Exterior v Interior plywood for floors

[roblatus]

Going to use some 18mm plywood to stiffen up a floor in my house. In the past i have used bog standard 18mm interior ply but i wondered if exterior stuff was stiffer?

If not what is the best (stiffest) type of 18mm ply i should be going for?


Thanks

 

[roblatus]

Anyone????

 

[JohnD]

18mm WBP is fine and will withstand water in kitchen and bathroom.

Spruce flooring ply may have a very rough and knotholed surface so unless you are going to put laminate over it I wouldn't use that.

 

[roblatus]

I really want the stiffest stuff i can get. I have already strengthened the joists and i still have some bounce so the stiffer the better for the ply wood.

Excuse my ignorance but i am guessing WBP is exterior grade??

Is this stiffer than interior stuff????


Thanks again for all the help.

 

[JohnD]

what is this floor made of that is bouncing?

 

[roblatus]

what is this floor made of that is bouncing?

It is just a normal joist with floorboard arrangement.

I had someone bolt some lengths of 8x2 along the length of the existing joists. I had this done 18 months ago and had a new ceiling done at the same time.

It seemed to make the bounce problem better but i have recently noticed that it seems to be a bit worse again.

I am intending to lift some of the floor and check that the lengths of wood are still firmly bolted to the old joists.

I was then going to cover the existing floor with 18mm ply to hopefully add stiffness.

 

[JohnD]

you mean it is made of floorboards like planks?

IMO instead of covering them with ply, you could take them up. ply is stiffer and spreads your weight better.

You can use 25mm ply if you want which is even stiffer and stronger than 18m. It is heavy and awkward so you may want to have it cut into 8x2 sheets rather than buy 8x4

You can also buy 8x2 Flooring which is T&G all round. but the surface is not very good so look at a sample before you buy.

Put noggins to support any joins which are not over joists even if they are T&G.

 

[roblatus]

you mean it is made of floorboards like planks?

IMO instead of covering them with ply, you could take them up. ply is stiffer and spreads your weight better.

You can use 25mm ply if you want which is even stiffer and stronger than 18m. It is heavy and awkward so you may want to have it cut into 8x2 sheets rather than buy 8x4

You can also buy 8x2 Flooring which is T&G all round. but the surface is not very good so look at a sample before you buy.

Put noggins to support any joins which are not over joists even if they are T&G.

It does bother me that the extra weight of the strengthening wood that has been put in has added to the problem over the last 18 months. Having said that it seemed better when it had first been done.

I can't take the full floor up as there is a interior wall that is also built on top of the floorboards.


I have used 18mm on the landing and another one of the bedrooms t ogood effect. I think 25mm may well be too heavy.

If i get 18mm ply and cut it to 8x2 will it still cover s large enough area to stiffen the floor? I was trying t oget as big a sheet of ply down in one go as is possible?

 

[JohnD]

I don't know why it is bouncing

maybe the joists are nor supported properly at the walls. You haven't made any alterations that include knocking down walls or enlarging windows, have you?

 

[roblatus]

I don't know why it is bouncing

maybe the joists are nor supported properly at the walls. You haven't made any alterations that include knocking down walls or enlarging windows, have you?

No alterations to the house from when i bought it. As far as i know nothing major has been done such as you mention. Also from what i remember the joists are not moving at either end.

I think i need to make sure that the extra wood is still firmly bolted to the joists and if not then make it so. Also then cover with ply to stiffen up over the area of the floor.

 

[topgazza]

Having read the number of threads on this board...when I buy my next house...next year...I will be using plywood and not chipboard for the flooring...or decent floorboards I guess. Anything but chipboard. Had 25 mm interior (I think) plywood laid when I had my loft conversion done and it just "feel" so much firmer than the 1st floor which is chipboard.

Isn't exterior plywood just treated interior ?

 

[JohnD]

exterior ply has a waterproof glue.

It is called WBP (water and boil proof) because when it was invented, it was shown at an exhibition, immersed in a container of boiling water, which did not affect it.

The plywood used until then would have fallen apart quickly in such conditions, so buyers were very impressed.

If you ever have any old plywood furniture and leave it outside in the rain, you will find it separates out quite quickly, and has no strength.

p.s. I agree about ply feeling much firmer than chip. I have some half-landings where people tend to jump of the bottom step, the old chip cracked and gave way. 18mm ply feels very solid and I think is quieter too. Chipboard is a terrible material. It is a real pain changing floors once they are covered in carpets and furniture though.

 

[gcol]

And screw (not nail) the ply down.

 

[Deluks]

This is a loft floor isn't it? (to the OP) either that or no noggins or strutting was fitted.