Home › Blog › Fenestration › Curtain Wall Glazing & Perimeter › Curtain wall glazing material selection
Setting Blocks, Structural Glazing Tape, and Perimeter Gaskets: Choosing Curtain Wall Glazing Materials
A curtain wall glazing pocket holds more decisions than it looks like it does: a block that carries dead load, a tape that fixtures a structural joint, a gasket that seals across years of movement, and a baffle that keeps the drainage path open. Each one is a different material class with a different governing property, and the reliable way to choose is by the job in the joint, not by the catalog. This guide walks the families H-O converts for curtain wall glazing and the standard each one answers to.
Request a quote for your project →
Which accessory family wins each job in the pocket?
The Curtain Wall Glazing and Perimeter application page splits the system into the parts that carry load, the parts that bond and fixture, the parts that seal, and the parts that drain. The families below follow that logic, each named by the job it wins, with standards by designation: ASTM C864 Option I for dense blocks, ASTM C1401 for the structural sealant glazing system, ASTM C1087 for accessory compatibility, ASTM C509 and D1056 for cellular perimeter gaskets, and the AAMA 501 series for mockup verification.
Values are per the technical data sheet on file for each grade.
Dense blocks carry the load and hold the dimension
Setting blocks and side blocks are the load-bearing and position-holding parts, so they are dense (non-cellular). Glazing-grade solid silicone in the 80 to 90 Shore A band per ASTM C864 Option I is the conservative default beside silicone sealants, placed at the quarter points per the GANA Glazing Manual.
Where the project spec names an alternative dense elastomer, dense EPDM brings weathering headroom for exposed positions and dense neoprene carries the long service history that legacy specs name. The softer commercial durometers in the silicone family, down to a 30 Shore A commercial grade, serve cushioning and anti-walk side-block duty, never the dead-load setting position.
Structural glazing tape is the spacer, not the attachment
In conventional structural sealant glazing per ASTM C1401, the structural silicone is the engineered attachment and the tape is the spacer that sets the joint bite and thickness and fixtures the lite while the silicone cures. Structural glazing tape (the SGB, SGG, and SGW classes at the 0.09 inch position) does exactly that job, with peel per ASTM D3330 and shear per ASTM D1002 on its TDS and compatibility verified under the ASTM C1087 framework.
The tape sets and holds geometry; it does not become the structural joint by being swapped in, which is a system-level qualification by the engineer of record.
Bedding tapes seat the glass and the metal
Two non-structural beds finish the assembly. BGT crosslinked PE glazing tape beds shop-glazed captured lites with uniform compression, plasticizer-free and immediately handleable. On the metal side, Poly-Seal butyl tape (the SB straight, AF aluminum-faced, TPO seam, and CR coating-ready facings) beds panel laps, copings, and flashing terminations where a non-curing, conformable seal outperforms a gasket. Butyl creeps by design and carries no dead load, so keep the load on the dense blocks.
Perimeter gasket foams seal across movement
Pressure-plate gaskets, unitized stack-joint seals, and perimeter closures are cellular parts that seal by compressing across a moving joint per ASTM C509, with the firmness class per ASTM D1056 matched to the closure force at both joint extremes.
Closed-cell EPDM foam (the RE-series blend, with UV and ozone headroom) covers most positions, with solid 553 / 563 EPDM sheet where the joint is built for a dense strip; where joint temperatures swing hard or the program wants silicone throughout, closed-cell silicone sponge (grades such as HT-800 medium and HT-820 firm) holds its recovery across the wider window.
Drainage media keep the cavity working
The pressure-equalized cavity has to keep draining, which is the job of the weep baffles and the dams. Reticulated polyurethane baffles (an uncoated 30 PPI grade for shaded weeps, coated grades for exposure) drain at the cavity while excluding insects and reverse flow, with the PPI grade tuning the balance and depth doing the exclusion. Closed-cell crosslinked PE dams with near-zero water absorption per ASTM D3575 route water toward the weeps. Die-cut both to the system geometry so the drainage design survives the production tolerance stack-up.
Curtain Wall Glazing Families Side by Side
| Family | Class | Job in the joint | Spec hook |
|---|---|---|---|
| Glazing-grade solid silicone | Dense (C864) | Dead-load setting and side blocks | ASTM C864 Option I |
| Dense EPDM / neoprene | Dense (C864) | Blocks, splice pads, shims | ASTM C864 Option I |
| Structural glazing tape | Acrylic foam | SSG spacer and cure fixturing | ASTM C1401 / C1087 |
| Poly-Seal butyl | Non-curing | Metal panel and coping beds | ASTM D3330 (TDS) |
| EPDM foam / silicone sponge | Cellular (C509) | Pressure-plate and stack-joint seals | ASTM C509 / D1056 |
| Reticulated PU / XLPE dams | Drainage media | Weeps, snorkels, dams | PPI per TDS / ASTM D3575 |
Illustrative and relative only; confirm each grade on its current technical data sheet. The structural joint design belongs to the engineer of record per ASTM C1401; the accessories support it.
Movement first, then chemistry, then class
For every cellular seal the order of decisions is the same: start from the joint movement range so the gasket stays in compression at the open extreme and does not over-compress at the closed extreme, then pick the chemistry by exposure, then set the ASTM D1056 firmness class against the closure force. Qualify one grade per program and hold it; the substitution failure mode, a firmer or softer grade swapped to make a shipment, is identical to the window-side weatherstrip case and surfaces as an opened air line after seasons of racking.
