How to check deflection on plywood across joists

[jesteh]

Time and time again, I see advice offered to check for deflection before starting to tile on floorboards/plywood across joists.

What I don't understand is - how do you check for deflection and how much deflection is acceptable? Is there a gadget or a certain way of doing it? Do you jump up and down looking for a bit of trampoline bounce. Do you use a spirit level and see if weight causes it to bend? Any other ideas?

 

[Colour Republic]

it's a bit like cooking a steak... you kinda just know by feel. Others sometimes place a glass of water on the floor and see how it reacts when stomping round the room

 

[jesteh]

I have tried the water test but even with 25mm ply, there are ripples in water when I bounce next to it. (I have too much time on my hands).

 

[charlie1]

Look at the floor as you apply pressure, there should be next to no visual movment.

 

[steve187]

use a long straight edge/level and stand in the centre, next to the level, and see if there is a gap between the level and the floor, get a friend/wife to help as well, or place some weight in the centre.
As colour republic posted you kind of get a feel for it.

 

[craigdon]

use a long straight edge/level and stand in the centre, next to the level, and see if there is a gap between the level and the floor, get a friend/wife to help as well, or place some weight in the centre.
As colour republic posted you kind of get a feel for it.

Most floors I come across, until I've preped them, have a gap under a straight edge lol!

 

[Ct Ceramic]

[DLMURL]http://www.proconweb.com/pdfs/publications/technical_articles/deflection_-_are_current_standards_realistic_2001.pdf[/DLMURL]

With a litle knowledge you soon understand that nearly all floors you tile on that are wooden have too much deflection.