Building Envelope
Weathersealants Technologies and Durability
What is most important to you? • • • • •
Watertight and leak free building Long term performance of the building façade Saving $$$/Euro during building construction Cost verses Value for long term savings. Completing a project with proven products and companies manufacturing quality products • Using most innovative, cutting edge technology • Aesthetics of building
What is the role of a sealant in your building? • • • • • • • • • •
Stop water and air intrusion Accommodate differential thermal movements and other structural movements Maintain the desired performance of the building Maintain and/or enhance the aesthetics of the building Prevent stress or damage occurring during movement Permit large panels to be erected and jointed Accommodate deviations in dimensions of the building components, during their manufacture or installation on site Accommodate induced and inherent deviations Provide sound insulation By closing an open joint, makes what would be a gap, visually acceptable
Important Sealant Properties • Flexibility – Modulus and movement capability – Sealant property change with temperature
• Adhesion to a variety of materials – Primer?
• Durability Life expectancy • • • • •
Sunlight Moisture Heat Cold Ozone
How Sealant Joints Fail • ADHESIVE FAILURE During movement the sealant would rather keep together as a whole and pull away from the substrates • COHESIVE FAILURE The sealant would rather tear through the centre then, pull away from the sealant
• Deterioration / Reversion Depolymerisation as a result of climatic conditions.
How Sealants Joints Fail Adhesively. • • • • • • •
Surface prep Primer Bondline stress Moisture Poor tooling Joint profile Substrate
How Sealants Joints Fail Cohesively • • • • •
Movement Joint profile Hardening Chalking Tear resistance
How Sealants Joints Fail Deterioration • • • • •
Hardening Chalking Compression set Moisture Reversion
Some examples of Joint failure
Sealant affecting Building Aesthetics • • • •
Fluid migration in the cured sealant Streaking Dirt pick-up Chalking
Fluid Migration Migration of fluids from the sealant into or onto porous or non-porous substrates. • Commonly referred to as staining • Substrate may look “dry” under wet conditions
Staining of Sensitive Substrates
Any sealant can stain if poorly formulated or used on a non recommended substrate ‌ this is a picture of polyurethane sealant staining!
Fluid Streaking
Accumulation of dirt in water run-off channels
Dirt streaking as a result of poor design
Dirt Pick-Up Accumulation of dirt on the sealant surface during, or after cure
Chalking
Whitening of a sealant surface due to weathering
Why do sealants fail? • • • •
Incorrect sealant specified Incorrect joint design Poor workmanship Poor design, not enough consideration of movement
Testing in controlled conditions • Many years of practical knowledge have been gained from sealants failing in use. What does the controlled testing tell us? RILEM developed a global durability test methods for sealants with an independent view point
Durability testing carried out by RILEM Global Evaluation • Test method incorporate four key degradation factors: – solar radiation, moisture, temperature and joint movement.
• Focus on cyclic tensile movement with trapezoidal waveforms • A default cycle consists of – 8 weeks in a weathering machine (humid, high temperature and UV) – Fatigue cycling (expansion at movement capability for 200 cycles at 5cycles/min) – Thermomechanical cycling (ISO 9047)
Durability Studies Based on Rilem Method (Jones, T. G. B.; Hutchinson, A. R.; Wolf, A. T)
Polyurethane sealant
Silicone
Durability Studies Based on Rilem Method (Jones, T. G. B.; Hutchinson, A. R.; Wolf, A. T)
Polysulphide sealant
Silicone
Durability Studies Based on Rilem Method (Jones, T. G. B.; Hutchinson, A. R.; Wolf, A. T)
Silicone sealant
Silicone
Durability Studies Based on Rilem Method • Oxford Brooks University Study Surface appearance of the silicone sealant was not affected by the durability cycles Polysulfide and MS polymer sealants started to loose adhesion and showed crazing of the surface
Best of the silicone sealants resemble the best of the polyurethane sealants – they remained clean The worst appearing sealants were certain aged polyurethane sealants
• Onouha Study Polyurethane and MS polymer sealants showed severe cracking in the surface - dirt was collecting in the surface cracks
Sealant Modulus vs. Temperature internal evaluation 80
Tens I le strength PSI
Silicone sealant keep their elastic properties over a wide temperature range ďƒ excellent weatherability
Pu @ -18C
70 60
Ps @ -18C
50
Pu @ 25C
40 Ps @ 25C
30
Si @ -18C
20 10
Si @ 25C
0 0%
25%
50%
elongation
75%
100%
How Can This Behavior Be Explained? Silicone and Organic Chemistry‌
Organic
Inorganic
Relative % of Various Elements on Earth Oxygen 49.2% Silicon 25.7% Aluminum 7.5% Iron 4.7% Calcium 3.4% Sodium 2.6% Potassium 2.4% Magnesium 1.9%
Hydrogen Titanium Chlorine Phosphorous Manganese Carbon Other
0.9% 0.6% 0.2% 0.1% 0.1% 0.1% 0.4%
Carbon vs. Silicone Organic describes carbon-based materials: petroleum, plastics (PVC), trees, plants, people, polyurethane and polysulphide sealants Silicone is an inorganic material based on silicon and oxygen. Examples include sealants, cosmetic products, water repellents, additives, etc.
