079200 – JOINT SEALANTS

Chapter 3 – Product Selection

More joint leakage is caused by using the wrong joint solution or the wrong sealant than by specifying the right sealant badly. There are certainly dozens of brand name products to choose from, possibly hundreds. Some sealant characteristics are critical to performance, others are arbitrary or user-preferences.

Back - Chapter 2 - Product Characteristics

Next - Chapter 4 - Implementation in the Construction Documents

Step 1:  Choose the correct design solution -- don't use a sealant for an application where something else is a better solution.

This may seem obvious but sometimes sealants are considered "cure-alls." But the life span of even the best sealing material available is finite -- usually much less than the expected building life span. If failure of the joint seal would be very costly, a water-shedding solution might be a better solution. Also, some joints have requirements that no joint sealant can achieve. Some other common joint treatment solutions are listed below -- are any of them applicable to the joint under consideration?

  • Manufactured expansion joint covers are often used for large joints having large movement, such as building expansion joints and seismic movement joints, especially elevated floor joints, as the cover is a better walking surface than a soft sealant joint.
  • Gaskets -- hollow preformed strips, usually rubber -- are sometimes used for pavement, parking deck, and bridge joints because they can be overcompressed before insertion into the joint, leaving them always in compression, without any adhesion stress.
  • Compressible Foam Sealers -- plastic foam strips with or without sealant applied on the face -- can sometimes make a very wide joint better looking and more successful.
  • Firestopping sealants are needed for joints and penetrations in fire-rated assemblies. These should be specified in a separate section (currently 078400 in SpecLink-E).

Step 2:  Low-hanging fruit.

  • Interior, non-wet, with low to no movement and not subject to any of the environmental conditions listed below;  use acrylic latex. It's the least expensive, contains no VOCs, will adhere to almost every interior material, comes in colors and clear, and can be painted. Some applications are:
    • Gypsum board and plaster control joints.
    • Painted wood trim -- sealing the trim joints and between the trim and the wall makes it all look better after painting.
  • Indoor 'wet' - but not continuously immersed - with low to no movement; the water exposure means that an exterior sealant type needs to be used. Because the environment is often without sufficient ventilation, mildew-resistance is desirable. Some applications are:
    • Between plumbing fixtures and floors and walls.
    • Between countertops and walls.
    • Control joints in ceramic tile field.
  • Concealed conditions that require a sealant applied before the assembly is completed; use non-curing butyl if all will be completely concealed. Use acrylic latex if portions will be exposed. Some applications are:
    • Acoustical assemblies:  Beads of sealant between stud channels and runners and the adjacent construction to close off flanking sound paths; also behind electrical boxes.
    • Under door thresholds.
    • Smoke partitions:  Sealing gypsum board top and bottom edges to adjacent construction and behind electrical boxes. This does not apply to fire-rated partitions.

For the above applications, the following selection criteria do not apply.

Step 3:  Environmental conditions or exposures.

Although the most common cause of failure is movement, exposure conditions often supersede movement in selection because of limited product availability. The most extreme exposures are listed first. Where limited availability is indicated, detailed review of manufacturers' data will probably be necessary, rather than reliance on generic product type characteristics. That means that you'll have to either ask manufacturers for help or read their product literature carefully. Multiple exposure criteria may apply.

  • Exposure to Solvents, Chemicals, Chlorine, Petroleum Products, and Cooking Grease:  Most sealants are not resistant to any of these. None of the ASTM standards govern these exposures. Always verify specific exposures with manufacturers. Some applications are:
    • Industrial activities.
    • Chemical and fuel storage tanks.
    • Wastewater treatment.
    • Swimming pools (chlorinated water, saline water).
    • Automotive.
    • Airfield pavement joints (aircraft fuel, jet fuel).
    • Food service.
    • Food processing.
  • Continuous Immersion in Water:  Exterior sealants can withstand intermittent exposure to water but many cannot withstand continuous immersion. ASTM C920 includes tests to verify that the sealant can withstand continuous immersion -- Use I (the letter I, not the numeral 1). This is essentially potable water without chlorination or other added chemicals. Some applications are:
    • Water Tanks.
    • Fountains.
    • Cooling tower basins.
    • Below grade walls without waterproofing.
    • Glass aquarium tanks.
    • Surfaces where water is likely to puddle for extended periods.
  • Exposure to High Temperatures:  The ASTM standards do not govern service temperature. Always verify specific exposures with manufacturers.
  • Need for FDA Approved Products:  FDA approval is a possible requirement for food processing facilities. No generalization can be made about products since each manufacturer makes its own choices about pursuing approval. 
  • NSF 61 - Drinking Water System Components - Health Effects Approval:  NSF 61 is approval for use in contact with potable water. No generalization can be made about products since each manufacturer makes its own choices about pursuing approval. 
  • Tampering:  In regard to joint sealants, tampering involves "picking" the sealant out of the joint, either with fingernails or the tools available. The occupants must have both an incentive to such vandalism and the time available -- such as, for example, in detention occupancies, or bored teenagers in study hall. Hardness of 75-85 is characteristic of products recommended by manufacturers for this application. These products are also referred to as "security" sealants. An epoxy sealant may be required.
  • Traffic - Concrete Slabs on Grade:  These are commonly control-joints created by saw-cutting into the surface but not through the entire slab. In this case, there is very little movement so the joint needs to be filled with a hard but slightly resilient material that can be installed flush with the floor surface. If heavy traffic is expected, such as in warehouses, the joint filler needs to be harder than usual, to support the sharp concrete edges that can be broken off easily. Hardness of 75-85 is characteristic of products recommended by manufacturers for this application. Available materials include epoxy, urethane, and polyurea. Suitable products are often referred to as "semi-rigid" joint fillers. Other desirable characteristics are 100% solids (no shrinkage), fast curing, and ability to be installed in deep joints without backer rod (the joint is usually too narrow for any backer).
  • Traffic - Outdoor Pavements:  Joints include expansion joints extending through the entire slab and saw-cuts for control joints. The point of sealing is to prevent freeze-thaw damage. The sealant needs to be hard enough to resist damage by grit ground in under traffic -- hardness of 40-45 is characteristic of products recommended by manufacturers for this purpose. Urethane is the most likely candidate.
  • General Outdoor Exposure:  Water and weather, in general, elastomeric sealants and solvent-release sealants are suitable for exterior use, while acrylic latex is not. The ASTM standard specifications require only minimal weather resistance testing, so field experience is more reliable. If the manufacturer doesn't explicitly recommend a product for outdoor use, don't use it outdoors.

