High-quality installation of aluminum structures is not just about fitting a product into an opening. It is about precisely following dozens of technical requirements, where a mistake in any point can lead to freezing, leaks, damage to insulated glass units, and voiding the warranty.
In this article, I will share my proprietary quality control checklist for installation, created based on many years of experience, system manufacturer recommendations, and work with dozens of installation teams. This document is the result of trials, errors, corrections, and analysis of hundreds of issues. I have never published it publicly — it is my internal standard, used by my teams and technical supervision.
This article will be useful for aluminum installers, PVC specialists looking to switch to aluminum, and clients for quality control. It is not just a list of requirements — I will explain why each point is critically important and what problems arise if it is ignored.
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Section 1. Connection of Mullions and Transoms
1. Only system screws
To connect the post and the beam, use only special system screws. In Alutech, this is a flat-head screw specifically designed so that the seal does not stick out and fits neatly at the joint.
If a regular round-head screw is used, the gasket will bulge, press against the insulated glass unit, and create pressure. This can lead to cracks in the glass unit and an unattractive appearance.
Why system screw heads break:
- The holes in the beam are not aligned with the nut on the post
- No countersinking in the beam holes
- Excessive torque on the screwdriver
Solution: holes must be punched using a special press matrix with countersinking. If the holes are crooked, align them and countersink manually. Set the correct torque on the screwdriver.
Important: use only stainless fasteners! Galvanized screws cause corrosion with aluminum. I have had cases where 10 mm galvanized bolts were completely eaten by corrosion, and the heads broke off. Forget about galvanized fasteners in aluminum structures.
2. Sufficient number of self-tapping screws
I use four screws for a single connection between the mullion and transom: two into the mullion, two into the block. This is the most reliable solution.
If you use cheap blocks without holes (only two screws into the mullion), on deep profiles of 100+ mm, a gap forms between the mullion and transom at the back. Four screws hold the structure better, minimize gaps, and prevent loosening.
Control:
Bend back the gasket on the assembled frame before installing the glass, check that all screws are present, the heads are intact, and the material is stainless steel.
3. Minimal gap at the connection
Common problem: the post and beam separate, creating a gap. This is unacceptable.
How to avoid it:
- During assembly, tighten the posts and beams with cargo straps before screwing in the fasteners
- Attach to the opening so that the plates press the post to the beam, not stretch it
- Install additional wedges near the beams to press the post
A micro-gap of no more than 0.5 mm is acceptable. If larger — redo it. In extreme cases, if tightening is impossible, fill the gap with color-matched sealant, but this is a compromise.
4. Transom tightly pressed to the mullion
The beam must be fully tightened to the post. This is especially critical for coplanar systems (when the post and beam are in the same plane on the inside).
If the beam is not fully tightened, the gaskets are not aligned, and they stick out. When installing the insulated glass unit, it may be distorted, and the glass could crack.
Check: verify the tightness of the beam against the post around the entire perimeter, ensure the screws are tightened, and the gaskets are in the same plane.
Section 2. Structural Fixing
5. Fixing windows and doors to the mullion-transom system
6. Paronite gasket under mounting plates
7. Mounting plates: stainless steel only, inside chamber only
A critically important point that many PVC installers do not understand.
Prohibited:
- Screwing into a thermal break (it is non-structural and will not hold)
- Screwing into the outer chamber (cold, creates a thermal bridge through the plate)
- Using galvanized fasteners
Correct: only stainless screws, only into the inner aluminum chamber.
I had a project where the plates were screwed into the thermal break using galvanized screws. From the outside, you could see the plate sticking out, touching the outer shell. 100% freezing, condensation, mold, and damage. Complete reinstallation required.
8. Features of fixing into the frame (wooden houses)
In a wooden house, fasteners MUST NOT penetrate the house structure! They should go only into the window casing.
The casing is designed so the window can move independently of the house during settling. If screws enter the house structure, the window will tilt during settling, the sashes will stop opening, and the insulated glass units may crack.