Sealant Chemistries There are two broad categories of sealant chemistries available: •
•
Organic which consists of a carbon based polymer (-C-C-O-C-C-) Single and multi-component polyurethane Polysulphide Acrylic MS Polymer Inorganic which consists of non-carbon based polymer (-Si-O-Si-O-Si-) Silicone
The inherent chemical nature of silicone chemistry •The Si Atom is bigger then the C atom •The bond length of the Si-O is longer and stronger then the C-O •This enables more rotation between molecules, giving inherent flexibility and elasticity
Helicoidal structure repeated each six chains
The inherent chemical nature of silicone chemistry • UV light will degrade the carbon-carbon or carbon-oxygen bond of an organic sealant. i.e. polyurethane and polysulfide sealants. • The energy from the sun is not enough in terms of ultraviolet (UV) light to degrade the Si-O bond of a silicone sealant
Bonding Energy Si-O 452kJ/mol C-O 357kJ/mol Sunlight 425kJ/mol
Common Properties of Silicone • Superior durability in outdoor UV exposure – ultimate properties may differ from initial cure • Long term movement capability and rubber properties • Modulus stability over broad temperature range • (-40°C to 150 °C) • Highly permeable polymer structure, excellent water repellency • Resistance to oxygen/ozone and corrosive gases • Good resistance to mechanical stress • Can be formulated for long term adhesion to many materials including glass, metal, stone, masonry, etc.
Competitors Silicones – Not all silicones are the same •Dow Corning neutral silicones – – – –
100% pure silicone High service temperature Formulated sealants to prevent staining Adhesion usually maintains when exposed to water
•Extended silicones – – – –
Shrinkage Lower service temperature Increased risk of staining Adhesion reduced in areas which are exposed to water
•MS Polymers – MS polymer sealants are not modified silicone…there is no silicone in an MS polymer
Performance is as well linked to good workmanship • Silicone sealant can be installed at low temperatures • Substrates must be clean, dry and frost free • Moisture on the surface of the substrate is most important. • Use primers if required by the manufacturer • Follow the sealant manufacturer’s installation guidelines
Proof is in Performance
Some success stories‌ Dow Corning Silicone sealants in action
US Steelworkers Union Building – Pittsburgh, PA Built in 1958 Original Silicone Sealant is Still Performing Today!
Georgia Pacific HQ Atlanta, GA Sealed in 1982 Inspected in 1999: Performing Successfully
One Magnificent Mile Chicago, Ill Polyurethane sealant Failed after two years Resealed with Dow Corning速 790 in 1992
BEW Product Range • Dow Corning 756 SMS: 1-component, low modulus, neutral silicone, non staining on porous substrates; unique mat surface • Dow Corning 791: 1-component, low modulus neutral silicone, 50% movement capability • Dow Corning 813: 1-component, low modulus neutral silicone, 25% movement capability
Fire Stop Product Range • Dow Corning 400: 1-part intumescent acrylic rubber, for internal perimeter pointing, fire rating up to 2h • Dow Corning 700: 1-part silicone rubber, movement capability of 50%, fire rating up to 4h • Dow Corning 800: 1-part self-leveling silicone sealant, +110%/-50% movement capability, fire rating up to 4h • Dow Corning 3-6548: 2-part silicone rubber foam, up to 4h fire rating, for sealing of penetrations containing cables, pipes or ductwork
Dow Corning Services • • • • • •
40+ Year Track Record in Construction Technical Leadership (R&D, Patents, EOTA) Application Sales Engineers, Technical Service TIC (Technical Information Center) Authorized Distributors Laboratory Testing for Adhesion, Compatibility and Staining • Offer 10 Year Weatherseal, Non-Stain and Structural Adhesion Warranties • Website: www.dowcorning.com
Questions?