How do I get rid of damp spots on a wooden floor?

Noel Larkin answers a readers question published in the Irish Times July 7th 2016


My late mother’s house is about 100 years old and she spent significant sums of money on dry lining and insulating it over the past number of years. However after replacing the wooden floor in the sittingroom I noticed staining on the wood around the door saddle. I removed the door saddle and subsequently the saddle board and the surrounding wood dried out. I also noticed a few other places at different locations in the room where small staining is visible too. We had the plumber check for leaks and the plumbing is okay. We then had the carpenter check it out and he had no answers. My sister lives in the house and I try and help her with house maintenance. What would you suggest?

A Older properties need constant care and attention and clearly your late mother was committed to constantly improving her home. This improvement has continued with your recent replacement of the timber floor to the sitting room.

It is however not unusual in older properties that the introduction of a new material can result in changes in how the house performs. The absence of any plumbing leak suggests that the cause of staining lies elsewhere.

In older properties, the floors were generally of suspended timber construction. This meant that a void existed below the floors. I suspect that this may be the case in your house. Modern prefinished or engineered flooring can be less breathable than natural timber. This type of flooring can be prone to the occurrence of condensation on its upper surface if conditions exist to allow this to happen.

Generally, condensation will occur in lesser-used rooms as these are generally cooler than other areas of the house. Cold points on the floor surface or where there are gaps in insulation are prone to this form of dampness. The area around the door at the threshold is one such area where insulation may have been omitted or where draughts are keeping this section of the floor at a slightly lower temperature than elsewhere. I have seen floors where condensation has formed on the concealed nail fixings leaving small rust stains at localised spots on the floor. This type of staining is not unusual in older properties particularly when the open-area below the floor is not insulated and humidity has built up in this void.

I believe that the only way to solve this issue, without taking up the new flooring, is to try to reduce condensation. Condensation can be reduced by increasing heating levels and improving ventilation. I have seen people block off under-floor vents as these can lead to internal draughts. I would recommend that you check that these remain clear and open so that humidity below the floor is controlled. Underfloor ventilation can reduce the surface temperature on the floor so there will be a balancing act to be performed between improving heating and ventilation.

You should advise your sister to review the situation once heating and internal ventilation is improved.

Checking and re-establishing underfloor ventilation should also help. If however the problem remains it would be worthwhile having the floor inspected by a chartered building surveyor as there may be additional aspects that need to be addressed to eliminate the problem.

Noel Larkin, Chartered Building Surveyor and member of the Society of Chartered Surveyors Ireland,