Criteria For Selecting Masonry Joint Sealants
- Procedure code:
- Outdoor Sculpture Manual - Center For Public Buildings
- Thermal And Moisture Protection
- Joint Sealers
- Last Modified:
CRITERIA FOR SELECTING MASONRY JOINT SEALANTS
THE USE OF CAULKS AND SEALANTS IN THE MASONRY JOINTS OF HISTORIC
STRUCTURES, IS ONLY AN APPROPRIATE MAINTENANCE TREATMENT WHEN IT IS
INTENDED TO REPLACE CAULKING OR SEALANTS USED AS PART OF THE
This standard includes guidance on selecting joint sealants for
masonry, based on composition, elasticity and durability. For
guidance on installing joint sealants, see 07900-01-P "Sealing
Masonry Joints to Make Them Airtight and Watertight".
- Sealants may be used for expansion joints, at intersections of
differing materials and to infill gaps where differential
settlement/movement is still active.
- Sealants should NOT be used as a substitute for proper masonry
repointing (i.e. facade surfaces, etc at vertical and
- The performance of sealants is affected by several factors:
1. Physical properties such as porosity, texture and
2. Chemical properties such as composition and salts.
3. Environmental factors affecting durability.
4. Joint design affecting performance (i.e. the width to
depth is directly related to sealant performance).
- Sealants in satisfactory condition should be:
1. be pliable enough to conform to masonry joints, cracks,
2. be able to withstand the anticipated joint movement.
3. be insensitive to moisture.
4. be resistant to alkalinity which is often present in
5. NOT stain or mar the appearance of the masonry.
- Masonry joints to receive sealants should be clean and free of
dirt, dust, grease, or oil, salts, chalk or lime and other
- In their 1987 report, "The Use of Sealants in Masonry Joints",
The National Institute of Standards and Technology (NIST) -
formerly known as The National Bureau of Standards (NBS) -
listed the following factors and properties of stone which can
affect sealant performance:
1. Porosity of masonry and stone
2. Permeability of masonry and stone
3. Moisture content of masonry and stone in presence of
freezing and thawing conditions
4. Salt crystallization within masonry and stone pores
5. Thermal and moisture expansion of joints
6. Surface texture of masonry and stone
- Sealants may be classified by composition, elasticity and
1. Chemical or composition types of sealants in 1 and 2-part
a. Oil based
2. Classification according to elasticity or joint movement
includes three levels as follows:
a. Low Movement - Up to 5% movement; this group is
generally composed of oil and resin based sealants.
b. Medium Movement - From 5 to 12.5% movement; this
group is typically comprised of polymer based
acrylic types and some urethanes. (Acrylics are
not generally recommended for outdoor use.)
c. High Movement - Up to 25% movement; this class
generally includes the urethanes, silicones and
3. Classification according to durability is as follows,
according to the (NIST) study of sealants:
a. Five-Year Durability
1) Oil based
b. Ten-Year Durability
c. Fifteen-to-Twenty-Year Durability
END OF SECTION