Bonding vs Screwing Windows in Campervan Conversions
One of the first decisions when fitting aftermarket windows to a panel van: should you bond them with adhesive or screw them with a clamping frame?
Both methods work, but the choice affects waterproofing, strength, and future removability.
The Two Methods
Bonded Windows (Glue-In)
The window is adhered directly to the van body panel using a structural polyurethane adhesive (typically Sikaflex 512 or 252). No screws or mechanical fixings.
How it works:
- Cut the hole 5mm larger than the window on all sides
- Apply a 10mm bead of adhesive around the window frame
- Press the window into place
- Hold with tape for 24 hours while the adhesive cures
Screwed Windows (Clamp-In)
The window has a flange that sits outside the van panel, and an internal clamping frame that screws into the window from inside, sandwiching the van panel.
How it works:
- Cut the hole to match the window template exactly
- Apply a thin bead of sealant as a gasket
- Insert the window from outside
- Fit the internal clamping frame and tighten screws
Comparison Table
| Factor | Bonded | Screwed |
|---|---|---|
| Strength | Excellent (structural) | Good (mechanical) |
| Waterproofing | Excellent (continuous seal) | Good (gasket + sealant) |
| Installation time | 24hr cure + 1hr work | 2hr work, immediate seal |
| Tools needed | Caulking gun, tape | Screwdriver, socket set |
| Removability | Difficult (cut through adhesive) | Easy (unscrew and remove) |
| Panel strength required | Good | Less critical (frame spreads load) |
| Visual profile | Flush (low profile) | Raised flange (visible frame) |
| Cost | Lower (no hardware) | Higher (frame + screws) |
Bonded Window Pros
-
Better waterproofing. The continuous adhesive bead creates a single seal line with no penetration points. Screwed windows have screw holes that are potential leak paths.
-
Cleaner appearance. Bonded windows sit flush with the van body. Screwed windows have a visible external flange.
-
Lower cost. No clamping frame hardware needed. Saving: £20-40 per window.
-
Better insulation. The adhesive layer provides some thermal break between the window frame and the van body.
Bonded Window Cons
-
Cannot remove easily. If the window cracks or the seal fails, you have to cut through cured Sikaflex with a cheese wire or oscillating tool. This can damage the paint around the window.
-
Requires 24-hour cure. The van is not weathertight until the adhesive cures. If it rains during cure, water can enter.
-
Needs good panel adhesion. The van panel must be clean, degreased, and free of rust. Adhesion fails on dirty or painted surfaces.
-
No structural clamping. In a crash, a bonded window relies entirely on the adhesive bond. A screwed window has mechanical retention.
Screwed Window Pros
-
Removable. You can take the window out for repainting, replacement, or storage. Bonded windows are permanent.
-
Instant weatherproof. Once the screws are tightened, the seal is compressed and the van is watertight.
-
Forgiving of imperfect holes. The clamping frame hides rough cut edges. Bonded windows show every imperfection.
-
Can be fitted to thinner panels. The clamping frame distributes the clamping force, so you do not need as much panel rigidity.
Screwed Window Cons
-
More leak paths. Each screw is a potential water entry point if the sealant around it fails.
-
Visible external frame. Some people prefer the cleaner look of bonded windows.
-
More expensive. The clamping frame adds manufacturing cost.
-
Can work loose. Over time, vibrations can loosen the screws. Check and retighten annually.
Which Is More Secure?
For security against theft: bonded windows are harder to remove from outside. A thief would need to cut through structural adhesive. A screwed window can be removed with a screwdriver from inside if the thief gains access, but from outside both are about equally secure (breaking the acrylic is easier than removing the frame).
UK Building Regulations
In the UK, motorhome windows must comply with:
- UN Regulation 43 (safety glazing): The glass or acrylic must be marked with an E-mark or BS 857 to show it meets safety standards.
- Construction and Use Regulations: Windows must not obscure the driver's view. Side windows behind the B-pillar have no specific restrictions.
- Type approval: Kit-built conversions do not need individual window type approval, but professionally built motorhomes do.
Both bonded and screwed windows from reputable manufacturers (Carver, Movera, Dometic) meet these requirements.
Sealant Recommendations
For bonded windows:
- Sikaflex 512 (premium, 5-year exterior durability)
- Sikaflex 252 (stronger, slightly stiffer)
- Teroson MS 939 (PU hybrid, paintable)
For screwed windows:
- Butyl tape (seals between frame and panel)
- Sikaflex 512 (around screw holes)
- Neoprene gasket (if included with window)
Recommendations
Choose bonded windows if:
- You want the cleanest look (flush fit)
- Waterproofing is your top priority
- You do not plan to change windows
- You have a well-prepared, clean van panel
Choose screwed windows if:
- You want the ability to remove windows later
- Your van panel has existing holes or cosmetic issues
- You are less confident in your installation skills
- You need the van weathertight immediately (rain expected)
Our Verdict
For most DIY van conversions, bonded windows are the better choice. The waterproofing is superior, the appearance is cleaner, and the lower cost is useful. The inability to remove them is rarely an issue — properly installed caravan windows last 15+ years.
Recommendation: Bond with Sikaflex 512, tape for 24 hours, and you will have a watertight installation that outlasts the van.
