Screwing down plywood

[chilluk]

I have searched and although there are loads of threads about tiling etc over timber I couldn't find a specific answer for what I am looking for.

I've ordered the 12mm WBP ply to go over what I think is 18mm chipboard (the greeny coloured stuff - I know it's chipboard just not the definite thickness).

What length and type of screws should I use? Presume I need zinc plated?

I take it I'm screwing just into the chipboard - obviously I don't want to go right through it as I'm not sure where pipes might be. I'm presuming that when I countersink the screw head will sit a couple of mm down in the ply?

Also what gap would you leave between screws - I was thinking 150mm centres?

Cheers

 

[Jasonb]

4.0x30mm plated screws at 200mm centers will do.

Jason

 

[chilluk]

Cheers Jason!!

 

[gcol]

30mm would be best as Jason says, just be careful that you don't screw through too far or else you risk piercing a pipe. 25mm will be fine and remove that risk if you're planning to sink the heads by a couple of mm.

 

[chilluk]

THis question was asked by me because I'm having my kitchen floor redone which was bodged up by the insurance companies appointed contractors.

The area under the washing machine - it's integrated and on a timber plinth - their contractors had screwed down the 1inch plinth with 3 inch screws.

You can guess what I heard and smelt as the first one came out can't you??

BTW I went with the 25mm slightly under the surface (i.e approx 15-17 mm into the chipboard) for safetys sake - shame they didn't