What is The Virginia Masonry Association?

The Virginia Masonry Association (VMA) is a trade organization which promotes the awareness and use of masonry products to Architects, Design Professionals and to the general public.  VMA also recruits, educates and trains new and existing masons.

What are the requirements for membership?

Our membership is comprised of masonry contractors, suppliers, distributors and manufacturers of masonry products.  If you or your organization wish to receive information about becoming a member of VMA, contact Marcia Meighan, Executive Director.

General Brick

Are there many color options available with brick?
Where can I find out about my color options in brick?
How can I match existing brick?
What is the "white stuff" on my brick after construction?
How do you remove efflorescence from masonry?

Commercial/Institutional

Should brickwork be painted?
Is there a test to determine the amount of efflorescence in brick?
What is the best weep system?
Why should steel stud parapets be avoided?
What is the best flashing?
Is there a freeze-thaw test for brick?
What spacing should be used for brick expansion joints?
How can paint be removed from brickwork?
Can stains be removed from brickwork?
Can water penetrate brickwork?

Landscape

What is the difference between ASTM C 902 pavers and ASTM C 1272 pavers?
What type of base should I use for brick paving?
Can brick pavers be installed over an existing concrete or asphalt driveway, patio or walk?
Can a do-it-yourselfer construct a new brick driveway, patio or walk?

Residential

Why should I buy a brick home?
Is brick that much more expensive than other siding materials?
What kind of maintenance does a brick home require?
Is brick energy efficient?
How does brick impact my home insurance costs?
Do brick homes have a better resale value?
Can I change my brick's color once it is in a wall?
Can I add brick to my existing home?
Can ivy or other plants growing on my brick damage it?
What are the correct procedures for repointing brickwork?
What is the fire resistance rating of a brick wall assembly?

Are there many color options available with brick?

Brick is an all-natural building material that is made from a mix of clay and water that is then baked, or "fired," in a kiln until hardened. Different clays produce different colors, and there are many different types of clays. In addition, various natural coatings, such as sand and limestone, can also be added during the firing process to produce different colors, effects, textures and finishes. Even a brick's position in the kiln can affect the final look. When you combine these with the tonal varieties of today's mortars, you can see that your color choices in brick are virtually endless.

Where can I find out about my color options in brick?

Visit a brick showroom near you to review your options. You'll have the chance to review hundreds of brick and mortar combinations. To locate a showroom, go to the online Member Directory. Also, be sure to check your local Yellow Pages under "Brick." You will find that there are hundreds of brick and mortar combinations.

How can I match existing brick?

Unfortunately, there is no national database of brick colors and textures. However, a local brick distributor representing a wide variety of manufacturers will probably be able to match your brick if it is still manufactured. A good brick salesman will know which brick in his stock comes closest to yours. This web site also has links to manufacturers many of whom have brick displayed on their web site. For names of local brick manufacturers and distributors, see your local Yellow Pages under "Brick".

What is the "white stuff" on my brick after construction?

It is a substance called "efflorescence" which is a deposit of soluble salts and bases, usually white in color that sometimes appears on the surfaces of masonry or concrete construction. Although it may be an aesthetic concern, efflorescence will not affect structural performance.

Often efflorescence is apparent just after the structure is completed. If the efflorescence is essentially uniform throughout the exterior facade, it indicates normal water loss from the materials and the building. Some identify this occurrence as "early age" efflorescence or "new building bloom." If unattended, the salts will eventually be removed by rain water.

If the deposit is heavy and essentially shows as white streaks immediately below mortar joints or covering localized areas of the masonry, it indicates that water has entered or is entering the wall at a higher elevation. These salts are called leachates, preferred to "lime spots," "lime runs" and "lime deposits;" and are sometimes identified as "late age" or recurrent efflorescence. Late age or recurrent efflorescence usually consists of more permanent surface accumulations and indicates a need for corrective measures.

How do you remove efflorescence from masonry?

Before any removal effort is made, the reason for the efflorescence should be established. If it is "early age efflorescence," moist construction materials may be to blame. If "late age efflorescence," the possibility of water leakage should be investigated. If the efflorescence is near ground level, ground water may be the cause. In any case, the problem should be repaired prior to removing the efflorescence. Generally, if efflorescence is the main concern regarding masonry surface discoloration, the masonry walls should be allowed to cure and then the salts should be removed.

