Welds, gaskets and weeps. How to read a sample corner.

A corner sample tells you more than a brochure. In five minutes you can check four things: how the corner is welded, how the gaskets run, how the frame drains, and what is inside the profile. None of it replaces a test report. It tells you how carefully the window is made, and the report tells you what it can do.

The weld.

A uPVC corner is not screwed or glued. The two profiles are cut to a miter, heated against a hot plate and pressed together until they fuse. Molten material squeezes out along the joint as a bead. What happens to that bead gives you the weld types you will hear about.

Weld	What you see	Worth knowing
Grooved	A shallow groove along the miter, where the bead was milled off	The long-standing method. On a colored frame the groove is touched in to match. Standard on the Vi5
Thin	A very fine, flat line	The same idea with a much narrower cut. Reads as a hairline
Seamless	The two faces meet with no groove	The machine shapes the bead instead of cutting it away. Looks like a mitered metal corner. Standard on the Vi6
Wood-look	A square butt joint on the visible face	Imitates a wooden window. The weld behind it is still a miter

The difference between these is mostly looks. It matters most on dark and metallic foils, where a groove shows more than it does on white.

Strength comes from somewhere else: clean cuts, the right plate temperature, the right time and pressure, and a welder that is kept in calibration. A careful fabricator breaks sample corners on a press to check the welds. Ask whether they do, and how often.

On Vistaza windows the series decides it. The Vi6 comes with the seamless weld. The Vi5 comes with the grooved weld.

On the sample, check:

• The joint line is straight and runs exactly corner to corner.
• The two faces are flush. Run a fingernail across the joint.
• The foil meets cleanly, with no white showing and no smeared touch-up.
• The inside corner, in the glazing rebate and the gasket groove, has been cleaned out. Leftover bead there stops the gasket or the glass from seating.

The gaskets.

Gaskets do three jobs in a window.

• Sash to frame. These are the compression seals. When the handle turns, the locking points pull the sash in and squeeze the gasket. Most are a hollow bulb shape that flattens under pressure and springs back.
• Glass to frame. A gasket on the outside of the glass and a wedge-shaped one pressed in with the bead on the inside. They hold the glass firmly and keep water out of the rebate.
• Joints between frames. Seals at mullions and couplings, where two frames meet.

Gaskets are made from rubber or from a flexible plastic. Some are pushed into a groove in the profile and can be pulled out and replaced from a coil. Others are extruded together with the profile and welded at the corners along with it. The first kind is easy to renew. The second is continuous at the corner by design. Vistaza lists gaskets and seals among its service parts.

On the sample, check:

• The gasket runs around the corner without a gap, a stretch mark or a pinch.
• Press it with a thumb. It should give, and come straight back.
• Any joint in the gasket is at the top of the frame, not at the sill.
• The glazing gasket sits evenly against the glass, with no waves.

On a full-size window, close the sash on a strip of paper and pull. It should drag, and it should drag about the same at every point around the sash. That is a rough check of compression, not a test.

In an existing building, worn sash gaskets show up as drafts, whistling in wind, more street noise, or water on the sill. The gasket will look flat, hard or cracked. It is a replaceable part. Mist between the panes is a different fault. That is the edge seal of the glass unit, and the glass is replaced, not the gasket.

The drainage.

No outer seal stops every drop in a storm. A good frame expects water to get in and gives it a way out. Slots in the glazing rebate let water fall into a drainage chamber. Weep slots in the outer face, or under the frame, let it out. Small covers keep wind and insects from coming back the same way.

On the sample, check:

• The slots are there, in the rebate and in the outer face.
• They are cleanly cut, with no swarf left inside.
• The water path goes through its own chamber, not through the chamber that holds the steel.
• The covers are fitted and match the frame color.

On site, a common way to defeat good drainage is to cover the weeps with sealant or bury them behind trim or flashing. Mark them on the installation details.

What is inside.

A cut-away sample shows the chambers and the reinforcement. Look for steel in the sash as well as in the frame, fixed with screws rather than loose in the chamber. Look at how the hinges and locking points are fixed. Screws that bite into steel, or through more than one wall of the profile, hold better than screws into a single wall of plastic.

Then ask for the paper.

A sample shows workmanship. Performance is on the reports.

1. The NAFS class and grade for the exact type, with the report number and the tested size. See what a window's class really tells you.
2. The air and water results on that report. As an example, the Vistaza Vi6 casement is rated AW-PG100, with water tested at 15.04 psf and air at 0.06 cfm/ft², under Intertek report S3614.03-525-44.
3. The NFRC-certified U-factor and SHGC for the glass you are specifying. See certified or simulated U-factor.
4. The sound test report, if the project needs one.
5. For a larger project, a factory mock-up test of your own window before production.

The sample shows the care. The report shows the performance. Ask for both.

To ask for samples and the reports for your project, send your plans. The details that go with them are on the shop drawings page.