe mortar, care should also be taken to 

match the original material, color, and texture. Most important, never replace adobe mud mortar with lime mortar or 

portland cement mortar. It is a common error to assume that 

mortar hardness or strength is a measure of its suitability in 

adobe repair or reconstruction . Mortars composed of portland cement or lime do not have the same thermal expansion 

rate as adobe brick. With the continual thermal expansion 

and contraction of adobe bricks, portland cement or lime 

mortars will cause the bricks-the weaker material-to 

crack, crumble, and eventually disintegrate. 

It is recognized, however, that some late historic adobe 

buildings have always had portland cement or lime mortars 

used in their initial construction. The removal and replacement of these mortars with mud mortar is not advised 

because their removal is usually destructive to the adobe 

bricks. 

In repairing adobe cracks, a procedure similar to repointing masonry joints may be used . It is necessary to rake out 

the cracks to a depth of 2 or 3 times the width of a mortar 

joint to obtain a good " key " (mechanical bond) of the 

mortar to the adobe bricks. The bricks should be sprayed 

lightly with water to increase the cohesive bond. A trowel or 

a large grout gun with new adobe mud mortar may then be 

used to fill the cracks. 

Repairing and Replacing Wooden Members: Rotted or termite infested wood members such as viXas, savinos, lintels, 

wall braces, or flooring should be repaired or replaced. 

Wood should always be replaced with wood . For carved 

corbels, however, specially formuJated low-strength epoxy 

consolidants and patching compounds may be used to make 

repairs, thus saving original craftsmanship. Tests, however, 

should be made prior to repairs to check on desired results 

since they usually are not reversible . This is an area of 

building repair that ought not be attempted by the amateur. 

For further information, see Epoxies for Wood Repairs in 

Historic Buildinxs, cited in the reading list of this brief. 

Patching and Replacing Surface Coatings: Historically , almost every adobe building surface was coated. When these 

coatings deteriorate, they need to be replaced . Every effort 

should be made to recoat the surface with the same material 

that originally coated the surface. 

When the coating has been mud plaster, the process 

requires that the deteriorated mud plaster be scraped off and 

replaced with like materials and similar techniques, attempting in all cases to match the repair work as close ly as 

possible to the original. It is always better to cover adobe 

with mud plaster even though the mud plaster must be 

renewed more frequently. 

The process is not so simple where lime plaster and 

portland cement stuccos are involved. As much of the 

deteriorated surface coating as possible should be removed 

without damaging the adobe brick fabric underneath. Never 

put another coat of lime plaster or portland cement stucco 

over a deteriorated surface coating. If serious deterioration 

does exist on the surface, then it is likely that far greater 

deterioration exists below. Generally this problem is related 

to water, in which case it is advisable to consult a professional. 

7 

If extensive recoatings in lime plaster or portland cement 

stucco are necessary, the owner of an adobe building might 

consider furring out the walls with lathing, then plastering 

over, thus creating a moisture barrier. Always patch with 

the same material that is being replaced. Although lime 

plaster and portland cement stucco are less satisfactory as a 

surface coating, many adobe buildings have always had them 

as a surface coating. Their complete removal is inadvisable 

as the process may prove to be more damaging than the 

natural deterioration . 

Roofs: Flat adobe roofs should be restored and maintained 

with their original form and materials; however, it may not 

be feasible or prudent to restore or reconstruct a flat adobe 

roof on a building if the roof has previously been modified to 

a gable roof with sheet metal, tiles, or wood shingles. 

If an existing flat adobe roof is restored with a fresh layer 

of adobe mud over an existing mud roof, care should be 

taken to temporarily support the roof during the work 

because adobe mud is heavier wet than after it has cured. If 

not supported, the roof may collapse or deflect. If the 

wooden roof supports are allowed to sag during such work, 

the wood may take a permanent deflection, reSUlting in 

inadequate drainage and/or "ponding" at low points. Ponding is especially damaging to adobe roofs since standing 

water will eventually soak through the mud and cause the 

wooden roof members to rot. 

On an adobe building, it is not advisable to construct a 

new roof that is heavier than the roof it is replacing. If the 

walls below have uncorrected moisture problems, the added 

weight of a new roof may cause the walls to bulge (a 

deformation caused while the adobe mud is in a plastic 

state). If the walls are dry but severely deteriorated, the 

added weight may cause the walls to crack or crumble 

(compression failure). 

Floors, Windows, Doors, Etc.: Windows, doors, floors, and 

other original details of the older adobe building should be 

retained whenever feasible. It is, however, understandable 

when the demands of modern living make it necessary to 

change some of these features: thermal windows and doors, 

easily maintained floors, etc. But every reasonable effort 

should be made to retain original interior and exterior details. 

Maintenance 

Cyclical maintenance has always been the key to successful 

adobe building survival. As soon as rehabilitation or restoration has been completed, some program of continuing 

maintenance should be initiated. Changes in the building 

should particularly be noted. The early stages of cracking, 

sagging, or bulging in adobe walls should be monitored 

regularly. All water damage should be noted and remedied 

at its earliest possible stages. Plant, animal, and insect 

damage should be halted before it becomes substantial. The 

roof should be inspected periodically. Surface coatings must 

be inspected frequently and repaired or replaced as the need 

indicates. 

Mechanical systems should be monitored for break-down. 

