Windows & Door fitting

Door threshold gap

David 21/10/2026 - 8.28 AM

I’m looking for some professional advice about the bottom of an external aluminium door frame/threshold. There is quite a large gap between the underside of the metal threshold and the concrete below, particularly at one end (roughly 20–25 mm at its largest). There are also small rectangular openings where the metal threshold meets the concrete, which I believe may be intentional drainage/weep outlets from the door frame. I was planning to tidy and seal the larger gap using backing rod and an exterior-grade sealant, but I’m concerned about accidentally blocking drainage from the frame. Could someone advise whether the gap shown in the photos should normally be sealed, and which parts need to remain open for drainage? If it should be sealed, would backing rod and exterior frame/construction sealant be an appropriate repair? I’d particularly appreciate an opinion from someone experienced with aluminium/uPVC door installation and thresholds.

Double Glazing Plus

Rating: 5 out of 5

5/53 reviews

Nottingham

Hi David. We are not able to see photos in these q&a sections so it’s hard for us to help you diagnose the issue. I’d suggest asking whoever installed the door to help you. If you are talking about the underside of the cil / low Ali threshold there shouldn’t be a gap under there unless they have had to pack the door up to make it fit better. In this case we’d usually sand and cement underneath. If it’s a low Ali threshold you will have a drip bar to take water away so cementing sewing underneath wouldn’t effect drainage but as I say without seeing photos it’s hard to give you a definitive answer. Thanks Double Glazing Plus

Answered21 October 2026

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