A window fits into an opening that is bigger than it is. That deliberate gap gives room to set the frame plumb, level and square in a wall that is none of those things, and it has to be closed in a way that keeps water and dust out while still allowing the frame and the wall to move independently. Aluminium expands and contracts noticeably between a February morning and an August afternoon; blockwork barely moves at all. Anything rigid spanning between them fails.

Sealant is not glue, and it needs a backer

A sealant joint works by stretching, and it can only stretch if it is the right shape and stuck to two faces rather than three. A backer rod pushed into the gap does two jobs: it stops the sealant bonding to the back of the joint, so the bead can flex, and it controls the depth so the joint is wider than it is deep. Fill a deep gap with sealant and no backer and you get a thick rigid plug bonded on three sides — which splits the first summer, usually along the top edge where movement is greatest. The split is hairline and nobody sees it until the dust arrives.

Which is why dust turns up around a new window

Fine dust finds any opening in a perimeter seal, and it finds it long before water does — Dubai gives you rain a handful of times a year and dust every day. A new window that lets dust onto the sill within months is almost never a faulty window. It is a perimeter joint that has cracked, was never filled properly behind the visible bead, or was skinned over a gap far too wide for a single application of sealant to bridge.

The outside face has to shed water away

External sills need a fall away from the building and a drip on the underside of the projection, so water runs off and drops clear instead of tracking back along the soffit toward the frame. A flat sill with no fall ponds, and when Dubai rain arrives it arrives all at once — a ponded sill drives water back under the frame at exactly the moment it matters. Where an existing sill has no fall, that gets corrected during installation rather than sealed over and hoped about.

And the fixings still have to reach something

Frame fixings must land in blockwork, not in plaster or tile adhesive. In Dubai the reveal is often tiled or marble-clad, which means drilling through a hard finish without cracking it and still reaching solid material behind. It is slower work than it looks, and it is the reason a window fitted in a tiled reveal takes longer than the same window in a plastered one.

An old aluminium frame can be levered out or cut out, and the difference shows up in the plasterer's bill rather than the window fitter's. Levering pulls the fixings through the reveal and takes plaster and tile edges with them. Cutting the frame into sections and lifting them out separately leaves the reveal largely intact, takes longer, and is what we would rather do on any opening with a tiled or marble finish around it.

Two things to agree before anyone starts. Who is making good the reveal, and to what standard — patching plaster is quick, matching an existing paint finish across a whole wall is not, and those are different conversations. And what happens to the sill, because a marble or large-format tile sill running into the opening is the item most likely to crack during removal and the most expensive to replace.

Plaster and paint work around a new opening sits with plaster repair, and where the sill or reveal tiling needs replacing rather than patching, that is tiling work. Coordinating all three onto the same visit is cheaper than three separate trips.