Field Performance and Accelerated Weathering of High Performance Acrylic and Polyurethane Sealants for Tilt-Up Applications

ABSTRACT: To demonstrate the suitability of high performance acrylic seal­ants to low rise industrial construction applications, a laboratory prepared high performance acrylic sealant was compared to a commonly used, com­mercially available two part polyurethane sealant. The centerpiece of this comparison is an exterior exposure in El Paso, TX, in which the two sealants were professionally installed in alternating joints around the perimeter of a tilt-up warehouse. The sealants were also subjected to a battery of labora­tory tests, including tensile testing, sealant specification testing, paintability, and accelerated weathering in both xenon arc and fluorescent UV devices. The 3 year El Paso exposure results, in combination with the laboratory, weathering, and application test results, demonstrate the performance ad­vantages of the high performance acrylic sealant and highlight its inherent suitability for use in low rise industrial applications such as tilt-up ware­houses.

KEYWORDS: acrylic sealant, polyurethane sealant, tilt-up, durability, crazing, accelerated weathering

Introduction

Perceptions of acrylic sealants in the construction industry have largely been formed by contractors’ experience with low-to-mid-performance formulations. Nonspec and ASTM C834-05 [1] compliant formulations were the first acrylic sealants to be introduced into the market and contractors collectively purchase huge volumes of these products every year for use in a variety of applications with minimal movement requirements. However, despite contractors’ lack of familiarity, high performance acrylic sealants with ±25 % joint movement ca­pability are widely available. These products fully comply with ASTM C920-05 [2], have the excellent weathering characteristics of acrylic chemistry, and have the added benefit of soap and water cleanup.

High performance polyurethane sealants are commonly used to seal exte­rior joints in low rise industrial buildings constructed of block, brick, and tilt-up panels. Although these sealants have been used for many years, they are not without problems. Commonly encountered issues include surface crazing and chalking caused by UV degradation, sealant burn-though in thin cross sec­tions, variable coatability, dirt pickup on coated joints due to plasticizer migra­tion, and the need for solvent cleanup.

ASTM C834-05 compliant acrylic sealants are frequently used to seal inte­rior joints in low rise tilt-up buildings. Although high performance acrylic seal­ants are readily available, they are rarely used to seal the exterior joints of these buildings. Despite the limitations listed above, contractors continue to use polyurethane sealants instead of high performance acrylic sealants. One of the reasons for this is that there is a general lack of knowledge about high perfor­mance acrylic sealants and how they compare to sealants based on alternative chemistries. Another is the lack of performance history of high performance acrylic sealants in commercial construction applications. To begin to fill these voids, a comprehensive study was undertaken to compare the performance of a high performance acrylic sealant to a commonly used two part polyurethane sealant.