Compared to other stains, the removal of most types of efflorescence is relatively easy. As stated previously, most efflorescing salts are water soluble and many will disappear with normal weathering unless there is some external source of salts.

In general, most efflorescence can be removed by drybrushing followed by flushing with clean water. If brushing is not satisfactory, it may be necessary to use a very light, or brush, sandblasting to remove the deposits. Brush sandblasting is sandblasting which is light enough that coarse aggregate is not exposed by the sand blasting. Sandblasting needs to be done with care, as it can alter the appearance of masonry by roughening the surface. There are also a variety of commercial cleaners available which may be effective for efflorescence removal. Consult manufacturer's information for applicability.

Commercial/Institutional

Should brickwork be painted?

A brick wall may be painted provided the correct preparation is done, the proper paint is selected, and the paint is applied correctly.  Generally, new brick walls are not painted.  However, if it is desired to paint a recently constructed brick wall, the wall should be allowed to fully cure 28 days and should not be cleaned or treated with acid solutions.  Alkali-resistant paints should be used and a zinc chloride or zinc sulfate solution may need to be applied to the wall to neutralize the surface.

Painting brick does not preclude good construction and detailing practices.  Any deficiencies such as surface deposits; broken brick; cracked, loose or missing mortar; or inadequate flashing and weep holes should be corrected prior to painting.  In addition, the brick should be thoroughly cleaned and given ample time to dry before application of paint. 

For brickwork to function properly, the wall must resist moisture penetration and be permeable to vapor from the structure.  Consequently, any paint applied to the wall must also have these same characteristics.  In addition, the inherent features of a brick wall which channel water out, such as weep holes and vents, must not be clogged by paint or caulk to inhibit the flow of water.

Latex and portland cement-based paints perform well on brick walls.  Oil-based, alkyd, rubber and epoxy paints do not allow any vapor in the wall to escape and consequently should not be applied to brick.  Prior to painting, the brick should receive a prime coat suitable for the paint application per manufacturer's instructions.

Should a water repellent be applied to a brick wall?

Generally, water repellents are only an interim solution to any water penetrating a brick wall since they loose their ability to repel water after 1 to 10 years.  However, in cases where all other options have been exhausted, it may be considered as long as one is aware of the inherent nature of water repellents.

There are basically two types of water repellents: films and penetrants.  Films such as acrylics, stearates, mineral gum waxes, urethanes and silicone resins form a thin membrane over the brick.  Penetrants such as silanes, siloxanes and blends actually penetrate the brick surface.  Films are good at repelling water but poor at permitting water vapor transmission which allows the wall to breathe.  Penetrants, on the other hand, are good at both.  They will usually have a matte finish while films may produce a higher sheen.  Penetrants are more acceptable since they allow any water present in the brick to exit the wall.  However, penetrants will not provide graffiti-resistance to a wall while some films will.

Application of a water repellent does not negate proper brick construction and detailing procedures.  Any deficiencies in a brick wall such as inadequate flashing, weep holes, mortar joints or broken brick should be corrected prior to the application of a water repellent.  The wall should also be cleaned and allowed to thoroughly dry before administering a water repellent.

Is there a test to determine the amount of efflorescence in brick? 

ASTM C 67 has a method to test for efflorescence, but it is meant to be conducted before the brick are shipped to the job.  While it will not result in a quantitative amount of efflorescence present, it will indicate if the brick effloresces or not.  Unfortunately, this test is not appropriate for brick that have already been built into a wall.

Chemical tests on existing efflorescence could be done to find the type of salt present.  A masonry consultant should be contacted to make this determination.

What is the best weep system?

Weep systems in use include wicks, oiled rods, weep tubes, open head joints, and vents.  BIA does not advocate one type of weep system over another.  Wicks should be spaced at 16" o.c. with the remainder of the weep systems spaced at 12" o.c.  Rope wicks can be made from cotton sash cord.  Drainage materials used at the bottom of the cavity are most effective for open type of weep holes like open head joints, weep tubes, etc., however it could be used with rope wicks.

It is important to maintain a clean, open cavity for weep holes to function properly.  If mortar droppings are anticipated, then it is best to detail a drainage material that will catch any mortar like pea gravel or mesh.

Why should steel stud parapets be avoided?

