Jason Thompson

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Everything posted by Jason Thompson

  1. I'm often asked if it feasible to grout 4 inch (100 mm) concrete masonry units. To which I reply "No"...or possibly "Good Luck". While there is no code prohibition on grouting hollow 4 inch CMU, the size of the cells makes doing so pretty impractical - especially if reinforcement is present. The primary reason is illustrated in the accompanying photos showing a 4 inch CMU from the top of the unit (as made) and the same unit from the bottom (as made). While the width of the cells at the top of the unit could lead one to believe grouting is possible, due to the tamper of the cells opening width transitions from about 1.5 inches to around 0.75 inches. Is it impossible to fill these hollow 4 inch units with grout - no. But if a solid 4 inch unit is needed for whatever reason(s), it's easier, faster, and less expensive to simply specify a solid 4 inch unit.
  2. The electrical conduit may be exposed (provided they are rated for such applications), which is common in retrofit applications or where aesthetics are not critical. Alternatively utilities can be run through the cells of the units allowing for the outlet boxes to be mounted on the surface of the assembly or flush mounted.
  3. 6 inch loadbearing CMU in low-rise construction is very feasible (and a system I personally feel is underutilized for many common applications). Structurally their design is the same as any other block size. The only unique consideration with 6 inch CMU (as with 10, 12, or other block sizes other than 8 inch) is maintaining bond when turning corners, etc.
  4. Personally, I do see numerous applications for the window/door surrounds that you describe...although typically they are installed as an anchored veneer along with the rest of the masonry veneer cladding. That said, there is nothing that would technically prevent an adhered veneer surround from being used - provided that it met current building code criteria...including the 15 pounds per square foot weight limit you reference. The challenge I foresee is whether such a product would be classified as a cast stone product (and accordingly meeting the requirements of ASTM C1364) or a manufactured stone veneer product (meeting the requirements of ASTM C1670). If intended to comply with ASTM C1364, establishing a mix design that met the compressive strength and absorption requirements of ASTM C1364 - while concurrently having a weight of 15 psf or less may be a challenge...but certainly possible.
  5. Very conditionally. In applications where the water will flow onto or impact the manufactured stone; I'd definitely recommend against such applications as the water will eventually erode the surface pigments...and eventually the stone. If, however, the manufactured stone is simply providing a backdrop to a waterfall without becoming wet due to the falling or splashing water, such applications may be acceptable. I would note that exterior waterfall applications such as this would require additional considerations to ensure the flowing water isn't diverted onto the surface of the stone by wind or other means.
  6. Yes. From a building code/design perspective, shelf angles are designed and detailed the same whether they are supporting anchored clay brick, CMU, or stone veneers. The one slight difference for clay masonry that might be a consideration for very tall walls is the shelf angles may need to be spaced more closely together to accommodate the vertical expansion of the clay brick over time.
  7. The empirical layout and detailing recommendations of NCMA TEK 10-2C are applicable regardless of whether the CMU assembly is hollow, partially grouted, or fully grouted. If the assembly is solidly grouted because the reinforcement is closely spaced together (e.g., 8 or 16 inches on center vertical/horizontal) then it may also be worth considering the alternative crack control recommendations of TEK 10-3, which provide for an option to remove control joints altogether due to the presence of a large amount of reinforcing steel. Removing the control joints, however, does depend on the wall thickness, percentage of grouting, and reinforcement size and spacing.
  8. How tall a concrete masonry wall can be designed and constructed is really a matter of vision rather than any prescriptive code requirement. I regularly see CMU walls in the 40 to 60 foot range, with some examples going even higher. Structural considerations can vary considerably from one project to another, but a general rule of thumb I use, for example, is an 8 inch block wall tends to hit its structural 'limit' around 20 to 30 feet...or more of high strength materials are used.
  9. No. Article 3.2 C of TMS 602 specifically permits wet-cutting of CMU on site. One could argue that the process of wet-cutting introduces additional water thereby subsequently increasing the potential for shrinkage cracking, however, given that the affected unit(s) is relatively small - coupled with the fact that existing industry crack control recommendations assume that units are not 'dry' at the time of installation, the potential for increased shrinkage potential is insignificant. Additional information is provided by TMS 602 Article 3.2 C Commentary: 3.2 C. Wetting masonry units — Concrete masonry units increase in volume when wetted and shrink upon subsequent drying. Water introduced during wet cutting is localized and does not significantly affect the shrinkage potential of concrete masonry.
