ᐅ Hard or semi-flexible adhesive for solid wood flooring, any experiences?

Hi,

I’m not entirely sure if this is the right forum or subtopic for my question, as it concerns wood (but also screed). I would really appreciate some opinions.

I’m currently facing the huge range of adhesives for solid wood planks (installed on an anhydrite screed with underfloor heating).

At first, I was (for whatever reason) leaning towards Stauf, as they also have a nice chart showing which adhesive suits which application. However, their FAQ suggests different adhesives. There are one-component, two-component, rigid, semi-flexible adhesives, and so on.

Does anyone have a good recommendation? I know the manufacturer names and product types, but deciding is hard... Maybe there’s a flooring installer here who’d be willing to share some insider knowledge.

I understand there is no perfect all-in-one solution, but honestly, I’d prefer an adhesive where I pay a bit more to exchange money for peace of mind. In other words: I’d rather spend a few extra dollars upfront than have trouble later.

Thanks!

Hello questioner.
The question you posted can only be answered by non-experts with responses like "we have that too..." which is not enough and not meaningful for your specific situation.
You mentioned a calcium sulfate screed as a heating screed. Apart from the fact that almost any parquet adhesive is suitable for this type of screed, the serious question is: which type of wood do you want to glue?
Background: for a heated screed, a dispersion adhesive or any single-component (1K) adhesive would be suitable, but when it comes to parquet woods, we differentiate between “nervous” wood species and “stable” wood species.
This means: “nervous woods” such as beech develop significant stresses on heated screeds, partly due to thermal expansion from the underfloor heating, and partly due to moisture absorption and release caused by room climate.
If a “firm grip” is needed to lock the parquet wood in place, two-component (2K) adhesives are the right choice.
If you are installing engineered wood flooring, a silane-based adhesive or a flexible single-component (1K) adhesive will be sufficient.
However, decisive is the preparation of the substrate, which includes sanding the screed surface, priming, applying a leveling compound about 2mm (0.08 inches) thick (this not only serves to ensure evenness but also to absorb the water contained in every adhesive without damage), and applying the correct amount of adhesive.
This is an extensive topic with several pitfalls you have brought up!
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Good luck: KlaRa

KlaRa schrieb:

can only be answered by non-experts in the way of "we also have ..."

Yep.
So far, I have always used adhesives from Bona. 848T for engineered parquet and Quantum for solid wood planks – but I’m not a professional installer, just DIY for my own floors. Wood types from oak to maple to wenge.
The mentioned adhesives are single-component adhesives.

Thanks @KlaRa.

About my wood: oak, solid wood plank, 15mm (0.6 inches) thick, 140mm (5.5 inches) wide, varying lengths up to 1600mm (63 inches).

Regarding substrate preparation: Stauf states for some of their adhesives that the substrate should not be pretreated, except for being dust-free. So no primer or filling, but directly applied on CA screed (if level).

Due to professional experience and personal practice, I recommend the following: prime the screed with PALLMANN P104, then glue down the parquet or floorboards using PALLMANN P5.

erdhaeschen schrieb:

Thanks @KlaRa.

Regarding substrate preparation: Stauf says for some of their adhesives that the substrate should not be pretreated, except for being dust-free. So neither priming nor filling, but with CA screed (if level) apply directly.

I can only advise caution here!
At minimum, a primer should be used to improve the bond between the screed surface and the adhesive layer.
If (in my experience) adhesion problems and therefore detachment of the wooden planks occur later, any expert will first examine the failure zone.
If this lies beneath the adhesive layer, that is, if we experts call it a cohesion failure within the upper screed edge zone, the adhesive manufacturer is then no longer liable.
“You don’t bond wood flooring onto a dust layer.”
And we are not talking about a millimeter-thick weak edge zone, but powder-like dust that every primer firmly binds.
Beware of manufacturer claims that try to gloss over this. Then the argument will be, “technical guidelines must be followed, our product is not the cause.”
And part of the technical guidelines is at least a dispersion-based primer, and from my point of view also a filler.
Even properly installed self-leveling screeds cannot exclude surface irregularities that exceed the limits given in DIN 18202 Table 3 Row 3 (4mm (0.16 inches) over 1 meter (3.3 feet) measuring point spacing).
Place a sufficiently long straightedge loosely on the screed surface and observe the size of any gaps beneath it.
The adhesive must compensate for tension caused by irregularities as small as 3mm (0.12 inches).
If the gap is larger, full surface contact between the back of the parquet element and the subfloor is no longer possible.
I will not detail the types of damage this can cause here.
Conclusion:
Don’t try to save money in the wrong place, and don’t rely on marketing claims from auxiliary product manufacturers!!
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Regards, KlaRa