Fibre Reinforced Facade Encyclopedia: Properties
Freeze thaw resistance is the ability of a material to survive repeated cycles of water freezing and thawing inside its pore structure without cracking, spalling or losing strength. It is a live design issue for the Australian alpine areas, Tasmania and the southern tablelands, and for any panel exported to a cold climate. Fibre reinforced polymer, which has effectively no open porosity, has no mechanism for the damage at all.
Water expands about 9 percent when it freezes. In a saturated pore with nowhere for it to go, that expansion generates pressures well above the tensile strength of a cement matrix.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Critical saturation | about 90 percent of pore volume filled | Below it, expansion has somewhere to go and no damage occurs |
| GRC water absorption | typically 8 to 12 percent by mass | Measured by immersion to BS EN 1170-6 |
| Polymer modified GRC | typically below 8 percent by mass | Acrylic polymer at roughly 4 to 6 percent of cement weight as solids |
| FRP laminate | below 0.5 percent by mass water absorption | ISO 62 and ASTM D570; no freeze thaw mechanism |
| Concrete freeze thaw test | ASTM C666 procedure A or B, 300 cycles | Durability factor reported against an unfrozen control |
| GRC cyclic weathering test | BS EN 1170-8, cycles of wetting and drying at 20 and 70 °C | Type test for long-term behaviour |
| Australian alpine exposure | repeated cycling through 0 °C across the winter |
The mechanism
Freeze thaw damage is not caused by cold. It is caused by water changing phase inside a confined pore. When free water in a pore freezes it expands, and if the pore is close to full the unfrozen water ahead of the ice front is driven through the surrounding capillaries under pressure. That hydraulic pressure, with osmotic pressure as dissolved salts concentrate in the remaining liquid, pulls the matrix apart from the inside. The damage is cumulative and irreversible.
Two consequences follow. A material only suffers if it can reach critical saturation, so drying between wetting events is protective. And the number of cycles matters more than the minimum temperature: a site that freezes each night and thaws each day is harsher than one that freezes hard in May and stays frozen until September.
Why thin cementitious sections perform well
Glass fibre reinforced concrete (GRC, GFRC) is made at a low water to cement ratio, compacted against the mould face, and formed as a 10 to 20 mm skin. That works in its favour at every step of the mechanism. A dense matrix has fewer and finer connected capillaries, so it takes up less water, and a thin section drained and ventilated on both faces dries between wetting events and rarely approaches critical saturation. Polymer modification lowers absorption further.
There is also nothing in a GRC skin for freezing water to corrode. Conventional precast fails at the reinforcement: water reaches the steel, the steel corrodes and the cover spalls. GRC has no steel in the skin, and the alkali resistant glass fibre bridges any microcracking that does start, so damage does not propagate into a spall. Where a steel stud frame sits behind the skin it is in a drained ventilated cavity and is galvanised or stainless, and it is that frame and the fixings, not the skin, that need attention in a cold and salty environment.
Test methods and what they prove
ASTM C666 is the standard rapid freezing and thawing test for concrete: specimens are cycled 300 times and the relative dynamic modulus is tracked, giving a durability factor against an unfrozen control. Procedure A freezes and thaws in water and is the more severe case. For GRC, BS EN 1170-8 sets a cyclic weathering type test, and thin fibre cement sheets have their own provisions under BS EN 12467 and ASTM C1185. Where de-icing salt is present, scaling is tested separately under ASTM C672.
FRP and GRG in cold climates
An FRP laminate absorbs less than half a percent of its mass in water and has no connected pore structure, so freeze thaw is not a degradation mechanism for it. The cold climate issues lie elsewhere: the coating system, where weathering shows; water trapped behind a gel coat defect or a poorly sealed cut edge, which can freeze and lift the coating locally; and the higher thermal movement of the laminate, which the joints and fixings have to take up.
GRG is an interior material and is never a cold climate external material. Alpha gypsum loses strength when it takes up water, and freezing only accelerates the outcome.
Detailing for freeze thaw exposure
- Drain and ventilate the cavity so the back of the panel dries; a rainscreen is the single most effective measure available
- Remove water traps: avoid upward facing ledges, flat sills and blind rebates where water sits and ice forms
- Keep panels out of the de-icing salt splash zone, or specify a mix and a treatment for it
- Size joints for the lower end of the temperature range as well as the upper, and check snow and ice loading on horizontal elements
- Specify galvanised or stainless fixings to suit the corrosivity category for the site
Water absorption, durability and rainscreen cladding all bear on this, and on an export project the receiving country’s test regime usually applies as well.
Standards and references
- ASTM C666 Resistance of Concrete to Rapid Freezing and Thawing
- BS EN 1170-8 Test method for glass-fibre reinforced cement, Cyclic weathering type test
- BS EN 1170-6 Test method for glass-fibre reinforced cement, Water absorption by immersion and dry density
- BS EN 12467 and ASTM C1185, freeze thaw provisions for thin fibre cement sheets
- ASTM C672 Scaling Resistance of Concrete Surfaces Exposed to Deicing Chemicals
- GRCA Specification for the Manufacture, Curing and Testing of GRC Products
Related terms
Questions specifiers ask
Does GRC suffer freeze thaw damage?
Well made GRC performs well. The matrix is dense and low in absorption, the section is thin and dries quickly, and there is no steel reinforcement to corrode and spall.
Is FRP affected by freezing?
Not by the freeze thaw mechanism, because there is no connected porosity to hold water. Coating defects, cut edges and increased thermal movement are the cold climate issues for FRP.
What test should be specified for a cold climate project?
Name the test, the procedure and the acceptance criterion. ASTM C666 for cementitious material and BS EN 1170-8 for GRC cyclic weathering are the usual references, with ASTM C672 where de-icing salts are present.
Does it matter how cold it gets?
Less than how often it crosses zero. Damage accumulates per cycle, so a site that freezes and thaws daily is harsher than one that freezes once and stays frozen.
Working on an alpine or export project? ShapeShift can advise on mix design, absorption testing and detailing for freeze thaw exposure. Contact ShapeShift
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.