  10. Edwin raises a couple excellent points Kate - the sealer could be applied at the plant or in the field depending on the final desired results. If the end goal is water penetration resistance, however, then a post-applied sealer is the way to go. The follow-up question I often receive is whether a sealer is needed for water penetration resistance if the units and mortar also contain an integral water repellent. Per NCMA TEK 19-2B, general industry guidance doesn't suggest that both integral water repellents and surface sealers be required in all applications, but does recommend considering when such redundancy may be warranted (as discussed in the TEK). If a post-applied sealer is to be used on units/mortar containing an integral water repellent, the compatibility of these two materials should be verified with the admix/sealer manufacturer. TEK 19-02B.pdf
  11. Hi Ryan - at this time we are not including interlocking pavers in the forum. For additional information, I would recommend ICPI (Interlocking Concrete Pavement Institute; www.icpi.org) or BIA (Brick Industry Association; www.gobrick.com) for additional information on concrete and clay pavers.
  12. This is a great question HJ – one that causes a lot of confusion and many (often conflicting) opinions. No, this assembly would not need a vapor retarder. In fact, I’m not a big fan of vapor retarders in single wythe masonry construction in general as they tend to cause two real problems for every pseudo-concern they intend to solve. (There are some exceptions – such as indoor pools in northern climates – which shouldn’t automatically trigger the inclusion of a vapor retarder, but rather an assessment of the vapor permeance of the wall assembly being used.) Dew point is another common point of confusion. For most of the U.S. where we heat during the winter (and the vapor drive is generally to the exterior) and cool during the summer (reversing the vapor drive to the interior), the vapor retarder will be on the wrong side of the wall for some portion of the year. (And the last thing any assembly deserves is a vapor retarder on both sides of the wall as the wall would never be allowed to dry.) Far more moisture can get into (or through) a wall assembly by air leakage rather than vapor diffusion. Hence, starting with a solid grouted assembly a great start – but good performance also relies on good design and construction practices. The units and mortar should contain an integral water repellent; openings (and if present) copings should be flashed; mortar joints tooled to a concave profile; and if appropriate, consider a post-applied sealant. More detailed discussion is provided in NCMA TEK 19-2B. TEK 19-02B.pdf
  13. Alas, there is no universal mix design for achieving a targeted unit weight. For your applicable, the density of the units would need to be pretty high (170 lb/ft3 or more) in order to meet this unit weight. You could use a very high density aggregate (magnetite for example as a density of around 5 g/cc). Another (possibly easier) alternative is to fill the cells of the units solid after construction. The combination of the weight of the unit and the weight of the group in the cells of the unit would greatly exceed the targeted weight of 57.3 lb.
  14. Site walls are in many ways a unique assembly Kate. Unlike the typical exterior masonry wall, which is directly exposed to the weather on only one surface, site walls have direct exposure on both sides as well as the top; making them more akin to parapets from an exposure perspective and therefore more susceptible to moisture intrusion and potential efflorescence concerns. Unlike parapets, however, it is pretty rare to flash the base of site walls and fences...not that doing so is technically unsound, but instead it typically doesn't provide the same level of performance-to-cost benefit as would flashing the exterior walls of a masonry building would. Instead, site walls are typically detailed with a focus of minimizing moisture intrusion rather than detailing for draining any incidental moisture that may accumulate within the assembly. For the vertical wall surfaces, this is accomplished by using and integral water repellent in the units and mortar and good workmanship and tooling of the mortar joints. The top of these assemblies tends to be where most moisture infiltrates, leading to potential efflorescence. To mitigate moisture intrusion at the top, caps should be sloped to prevent standing water from accumulating and provided with an overhang and drip (kerf) to prevent water from draining under the cap or down the surface of the assembly. In extreme exposure conditions, one can also consider filling the top course of units below the cap with mortar or grout to provide an added layer of protection.
  15. Great video summarizing mortar requirements from a mason's perspective.
  16. Great question Steve. As a general rule of thumb, the bearing plate the steel joist rests on is set back about 1/2 inch from the face of the CMU assembly. This allows the steel joist to deflect and some rotation to occur at the connection without the joist contacting the CMU and causing cracking. The amount of rotation does, however, depend upon the span of the joist and the anticipated deflection under load. Another variable to take into consideration is the type of joist used, as this could impact the permitted depth of the joist bearing plate. The Steel Joist Institute has some good recommendations for CMU connection details HERE. There are also some good details illustrating these recommendations HERE.
  17. Units used for concrete masonry veneer are specified to meet either ASTM C90 (specification for loadbearing CMU) or ASTM C1634 (specification for concrete facing brick). ASTM C55 (concrete building brick) is not usually used for veneer as that standard limits application to non-facing applications. You can find more details on CMU veneers in NCMA TEK Note 3-6C.
