Screw Length for Tile Backer Board

[It's me]

I am using 12mm insulated tile backer board, similar to Wedi, in our bathroom. To give space to run pipes behind the board, I am screwing 18mm by 44mm battening to the wall at 300mm spacing. The board will be glued with Mega polyurethane glue and screwed as well with washers. Will 18mm screws be long enough or do I need longer, into the wall as well?

James.

 

[jeds]

Not 100% certain about tile backer but plasterboard specifications are board thickness plus 10mm of screw into timber, for single borads. Tile backer wouldn't be too different. If I were you I would use 25mm screws.

 

[It's me]

Thank you.

 

[robinbanks]

General rule of thumb for fixing something using screws is to have one third of the screw in the thing being fixed and two thirds in the thing being fixed to. You can have more of the screw in the substrate, but avoid having less

I'd normally use at least 35mm screws for 12mm boards (one third/two thirds rule) but in this case you don't have enough substrate before the screw hits the wall so I'd go to the max possible (30mm) given that you've also got a washer standing things off a few mm. 18mm screws for 12mm boards is the thirds rule the wrong way round and, with the washer as well would mean that you probably wouldn't get much more than just the top of the screw into the batten (and there isn't any appreciable thread depth on a screw tip)

 

[It's me]

Thank you, Robin.

I shall use the proper length screw, but go into the wall as well with a Rawl plug.

 

[robinbanks]

What's the wall made of?

 

[It's me]

Solid brick.

 

[robinbanks]

I think you'll get really bored plugging the wall sufficiently for the backer boards as well as the battens..

 

[It's me]

I think you'll get really bored plugging the wall sufficiently for the backer boards as well as the battens..

I am. Very....

 

[freddiemercurystwin]

I'd go 25mm, the screws will countersink into the boards slightly, in theory you could go to 30mm but there's a danger the scr pluging into the brick seems a bit extreme.

Thank you, Robin.

I shall use the proper length screw

What does the manufacturer recommend as the 'proper length'? I had a quick squidge at the Wedi website (rubbish website I thought btw and I know you're not using that board) I don't really see the point of it at 12.5mm?

 

[It's me]

I'd go 25mm, the screws will countersink into the boards slightly, in theory you could go to 30mm but there's a danger the scr pluging into the brick seems a bit extreme.

What does the manufacturer recommend as the 'proper length'? I had a quick squidge at the Wedi website (rubbish website I thought btw and I know you're not using that board) I don't really see the point of it at 12.5

I used the chat tool on STS's website: they advised to use 30mm screws. I used 70mm screws to secure the stud work to the wall and 60mm screws with hammer-in plugs to secure the board to the stud work and into the wall.