Ask Your Inspector: "Masonry"

Posted by on Wednesday, September 20th, 2017 at 1:10pm.

Mansour Nasiri, RHI, Master Home Inspector, and an NPG consultant, has taken the time to answer a few questions. Follow Mansour in the "Ask Your Inspector" for answers to some common question we have received here at NPG, or post your own in the contact form below! 

 

Question: I'm currently looking at purchasing a home with some masonry. What could you tell me about masonry walls?

 

Thank you ever so much for the question. I'm not entirely sure if there is a specific question you have about masonry walls - the question posed is quite broad. If I don't specifically answer the question you have in the segment below, please do re-submit it, and I'll happily re-answer for you.

 

Answer: Masonry has been used in building construction for thousands of years. It can be used to form a simple durable cladding system or a more decorative yet functional system using different patterns, designs and the integration of different products. In addition to forming the exterior cladding, masonry walls can serve as a portion of the structural framing for the building. Masonry walls also typically increase the fire resistance of the wall system or structural elements.

Masonry is typically installed on site using manufactured masonry units and site mixed mortar. The units are laid in mortar to various heights, with the strength of the assembly being achieved during the curing of the mortar. Common masonry unit types include clay and concrete units, which may be solid or hollow, and glazed or unglazed.

Clay brick units use natural clay that is formed into the required shape at the manufacturing plant. Several different finishes can be formed on the exterior surface of the brick such as wire cut or sand finished. Different colors of sand and glazing can also be applied to the brick. Brick units are heated in a kiln to a temperature of 1100 to 1200 degrees Fahrenheit to create the structural properties of the units.

Clay units are categorized by grade and type. The masonry grade depends on the required durability of the units. Typically, Grade SW (severe weathering) is recommended in most areas. These units are much more resistant to the freeze-thaw cycle. MW (moderate weathering) units should be used in areas where freezing cycles are not anticipated. NW (negligible weathering) units should only be used in interior conditions where the interior air is conditioned and there is no exposure to moisture. The type of units depends on the required dimensional tolerances. Typically Type FBS is specified unless unusually tight tolerances area required. Where tight tolerances are required, Type FBX should be specified. Type FBA units are typically used to create a rustic appearance with a high dimensional tolerance. Type FBS, for example, allows for waste up to 20 percent, chips up to 5/16” on the edges and up to ½” on the corners, cracks in the brick that can’t be seen from 20’ away and up to ½” in size variation from one brick to the next.

The mortar used to bond the brick together usually consists of portland cement, lime sand and water. There are different mortar types depending on the required strength. The most common masonry mortars used in new construction are as follows:

Type N: Used in general masonry walls above grade. This is the most common masonry mortar used in non-structural applications in new construction. This has good bond qualities and good resistance to water penetration.

Type S: Typically used in structural masonry applications. Has a higher proportion of cement and subsequently can have increased shrinkage of the mortar.

Type M: Typically used only in below grade applications.

Brick exterior walls can be classified as either barrier walls or drainage walls. Barrier walls are constructed of solid masonry without drainage cavities. Barrier walls are designed to prevent water infiltration to interior spaces through mass. Ideally, the amount of water absorbed by a wall over a given period of time is less that can be dissipated in the same time period. Drainage walls are designed with cavities between outer face brick (veneer) and the back up walls. The back up walls can be brick, concrete masonry units or a metal or wood framed wall. Ideally, water that penetrates the face brick or enters the cavity is collected at flashing where it is expelled through a bed joint and/or at weeps.

Deterioration in brick exterior walls is generally attributed to water infiltration and includes staining and efflorescence, cracking, spalling, displacement and deterioration in mortar joints. Efflorescence occurs when water washes soluble salts out of mortar and onto the surface of the brick. It is apparent in the form of white crystalline particles that develop on brick surfaces as water evaporates. Cracks and spalling in brick can result when water absorbed and retained in the brick freezes. The expansion of reinforcing steel or lintels from rust in brick wall systems can also cause cracking and displacement.

Fretting of Brickwork (Salt Attack) is caused by the action of salt migration in the wall system. Water which has salt dissolved in it migrates through the brick to the brick surface. As the brick dries, the salt is left behind and forms salt crystal. The salt crystals grow in the voids within the brick. As more salt is left behind by the evaporation of water, the salt crystal grows larger and larger. The strength of the growing salt crystal can be stronger that the elements that hold the brick together. If this occurs, the brick face begins to crumble and fall away. This is also true of mortar joints.

Mortar, used to bond bricks together, must be softer than the brick it binds, so the bricks don’t crack during expansion, and must be tooled in a way that discourages the collection of water in the joint. Bricks undergo long term permanent expansion over time. This expansion continues for the life of the brick, but the majority of the growth occurs early in its life. Most brick expand 1/32” to 1/16” over fifteen years. For this reason, expansion joints are typically required at corners, offsets, and at a regular spacing, usually 20 to 30 feet, depending on the units. Bricks undergo cyclic thermal movements. These materials expand in warm temperatures and contract in cold temperatures. The movement joints must also accommodate these movements.

 

I hope the above has served to shed some light on masonry walls for you, and has answered your particular question(s). If there is any follow-up that you would like, please do not hesitate to fill out the contact form below.

 

Wishing you all the very best,

 

Mansour Nasiri
GPI RHI, and Master Home Inspector
Owner/Inspector
NPG Consultant

 

If you have a question for Mansour, and would like to have it answered on our blog series, please feel free to fill out the form below with the subject line: "Ask Your Inspector", and we will make every attempt to address the question in the next "Ask Your Inspector" series. All other inquiries may be made through the form with your own subject heading.

Please provide a valid email address.

 


Please note that these Question and Answer series ought to be treated as general in nature, and should not be considered to be technically exhaustive. It is our strongest recommendation and encouragement that you seek out the advice of Mansour Nasiri directly; another Home Inspection professional (with comparable qualifications); or a trained professional before carrying out or administering any of the recommendations here. Please use the form above, in order to contact Mansour Nasiri regarding this session.


 


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