Are bowing doors acceptable?

Bowing in composite door slabs is a known problem, so how is the industry responding, asks Steve Mines, sales director at Sliders UK, and when is bowing tolerance too much?

When it was introduced in 2015, Part Q triggered a mini-arms race in composite door manufacture. New cut-through tests introduced to PAS24 exposed a fundamental vulnerability in those composite door slabs manufactured solely from high density polyurethane foam cores.

That’s prompted change and redesign, which has come at a cost, and one that is being paid for by installers.

The net effect of these vulnerabilities has driven composite door manufacturers to introduce more timber to their design. The perceived weaknesses in foam-only slabs were exploited by manufacturers of timber slabs to promote their own sales. We saw it within our own business.

The problem is that timber expands and contracts. The irony is that in increasing the use of timber in composites, the industry has made something of a rod for its own back.

This is costing installers, collectively, £tens-of-thousands a year in call backs. Composites have been sold against timber doors on the basis that they won’t warp, bow and crack.

In using timber as a greater percentage of the slab itself, you are, by definition, increasing the risk of introducing the problems which moved the industry away from timber in the first place – that means call backs and cost to the installer.

This was instrumental in driving Sliders UK’s decision to move away from its previous supplier, which it had used since 2013, to a new offer from Capstone earlier this year.

This uses ‘intelligent timber inserts’, manufactured from 15mm LVL, which are deployed to strengthen the slab at points historically vulnerable to attack in other leaf systems.

Encased inside a foam core and durable GRP skin, these provide additional core strength, which means that the Ultimate Door has been independently tested to and passed PAS24:2016 – including cut-through testing.

Security is further enhanced through Capstone’s patented three-stage glazing cassette system, which supports easy replacement of glass but maximises security.

This not only allowed us to beef up the security performance of our composite offer but it allowed us to offer our customers a new and industry leading guarantee against through life performance.

This is because the technically advanced combination of timber inserts and thermally insulating foam used in Ultimate Composite Doors delivers on security while balancing it with the core structural stability of the slab – giving it a maximum bowing tolerance of just 3mm.

In minimising movement in the door slab we maximise the performance of the locking mechanism and the product. We have picked up new customers who were told that 6mm bowing tolerance was acceptable.

As an installer, or for that matter the end-user, you can’t legislate for dimensional change in product on that scale.

For us, if it’s above 3mm it’s a manufacturing fault and it goes back at our and Capstone’s cost as a manufacturing fault – that’s guaranteed.

Sliders UK has combined this solid foundation with a range of carefully selected styles. Standard colours are black, red, blue, green, gold oak and rosewood, with doors available in lead times of five days or under. A custom range of 36 premium finishes is also available.

This is combined with a choice of standard or colour-matched, fully reinforced Duraflex and Eurocell 70mm PVCU outer frames and slim, low line aluminium thresholds with twin seals. Both Duraflex and Eurocell framed doors have been tested to PAS24:2016.

Door furniture and hardware is Trojan, while standard hinges and locks are manufactured by Ingenious, with heritage and auto-locking options from Winkhaus. Door cylinders are six-pin anti-drill and anti-pick as standard with the Ukas-accredited 3-Star BSI TS007 tested Ingenious cylinder, also available as an upgrade option.

Glass options include a choice of double or triple-glazed options, achieving U-values as low as 1.0W/m2K including laminated and toughened options.

However, without slab dimensional stability, none of the other features matter because the door won’t perform.

Yet installers are being told that a 6mm bowing tolerance is acceptable. As an installer you have to ask at what point to the cost of call backs become too much?