Use dowels or turbo screws of precisely calculated length so that the fastener enters the casing but does not go beyond it.
9. Fixing into different types of substrates
Concrete: 10×100 mm anchor bolts, at least two at the bottom and two at the top per post.
Hollow ceramic block: Blaugelb turbo screws, 10×100 nylon anchors, or chemical anchors. Regular anchors will not hold! Drill without impact, using a special drill with a diamond coating.
Aerated concrete: turbo screws or special anchors for aerated concrete.
10. Plate should not hang in the air
There was a case: in winter, there was ice up to 1 cm thick on the windowsill. The installers attached the plate directly onto the ice instead of removing it.
The opening must be cleared of ice, debris, and dust. The plate must fit snugly against the wall and be correctly bent: first bend along the frame, then press against the wall at approximately 90°.
Section 3. Mullion-Transom Systems
11. Lower fixing leveled
Before installing insulated glass units, the lower part of the post-and-beam system must be leveled and securely fixed.
Standard solution: extend the post from below, M8–M10 bolts through aluminum sleeves. Sleeves are mandatory — they prevent the bolt from crushing the post and act as spacers.
Alternative (for lightweight structures up to 200 kg): fastening with screws from the exterior into the post, 4–6 screws.
For heavy structures: visible fastening on the beam — stainless sleeve 50 mm with threading, M8×20 countersunk screws, decorative washers.
All the load from the weight of the insulated glass units goes to the lower fastening — monitor it carefully.
12. Drip caps: installation and trimming
The drip cap is a critically important element for water drainage. Condensate flows along the beams into the posts and exits through the drip cap. With large temperature differences, there can be a lot of condensate.
Lower drip cap:
- Installed in the workshop with sealant, fastened with a screw
- Must be level with or below the lower beams (not above!)
- After installing the insulated glass unit, it is trimmed with a special shape to fit the thickness of the unit
Upper drip cap:
- Installed in a mirrored position for ventilation (air circulation from bottom to top)
Common mistakes:
- Drip cap is not sealed to the post
- Drip cap sticks out 2–3 cm, pressed by the cover, and does not function
- Drip cap is bent downwards or upwards by the cover
The clamping strip must have a hole for the drip cap outlet. If not — drill it on site.
13. Sealing of gaskets between mullion and transom
Use a special sealant (Cosmo 412 or equivalent) to seal the joints of EPDM gaskets.
When the post and beam are connected, the gaskets are trimmed and meet. At the joint, you need to: bend back the gaskets, apply sealant into the beam and post, fill between them, and then join.
Why this is necessary: Alutech conducted tests — when air is blown under pressure, there are micro-leaks at the joints. After sealing, the structure becomes more airtight and reliable.
I had a project where the client called an Alutech representative. The report noted the lack of gasket sealing. All insulated glass units had to be removed and redone. Huge losses.
14. Thermal bridge and butyl tape
After installing the insulated glass unit, a thermal break (foam or plastic) is installed. I use only foam — the system becomes warmer.
The thermal break is inserted into the groove, and the clamping screw passes through it.
After installing the thermal break, a butyl tape must be applied along the entire length (not just in a cross at the joints!). It protects against leaks if the clamping plate does not fit tightly in some areas.
Common mistake: Installers often skip the thermal break and butyl tape entirely, even though they arrived with the unit. They immediately press the plates. Always check!
Section 4. Supports for Insulated Glass Units
15. Correct selection of supports
Aluminum supports for the insulated glass unit are inserted into the beam, on top of them — plastic leveling pads, and then the insulated glass unit is placed.
There are dozens of types of supports: standard, reinforced, cross-shaped, steel — for different weights and thicknesses of glass units.
Critical: ALL panes in the insulated glass unit must rest on the supports! If it’s a double-chamber unit (3 panes) — all three must rest on both the aluminum support and the plastic pad.
16. Terrible story with an inverted support
I had a case where cross-shaped reinforced supports (vertical part attached to the post, horizontal to the beam) were installed mirrored the wrong way. The tip of the support, which should be on top, ended up at the bottom.
