Examine the floorboards to check that there are no signs of woodworm. If there are, injecting a woodworm fluid will be of little use because the trouble will very likely extend to the joists underneath. The affected boards will have to be lifted and the fluid brushed on to the joist to form a toxic ‘envelope’ which will eventually kill emerging beetles. Apply the fluid on both sides of the boards as well.
Woodworm fluid has a deleterious effect on linoleum, so seal it off with a protective sheet of PVC between it and the treated boards.
Where a floor is badly affected, rip the whole lot up and renew. But if there are only a few holes and they cover not just one or two boards but are all over the floor, only about every fifth board needs removing. By using a long-handled sprayer, such as the type employed by gardeners, you can then insert the nozzle underneath and spray all underfloor surfaces from that direction.
Make sure all boards are secure by exerting extra foot pressure wherever there is an underlying joist and at the same time see that no nail heads are projecting. If you detect any movement insert a countersunk screw — taking care not to pierce water pipes or electric cables that may run in a groove cut in the top edge of the joist.
This will mean lifting the faulty floorboard, which is a time-consuming nuisance. So, if you are ever having your house rewired, pay a little extra to have holes bored to take cables half-way down the joist. Then you will not have to worry.
Modern houses are generally fitted with tongued-and-grooved floorboards. With older houses the boards will be square-edged, flat-sawn and butted up to one another. Having nothing to anchor them together they may tend to curve upwards at the edges. Plane these protruding parts level and fill gaps proud with cellulose filler, sanding level when dry.
In the event of wide gaps, glue in fillets of wood proud and plane level. An extremely uneven floor may need a covering of hardboard to even it out.