Frequently Asked Questions

What is the difference between Nitofoam 40 and Nitofoam 45 and how do I select the correct grade for my joint?

Nitofoam 40 and Nitofoam 45 are both closed-cell polyurethane foam backer rods from Fosroc for sealant joint backing — the number in the designation indicates the foam density in kilograms per cubic metre (40 kg per cubic metre for Nitofoam 40, and 45 kg per cubic metre for Nitofoam 45). The slightly higher density of Nitofoam 45 means it is marginally firmer and provides better resistance to deformation under sealant pressure during application and under the weight of a loaded joint (such as a horizontal floor joint subject to forklift or vehicle traffic). For most standard vertical joint and facade joint applications, both grades are appropriate. Nitofoam 45 is typically preferred for horizontal joints in floors and pavements where a firmer backer rod is needed to resist sealant flow and maintain the joint profile under the sealant weight and traffic loading; for wider joints (above 25 mm) where a larger diameter backer rod is used and the slightly higher density provides better joint filling; and for hot climate applications (India summer) where the foam must maintain its shape at elevated joint temperatures. For standard vertical joints in concrete structures and building facades, either grade can be specified — the final choice is typically based on local availability and project specification.

How is Nitofoam 45 sized and installed in an expansion joint before sealant application?

The Nitofoam 45 backer rod diameter should be selected to be approximately 20 to 30 per cent larger than the nominal joint width — a backer rod that is the same diameter as the joint or smaller will not achieve the friction fit and may fall into the joint or move during sealant application. For example, in a 20 mm wide expansion joint, a 25 mm diameter Nitofoam 45 backer rod should be used — the 5 mm oversize requires the rod to be compressed by 20 per cent as it is pressed into the joint, which provides the friction necessary to hold the rod in position. Installation is straightforward: cut the backer rod to the required length (leaving small compression gaps at joints between rod lengths to accommodate thermal expansion); press the rod into the joint by hand or with a blunt-ended tool (a flat piece of timber or a roller), pushing it to the required depth below the concrete surface to leave the specified sealant depth above the rod. A typical sealant depth above the backer rod is half the joint width — so a 20 mm joint with a 25 mm backer rod positioned at 10 mm below the concrete surface provides the correct 1:0.5 width-to-depth sealant profile. The sealant is then applied over the backer rod, tooled to a concave profile, and allowed to cure.

Can Nitofoam 45 be left in place if an existing sealant joint needs to be resealed and the old sealant is removed?

When resealing an existing expansion joint where the old sealant has failed and must be removed, the existing backer rod (whether Nitofoam 45 or another brand) should be inspected during the old sealant removal process. If the old backer rod is intact, undamaged, and correctly positioned at the right depth, it can be left in place and the new sealant applied over it — there is no need to remove and replace a backer rod that is performing correctly. However, the old backer rod must be checked for: physical damage (cuts, compression set, or crushing from years of joint movement); oil or sealant contamination on the rod surface that would prevent adhesion of the new sealant to the side faces of the joint (the sealant bonds to the concrete side faces, not to the backer rod, so contamination of the rod is less critical than contamination of the joint faces); and correct position at the right depth. If the old backer rod is damaged, deformed, or at the wrong depth, it should be removed and replaced with a correctly sized Nitofoam 45 rod before the new sealant is applied. Old sealant residue on the concrete joint faces must be fully removed by grinding or cutting before new sealant application, regardless of whether the backer rod is replaced.