Step 4:  Compatibility with substrates.

Check your choice for limitations regarding particular substrate. Some problematic substrates are:

  • Stone, particularly light-colored, and marble. Despite seeming very solid, most stone is slightly porous.  Silicones, in particular, historically have had limited positive results in their use with stone.
  • Masonry and concrete. Of the standard substrate tests in ASTM C920, Use M (for mortar) is the one that some C920 sealants are not listed for.
  • Green Concrete. Highly unusual, but available.
  • Unusual substrates should always be field tested for adhesion.

Step 5:  Physical and dimensional conditions.

  • Vertical and Sloped Surfaces:  Requires a nonsag sealant. ASTM C834 (latex), ASTM C920 (elastomeric, Grade NS), or ASTM C1311 (solvent).
  • Horizontal Surfaces:  If the sealant needs to self-level into the joint, use ASTM C920 Grade P. (ASTM C1311 and C834 sealants are not made in self-leveling consistency.)  Note that nonsag sealants can be used in horizontal joints but they require slightly more labor -- gunning into joint rather than pouring, followed by tooling.
  • Lap Joints:  Concealed.
  • Very Wide Joints:  Especially if high-movement. See the discussion of joint width in Chapter 2..
  • Very Narrow Moving Joints:  Look for something called a "seam sealer", that can be poured into the joint.

Step 6:  Remaining options, if any.

  • Single or multi-component; ASTM C920, Type S and Type M.
  • VOC content and emissions.
  • Color.
  • To Be Painted Over:  Acrylic latex, some urethanes, some silyl-terminated polyethers.
  • Textured surface.
  • Longest lasting.

Step 7:  Movement capability.

At this point in the selection process, there may or may not be any movement capability options -- you may have arrived at the only suitable product, with its inherent movement capability. The movement capability effects the joint design directly. "Design" of the joint means defining the width so that the actual movement is not beyond the range of the estimated sealant or joint movement. The actual width will depend on the width shown in construction documents, construction tolerances, the thermal range, other loadings, and the point in the thermal cycle that it will be installed. There are a lot of variables that are not particularly well understood. ASTM C1472 is as scientific as anyone is likely to get -- it's got a lot of math. Estimate the amount of movement as closely as possible, using the distance between joints, the thermal range, and the type of movement:

  • Expansion and contraction (the joint gets wider or narrower) -- the sealant must remain in contact with the sides of the joint, by adhesion, during extension and compression.
  • Shear (the faces of the joint slide past each other) -- the sealant is placed between the two faces. The sealer undergoes twisting and stretching but no compression. Shear most commonly occurs in lap joints but can also happen in butt joints.
  • Expansion, contraction, and lap shear, all at once.

Here are a few tips:

  • Read all the commentary in ASTM C1472.
  • There's no substitute for doing the math.
  • Don't be unrealistic. 1/4-inch facade expansion joints may be all the aesthetic will tolerate, but in a temperate climate, it's very unlikely they'll work unless they are much closer together than the aesthetic will tolerate.
  • If a 50% movement class sealant is acceptable, be grateful but don't push it. Take advantage of the extra movement capability to ensure long-term success by sizing the joint as if a lower movement sealant is to be used.
  • Follow the manufacturers' rules of thumb. If the data sheet says make the joint width 3 times the expected movement, do at least that.
  • If one of the more stringent exposures is present, it would be prudent to select a sealant before designing the joint.

Exercise

Using the information in this guide, choose a sealant for expansion joints in a brick masonry exterior wall. Obtain the product data sheets of at least 3 brand name products that are suitable.

Review

1. Which of the following joint applications are considered pretty easy to select a product for?

  • Swimming pools
  • Exterior walls
  • Interior "wet" but not continuously immersed joints with no to low movement.
  • Pavement joints.
  • Food service areas.

2. Nonsag sealants may be used in:

  • Joints in vertical surfaces.
  • Joints in horizontal surfaces.

3. The main advantage of using a self-leveling sealant is:

  • The product costs less than nonsag type.
  • They are easier to install than nonsag type.
  • They come in more colors.
4. The best approach to designing moving joints is:
  • Size the joint first, then choose a sealant to suit it.
  • First choose a sealant based on its exposure, orientation, and substrate compatibility, then size the joint to suit the sealant.
  • First choose a sealant, then calculate expected joint movement, and finally size the joint to avoid stressing the sealant to its limit.
5. Which type of sealant is likely to be suitable for continuous immersion in potable water?
  • Silicone rubber.
  • Silyl-terminated polyether/polyurethane.
  • Urethane.
  • Polysulfide.
  • Polyurea.
  • Epoxy.
  • Butyl rubber.
  • Acrylic emulsion latex.
  • Siliconized acrylic latex.

Next - Chapter 4 - Implementation in the Construction Documents