For instance, leaking water pipes and condensation can be 

potentially more damaging to the adobe building than to a 

brick, stone, or frame structure. Observing adobe buildings 

for subtle changes and performing maintenance on a regular 

basis is a policy which cannot be over emphasized. It is the 

nature of adobe buildings to deteriorate, but cyclical maintenance can substantially deter this process, thus producing a 

relatively stable historic adobe building. 
Summary 

In conclusion, to attempt the preservation of an adobe 

building is almost a contradiction. Adobe is a formed-earth 

material, a little stronger perhaps than the soil itself, but a 

material whose nature is to deteriorate. The preservation of 

historic adobe buildings, then, is a broader and more 

complex problem than most people realize. The propensity 

of adobe to deteriorate is a natural, on-going process. While 

it would be desirable to arrest that process in order to 

safeguard the building, no satisfactory method has yet been 

developed. Competent preservation and maintenance of 

historic adobe buildings in the American Southwest must (I) 

accept the adobe material and its natural deterioration, (2) 

understand the building as a system, and (3) understand the 

forces of nature which seek to return the building to its 

original state. 

BIBLIOGRAPHY 

,Books: 

Baer, Kurt; and Rudinger, Huge. ArchiteCfure of the ClIlifornill 

Mi.l.lilln.l. Los Angeles: University of California Press. 1958. 

Boundreau, E. H. Makin!-( the Adohe Brick . Berkeley, Calif.: Fifth 

Street Press, 1971. 

Bunting, Bainbridge. Early Architecture in New Mexico . Albuquerque: University of New Mexico Press, 1976. 

Of ElIrth and Timhers Made : Nell' Mexico Architecture. 

Albuquerque: University of N'ew Mexico Press. 1974. 

Clifton. James R. Pre.ll'/'vlItion of Hi.ltoric Adohe Structure.l: A 

SllItU.I Report. Washington, D.C.: National Bureau of Standards Technical Note 934, US Government Printing Office, 

Stock No. 003-OO3-D1740-0, Feb. 1977. 

McHenry, Paul Graham, Jr. Adohe-Build it Your.le/f. Tucson , 

Ariz.: University of Arizona Press, 1973 . 

Phillips, Morgan W.; and Selwyn. Judith E. Epoxie.1 for Wood 

Repair.1 in Hi.ltoric Buildin!-(.\'. Washington, D.C.: Heritage 

Conservation and Recreation Service, 1978. 

Articles, Periodicals, and Bibliographies: 

" Adobe, Past and Present." Reprinted from EI Palacio. Vol. 77. 

no . 4 (1971). 

" An Architectural Guide to Northern New Mexico." New Mexico 

Architecture. Vol. 12, nos. 9 and 10 (Sept.-Oct. 1970). 

Adohe New.\. Los Lunas New Mexico. Published bimonthly. 

Barnes, Mark R. "Adobe Bibliography . " The Association for 

Preservation Technology Bulletin. Vol. 7, no. 1(1975). 

Eyre. T. A. "The Physical Properties of Adobe Used as a Building 

Material." The Univer.lity of Nell' Mexico Bulletin . Engineering Series. Vol. I, no. 3 (1935). 

George, Eugene ... Adobe Bibliography." The Association for 

Preservation Technology Bulletin. Vol. 5, no. 4 (1974). 

Haapala, K. V. "Stabilizing and Restoring Old Adobe Structures 

in California." New.l/eller of the National Association of 

Restoration Specialist.v. Murphy, Calif., June 1972. 

Hooker, Van Dorn. "To Hand Plaster or Not?" New Mexico 

Architecture . Vol. 19. no. 5 (Sept.-Oct. 1977). 

Many individuals have contributed to the direction. the content and the final 

form of this Preservation Brief. The text and illustration materials were 

prepared by de Teel Patterson Tiller. Architectural Historian. and 

David W. Look. AlA. Technical Preservation Services Division. Much 

of the technical information was based upon an unpublished report 

prepared under contract for this office by Ralph H. Comey, Robert C. 

Giebner. and Albert N. Hopper, College of Architecture. University of 

Arizona. Tucson . Valuable suggestions and comments were made by 

architects Eugene George . Austin. Texas; John P. Conron. Santa Fe; 

and David G. Battle. Santa Fe. Other staff members who provided 

editorial assistance include H. Ward Jand!. and Kay D. Weeks. 

This publication was prepared pursuant to Executive Order 11593, "Protection and Enhancement of the Cultural Environment," which directs the 

Secretary of the Interior to "develop and make available to Federal agencies 

and State and local governments information concerning professional methods 

and techniques for preserving, improving, restoring and maintaining historic 

properties." The Brief has been developed under the technical editorship of 

Lee H. Nelson, AlA, Chief, Preservation Assistance Division, National Park 

Service, U.S. Department of the Interior, Washington, D.C. 20240. Comments 

on the usefulness of this information are welcome and can be sent to Mr. 

Nelson at the above address. This publication is not copyrighted and can be 

reproduced without penalty. Normal procedures for credit to the author and 

the National Park Service are appreciated. August 1978. 

Renewing the Surface Coating. Traditionally, adohe .IIIrfllce cOll/ill!-(.1 that protected the fra!-(ile adohe huildill!-( fahrlc were renewed I' very 

fel\' years. Recently however, hi!-(h lahor costs have made thi.\' 1I reilltively expen.\'ive proce.\'.I. Women lire .Ieell here recoatin!-( all lIdohe wlIlI 

with mud plaster mixed with .\'traw at Chami.wl, Nell' Mexico . (Photo hv Ru.uell Lee , FlIrm Securitv Administratioll Collection, 

Lihrary ofColl!-(res.\') . -

8