Ordinarily you can fill the gaps with wood filler putty or with pieces of rope and then finish with stain to match the floor.
How to fix gaps in old wood floors.
Engineered flooring is made with layers of plywood placed in different directions.
Filling large gaps in old wood floors.
You can fix floor gaps in a number of different ways.
Wood fillers are also not meant for use with large gaps.
If gaps remain or the floor is old it is possible to make the gaps less noticeable and prevent dirt and debris from building up in them by filling them with rope.
The problem is magnified when the boards were not tightly laid in the first place.
Over time however the putty hardens chips and flakes.
Why you should avoid putty fillers.
With older tongue and groove hardwood or even wide plank floors gaps inevitably develop between the boards mostly because the wood shrinks over time as it dries out and loses moisture content.
Water logged wood will first swell then shrink as it dries out.
Different gap repair methods.
This leaves your floor looking even worse and requiring you to dig out the old putty and replace it.
Wood expands and contracts with seasonal differences in humidity and the older a floor gets the greater the chance that these movements will.
Like many products both kinds of wood floors have pros and cons.
Another exacerbating condition is water damage.
How to fix old hardwood floors with gaps and cupping.
Putty fillers were once a mainstay of hardwood floor repair.
This allows the layers to shift and move without gaps developing between boards.
If you cannot fix the problem by installing a humidifier you may need to take more drastic action when it comes to filling wide gaps.