I. Provisional fixing:
After the bending Bendywood®-handrails should only be fixed provisionally to the banister, so that they can shrink along their length.
Handrails that are bent at 12% moisture content will shrink in length by up to 0,5 cm per running metre until the equilibrium moisture content is reached or until the wood moisture content has adjusted to the indoor climate.
II. Final assembly:
Start with a fix mounting point halfway its length and mount the handrail from there towards the ends in such a way that it can still shrink a bit along its length, especially in the case of long handrails. It is best to use handrail supports which you can provide with slotted holes.
Please consider that a 6 m long handrail, for instance, will further shrink by up to 1 cm (on its total length) within the first year after final assembly.
The shrinkage can be greater if the ambience is heated or air-conditioned a lot without regulating the equilibrium moisture content.
Only in the following cases the problem of shrinkage doesn’t occur:
- In case the handrail is bolted down to a continuous metal rail of the banister (from below) at intervals of about 20 cm. Only this type of mounting prevents shrinkage in length: however, only use strong, deep penetrating screws, especially for handrails with a diameter of ø42 mm or more;
- In case the mitre joint is under tension: this occurs when bent parts (which always open up a little) exert pressure on the mitre joint.
III. CONNECTIONS OF HANDRAIL PARTS:
1. MITRE JOINTS
Mitre joints at the ends should be avoided: the risk that they will "open up" in the long term is high.
Check whether a solution is possible as shown here:
In case mitre joints cannot be avoided, there are 2 options:
a. Mitre joints with synthetic resin glue and a threaded rod:
- Drill sufficiently big and profound holes into the handrail ends that need to be jointed;
- Fill these drill holes at both ends with a synthetic resin glue and insert a threaded rod, which diameter should be a bit smaller than the one of the drill hole;
- Press both handrail ends together with clamps and keep them in position until the glue has dried.
The use of a threaded rod as well as the use of synthetic resin glue are both necessary to prevent the joints from opening up.
b. "Open" butt joints:
Such joints are secure and in certain cases also decorative, e.g. on platform transitions and holders.
Is is important to drill holes at the ends and insert guide pins so that the parts stay in position: this also allows
for further length shrinkage!
2. JOINTS ON STRAIGHT PARTS
Butt joints must be strengthened with strong and long dowels, as Bendywood® is not as stable in length as normal wood. Handrails under tension due to decrease in length of the Bendywood® must be joined, where possible, with diagonal cuts. Always glue/joint by means of a diagonal cut.
The length of the diagonal cut should equal 2 times the cross section of the handrail.
Only long gluings prevent the bonding from collapsing under tension.
IV. Painting after Assembly:
It is recommended to use:
- synthetic paints or oils, such as "Danish Oil" (Rustins) or, LOBA LOBASOL® 2K ImpactOil Hartöl 750 ml - Dose, transparent kaufen (hygi.de) with hardener
- Hydro-oils with hardeners for wood with waxy effect, such as the “Renner wood-oil YS---M009 with 5% hardener YC M402” tonet AG Webshop - Wasserbasierendes Holz- und Möbelöl YS---M009
Technical data: WT IP 0418 (tonet.ch)
All this and similar products can be applied on side, without having to dismantle the handrails.