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Carpets, Lino & Flooring

Secret screw length for 18mm engineered wood + 6mm ply + 20mm existing boards

Anonymous user 15/03/2024 - 2.56 PM

I've bought some Lost Tite 3.5 x 45mm screws to secret screw some 18mm engineered wood flooring. The subfloor is 20mm original floorboards (in good condition), which has been overboarded with 6mm ply (screwed at 150mm centres). Before I start driving 1,400 of these things, just wanted to double check that 45mm will be sufficient, or whether I should have gone for 49mm (which are currently out of stock). EDIT: Just to clarify - secret nailing/screwing involves nailing/screwing through the GROOVE of t&g flooring (hence "secret") and is recommended/supported by most manufacturers. Tongue Tite screws are designed specifically for this purpose and do not split the wood. Here is some information if you would like to learn about secret nailing/screwing: https://www.britishhardwoods.co.uk/shop/media/flooring-guide/hardwood-floor-fitting-guide-new.pdf

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4 Answers

Anonymous user

Hi Steven. To answer your question in short yes 45mm tongue tight screws will be plenty sufficient. Anything over a 15mm grab to existing subfloor is sufficient. 18mm flooring halfed as you will be going threw the tongue (9mm) 6mm ply (15mm) 20mm floor board (35mm) accounting for the fact you will be screwing at a 45degree angle means 45mm screws are the perfect length. (try to keep the screws at a 45degree angle. if you dont you run the risk of hitting pipes underneath and also making the next row of boards very difficult to join). Just a bit of advice I would think about buying or renting a porta nailer. (google this) this will get the job done a lot quicker and easier and will give it just as strong fix as using tongue tights. When you get to the edges where the porta nailer will no long fit then use the tongue tights for fixing the flooring down. Hope this helps. Regards Supreme Sanding

Answered29 April 2020

Anonymous user

Hi Steven, most engineered wood floors are normally 14mm and solid wood are usually 18mm. Check the manufacturer's leaflet as it will tell you what is needed for the correct installation of their product. Manufacturers will void the warranty if their instructions are not complied with, most say it needs to be installed by a professional flooring installer but if you are confident to do it yourself then go for it. Make sure you leave a big enough expansion gap and let it acclimatise to the room for at least 72 hours.

Answered1 May 2020

Joe Master

Rating: 4.4 out of 5

Dewsbury

Hi Steven, My first question is why are you screwing down engineered flooring? Engineered flooring can be laid in 2 ways, glued down fully stuck or loose laid gluing the tongue and groove joints. What does the instructions on fitting say? Also where do you plan to drive these screws in?, do it on the tongue you may slip part of the tongue, on the face and they will be visible. This is how you lay Engineered timber flooring: 1, Fully stuck to the subfloor with the correct adhesive. 2, On suitable underlay 2mm thick will do and glue the joints (floating floor). All the best Joe

Answered28 April 2020

cmw floors and wetrooms

Rating: 4.9 out of 5

Frinton On Sea

Hi Steven, as the above have said, the method you have been recommended is not a viable one.You WILL indeed split the tongues or cause a bulge, stopping smooth fitting. I would go for the portanail option, or float it, (PVA`ing the t & g`s). Glue down is an option, but can be messy & more a pro option, in my opinion.I m selling my spare nailer, `just saying`, lol. Hope this helps, Chris.

Answered29 April 2020