Firth DRYbloc - New Industry Standards
< Back Wednesday, 13 April 2011
The Cement and Concrete Association has published a document called "Weathertight Concrete and Concrete Masonry Construction" CCANZ CP 01:2011 which is intended as a means of compliance with New Zealand Building Code (NZBC) Clause E2- External moisture.
It covers the weather tightness of the building envelope for:
- Concrete slab on ground
- Concrete and concrete masonry wall systems
- Concrete flat roofs and decks and
- Concrete to timber construction junctions
In this document there are requirements for masonry blocks being used with a clear seal application. There are now compliance criteria for acceptable clear coatings systems for masonry walls.
Extract from CCANZ CO 01:2011Pg 36
4.4 Clear coating system
This section specifies clear coating systems applied
directly to either:
a) A Concrete Masonry Wall type A1 or A3, or
b) An Insitu Concrete Wall type B1 or B3, or
c) A Precast Concrete Wall type C1 or C3.
Clear coating systems complying with section 4.4.2 are weathertight.
The coating system shall be supplied by a single supplier
who takes responsibility for the system as a whole, encompassing
the weathertight coating. The system shall be applied by the
coating manufacturer's approved applicator. Clear coating systems
are to be recoated every five years at a minimum or in accordance
with the manufacturer's specifications. The clear coating system
shall be designed to prevent water ingress into the pores of the
concrete or masonry. The system shall allow the passage of water
vapour from the interior to the exterior.
Comment:
Clear coatings have been included in this Code of
Practice recognising the move to 'minimalist architecture' using
unpainted concrete and masonry. Clear coatings do not always have
the flexible film forming ability that acrylic coatings have.
Therfore they require a strict maintenance regime and need
recoating at shorter intervals.
4.4.1 Permeability test
Clear coating system shall be tested for permeability in
accordance with AS?NZS 4456.16. The test shall be conducted on a
standard masonry block with a density of between 1350-1500
kg/m3 over a test period of two hours.
4.4.2 Acceptable clear coating systems
Clear sealers for instu and precast concrete walls shall have a
permeability of 3mm/hr or less when tested in accordance with
section 4.4.1.
Clear sealers for concrete masonry walls shall have:
a) A permeability of 1mm/hr or less when tested in accordance with
section 4.4.1, or
b) A permeability of 3mm/hr or less when tested in accordance with
section 4.4.1 if the wall is constructed of low permeability
blocks. Low permeability blocks shall have a permeability of less
than 10mm/hr when tested in accordance with section 4.4.1.
Note: Firths Drybloc or any Architectural block is NOT consistently compliant with Section 4.4.2 b) i.e. "Low permeability blocks shall have a permeability of less than 10mm/hr when tested in accordance with section 4.4.1"
Firth has decided to suspend manufacture of DRYbloc to continue research to improve the product ensuring that it will be compliant with this document as per section 4.4.2 b).
However if a clear sealer is used that has a compliance of 1mm/hr or less (section 4.4.2 a)) when tested in accordance with section 4.4.1 there is no impermeability requirement from the block.
Should you have any queries in relation to DRYbloc or other masonry alternatives, please contact your nearest distributor or contact Firth Industries on 0800 800 576.