Levelling/flattening floorboards for engineered wood

I’ve started installing 14mm click fit engineered wood in my first floor (which has floorboards)

All I did for preparation was screwing down the loose floorboards and replacing the ones in bad shape with 18 mm plywood; I also used a sander to bring down a couple peaks in the floorboards edges (mainly where two joists meet)


I used a 3mm underlay (this one from wickes /Arbiton-Easy-Fit-Laminate+Solid-Wood-Flooring-Underlay---10-2m2-Pack/p/191372) and started installing the planks parallel to the existing floorboards


After completing the first room I realised the floor squeaks when stepped over, and in some cases it even moves by 3 mm (measured using a 60cm spirit level and puttin my weight next to it)


The subfloor is clearly not levelled and maybe I haven’t used the correct underlay


I am thinking of taking the planks up (I should only break the 6 that I’ve had to glue, but save the rest) and do whatever is necessary to stop the floor from moving and make noise


I am thinking of using a planer wherever there is a step between two adjacent floorboards and then nail down some 3mm hardboard (2.5£/m2) and maybe use a different (thicker? Fibreboard?) underlay

Now I wrote levelling, but I think what I need is just a flat surface, not one necessarily parallel to the horizon, so I’m not sure if I need to use a self levelling compound
What do you suggest?

 

6mm ply

 

and?

 

What a surprise, your floor isn’t flat. You could of put down 6mm ply and then chucked 10mm-20mm of flexible levelling compound down to get your floor flat and possibly level (this is not cheap) or as you say go around the floor with a level and as much packing materials as you can levelling out the low spots and planing down the high spots. Can be very time consuming but should work eventually....maybe. Some floors are so far out you can’t fix them with this method


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You mean packing the 6mm ply or add material between joists and floorboards?

 

You over board your floorboards with it.


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Yes, but then it will just follow the slope of the room, and if I pack it to keep it level I might get soft unsupported spots with bouncy floor, right?

 

Also, why isn’t anyone suggesting to just lay a damp proof membrane or similar over floorboards and then use self levelling compound over it? That would make sure the slc gets in every dip in the floor (but not through the gaps)

 

No ply 6mm completely covered with 6 inch centre so no gaps then flood with levelling compound. Check the subfloor is dry before you do this


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Don't forget to check the moisture within the ply to make sure it's same as the floorboards

 

What do you mean by 6 inch centre?

Wouldn’t the ply sound hollow and deform under weight where I have dips in the floor?

 

Just said most of this lol

 

Nail the ply or screw, every 6 inches with 20 or 22mm nails or screws (this should ensure no hollow spots),then screed over the ply with a flexible screed (follow every instruction on the bag),you're aiming for at least a 3mm thickness over the highest points, also make sure there are no small gaps or holes round skirting etc. otherwise the screed will just run away

 

Yes, I missed that, whole board covered... it makes sense now

What I don’t understand is why you can’t use a thinner ply like 3mm

 

Not so easy... there are walls resting over the floorboards and some joists don’t meet straight causing the boards not to be flat

 

Another option that may be worth looking at is jacking up the joists where they sit on the wall, chances are,the joists may have rotted slightly where they rest on the outside walls, causing them to drop, which acts like a seesaw over the middle supports, jacking up the ends and re packing underneath with slate or plastic packers should cause the other end to drop back down

 

Stability