Renovate mosaic parquet, as the floor has sunk

Hello everyone,

in the property we purchased, the floor in an extension has sagged, or rather, a row of chipboards has bent downwards by about 1-1.5 cm under the weight of two 300 kg heavy night storage heaters. The night storage heaters have already been removed; we have switched to a classic gas condensing boiler. Such a load is not expected again in the same place.

I was able to inspect the construction from the basement and rule out cracks in the chipboards or even in the supporting beams.

My plan now is to remove the existing parquet in the affected areas, fill the sink with good flexible tile adhesive, pour out remaining unevenness with leveling compound, and then rebuild the parquet. The new parquet is apparently necessary due to burns, probably caused by the night storage heaters.

I am always grateful for tips; if you notice an error in my plan, please let me know :)

Now to the problems:
The mosaic parquet has dimensions of 156 x 156 x 8 mm distributed over 7 slats. So far, I have only seen 160 x 160 x 8 mm parquet online and in specialty stores.

The previous owners have some of the required parquet as a reserve, unfortunately only for about 50% of the area, and the material came into contact with dirt and moisture untreated.

Due to my inattention, I have already bought parquet with the dimensions 160 x 160 x 8 mm for the damaged area.

I now have the following questions:

- Does it make sense to still use the old worn parquet, or are discolorations still likely after sanding, filling, and oiling?

- Is it conceivable to integrate parquet with the wrong dimensions to some extent so that in everyday life you hardly notice a difference? Later, a sideboard and a highboard will be placed in that area. However, the furniture will not completely hide the flaw.

- Where else could one get parquet in the sought dimensions? (I have already checked eBay :))

I would first check whether the old installed parquet is still suitable for sanding at all. In our old apartment, everything was only re-sealed because sanding was no longer possible as it would have become too thin otherwise. But after a year, more and more panels detached from the floor and creaked when walking. Fortunately, it was only a rental apartment and is no longer my problem now. What I mean is, maybe tear out the floor completely and plan for the long term.

Lay the new mosaic exactly in place, then you'll see if the offset is extremely visible, which I don't believe. But check, as pointed out by , whether the old mosaic still has enough material to be sanded.
I honestly don't quite understand this statement

........ or rather a row of chipboards has bent downwards by about 1-1.5 cm under the weight of two 300 kg heavy night storage heaters.

just like this one

I was able to check the construction from the basement and rule out breaks in the chipboards or even in the supporting beams.

I don't know your profession, but I doubt whether one can assess static structural integrity just by looking at beams and chipboards. Mind you, I myself cannot judge this (especially not based on pictures), so I cannot comment on the proposed floor structure. Maybe a specialist will still be found here who can assess the floor structure.