Caulks and Sealants for Flat Roofs and Skylights

Caulk and Sealant: Used Interchangeably, but Which is Best?

This Lap sealer is used for EPDM rubber roofs

Firestone EcoWhite™ EDPM Lap Sealant is a high quality sealant with excellent adhesion to a variety of surfaces, and for
use in conjunction with Firestone EcoWhite EPDM Systems. Specifically, it is used for seam edge treatment applications, as well as, other uses outlined in the Firestone Specifications, in conjunction with Firestone EcoWhite EPDM membrane systems.

When it comes to sealants and caulking there are many brands and varieties to choose from. The main difference between a caulk and a sealant is its elasticity. Caulks are fairly rigid when dry, and are intended for use in areas with minimal expansion and contraction. Sealants are made from flexible material, most commonly silicone, making them ideal for areas prone to expansion and contraction.

Consider Caulk Applications

  • Caulk is less movable.
  • It is a substance that can accommodate less than 12 percent movement outward or inward without risk of having cracks, permanent deformation or delamination.
  • Caulk’s durability can only last within three years because of its limited weathering properties.
  • Caulk has a potential shrinkage tendency up to 30% of its volume due to solvent loss, condensation, or oxidation. When it shrinks, the interface between the construction material and caulk mass is severely stressed.
  • Caulk has a tendency to provide fair to poor adhesion on construction materials which is intensified by increased volume shrinkage.
  • Caulks do not meet the requirements and standards of Federal Spec TTS 00230 or Canadian Spec CAN 19, 13-M 82.
  • Caulk can be purchased for less than $2.50, and such is designed for “do it yourself” market.

To understand further about caulks, let us cover butyl caulks, acrylic latex caulks, and vinyl acetate.
Butyl caulk tends to be more plastic than elastomeric during solvent loss. It is movable in dynamic joints but couldn’t regain back its structure when there is extension or compression done against it. The solvent loss as well as shrinkage limits altogether can make this product show a less appealing performance to small joints. However, there are some butyl caulks which can fairly play in small joints with less than 15% movement.Yet,buying this kind of product requires careful consideration through verifying its conformity with ASTM C 1085 and TTS-001657.

Acrylic latex caulk earned its popularity during 1960s. Some of its forms in earlier periods showed good performance such as residential siding and trim. However,during economic crisis formulators were forced to use vinyl acetate as co-polymer or higher quality acrylic resins. These kind of caulks have less adhesion and weathering properties, but are duly governed by ASTM C 834.

Vinyl acetate caulk has wide-ranged applications because of its ability to to seal almost all types of building materials and substrates. As a matter of fact, it is considered as an all-purpose caulk with high level moisture-resistant properties. However, repetitive exposures and direct contact with this product can be hazardous to health both to users and manufacturing workers. Moreover, it is has a combustibility tendency that it should be stored away from extreme heat.

High-performance latex-based intumescent firestop sealant. When properly installed, this product provides up to 4-hour fire protection in tested and listed systems. Firestops items penetrating through fire-rated construction assemblies. Dries to red color, no mixing required.

Caulks and Sealants Difference /Common Features

Caulk’s susceptibility to cracking and getting dry over time due to its limited elasticity makes it apart from sealants. Sealants perform better even during temperature swings because of the flexibility of silicone which maintains the watertight seal. Moreover, they have strong fumes when freshly used as compared to caulks.

Nevertheless, caulk earned more favor from homeowners despite its downside factors due to its economical price as compared to a professional-grade sealant. Besides, caulk in some instances serve better purpose especially in small seams with gaps of less than 1/4 inch across, and in little or static objects. Moreover, it is useful in situations where a building must undergo re-painting which commonly takes place every four years.

The only common thing between these two interchangeably used words are the failures pertaining to adhesion and cohesion.

Silicone Caulk or sealants are the worst to use for any roofing application

Finding Best Applications and Types of Caulks or Sealants

Caulks or Sealants are used in different kinds of construction materials such as tiles, glass, woods, metals, and sometimes porcelains. Therefore, it is important to identify the best type of caulks or sealants to maximize the benefits.

Here are the four primary considerations when using a sealant which are as follows:





For instance, if you intend to seal sinks, bathroom, or kitchen where mildew and water are common, it is recommended that the caulk or sealant contain biocide.

Biocide is a mold-inhibiting agent which helps to prevent the growth of allergens that could be risky to your health. Studies encourage the use of GE silicone caulks with high levels of biocide to fight off fungus, bacteria, and to keep these areas looking pristine (no stains).

Alex Plus latex sealant

Superior quality, all-purpose acrylic latex caulk plus silicone. Highly flexible and durable for a waterproof seal. Excellent adhesion. Cured caulk is mold and mildew resistant.

Silicone caulks or sealants are highly recommended in most cases because of its strength on hard surfaces such as glass, metals, and tiles. Moreover, it is not toxic (inorganic chemical) which can stand against the severity of weather conditions. However, on wood materials, it poorly demonstrates a good level of adhesion.

Solvent-base rubber caulks or sealants are recommended for homes built from wood materials which the areas are having joints characterized by frequent movements like wood siding and roofs. These products have a high level of elasticity and have resistance to mildew as well as wet and cold weather conditions. However, this is not recommended for indoor applications because of its high flammable properties.

Butyl caulks or sealants are found to fit in watery areas such as gutters. Besides water resistance, they can withstand moisture as well as in random movement of shear joints. However, they tend to be messy as they stretch like chewing gum with less point of recovery.

Polyurethane caulks or sealants are abrasion-resistants, therefore recommended for high-traffic areas, garages, and in sealing joints in the floor. However, these products are toxic and hazardous to your health.

Modern caulks or sealants characterized by modified silicone polymers like DAP’s Side Winder and OSI’s Advantage are now available on the market. These sealants or caulks have a combined chemistry and benefit of water-based, silicone, and polyurethane product. Thus, they cost a lot but are worth spending the money on for outdoor sealing concerns that require higher level of assurance pertaining to durability, weatherability, and flexibility.

Caulk is just a term that signifies “sealing activity”. However, this word earns a more fashionable label called, sealant(s). Precisely, this evolution of terminology is for better understanding because the word caulk is a bit of a remote idea. Sealant on the other hand, is self-explanatory terminology for fixing joints and holes.

Having the acceptance for both terms, the focus of this article was on quality and applications to which homeowners must give careful consideration. Failure to understand sealant’s composition and suitable applications can mean health risks and dangers as this article has covered.

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