The insulated glass units were installed. A month later, when the sun warmed up, the outer glass slipped down 5-6 mm, and the frames were twisted. We had to dismantle, replace the glass units, and flip the supports.
Check: Before installing the glass, make sure the supports are installed correctly, the tip is on top, and all panes will rest on the supports.
17. Shimming pads
Plastic leveling pads must have the correct depth — under all panes of glass.
Common mistake: the pad was inserted too deep, leaving a 5 mm gap under the outer glass. The outer glass will slip, press against the aluminum support, and exert pressure. Tempered glass may shatter, and annealed glass may crack.
Pro solution: some installers rotate the pads lengthwise, place 2–3 pieces, install the glass unit, then trim along the edge of the unit with a knife. This ensures the entire glass surface rests evenly on the pads.
18. Reinforced supports are fastened with screws
The reinforced support is additionally fastened to the beam with special 5.5×23TX screws. Do not use random screws — always use the system-specified fasteners.
Section 5. Sliding Systems
19. Fixing under the gutter
I fasten the sliding system under the gutter (bottom, side, top). The gutter is removed, the frame is fixed with turbo screws, then the gutter is reinstalled and must be properly sealed.
Important: the fastening step at the bottom is 350 mm (according to the Alutech catalog). Yes, it seems frequent, but this is the manufacturer’s requirement.
On the side, the step is larger — 600 mm.
Do not: fasten through the gutter! Do not drill the gutter.
Alternative: fasten into the aluminum profile cup with visible fasteners and caps.
20. Shimming scheme for sliding system
Shimming the sliding system is a separate art. Without understanding the correct scheme, nothing will align properly: gaps with the frame, between sashes, and the sashes won’t move smoothly.
The wedges are installed in a specific pattern from the hinges, mirrored on the other side. There is an exact scheme for each type of sliding system. When shimmed correctly, everything works perfectly.
Section 6. Shimming of Windows and Doors
21. Scheme of mounting wedges in the opening
Even experienced PVC installers often incorrectly shim aluminum windows.
Correct shimming scheme:
- Wedges at the corners (150 mm from each corner)
- Wedges near mullions (150 mm on each side of the mullion)
- Maximum spacing between fasteners — 700 mm
- At joints of two units — sealant (foam or PSUL)
22. Shimming scheme for sashes
If the sashes are shimmed incorrectly, they will sag. I had a project where all the sashes sagged — it turned out the shimming under the glass units of the sashes was done incorrectly.
Different shimming schemes:
- Casement window — one scheme
- Tilt-and-turn — another scheme
- Transom — third scheme
- Doors — fourth scheme
- Sliding — fifth scheme
- Accordion — special scheme (wedges mirrored from the hinges)
Shimming is done diagonally from the hinge. Do not install without knowing the correct schemes!
Section 7. Sealing and Joints
23. Drainage is mandatory everywhere
If the sashes are shimmed incorrectly, they will sag. On one project, all the sashes sagged because the shimming under the glass units was done incorrectly.
Shimming schemes for different types:
- Casement window — specific scheme
- Tilt-and-turn window — another scheme
- Transom — third scheme
- Doors — fourth scheme
- Sliding — fifth scheme
- Accordion — special scheme (wedges mirrored from the hinges)
Shimming should be done diagonally from the hinge. Do not attempt installation without knowing the correct schemes!
24. Sealants: correct application
Vapor-permeable — on the outside.
Vapor-barrier — on the inside.
If installed incorrectly, moisture won’t escape outside, will move inward, and mold will appear.
For the bottom (waterproofing): Cartlinger 791 or liquid waterproofing.
For structural joints: special structural sealant (Dow Corning 995, Sika).
25. Lower node — the most critical
- Galvanized drip edge with sealant
- Coat with Cartlinger or liquid waterproofing
- Bitumen mastic, EPDM membrane, or Frankoseal can also be used
26. Mounting foam: correct technique
If the opening is wide or deep — apply foam in several passes, misting with water. There should be no voids.
