Adhesive for engineered flooring on mixed concrete/wood

[rar4s]

Hi, guys. I am part way through laying 14mm engineered flooring over a pretty rough and uneven mixed concrete/wood floor. I have consciously NOT done this the "right" way (e.g. https://www.diynot.com/diy/threads/...neven-wooden-subfloor-or-concrete-wood.77960/) and am just sticking it down as best I can. The floor is pretty uneven, but at least sound, and I'm using weights and straps etc. It seems to be OK for now.

Logistically, time-wise and financially it's just not feasible for me to put down ply, screed, etc. So, given this situation, do you guys have any favourite adhesives? I have used most of a tub of SikaBond MS Wood Floor Adhesive already, and I'm wondering if there is something better. It was meant to cover the whole area but I will need several more containers.

It's alright - pretty stiff to spread and sadly a couple of cm of skin on the 2nd day despite my efforts to seal it. I wonder if it came to me partly cured. I can't find a video of this specific product but videos of different adhesives show them being MUCH more fluid than this.

Since I have to more containers anyway, would anyone like to recommend a different adhesive or should I stick to this one? Something suitable for wood and concrete.

 

[rar4s]

Despite hammering the lid down yesterday, and wrapping the whole thing in a bag, I found another 2cm of skin on this product today! Really bad.

 

[crazydaze]

Keep us updated as to how the installation stands up over the next few months/summer, glueing the floor down requires an even spread of adhesive and good adhesion/grip over a uniformed area, the glues have to work under a significant amount or pressure exerted laterally by the wood flooring as it moves seasonally, as well as being able to cope with pressure exerted from above through weight and movement of foot traffic hence why the floor needs to be flat and smooth before installation.

 

[Flooring365]

I’ll be honest, the bigger concern here isn’t the adhesive, it’s the subfloor prep.

Engineered boards are more forgiving than solid, but they still need a reasonably flat base. If the floor is uneven, the adhesive won’t compensate for voids underneath. That’s when you start getting hollow spots, movement, and eventually joint stress.

SikaBond MS is actually a decent adhesive. It’s meant to be fairly thick, it shouldn’t be runny. However, it shouldn’t be skinning over quickly either. If you’re getting a thick cured layer inside the tub after a day, it may not have been sealed well or could have been older stock.

In terms of alternatives, you’re looking for:

• A flexible MS polymer wood flooring adhesive
• Suitable for concrete and timber
• Designed for full stick installation

Brands like Woodstikk, Bona R850, Mapei Ultrabond Eco S955, or similar flexible MS adhesives are all in the same category. None of them will be dramatically more “fluid” though, they’re designed to hold ridges from a notched trowel.

That said, no adhesive will fix significant unevenness. If you’ve got dips and highs, you may end up using a lot more product trying to fill them, which gets expensive fast.

If time and budget won’t allow ply or screed, at the very least I’d try to knock down high spots and fill the worst dips before carrying on. It’ll save you problems later.

If the boards are 14mm and fully bonded, you’ve got a decent chance — but I wouldn’t switch adhesives expecting a miracle difference in consistency.