There are two primary reasons steel stud parapets are advised against. The increased possibility of water penetration and resulting corrosion is one issue.  A parapet is externally exposed on three sides making it one of the most vulnerable areas of a building.  Furthermore, it is insulated differently than the wall below and can potentially be subjected to more thermal-related issues than other parts of a wall.  Water penetration is also more likely due to rain or condensation.  This water penetration could lead to corrosion and other future problems.

The second issue deals with the differential movement of the brick and steel stud.  The stud can expand at a much higher rate than the brick.  This could affect the coping used on the top of the wall and surrounding mortar joints.

Obviously, these issues can be dealt with in design and construction, but BIA has seen some problems in the past with this type of assembly.

What is the best flashing?

A flashing material must be impervious to water, tough enough to withstand construction abuse and yet flexible enough to conform to the desired shape, and not deteriorate while in service.  It should also not react with mortar or corrode and should be compatible with joint sealants.

Traditionally, copper sheet has been used as flashing in masonry walls.  Stainless and galvanized steel sheet have also been used as flashing.  More recently, plastics and combination flashings have found their way into masonry walls.  While there are pros and cons to each type of flashing and a range of cost associated with each, they will all perform satisfactorily as long as they meet the basic criteria for a flashing material.

Is there a freeze-thaw test for brick?

ASTM C 67 contains a freezing and thawing test which is presently the industry accepted standard.  This test should be conducted prior to delivery of brick to the job site.  Bricks pass the test if, after 50 freeze/thaw cycles, they do not exhibit significant weight loss, breaking, or cracking.  The test is designed to be performed on brick that have not yet been built into a wall.

There are many factors that contribute to brickwork's ability to withstand cyclical freeze/thaw including workmanship; the mortar type, its air content and consistency when laid; and the degree of saturation in a wall.  These factors cannot be tested for in ASTM C 67 since they involve other elements outside the brick itself.

Consequently, it is not a forgone conclusion that a brick that passes the test will not experience adverse effects when incorporated into brickwork.  Attention to proper design, detailing and workmanship can assure a durable wall assembly.

What spacing should be used for brick expansion joints?

Brick is the smallest dimension it will be in its long service life when it leaves the kiln.  As it is exposed to moisture from a variety of sources including the air, wet mortar, rain and condensation, it will naturally expand since it is a clay product.  Temperature will also cause brick to expand and contract.  Consequently, it is important to incorporate expansion joints into brickwork to accommodate this movement.

Expansion joints should be located where stresses or cracks are likely to develop in brickwork.  Prime candidates for expansion joints include long expanses of walls, corners, offsets, setbacks, and parapets.  Expansion joints should also be located below shelf angles to account for vertical expansion of brick.

When accent bands of other materials such as precast or concrete masonry units are included in a wall, it may be prudent to include a bond break or slip joint between the two dissimilar materials if their coefficients of expansion are significantly different.  Bond breaks are created by embedding a smooth sheet such as flashing materials in the mortar bed which allow the materials to move independent of each other.

When determining where expansion joints should be placed, it may be necessary to calculate the amount of expansion anticipated.  This can be done by knowing the coefficients of expansion of the brickwork and the parameters of its environment.

How can paint be removed from brickwork?

As always, the wall should be thoroughly saturated with water before and after any cleaning application. Also, a small inconspicuous area of wall should be tested to confirm that any solutions used will not harm the brick.

Freshly applied paint can be removed with a solution of trisodium phosphate mixed with water at a rate of 2 lb. per gallon of water.  Apply the solution to the brick; allow it to soften paint; and remove with scraper and stiff bristle brush.  Proprietary chemical compounds are also available through local distributors to remove fresh paint.

Existing paint which has been in place for some time is more difficult to remove and may require the use of abrasive techniques with non-steel scrapers or sandblasting by a professional.  Certain brick should not be sandblasted.  Proprietary chemical compounds from local distributors in the form of a gel solvent may be necessary to soften existing paint.  Numerous applications may be necessary depending on the number of paint layers.

Can stains be removed from brickwork?

Most stains and discoloration can be removed from brickwork if the proper cleaning technique is employed.  There are essentially two categories of stains; those which are externally applied to the wall and those which originate from within the wall.  Those which come from within a wall may need additional investigation to prevent the stain from returning.

As always, it is important to thoroughly saturate a brick wall before application of any cleaning solution.  As a general rule, acidic cleaning solutions should only be applied to red brick with no surface finish such as sand.  Also, an inconspicuous area of the wall should be tested with any cleaning solution for compatibility prior to application on the entire wall.  Any cleaning solutions should be thoroughly rinsed from the wall.

