What Matters: Strength, Durability, Flexibility and Indoor Air Quality
Buildings are often thought of as fixed objects. But in the real world, changes in the weather cause buildings to move – and we need to plan for the fact that they will expand, shrink, adjust and settle. If we are building an airtight building, such as a Passive House, we want to make sure that these movements won’t lead to air leaks. Closed cell spray foams don’t have the flexibility to move with the building. But what will?
Caulks and sealants are typically “stand-alone” solutions designed to bridge construction gaps. Caulks are widely used in weatherization programs, and they do indeed reduce air leaks around windows reasonably well (at least initially). But as most homeowners, building managers and handymen know, latex and silicone caulks will start to crack after a year or two. In fact, caulk applied during new construction might only last until punch lists are completed! This happens because the chemical drying reaction doesn’t stop, and consequently the mass continues to shrink. More importantly, the material becomes dry and brittle. The slightest movement between two connected members will then cause the caulk to crack, and just like that, your all-important air barrier is compromised.
Even materials on the interior of a structure will be exposed to changes in environmental conditions. In particular, temperature and humidity fluctuations make different building components expand and contract at different rates, subjecting them to small differential movements. There are two ways to seal such junctions. One is with highly flexible Pro Clima tapes that span over gaps and stretch to keep the airtightness intact. Another way is with materials that fill the gaps and still allow slight movements to occur while not compromising airtightness. For that, Pro Clima makes CONTEGA HF.
Make Airtightness Last with CONTEGA HF Acrylic Adhesives
CONTEGA HF and CONTEGA CLASSIC adhesives offer both superb adhesion and exceptional durability. Their most important feature is that the adhesive never dries out or embrittles, and hence it won’t crack or peel away. So these adhesives combine high strength and elasticity with permanent flexibility. They also penetrate deep into the substrate, including concrete and other porous masonry materials (though TESCON Primer is still recommended). Because of their extreme cold and moisture tolerance, they also adhere to cold and slightly damp surfaces where other caulks routinely fail. And unlike most caulks, CONTEGA adhesives are formulated for connecting flexible membranes to solid materials – hence ideal for connecting airtight membranes like INTELLO PLUS and SOLITEX MENTO 1000 to supporting structures such as concrete and rough wood.
To keep from embrittlement, CONTEGA adhesives are made of non-ageing acrylate polymers, without softeners or halogenated compounds. For this reason they are also zero-VOC (CONTEGA CLASSIC) or low-VOC (CONTEGA HF contains natural ethanol as a solvent to allow for storage below freezing). CONTEGA adhesives also comply with the very stringent German Sentinel IAQ standards. So unlike some well-known acoustical sealants, you won’t be bothered by toxic smells – especially if you’re working indoors without ventilation.
How to Apply CONTEGA HF Adhesive Caulk
With any tapes, caulks, or adhesives, the first step is always to clean the application area of dust, debris, or construction waste. Because dust is not airtight.
CONTEGA HF adhesive is ideal for connecting adjacent airtight surfaces. A common scenario involves connecting INTELLO Plus membrane at an interior wall to a solid concrete subfloor or taped plywood subfloor. All it takes is a bead of CONTEGA HF. The membrane is connected with CONTEGA HF directly to the concrete floor. If the concrete is dusting or unstable, TESCON Primer RP is recommended for optimal adhesion.
Installation Video by ecologicalbuildingsystems.com (Note: CONTEGA HF is called ORCON F in Europe).
CONTEGA HF works both at the interior and exterior and is airtight and strong enough to lift a brick! It attaches well to uneven surfaces and fills all the voids. (Masonry still leaks, of course, and needs to be plastered or airsealed).
Wet process: for typical membrane connections to sheathing or concrete
One of the materials being joined – either the membrane or the adjoining structure – must be absorbent. For example, porous foundation materials like concrete or brick, as well as Pro Clima vapor retarders and weather resistant barriers. Apply CONTEGA HF and then lay the membrane directly onto the bed of adhesive. Do not press the bead completely flat. The wet method can be used for all applications.
Dry process: for non-absorbent materials like polyethylene
This process is more complex and is recommended if the membrane and the structure it is being joined to are not (or not very) absorbent, for example for joining PE film to concrete. Apply CONTEGA HF and leave to dry for 1-2 days before pressing the membrane onto the dry adhesive and it will stick immediately.
Instantly Bonding Adhesive: for airtight joint connections
CONTEGA MULTIBOND is a pre-cured line of adhesive that is activated by pressure, just as with adhesive in Pro Clima tapes. This allows for a flexible, instantly bonding joint adhesive suitable for interior and exterior use.
Because of its malleability, CONTEGA MULTIBOND can fill the cracks on an uneven surface for an airtight bond. For particularly rough surfaces, two strips can be applied to one another for extra protection. Once pressure is applied, CONTEGA MULTIBOND instantly bonds to both the substrate and the membrane – ensuring immediate and long-lasting airtightness.
CONTEGA MULTIBOND can be applied to a wide range of substrates, including plaster, concrete, masonry, roughly sawn or painted wood, OSB, and rustproof metal. Although priming the surface isn’t necessary in most cases, an adhesion test can tell you whether pre-treating the surface with primer could increase the stability of the system.
Ducts, pipes, cables and other penetrations
Water, sewer and electric services as well as HRV ducts penetrate your airtight layer. These connections must be able to accommodate substantial movement and are poorly served with caulk joints of any type. How to deal with them is described in the blogpost Intentional “holes” in your airbarrier (and sealing them). But here’s a quick summary:
EPDM gaskets from Pro Clima are often the best – and easiest – solutions for sealing gaps around these types of penetrations. For wires and cables, use KAFLEX gaskets with self-adhered backing. For pipes and ducts, use ROFLEX gaskets. Gaskets need to be slid over the penetrations, so be sure to think ahead when sealing long wires, pipes, etc.
The added benefit of gaskets is that the air seal is not adhered to the surface, but still seals snugly around it. Unlike spray foams, mastic and caulk, this seal has the flexibility to adapt to repeated expansion and contraction movements of the materials to keep the connections reliably airtight (and waterproof).