Welcome to Koi Forum. Is this your first visit? Register
Results 1 to 6 of 6

Thread: Screw length

  1. #1
    Senior Member Rank = Mature Champion Ant62's Avatar
    Join Date
    Aug 2016
    Location
    North Manchester M66 area
    Posts
    2,433
    Thanks / Likes
    1356

    Screw length

    Ive got some 4x4 posts which are pressure treated.
    The have come from the dismantling of the pond etc and im thinking of using them as the weight bearers to support the decking..
    So what i would like to know is what size screw is required to attach them to a concrete base..



  2. #2
    Extreme Koi Member Rank = Supreme Champion Frimley Koi keeper's Avatar
    Join Date
    Jun 2012
    Posts
    13,544
    Thanks / Likes
    19237
    If you are screwing down through the full thickness of the wood and into the concrete base I would say you'd need something like 120 to 130mm minimum as 100mm gets you through the post and gives you 20mm to 30mm in the concrete. Depending on how solid you need the posts to be fixed you could go even longer and go for something in the region of 140mm to 150mm so you have more of a fixing in the base. I think the minimum thickness you can get screws of that length are 6mm which is the equivalent to a 12 gauge screw in old money. Screwfix do plenty of size options but just be careful with what the screws are made of as there could potentially be a rust or corrosion issue with certain types of screws even ones you think are plated.

  3. Thanks freddyboy Thanked / Liked this Post
  4. #3
    Senior Member Rank = Mature Champion Ant62's Avatar
    Join Date
    Aug 2016
    Location
    North Manchester M66 area
    Posts
    2,433
    Thanks / Likes
    1356
    Quote Originally Posted by Frimley Koi keeper View Post
    If you are screwing down through the full thickness of the wood and into the concrete base I would say you'd need something like 120 to 130mm minimum as 100mm gets you through the post and gives you 20mm to 30mm in the concrete. Depending on how solid you need the posts to be fixed you could go even longer and go for something in the region of 140mm to 150mm so you have more of a fixing in the base. I think the minimum thickness you can get screws of that length are 6mm which is the equivalent to a 12 gauge screw in old money. Screwfix do plenty of size options but just be careful with what the screws are made of as there could potentially be a rust or corrosion issue with certain types of screws even ones you think are plated.
    I have some 140mm screws but i cant find the plugs that came with them...

    I may have a gander on screw fix and see what they have..

  5. #4
    Extreme Koi Member Rank = Supreme Champion Frimley Koi keeper's Avatar
    Join Date
    Jun 2012
    Posts
    13,544
    Thanks / Likes
    19237
    Ordinary brown rawlings will do for 6mm wide screws

  6. #5
    Senior Member Rank = Gosai Brandlin's Avatar
    Join Date
    May 2018
    Location
    North Wales
    Posts
    272
    Thanks / Likes
    268
    Why do you want to fix it down?

    The mass of the decking boards on top of it, it wont be going anywhere.

    However, the point of bearers under a deck is to get them up off anywhere that would be permanently wet so they don't rot.

    You would eaither place each end on a concrete pad, or at least a couple of bricks raised above ground level and span between them.

    Those fence posts you have are 4x4, typical deck beams are 6x2 or 8x2 depending on the span. 4x4 Is going to bounce and bow noticably unless you are only spanning a couple of feet.

    My suggestion would be to place bricks on your concrete at 2 foot centres. They need to be levelled - just a normal mortar mix would do for this. Then lay the posts over them so they are supported at 5 points along the length (assuming 8 foot posts). Then build your deck on that.

    If you remain concerned about movement laterally then the thing to do is go and look at strapping in the builders metalwork section of your local DIY place. Sole plate anchors or even just galvanised strap would allow you to screw the strap into the concrete with say 60mm screws and plugs and then the same 60mm screws into the beams to hold them in place.


    The standard though slightly OTT rule of thumb for screwing things togeher is the same distance of screw in each thing you are connecting. For this size of fixing you want to be in the realms of number 12 or 14 screws. I'd go for 150 minimums and counterbore the screws halfway into the beam so you get 100mm into the concrete. This gives its own problems as you leave the screw counterbore open to collect water.

    A much better fastening if you must do ot is to use sleeve anchors which are pretty much designed for attaching load bearing things to concrete.

  7. #6
    Banned Rank = Mature Champion Trace's Avatar
    Join Date
    Nov 2015
    Posts
    2,214
    Thanks / Likes
    1514
    +1 for sleeve anchors or large hammer fixings are cheap and fast too ...

 

 

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
All times are GMT +1. The time now is 04:35 PM. Online Koi Mag Forum
Powered by vBulletin® Version 4.2.3
Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.

vBulletin Improved By vBFoster® (Lite Version), © UltimateScheme, Ltd.