Most stains can be dealt with by thoroughly washing the wall with a common household or kitchen cleanser dissolved in water and applied to the wall with a stiff bristle brush.  If this is ineffective, a poultice which dissolves the stain and pulls it into an inert material may be necessary.  The inert material can be talc, whiting or fuller's earth while the solvent will vary based on the type of stain.  Proprietary cleaning agents can also be employed to remove specific stains.

Sandblasting and pressure washing brickwork can also be options for certain brick when especially stubborn mortar or externally applied stains are involved.  Bricks with coatings such as sand or slurry finishes should not be cleaned in this manner.  Sandblasting and pressure washing should usually only be undertaken by a competent professional with experience.  If improperly executed, either of these methods can permanently damage the brick.

Can water penetrate brickwork?

Homes have been built for hundreds of years with the knowledge that brickwork is not impervious to water.  Water can migrate into brickwork.  Brickwork handles this moisture by either having a cavity or separation between itself and the wall behind it or by being so thick that it acts as a barrier to the water.

For a drainage wall, water travels down the backside of the brick in the air space and is then channeled out with flashing (metal or plastic sheet) sloped toward the face of the wall and weep holes (small openings or tubes) spaced every few brick at the mortar joints.  These flashing and weep holes should be located above all doors and windows, below all window sills, and above the ground at the base of the wall.  In a barrier wall, the mass of the brickwork keeps the interior of the wall dry by allowing water to evaporate before proceeding all the way through the wall.  Only under prolonged exposure to sustained moisture or rain will a barrier wall exhibit moisture on the interior.  When this occurs, the moisture then drains down the back of the wall into flashing at the base which channels it out through weep holes.

The overwhelming majority of brickwork is properly detailed and constructed, experiencing no moisture problems.  In the few instances where moisture is a problem, it can be attributed to poor construction or detailing in the brickwork.  It is important to maintain a clean space behind the brick in drainage walls.  Full contact between mortar and bricks and proper installation of flashing and weep holes are also important to ensure the highest water penetration resistance.  Applying and maintaining a proper sealant around window and door openings also plays a vital role in keeping moisture out.

Landscape

What is the difference between ASTM C 902 pavers and ASTM C 1272 pavers?

ASTM C 902 is entitled "Specification for Pedestrian and Light Traffic Paving Brick." The scope mentions applications such as patios, walkways, floors, plazas and driveways. ASTM C 1272 is entitled "Specification for Heavy Vehicular Paving Brick." These pavers are used in areas with a high volume of heavy vehicles. Heavy vehicular traffic is defined as many repeated passes of tractor-trailer trucks. This includes streets, commercial driveways and aircraft taxiways. Pavers conforming to ASTM C 902 can be used in most applications, except those that receive truck traffic.

What type of base should I use for brick paving?

A flexible base consists of compacted crushed stone, gravel or coarse sand. Only mortarless brick paving is suitable for this type of base. A semi-rigid base consists of asphalt concrete, commonly referred to as asphalt. Once again, only mortarless brick paving is suitable over this type of base. A rigid base is defined as a reinforced or unreinforced concrete slab on grade. Mortarless or mortared brick paving may be placed over this type of base.

Flexible bases include crushed stone, gravel or coarse sand. Applications for flexible bases range from residential patios to city streets. Flexible paving systems are typically the most economical to install since less labor and fewer materials are involved. A flexible paving system allows easier repairs to utilities located beneath the pavement. Flexible pavements also allow for water to percolate down through the system instead of running off on the surface. The thickness of each layer in a flexible pavement depends upon the imposed loads and the properties of each layer. A pavement subjected to heavy vehicular traffic requires a thicker base than a pavement subjected to pedestrian traffic.

Mortared brick paving can be used for any type of pedestrian or vehicular traffic in both interior and exterior applications. This type of assembly is especially well-suited for heavy vehicular areas such as streets or parking lots and where surface drainage is necessary.

Can brick pavers be installed over an existing concrete or asphalt driveway, patio or walk?

Brick paving can be installed over existing concrete or asphalt as long as it is in reasonably good shape. To ensure an adequate foundation for the brick, the existing concrete slab or asphalt should be inspected and repaired as necessary. Any cracks, chips, holes, ruts or spalls should be repaired in order to achieve a flat surface.

