About Fosroc Nitoseal AC115

Fosroc Nitoseal AC115 is a one-part, water-based acrylic emulsion joint sealant (a “siliconised acrylic” in trade terms) supplied ready to use in cartridge form. It belongs to the economy, low-movement end of the Fosroc Nitoseal sealant family and is intended for general building joints where appearance, paintability and clean application matter more than high dynamic movement capability. Unlike reaction-cure sealants, AC115 cures simply by the evaporation of water from the emulsion: it forms a surface skin in roughly 30 to 60 minutes at 25°C and 50% relative humidity, then continues to cure inward at about 2 mm per day, so deeper joints take proportionally longer to develop full properties.\n\nThe sealant is gun-grade and non-sag, meaning it holds its shape in vertical and overhead joints without slumping, and it tools to a smooth finish. It is supplied in white and grey, and a key practical advantage over silicones is that once cured it can be overpainted with most emulsion and masonry paints — making it the natural choice for joints that will be decorated as part of the wall finish. AC115 develops strong adhesion to the substrates most common on Indian sites: concrete, cement mortar, blockwork, timber and anodised bronze, and it will also bond to many painted surfaces, though a site adhesion trial is always sensible on coated or unusual substrates.\n\nFor a contractor in Delhi NCR or anywhere across India, AC115 fills the gap between cheap general-purpose decorator’s caulk and the premium polyurethane and MS-polymer sealants. It is the right product for static and low-movement perimeter joints — sealing the gap where an aluminium or uPVC window meets the reveal, pointing brick and block junctions, or closing the perimeter of lightweight cladding boards — where you want a neat, paintable, weather-resistant line without paying for a high-performance elastomeric. Space Arc Engineering, as an authorised Fosroc distributor and applicator, supplies AC115 alongside the wider Nitoseal, Thioflex and Colpor ranges so that the correct grade can be matched to each joint on a project.

The technical insight

The single most important thing to understand about AC115 is its movement accommodation factor (MAF) of about 10%. That figure governs everything: it tells you the joint can only safely absorb cyclic movement equal to roughly 10% of its designed width, so a 10 mm wide joint should not see more than about ±1 mm of total movement in service. This is why AC115 is correctly specified for static and low-movement joints — window perimeters, masonry pointing, cladding edges — and is the wrong product for true expansion or structural movement joints, where a polyurethane (Nitoseal PU series), polysulphide (Thioflex 600) or MS-polymer (Nitoseal MS300/MS600) with a 25% MAF is required instead. Because it cures by drying rather than by chemical reaction, AC115 also shrinks slightly as the water leaves; this reinforces the rule that it must be backed and not over-deep, so the sealant cures evenly and the bead is not pulled thin. It is a one-part, ready-mixed material, so there is no mixing error to manage on site — but it must be protected from rain and freezing until the surface has skinned, and it should never be used below the waterline or in continuously immersed joints, where Fosroc directs users to Nitoseal MS600 instead.

Where it is used

• Perimeter (mouth) joints where aluminium, uPVC or timber window and door frames meet concrete, plaster or masonry reveals
• Pointing and sealing of joints in brickwork and blockwork on internal and external walls
• Sealing the perimeter and butt joints of lightweight cladding and infill panels
• Internal decorative joints and gaps that will be overpainted as part of the wall finish
• Junctions between dissimilar building materials subject to only minor thermal movement
• Cosmetic crack and gap filling in plastered and rendered surfaces ahead of painting

Key advantages

• One-part, ready to use straight from the cartridge — no mixing, no waste, minimal site error
• Overpaintable once cured with most emulsion and masonry paints, giving a continuous decorated finish
• Excellent adhesion to concrete, mortar, blockwork, timber and anodised bronze, often without a primer
• Low odour and water-based — easy and pleasant to apply in occupied and internal spaces
• Gun-grade and non-sag, so it holds its shape in vertical and overhead joints
• Tools to a clean, smooth bead with white spirit or a wet sponge
• Economical compared with PU, polysulphide and MS-polymer sealants for low-movement work
• Backed by Fosroc’s technical support and supplied locally by Space Arc across Delhi NCR and Pan-India

Limitations & considerations

• Low movement accommodation (about 10% MAF) — unsuitable for expansion or structural movement joints
• Not recommended for joints subject to water immersion or permanent wet conditions; use Nitoseal MS600 instead
• Cures by drying and shrinks slightly, so deep or unbacked joints can cure unevenly or thin out
• Must not be applied below 5°C and must be protected from rain and frost until skinned
• Slower to reach full cure than reaction-cure sealants (about 2 mm per day inward)
• Limited standard colour range (white and grey) — not a colour-matched façade sealant
• Not chemical- or fuel-resistant and not intended for trafficked floor or pavement joints
• Site adhesion trial advised on painted, coated or unusual substrates before full application

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Nitoseal AC115

Within the Fosroc sealant range, Nitoseal AC115 sits at the economical, low-movement, paintable end — alongside its sibling Nitoseal AC105 — and is best reserved for static perimeter and masonry joints rather than dynamic ones. As soon as a joint must accommodate real movement, step up to an MS-polymer (Nitoseal MS300 or MS600), a polyurethane (the Nitoseal PU range) or a polysulphide (Thioflex 600) with roughly 25% movement capability; for heavy-duty trafficked and pavement joints, Colpor 200PF is Fosroc’s pour-grade option. Against competitor products, AC115 occupies the same niche as acrylic frame sealants such as Sika Sikaflex AT-Connection’s acrylic equivalents, MBCC/Master Builders Solutions MasterSeal caulks and STP (Choksey/Pidilite) acrylic sealants; where joints demand higher movement or immersion resistance, the comparison shifts to Sikaflex polyurethane and MasterSeal MS-polymer grades. The honest positioning is simple: choose AC115 when you want a clean, overpaintable, low-odour seal on a low-movement joint at sensible cost — and choose a higher-grade Nitoseal, Thioflex or Colpor product, or an equivalent Sika/MasterSeal sealant, when movement, water immersion or chemical exposure are involved. Space Arc Engineering, as an authorised Fosroc distributor and applicator across Delhi NCR and Pan-India, can supply the right grade and advise on joint design for each application.

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