What changes in commercial work
On a concrete, panel or glass façade, joints are there to absorb movement. The building expands in the heat, contracts in the cold and flexes under wind. A joint that doesn't follow this movement ends up cracking or pulling away.
Joints are also more numerous and more varied: window and door perimeters, expansion joints, joints between panels, curtain wall connections. They are often high up, which calls for access equipment and a crew trained to work safely.
Finally, there is a specification. In many projects, an architect or engineer specifies the product, the joint dimensions and the method. The caulker must follow this document to the letter.
Understanding the ASTM C920 standard
The ASTM C920 standard classifies elastomeric sealants used in construction. The class indicates the joint's movement capability. The higher the class, the more the sealant can stretch and compress without failing. Other letters specify the type of product and the substrates it was tested on.
Take DOWSIL™ 791, which we apply regularly. According to Dow's data sheet, it is a one-part, neutral-cure, architectural-grade silicone. It meets ASTM C920, Type S, Grade NS, Class 50, and its movement capability is ±50%. Dow intends it for uses including expansion and perimeter joints, glazing, curtain walls and façades.
The architectural specification published by Dow describes this type of product as a medium-modulus, neutral-cure sealant with a hardness of 30 to 40 Shore A. These are the properties we compare when a specification calls for an equivalent product.
Designing and preparing the joint
A good product applied poorly won't hold. Preparation matters as much as the sealant. The joint must be clean, dry and free of frost. The 791 data sheet states that it must not be applied to a frosty or wet surface, or in a fully confined joint.
Joint depth is controlled with a backer rod, a compressible foam cord. Natural Resources Canada recommends using one in gaps of 6 mm or more. It gives the bead the right shape and keeps the sealant from sticking to the back of the joint, so it can move freely between the two sides.
For the 791, the data sheet calls for tooling before a skin forms, generally within 15 minutes, and a full cure of 7 to 14 days. The other dimensions follow the specification or the data sheet of the specified product. As for tools, we apply our beads with an Adfast gun.
Removing the old joint completely
Applying new sealant over an old cracked joint solves nothing. The new sealant sticks to the old one, and the old one keeps pulling away from the substrate. So we remove the old joint completely, clean the sides and check the condition of the substrate before applying.
It's also the time to spot what caulking won't fix: a panel moving abnormally, crumbling masonry, a damaged frame. We flag it in the survey so the right crew can take care of it.
One more thing to plan for: the 791 can't be painted. According to Dow, paint generally doesn't adhere to it. If the façade is to be repainted, the choice of product must take that into account from the start.
The specified product, or the one you supply
We mainly apply DOWSIL™ 791 and CWS sealants. CWS is a medium-modulus silicone that Dow intends for uses including expansion joints, concrete panels and window and door perimeters.
If your specification calls for another product, we apply that one. If you supply the product, we apply it too, on request. And if you're looking for an equivalent, we suggest a product from the DOWSIL™ line to compare with the requested data sheet.
- Building visit and survey of the openings
- Detailed quote by façade, by phase or by building
- Schedule coordinated with your operations and your occupants
- Subcontracting for general contractors
Inspection, warranty and follow-up
On DOWSIL™ 791, we offer a lifetime warranty on materials and labour, under the terms set out in the contract. For other products, the written warranty depends on the product applied.
Regular façade inspections help catch a joint that is pulling away early. For a property manager, keeping a record of the joints redone, by façade and by date, makes it easier to plan the next round of work.
We work in Greater Montréal, Lanaudière, Quebec City, Beauce, Estrie, Outaouais and Saguenay. We caulk year-round, with short lead times.
Frequently asked questions
Does all the old sealant have to be removed?
Yes. A new joint applied over an old cracked joint inherits its flaws. We remove the old one completely, clean and check the substrate before applying.
What warranty can we get?
On DOWSIL™ 791, we offer a lifetime warranty on materials and labour, under the terms of the contract. For another product, the written warranty depends on the product applied.
Do you work as a subcontractor for a general contractor?
Yes. We fit into the site schedule and apply the product named in the specification.