Bad Ideas - Floors
Tinted varnish on wood
As it chips, light patches are seen on the darker floor, which looks particularly bad. Better to either let wood mellow of its own accord, or stain it if a darker colour is wanted.
Vinyl on a damp concrete floor
Traps damp. By stopping evaporation, damp level increases. Results may include mould growth and rising damp in adjoining walls.
Carpet in bathroom
Toilet aerosol is produced when flushing, and contaminates the carpet. Its not easy to clean out. Bathroom grade carpets are available, but avoiding carpet is preferred.
Patching damaged old floorboards with new boards
The appearance of the new boards is very different, and the combination of the 2 really looks bad. Fitting used boards avoids the problem.
Sanding boarded floors
Although fashionable in recent years, its really not necessary for domestic floors, and sometimes exposes woodworm eaten cores, which aren't too unusual in old floors. This ruins the appearance of the floor and creates a saleability problem. An hour of repeated washing is typically very effective, paint spots can often be scraped off, and spot sanding with a handheld power tool can be used to remove the infamous black stuff without removing any noticeable bulk.
Very difficult to keep clean.
Chipboard floor in bathroom
Small or narrow pieces of chipboard in a chip floor
They just don't have the necessary strength. Chipboard is not one of the stronger flooring materials, and flooring pieces need to be a fair size to be strong enough.
1/4" plywood floor
It shouldn't need saying, but I've seen it done. The plywood would bend as people walked over it.
Create your own interior fountain. A shocking way to redecorate.
Replacing floors with concrete in timber frame buildings
It reduces the ability of the wood at floor level to evaporate damp away, and sometimes leads to rot. And rotten sole plates are not cheap to put right.
Vinyl tiles on uneven floors
Vinyl tiles are prone to come unstuck on uneven surfaces, or to wear through prematurely.