The brick can be installed either with or without mortar. If no mortar is used, a half-inch setting bed of coarse sand should be laid and compacted. An edging of metal or heavy-duty plastic should be placed around the perimeter of the brickwork and set to just below the height of the finished brick surface. Pavers can then be placed in the desired pattern on top of the sand. The bricks should be placed as close to each other as possible. It may be necessary to cut some of the brick near the edging. Once the brick are all in place, install mason's sand between the brick and over the surface. Sweep away excess surface sand and the brick pavement is ready for traffic.

If mortar is used, the concrete slab should be prepared in the same manner as above. A half-inch mortar setting bed should then be applied upon which the bricks are set with mortar placed between the pavers. Only a small area should receive the setting bed at a time in order to ensure that it does not set prior to laying the brick. Mortared brickwork should not be laid on asphalt.

Can a do-it-yourselfer construct a new brick driveway, patio or walk?

A new brick pavement can be constructed on asphalt, concrete, or compacted gravel as a base. For asphalt and concrete bases, the base material should be installed according to standard construction procedure and then the brick can be constructed on top. (See previous question.)

For a compacted aggregate base, the earth below should be well compacted. All brick pavements should have the earth graded to a minimum slope of a quarter-inch per foot for drainage. Then four-inches of crushed stone, followed by a layer of geotextile material, if desired, and one inch sand setting bed of coarse concrete sand is laid. An edging of heavy plastic or metal should be installed at the perimeter of the brick. The brick should then be laid on top of the sand and cut as needed at the edging. Mason's sand should then be spread on the top and in between the brick and consolidated with a plate compactor if necessary. Mason's sand should be added until all the joints are filled and any excess sand should be removed.

For pavements such as driveways, a six to eight-inch gravel base should be installed and compacted with a plate compactor. Then a geotextile material should be installed and a one-inch setting bed of coarse sand should be laid. Placing edging, brick and mason's sand between the joints should then proceed as outlined above. Heavier duty pavements can be laid in the same manner, but the base is thicker.

Adequate preparation of the earth before installation and compaction of the entire assembly after installation with a plate compactor are essential to a well-constructed brick pavement.

Residential

Why should I buy a brick home?

Nothing else can match the classic beauty and elegance of a brick home. Building with brick says, "You have arrived." But there's more to brick than just looks. Brick offers lasting value. It can enhance the resale value of your home by as much as 6 percent. Brick is virtually maintenance free. It doesn't rot, dent, or need to be painted and it won't be eaten by termites. Brick is also energy efficient, keeping you cool in the summer and warm in the winter. In short, brick offers you a combination of advantages not found in any other siding material. The world's most beautiful and most practical homes are built with brick.

Is brick that much more expensive than other siding materials?

Brick costs more than some other commonly used siding materials because brick is a premium product, but it's not nearly as expensive as you might think. In many parts of the country, a new brick home will cost you only a small percentage more than a comparable vinyl-sided home. Other products, such as artificial stucco, cost about the same as brick, but are far less durable and require much greater maintenance and upkeep.

What kind of maintenance does a brick home require?

A brick home is virtually maintenance free. Brick is one of the oldest building materials in the world, and one of the reasons it's still so popular is brick's ease of upkeep. Brick never needs painting, never rots, will never be eaten by termites and will never dent or tear. Brick homes built hundreds of years ago still stand today.

Is brick energy efficient?

Brick is a building material that has exceptional "thermal mass” properties. Thermal mass is the ability of a heavy, dense material to store heat and then slowly release it. For you, this means that during the summer months your brick home stays cool during the hottest part of the day. During the winter, brick walls store your home's heat and radiate it back to you. Vinyl, aluminum, wood or EIFS (artificial stucco) are all thin, light building materials that don't have good thermal mass properties. The superior thermal mass qualities of brick have been known for centuries. Most notably, the Pueblo Indians in the Southwest used adobe masonry to moderate weather extremes and keep their homes comfortable.

How does brick impact my home insurance costs?

A brick home is fire resistant, pest resistant and weather resistant. Brick is such a strong and durable building material that your insurance companies may even offer you a discount on your home insurance costs. Check with your agent for more details.

Do brick homes have a better resale value?

Take a look through this Sunday's real estate section of your local newspaper and read the home listings. Notice how people always list brick as a primary selling point. Brick's beauty and practicality are always a plus when you resell. On average, a brick exterior adds 6% to the resale value of your home.

