Structural Silicone Sealant for Structural Glazing

Structural silicone transfers wind load from the glass into the frame and is part of the structural design. Weatherseal silicone keeps water out of the perimeter joint and carries no load. A curtain wall usually uses both, in different positions, and the two must be chemically compatible with each other.

No. They are specified against different standards and different test regimes. Using a weatherseal product structurally, or a structural product where a low-modulus weatherseal is needed, is a common and expensive mistake.

Only after the bead has fully cured. Cure time depends on bead thickness, temperature and humidity — a thick bead in cool, dry weather can stay soft inside for days. Tell us your site conditions and we will give you a realistic figure.

Yes. GB 16776-2025 tensile adhesion strength is 0.85 MPa against a 0.60 MPa minimum, elongation at maximum tensile strength is 205%, and shear strength is 0.89 MPa. We send the full test report on request.

Yes — it is neutral cure, so no acetic acid is released to attack anodised surfaces or laminated glass interlayers. Adhesion still has to be confirmed on the actual coating used on your project.

A glazing joint sealant sits inside an engineered structural glazing system and carries part of the wind load from the glass into the frame, so it is specified, tested and documented as a structural component. A weatherseal sits in the perimeter joint and only keeps water out. Confusing the two is the most expensive mistake on a facade. Tell us which position you are sealing and we will send the matching grade.

For structural glazing use PR-999, a one-component neutral cure structural silicone manufactured to GB 16776-2025. For the perimeter weatherseal on the same project use PR-666 or PR-638. All three are neutral cure, so they will not etch anodised aluminium or laminated glass interlayers. Send us your joint detail and we will confirm the grade before you order.

No. A caulk for window glazing is a perimeter weatherseal product and carries no structural load. Where the joint has to transfer wind load — structural glazing, glass fins, overhead glass — you need a structural silicone specified inside an engineered system instead. PIROI supplies both categories, and if your facade needs two chemistries we send matched pairs so they stay compatible.

Neutral cure, every time. Glass to metal joints are exactly where acid cure does its damage: the acetic acid released during cure attacks anodised and powder-coated aluminium surfaces. PR-999 for the structural bond to GB 16776-2025, and PR-666 or PR-638 for the perimeter joint. We can run an adhesion test on your actual frame finish before you commit to the project.

Not necessarily. Window glazing joints are generally smaller, drier and see less movement than a curtain wall grid, so a window-grade sealant is often sufficient. A curtain wall needs a defined movement class and, in the structural position, a structural silicone. If the joint sits on the curtain wall grid, specify the facade grade — PR-999 structural plus PR-666 or PR-638 weatherseal.

It has to bond to two very different surfaces and corrode neither. Our glass and metal sealants are neutral cure, so no acetic acid is released to attack the metal finish or the glass interlayer. Adhesion still has to be confirmed on the actual coating and glass type on your project — send us samples of both and we will report the result.

Yes. PR-999 is tested to GB 16776-2025: tensile adhesion strength 0.85 MPa against a 0.60 MPa minimum, elongation at maximum tensile strength 205%, and shear strength 0.89 MPa. We send the full test report with the submittal package. Neutral cure, so it is safe on anodised and coated aluminium frames.

Only run the field adhesion test after the bead has fully cured. Cure time depends on bead thickness, temperature and humidity — a thick bead in cool, dry weather can stay soft inside for days. Give us your site conditions and joint width and we will give you a realistic figure rather than a catalogue number.

Four causes account for most of it: pushing the nozzle instead of pulling it folds air into the bead; laying the bead faster than the sealant can flow leaves voids behind the nozzle; a butt joint with no backer rod has no depth control so thickness varies; and tooling either before the skin forms or after it has skinned damages the surface. Where a void has already formed in a cured structural bead, cut out the affected section to sound sealant and re-gun it rather than injecting into the void.

Off-site bonding in a factory is preferred wherever transport allows, because substrate preparation and cure conditions are both controllable there and neither is controllable on a scaffold. Where field bonding is unavoidable, require a test panel bonded on site under the same conditions before production bonding begins. Both routes use the same grade: PR-999 to GB 16776-2025.