Building Construction Handbook, Eighth Edition

Single-Stage ~ the application of a compressible filling material

and a weatherproofing sealant between adjacent cladding panels.

This may be adequate for relatively small areas and where

exposure to thermal or structural movement is limited. Elsewhere,

in order to accommodate extremes of thermal movement between

exposed claddings, the use of only a sealant and filler would

require an over-frequency of joints or over-wide joints that could

slump or fracture.

Two-Stage ~ otherwise known as open drained joints. The

preferred choice as there is a greater facility to absorb movement.

Drained joints to cladding panels comprise a sealant to the inside

or back of the joint and a baffle to the front, both separated by

an air seal.

Comparison of single- and two-stage jointing principles ~

SINGLE

STAGE

TWO

STAGE

Plan views

open joint

metal or

plastic

baffle strip

air seal

sealant

sealant

bond breaker

tape

backup

compressible

filling material

optional plastic

or metal cover

strip

Typical coefficients of linear thermal expansion (10^6 m/mK) ~

Dense concrete aggregate 14, lightweight aggregate 10.

Ref. BS 6093: Design of joints and jointing in building construction.

Concrete Cladding--Joints