The same dense-block discipline, including why softer durometers fail under dead load, lives on Window and Door Systems.
How H-O Products helps
H-O Products die-cuts and converts; we supply the converted accessories and the documentation that travels with them, not the wet sealants or the structural silicone.
We take roll, sheet, and bun stock and die-cut, kiss-cut on liner, slit, and laminate it to your drawing: keyed and notched setting blocks, structural glazing tape cut to the joint, corner-matched pressure-plate gaskets, butyl beds, and weep baffles and dams die-cut to the system geometry, all made to order with lot-code TDS records under our ISO 9001:2015 certified quality management system in Winsted, Connecticut.
Extruded bulb profiles come through a partner network while H-O converts the die-cut accessory set around them, and on the sealant side we review your package and flag the pairings that warrant an ASTM C1087 letter before submittal.
Frequently asked questions
Silicone, EPDM, or neoprene setting blocks: which should I specify?
ASTM C864 Option I accepts all three as dense elastomeric blocks in the 80 to 90 Shore A band, so the decision is compatibility and aging, not load capacity. Solid silicone is the conservative default beside silicone sealants and across temperature extremes; dense EPDM brings weathering headroom where the spec names it; dense neoprene carries the longest service history and remains common in legacy specs.
Whichever you choose, run the block-to-sealant pairing through the sealant maker compatibility program under the ASTM C1087 framework and keep the letter in the submittal.
Can structural glazing tape replace structural silicone?
Not as a material substitution. In conventional structural sealant glazing per ASTM C1401, the structural silicone is the engineered attachment and the tape is the spacer that sets joint bite and thickness and fixtures the lite during cure. Systems do exist in which a tape is the tested, engineered retention, but that is a system-level qualification by the system supplier and engineer of record with project-specific testing.
H-O supplies the structural glazing tape for the spacer and fixturing duty with compatibility verified per ASTM C1087; the structural joint design stays with the engineer.
What gasket material should a unitized stack joint use?
Start from the joint movement range, not the material. The gasket must stay in compression at the open extreme and not over-compress at the closed extreme, which sets the working deflection and, through the ASTM D1056 class, the firmness grade.
Then chemistry by exposure: closed-cell EPDM foam (the RE-series blend) or solid 553/563 EPDM sheet where the joint takes a dense strip for general duty, closed-cell silicone sponge where joint temperatures swing hard or the program wants silicone throughout. Stack joints are access-never positions, so qualify one grade, hold it, and verify with AAMA 501-series mockup testing.
Does H-O supply the structural silicone or the wet sealants?
No. H-O is a die-cut converter: we supply the converted accessories, blocks, pads, tapes, gaskets, baffles, and dams, and the documentation that travels with them. The wet sealants come from the sealant makers, and the structural joint design belongs to the system engineer per ASTM C1401 practice. What we add on the sealant side is the compatibility review: send the sealant package with the RFQ and we check the accessory pairings against the TDS and flag what needs a C1087-framework letter before submittal.
Get a curtain wall glazing accessory recommendation
Send the system profile or shop drawing, the structural and weather sealant package, the joint movement range, and the exposure, and we will recommend the block, tape, gasket, and baffle families and quote die-cut accessories to your geometry.
Samples typically ship in 3 to 5 business days for common die-cut configurations on materials we keep on hand; standard production runs about two weeks after drawing approval; expedited service is available. MOQ varies by material and part.
Family-owned in Winsted, Connecticut since 1971 · ISO 9001:2015 certified · OEMs worldwide send us a drawing — and get back their part.
Related reading
IndustryFenestration industry hubRead →
Request a quote for your curtain-wall glazing & perimeter sealing part
Send H-O your drawing or describe the part—engineering reviews every RFQ and converts samples on your geometry.
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- ASTM C864 Option I (dense elastomeric gaskets, setting blocks, and spacers); GANA Glazing Manual (setting-block placement); ASTM D2240 (durometer).
- ASTM C1401 (structural sealant glazing guide); ASTM C1087 (accessory-sealant compatibility framework); ASTM D3330 (peel); ASTM D1002 (lap shear); ASTM C920 (elastomeric sealants).
- ASTM C509 (cellular elastomeric preformed gaskets); ASTM D1056 (cellular compression-deflection grades); ASTM D3575 (crosslinked polyethylene foam); ASTM D1149 (ozone resistance); AAMA 501 series (field and mockup test methods); ASTM E283 / E331 (air and water).
- Manufacturer technical data sheets for the glazing-grade silicone, dense EPDM and neoprene, structural glazing tape, BGT, Poly-Seal butyl, silicone sponge, and reticulated polyurethane families named on the parent application page.
This article summarizes curtain wall glazing accessory material-selection principles using the families and published methods cited on the parent application page. Comparisons are qualitative; per-grade values are TDS figures and must be confirmed on the manufacturer's current technical data sheet. The structural joint design belongs to the engineer of record under ASTM C1401 practice; accessory-sealant compatibility is settled under the ASTM C1087 framework.
All parts are custom manufactured to order; minimum production run quantities vary by material and part. H-O is a die-cut converter and does not supply wet sealants, structural silicone, or extruded profiles in-house.