  18. When a concrete masonry assembly is provided with an exterior wall covering (such as an anchored or adhered veneer, stucco, etc.), then the requirements of Section 1405 of the 2015 International Building Code would apply as noted. As stipulated in Section 1403.2 of the IBC however: "A weather-resistant exterior wall envelope shall not be required over concrete or masonry walls designed in accordance with Chapters 19 and 21, respectively." If any of the materials listed in Table 1405.2 are installed over a concrete masonry assembly in accordance with the provisions of Section 1405, then they are essentially deemed-to-comply as an 'exterior wall covering'. But as stated in Section 1403.2, these coverings are optional for concrete masonry systems. Certainly exterior concrete masonry assemblies are still required to provide weather protection, but there are many other ways to accomplish this without the use of wall coverings. As discussed in TEK 19-2B (attached in previous post), a single wythe concrete masonry assembly can be detailed as a drainage system (including the use of flashing), or as a barrier system (with would not employ the use of flashing).
  19. While industry recommendations encourage the use of flashing and other water control technologies in concrete masonry construction, it is not required by code. Cladding systems, however, such as masonry veneers, are required by code to be flashed to direct any moisture that penetrates the cladding to the exterior of the building. Because flashing is not code-required, it is often a victim of value engineering. While the strength of concrete masonry isn’t negatively impacted by the presence of moisture, if water is trapped inside of a concrete masonry assembly it can lead to aesthetic and serviceability issues. Efflorescence is the most common byproduct of poor moisture control strategies in concrete masonry construction, but others include corrosion of metal accessories and rust streaks on the surface of the wall, and moisture leaking into the interior of a structure. A number of industry recommendations for the control of moisture in single wythe concrete masonry construction is included in TEK 19-2B (attached). Many other related resources are available on NCMA's Solutions Center (www.ncma-br.org). TEK 19-02B.pdf
  20. This Guide has undergone multiple revisions and is currently in its 4th Edition. The first edition was published in January of 2009; the second edition in June of 2010; the third edition in May of 2012; and the fourth edition in May of 2014.
  21. There are many great resources available through the producers of adhered, manufactured stone products. Many of these resources are summarized in the industry’s recommendations contained within the Installation Guide and Detailing Options for Compliance with ASTM C1780 for Adhered Manufactured Stone Veneer, which is available for free download HERE.
  22. The minimum physical properties for adhered, manufactured stone veneer are covered under ASTM C1670/C1670M, Standard Specification for Adhered Manufactured Stone Masonry Veneer Units. The minimum average compressive strength of the concrete used to produce manufactured stone units is 2,100 psi (15 MPa). In addition to compressive strength, ASTM C1670/C1670M also addresses a number of other key physical requirements for manufactured stone units to ensure quality and successful field performance. These properties include freeze/thaw durability, minimum bond strength, and drying shrinkage. A summary of the minimum requirements of ASTM C1670/C1670M is provided in the attached document. FAQ 04-16 - MSV ASTM Standards.pdf
  23. First, TMS 402 (previously referred to ACI 530 or MSJC, an acronym for Masonry Standards Joint Committee) is the masonry design and construction standard first published in 1988 and the contemporary reference standard for masonry included in the International Building and Residential Codes. TMS 402 can be used for the structural design and construction of virtually any concrete masonry building. TMS 403 is a simplified version of TMS 402 addressing only common applications of concrete masonry construction. With this simplification, however, comes limitations on where and how TMS 403 can be used. Depending upon the type of project, either TMS 402 or TMS 403 may be the better fit. More information on the Direct Design Handbook, including a free video tutorial, is available HERE. TMS 403 also has companion software, a free trial version can be downloaded here: www.directdesignsoftware.com
  24. For a single publication, I’d recommend the Masonry Designers’ Guide (MDG) published by The Masonry Society (www.masonrysociety.org). The MDG reviews each section of TMS 402 and TMS 602, provides background discussion and context to the provisions, and presents numerous design examples applying these requirements to real-world applications. Because the provisions of TMS 402/602 are continuously being updated, a new edition of the Masonry Designers’ Guide is produced with each new edition of TMS 402/602. While not packaged as a single publication, all of NCMA’s design and construction resources are available for free download on the NCMA Solutions Center (www.ncma-br.org).
  25. Fundamentally there is very little difference as each block is produced using the same three basic constituent materials: cement, water, and aggregate. The term ‘cinder block’ was coined in the early 20th century when producers of concrete masonry units began to use cinder aggregates during the manufacturing process. These cinder aggregates could be naturally occurring (such as pumice and scoria), manufactured (such as expanded shale or clay), or a by-product of another process (such as bottom ash from coal combustion). Eventually the name stuck and the terms cinder block and concrete block became interchangeable references to concrete masonry units. A more detailed discussion on this topic can be found in the attached document. FAQ 20-14 - Concrete Block vs Cinder Block.pdf