For large gaps: insert a strip of foam board (Penoplex), then foam from both sides. Do not pour foam in one big batch.
Use professional foam and a foam gun.
27. Tapes: why I stopped using them
Vapor-permeable and vapor-proof tapes must be applied according to the proper procedure:
- Apply foam
- Wait for the foam to dry
- Trim carefully
- Prime the wall
- Apply the tape at 90° to the frame
90% of installers do this incorrectly — they apply tape crookedly, without primer, or on foam that hasn’t dried. The tape peels off.
I switched to sealants — it’s easier to control quality.
28. Foam board on extensions
For mounting on an extension, a foam-plex frame is installed around the perimeter from the outside. It is attached to the concrete with adhesive foam and mushroom-shaped anchors.
Important: the foam-plex must be cut precisely! Not with a utility knife. At minimum use a jigsaw, ideally a heated wire or a special cutting machine.
If the foam-plex is crooked on a multi-million project — it’s unacceptable.
Section 8. Finishing Assembly
29. Pressure plates and covers
Clamping strips must be in the same plane, not twisted. If they are misaligned — replace the gasket or other elements.
The clamping strip and cover should meet with minimal gap (0.5–1 mm maximum). 2–3 mm is unacceptable.
How to align: loosen the screws on the vertical strips, pull them toward the horizontal beam, and retighten. You can slightly adjust the hole if necessary.
30. Rubber on the ends of pressure plates
After installation, there is excess gasket (3–10 cm) at the ends of the clamping strips. It must be trimmed! Do not leave it sticking out.
31. Gasket under glazing bead
Common issue: the gasket is inserted the wrong way. The skirt should face downward.
If it doesn’t fit:
- Use spatulas to adjust the glass and tap in wedges
- Lubricate with soapy water or silicone spray
- If it still doesn’t fit — it’s the wrong gasket
Important: do not stretch it! Install it with slight spacing, otherwise it will contract and create 3 cm gaps at the corners.
Ideal: one continuous gasket, trimmed at the corners at 45° and glued on top.
32. Structural corner
Two glass units meet at a 90° angle. The corner must be insulated from the inside (Vilatherm or foam board).
Gap: consistent along the entire height (I use 5 mm). Glasses must be in the same plane.
If the insulated glass unit bends: tighten with suction cups or tape, apply sealant, and release after it sets.
Sealing: painter’s tape + structural sealant (not regular!) + spatula in a single stroke. You can smooth with a sponge and soapy water or finish with ultra-fine sandpaper.
33. Cover strips and joints
Cover profiles must be installed evenly, cut to size, joined properly, and sealed with sealant. There should be no twisted or crooked elements.
34. Drain caps
Each drainage hole must have a cap installed.
Section 9. Quality Control
35. Glass inspection
Before installation, check the glass for chips, scratches, voids in the sealant, and proper assembly.
Determining the glass side: do not rely on stickers! Check the edge: where the coating is removed, what color stripe remains. Multifunctional glass should be reflective on the outside.
I’ve had several projects where insulated glass units were installed the wrong way around. We had to flip them afterward.
36. Gaskets
Check that the gaskets are not pinched anywhere (especially in post-and-beam systems when installing the insulated glass unit).
37. Vertical, horizontal, diagonals
Checking with a level, laser, and diagonals is mandatory at every stage.
38. Cleanliness of the product
After installation, the product must be clean. Wipe off sealant, foam, and dirt. The work should look neat and presentable to the client.
Conclusion
This checklist is the result of years of experience and hundreds of mistakes that I have analyzed and systematized. Each item is not just a formal requirement — behind it are real problems, losses, and rework.
If you are an installer — study this material, print it out, and keep it on-site. If you are a client — use it to control the quality of work. If you are a manager of an installation company — implement it as a standard.
High-quality installation is not talent; it is adherence to technology. Follow these 38 points, and your projects will serve for decades without issues.
If you have questions or want the full document with drawings and diagrams — reach out! I am ready to share my experience to raise the skill level across the entire market.
