Prep for wooden laminate on screed

[saveasteading]

I'm getting conflicting info re preparing the screed for timber flooring.

In other words, people like spending my money.

 

Where there is tiling, we have no issues. The screed has not been ground back to remove ripples or laitence. Dips and ridges disappear using the tiler's skill and some double buttering.

 In the other rooms we will have oak faced  multi ply planks, t and g, 12mm thick.

I can't see what is different in laying this instead of tiles. 

But someone says the screed needs to be ground to remove ripples and laitance.

Someone else says it needs latex at any dips.

 

The floor planks are very high quality and won't be bending or slapping in use unless the gap is significant.

I'm about to survey all the floors using a 3m straightedge, and will consider the 3mm rule as a pass.  Any thoughts on that?

Does anyone know how thick the adhesive is as standard, or what might be considered acceptable at any dips?

 

Then the laitance thing.  These floors only receive downwards loading and won't be flying up in a draught.

But is the screed surface so soft that it comes off if the floor moves?

 

I was thinking that a coat of primer would suffice. And if it's a blue colour then everyone will be happy to see it.

 

Any very big dips or ridges will be dealt with on their demerits... I will soon know the significance.

 

[-rick-]

22 minutes ago, saveasteading said:

The screed has not been ground back to remove ripples or laitence.

 

Forgive me for not answering your question and asking another but I thought you always wanted to remove laitence because it was a weaker layer so if you bond on top you risk separation later. If your tiler isn't bothered by it then I'm probably wrong, but would appreciate to know what I've got wrong.

[saveasteading]

30 minutes ago, -rick- said:

always wanted to remove laitence because it was a weaker layer

That's the theory. But most warehouse floors are left as they are. And structures likewise.

So I think it's overstated, unless the laitance ("fat" to concretors) is very severely overworked and is a paste of very wet gypsum.

Even then I am not convinced it's an issue in a domestic situation.

[saveasteading]

Done that, using a 3m drywall stud which is nicely straight and is stiff enough.

2mm under the straightedge  is generally the worst so that is not significant.

2 areas of about .5m2 are a little worse  so I'm going to try the old fashioned 'rub it with a brick' first.

I'm still keen to find how thick the adhesive is generally applied.

Also any recommendations on brands for primer. As often, the wickes price sets a target.. less 10% and including vat.

 

And of course I am open to being told that I'm wrong on any of the above.

[scottishjohn]

On 20/08/2026 at 13:20, saveasteading said:

That's the theory. But most warehouse floors are left as they are. And structures likewise.

So I think it's overstated, unless the laitance ("fat" to concretors) is very severely overworked and is a paste of very wet gypsum.

Even then I am not convinced it's an issue in a domestic situation.

the right thing is to hire floor grinder  and make it totally flat 

[JohnMo]

We did a couple of mm over 3m or so,as target and then the installer applied loads of glue, so nothing has moved anyway.  All feels flat under foot.

[saveasteading]

2 hours ago, scottishjohn said:

the right thing is to hire floor grinder

That's my point really.  I've spent 40 years asking 'why? and am still doing it.
It is not cutting corners, it is understanding whether it is a real need or a costly habit.

At a cost of £1,800 it is right for the contractor but not necessarily for me. That's a lot out of my pension.

 

I have found a flooring company's website with useful advice.  They mention doing everything you can think of, but do so reasonably and with sensible numbers about humidity, levels etc.

Among them is the 3mm in 3m standard, so if they say its ok, and so do all the industry standards, then I'm happy too. (3m is a very long straight-edge I've suddenly remembered, esp when carrying it through rooms without hitting doors or new kitchens.)

They say that the adhesive spreading tool has 3 to 4mm teeth so the glue goes down as 3mm and squishes to 1mm except where it isn't squished and remains as 3mm.

and that if one lifts a laid plank for interest, the glue should be apparent on 90% of the surface.

 

I am working to 2mm tolerance under the straight-edge, and rubbing off any ridges or mounds that are causing 3mm.  I have had a go with an engineering brick and that is successful though unglamorous.  I've only to take 1mm off.

For a surface that is supposedly friable and a big risk  ('pay us more to make it safe') , it is proving to be very robust.

 

I will use a primer. its very difficult to compare brands due to pack size, dilution, coverage. Ardex is the big name  but silly money... or is it?.

I'm sure Unibond would be great, but it isn't coloured so won't be so easy to do or to impress the floorers.

 

Bostik Cempolay looks an option.  Branded, £8/litre and then dilute x 2 or 3 for porous surfaces according to different bits of their blurb.  Blue.

Then somewhere else it says use 2 coats.... we will see how the first coat looks and feels.

 So over 200m2 that will be about £80 to £160 plus my own time.  Plus single use of brush and roller.