Exterior Sealant Joint Design
Issues
Building Integrity
First Line of Defense
Prevents Serious Damage
Engergy Savings
 2 Primary Formulations
Polyurethane
Silicone
Failures
Cohesive Failure
Adhesive Failure
Cohesive failure indicates the sealant could
not resist the stress applied when the adjacent materials contracted during cold temperatures
Adhesive failures occur at the bond line
between the sealant and the joint substrate
Dirty Joints
Wrong Primer
No Primer
Bonding to Backer
Failures
Can result in the entire exterior wall system being replaced
Sealant Materials
Exterior sealants are normally an elastomeric type

Elastomeric sealants means sealants will withstand
joint compression & extension due to thermal expansion
and contraction of the adjacent materials
ASTM C 920
Rates sealants according to their ability to withstand movement
% of joint width

Example:
Class 25 = +/- 25% movement
1" joint w/ Class 25 Sealant can move from 3/4" to 1-1/4" in width

Example:
Class 100/50 = 100% extension & 50% compression
classifies sealants by type, grade, and use

Example:
Type S - Single Component
Type M - Multi-Component
Grade P - Pourable or self-leveling
Grade NS - Nonsag or gunable
Use T - Traffic conditions
Use NT - Non-traffic conditions
Use I - Immersion conditions
Use M - Mortar contact
Use G - Glass contact
Use A - Aluminum contact
Use O - Other material contact
Single Component Sealants
Rely on ambient moisture to cure
Cure time dependent upon temperature & relative humidity (unpredictable)
Simple to apply

Multi-Component Sealants
Chemically cured
Cure time independent of temperature & relative humidity (predictable)
Requires experience to mix properly

Joint Movement
Design to accomodate FULL range of movement
Full range of temperatures (120° F)
Surface temperature
Expansion/Contraction Coefficients of Materials

Example:
Joint movement is:
1/8 inch compression
and
1/8 inch extension

Class 25 Sealant

Joint width is 1/2 inch

Joint Design
Design and Application Guidelines:

ASTM C 1193 Standard Guide for Use of Joint Sealants



Joint Design
Joint Design
Substrate MUST be clean
Silicone Sealants require primer on substrates (except on glass surfaces)
Different Substrates require different Primers
Preconstruction Adhesion Tests (ASTM C 794)
Preconstruction Stain Tests (ASTM C 510)
Joint Design
Joint Width:
Function of construction materials and joint spacing
Silicone seals become more cost effective for wider joints
ASTM C 1193 


copyright Conspectus 2010
Joint Design
Elements: Substrate, Backer, & Sealant
Backer = Depth Control + Bond Breaker
Sealant must adhere to Substrates (2-sided adhesion only)
No fillet joints


Joint depth
= 50% Joint width
Silicones, Maximum Joint Depth = 1/2"
Polyurethanes, Maximum Joint Depth = 3/4"

Badly Designed Joints