Proper corner assembly and sealing are essential factors in ensuring structural durability, air tightness, and long-term weatherproofing in modern architectural aluminum window systems. In this detailed step-by-step video tutorial, Paula demonstrates the complete technical assembly process for joining aluminum window frames using corner keys, structural sealant, and specialized waterproofing pads.

Whether you are a professional glazier, window fabricator, contractor, or commercial Installer, following proper corner joint sealing protocols prevents air leakage, water infiltration, and long-term frame corrosion.

Step-by-Step Corner Assembly & Sealing Guide

Step 1: Applying Primary Corner Joint Sealant

• Locate the high-strength aluminum joint/corner glue (structural bonding adhesive).

• Apply an even layer of sealant across all $45^\circ$ mitered frame profile surfaces.

• Ensure total coverage across all interior and exterior mating faces to guarantee a seamless structural bond and preliminary weather barrier.

Step 2: Installing Corner Keys & Securing Set Screws

• Retrieve the two matching aluminum corner keys/cleats.

• Combine the corner pieces and slide them flush into the inner profile channels of the aluminum frame.

• Align the pre-drilled fastener holes on the frame profile with the corner key threads.

• Insert the heavy-duty fastening screws and securely tighten them down using appropriate hand tools to lock the joint assembly in place.

Step 3: Injecting Internal Corner Sealant

• Prepare the injection sealant cartridge equipped with an extended applicator nozzle.

• Insert the nozzle directly into the dedicated corner injection port.

• Steadily inject the sealant into the interior cavity until it visibly flows out of the adjacent relief relief ports.

• Note: Completely filling the internal corner void ensures optimal wind-load resistance, acoustic insulation, and maximum sealing performance against extreme weather conditions.

Step 4: Placing Waterproof Sealing Pads on Bottom Tracks

• Take the two custom-molded waterproof rubber/EPDM sealing pads.

• Locate the bottom track drain/corner channels on both the left and right ends of the frame profile.

• Insert the sealing pads firmly into place on the bottom track only.

• Key Function: These bottom track pads act as crucial water barriers, preventing water pooling and redirecting drainage away from structural wall openings.

Step 5: Final Exterior Corner Edge Waterproofing

• Once the main frame assembly is fully connected, open the final corner corner-sealant packet.

• Carefully apply a continuous bead of high-performance exterior silicone along the entire exterior miter joint seam.

• Smooth out the sealant line across the edge to complete the dual-layer weatherproofing barrier, providing long-term insulation and draft prevention.

Key Tools & Materials Used in This Video

• Mitered Aluminum Profile Frame Channels ($45^\circ$)

• Corner Keys / Aluminum Joinery Cleats

• Fastening Screws & Hex Tools

• High-Strength Corner Bonding Glue / Joint Adhesive

• Cavity Injection Corner Sealant

• Bottom Track EPDM Waterproof Sealing Pads

• Exterior Frame Finishing Sealant