How to repair water damaged chipboard

A few weeks ago we had some unusually windy rain and a small amount of water has got in between the bricks and the glass insert in the stairwell.

The wall in question is half inch thick chipboard. It is NOT structural and it is really only there to finish the stairwell and stop people falling off the stair into the garage.

It is one very large sheet and the damage is only to a section about 50cm long and 15cm deep so we are hoping a repair can be done. What would be the best way to fix this. A product called wood hardener was suggested to me. Will this work on chipboard. I really only want a solid base so as to bog up and plaster over the section and repaint. The damage is almost 2m off the ground so strength is not a real concern as it can not be touched by busy hands from the ground.

If wood hardener is used do we have to remove all the flakey softer chipboard or will the hardener set this softer bit as well.

Any help greatly appreciated


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