Very often we have seen that old worn out paintings are pasted on thicker backing board or sheet. This initially looks good as the worn out or crushed paper or fabric looks much better as it acquires the smoothness and strength of the new backing; but, we tend to ignore that this is not for ever. Whenever the adhesive chemistry weakens with ageing and time, the adhered sheets would slowly start getting separated and then, the thinner or the weaker original sheet would get sacrificed or damaged.

So, one has to decide between the easier, fast and apparently more appealing treatment , and the one that requires more skill, is more long lasting and ethically correct (may be not that smooth looking initially!).
The backing, if required, should be thinner than the original painting. This way, whenever the original painting and the backing would get detached, the backing would be sacrificed, not the original!!