I have whinged before about access and repair issues where a layer of
sound reducing foam has been laid on top of original flooring.

In this particular case my daughter has a London flat with vinyl strip
wood effect glued to chipboard over a 25mm layer of foam. Directly in
front of the kitchen sink is a join in the chipboard which does not
appear to be tongue and grooved. Needless to say, movement has caused
the vinyl to crack badly.

We have spare vinyl but need to stop further movement to avoid a
recurrence.

The foam is obviously compressible and 8 stone applied close to the
flooring edge gives several mm of differential movement. There is only
enough spare flooring to tackle 300mm or so. Prising up the chipboard
for a proper job not practical within her budget.

Thoughts so far after taking off the damaged vinyl:-

prise up one board and slide a stiff steel sheet under. Problems
with getting it back under the second sheet, some holes might help.
Difficult to spread the load very far and the polystyrene will already
be compacted at the fault.

cut a strip off the edge of one board and trim the foam away.
Insert an inverted *T* shaped wood support to carry the load to the
original floor. This could be assembled from two pieces on site so
should be easy to do.

or? routing grooves or rebates is probably outside my skills.

regards
--
Tim Lamb