Does brick allow me to personalize the look of my home?

Brick is not a one-dimensional product like stucco or siding. Brick allows you to personalize the look of your home with elegant detailing, such as arches and quoins, different bond patterns and special shapes. Brick expresses your personality and style like no other building product can.

Can I change my brick's color once it is in a wall?

A brick's color can be attributed to its clay composition, any added compounds, its firing temperature and any surface treatments. Because brick is composed of naturally occurring materials, all brick will not necessarily be exactly the same. For this reason, some brick may be of a slightly different color than others in a given batch. Usually, this adds character to a wall, but occasionally it is desired to blend these brick with other brick in the wall. This can be done by individually staining the brick in question.

Staining is a common practice and is usually done by a professional with expertise in its application. The stain itself is a proprietary product made specifically for brick. A local brick supplier in your Yellow Pages should be consulted for a product and professional applicator. Since the surrounding mortar joints must be masked, it is a time consuming process and is usually only done when a limited number of brick are involved. If staining is done properly, it should have no detrimental effect on the bricks and should provide a long lasting finish.

Can I add brick to my existing home?

Brick can be added to an existing home. This can be done by adding a nominal three- or four-inch thick brick in front of the wall and supporting it by either the existing footing or on an angle fastened to the existing concrete or block foundation wall. It is important to properly detail the wall by providing flashing and weep holes at all points of support. The area beneath the angle at or below the ground level should have gravel at least six-inches deep to provide good drainage. The brick should also have at least a one-inch air space between itself and the existing siding. Building paper should cover the existing siding unless it is already provided behind the existing siding. Corrosion-resistant metal anchors should tie the brick to the studs in the existing wall. The joint between the brickwork and all doors and windows should be closed with silicone caulk. Insulation may also be added to increase the total thermal value of the wall.

Another alternative is to use thin brick in panels and attach them directly to wall studs. This may mean removing the existing siding in order to attach the thin brick. Insulation may also be added if desired.

Can ivy or other plants growing on my brick damage it?

To answer this question, you need to understand the consequences of leaving or removing plant growth. This growth on brick can potentially damage it by forcing root tendrils into the mortar joints. Moisture can then find its way into the wall and freeze-thaw action or other moisture related events can occur resulting in damage. However, ivy also sheds rainwater and reduces the surface temperature of the wall. Properly constructed walls with good workmanship and well-tooled joints can also resist tendril intrusion better than poorly constructed walls.

When existing plant growth is removed from a brick wall, it may also remove part of the mortar from the joint. This could result in the wall having to be repointed by removing any broken mortar and repacking with new. Further, complete removal of the tendrils is difficult. Failure to do so may result in stains on the wall.

Therefore, it is an evaluation which is best made by the owners taking these as well as the aesthetic and economic considerations into account. While plant growth can shorten the life of brickwork, a well-constructed wall should still last for many decades.

What are the correct procedures for repointing brickwork?

Repointing or tuck-pointing existing brickwork may be in order when mortar joints have softened, deteriorated or exhibited pronounced cracking. Generally, repointing involves carefully removing existing damaged mortar while not disturbing or cutting the existing brick. The joint is then repacked with mortar in layers.

It is important to remember that the mortar should always have slightly less strength than the brick. Usually, the best mortar for use in repointing is what was in the wall to begin with. For most walls less than 70 years old, generally Type N or O mortar should be used when repointing. For structures older than this, it is best to try and determine what the original mortar consisted of and match that.

What is the fire resistance rating of a brick wall assembly?

Since the primary ingredient in brick is clay which is fired to around 20008 F, it is a non-combustible material. As such, it is an excellent cladding choice to resist or confine fires.

A brick wall's fire resistance rating can be calculated. This is done by extrapolating from known fire resistance periods for a given thickness of wall. Refer to Technical Notes 16B for further information on how to calculate fire resistance ratings for specific brick walls.

Currently, there are four Underwriters Laboratories tests which have assigned fire resistant ratings to specific wall assemblies. They include U302, U418, U425 and U902. U302 yields a 2 hour rating and involves a brick veneer drainage wall with wood studs and gypsum sheathing and wallboard. U418 and U425 vary in rating between æ to 2 hours and are brick veneer drainage walls with steel studs and gypsum sheathing and wallboard. U902 consists of a drainage wall with brick veneer and concrete masonry units and has a 4 hour rating.