Southgate Timber
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The Definitive Guide to HIDDEN FIXINGS for Hardwood Decking

1. Hidden fixings make a stunning deck, but…
There’s no doubt about it, the clean look of natural hardwood decking with no visible fixings is what garden lovers aspire to, but before you jump in, please read through this guide to make an informed choice.

2. Strength is a factor
For ultimate fixing strength, you can’t beat securing hardwood decking boards with face fixing screws. So hidden fixings are a compromise on this score. If you are going down the route of fixing through the face, we sell market leading Spax Stainless steel decking screws in the recommended size 5.0 x 60mm (for 19 > 21mm thick decking boards). These surface screws have an attractive T25 head which is small and not too obtrusive. We recommend this be coupled with the Spax step drill for perfect pilot and counter sink size to fit neatly around the screw head with no crushing of the timber.

3. Different timbers have different characteristics effecting the suitability of hidden fixing
Southgate Timber recommends IPE hardwood decking for hidden fixings due to the minimum movement in this specie. You can expect some initial shrinkage with IPE, so we recommend installation with our regular ‘extreme’ hidden fix kits, which give an initial board gap of 2mm. In addition to IPE, we also sell Iroko hardwood decking. Unlike IPE, this is a Kiln Dried timber so requires the ‘Extreme4’, 4mm spacing kit which allows for contraction, but through clever design, the crush zone on the leg of the clip also allows for expansion which will happen with a dried timber. We DO NOT recommend hidden fixing with Yellow Balau hardwood decking due to the level of expansion and contraction in this timber. Yellow Balau is perfectly suited to pre-drill and screw through the face.

4. Not all hidden fixings are made equal
At Southgate Timber, we have been the main UK importer and distributor of Deckwise Extreme hidden fixings for a number of years, and we believe this is the ‘best system on the market’. To complement the fixings, we also import IPE hardwood decking in regular fit or hidden fit which are pre-grooved on the sides to accept Deckwise hidden fixings. The Deckwise clip has a tempered stainless steel insert with Polypropylene plastic resin outer giving unrivaled durability. The kits include 4 x 50mm stainless steel screws with T15 drive, a drive bit, pilot hole drill bit, IPE plugs for outer edges and an instruction guide. There are a number of lesser quality products on the market, some are plastic only, some give large gaps, and some allow no expansion/contraction. We have seen first-hand the horror stories and images of unusable decking and wasted material.

 

5. Board size is a consideration
We import hidden fix IPE decking in 19 x 90mm and 21 x 145mm. For the best possible scenario, a narrower 90mm wide board will always give less expansion/contraction issues and also less likely to buckle and twist. So this is another thing to factor in when you choose your decking board. The wider board 145mm, whilst still being suitable, is more likely to suffer movement and can result in occasional lifted edges in particular on butt joints. This is not a major issue, but just another consideration.

6. All good decks start with a solid frame
The vast majority of hardwood decking installed in the UK is over a Tanalised Softwood Frame. The problem being in many cases the decking will way outlast the frame. For this reason, we recommend the following: upscale the size of the frame cross section i.e., increase from 50x100 to 50x150 or even 50x200mm where possible, this will add strength and longevity; ensure adequate drainage under the frame as this will dramatically affect the lifespan of the frame; finally, airflow is crucial to keep the frame dry and rot free for years so factor this into your design.

7. Where NOT to use hidden fixings

  • With timber with too much expansion/contraction
  • On frames that have poor ventilation and in areas that are likely to be damp, opt for stronger face fixings
  • On frames with bad drainage, although this should be resolved regardless
  • Wide boards, maximum 145mm decking boards recommend for hidden fix and for stronger hold 90mm are a good option.

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