Author : Allan Green

Diagnosing The Cause Of And Avoiding Cupping In Solid Wood Flooring

Cupping or dishing in solid wooden means the boards raise slightly at their edges making the wooden flooring uneven across it�s width The cause of cupping is an imbalance of moisture through the timber This can be a result of a spillage on the floor, or due to the hardwood flooring gaining moisture from the sub-floor material

Taking a moisture reading of the underside of the timber and comparing this with a reading taken from the upper side will confirm this

Wood always expands when it takes on moisture It therefore follows that moisture on the underside of the wood will make the underside expand laterally However, the upper side of the wood which has not absorbed any moisture, so this stays at near its original size The immense strength of the expansion of the underside of the wood is what causes the edges of the wood curl

On nearly every incidence of cupping that I have inspected, the flooring was fitted onto a solid floor with adhesive- meaning that the sub-floor was too high a moisture content A quick and simple way of identifying the the problem is by taking a moisture reading of the sub-floor Usually this is just a matter of drilling a small hole into the sub-floor between the gaps in the board, and inserting the probe from a moisture meter The reading of the sub-floor should be around 9- 11% moisture content If it is greater , then this could be the source of the moisture

As part of an inspection process, I also look for evidence of leaks from appliances eg dishwashers, and leaks from heating pipes, and poor or zero ventilation in the room

I also take a reading of the humidity at the time of the inspection, although this is merely a snapshot of one moment in time and does not necessarily give an indication of the humidity at an earlier time that may have caused the cupping

However, another scenario could be that the sub-floor was within the above parameters, but the wood could have been dried too aggressively before being installed This could mean that the sub-floor was at the correct moisture content, but the wood was too dry to be installed In a case like this, the humidity needs to be regulated quickly which can usually stabilize the problem

Dealing With The Cupping

Step one is to check the integrity of the fixing of the floor In extreme cases of buckling, the flooring can (in the case of adhesive installations), de-bond from the sub-floor If this is the case, the floormay be beyond repair if in excess of 40% of the floor area is affected in this way

Stabilize the humidity in the room as quickly as possible If the relative humidity of the room is below 40% then this is too dry A healthy humidity level is between 45% and 60% R H This can be achieved by the use of a humidifier

It may then ne necessary to have the floor sanded and re-finished, which should then eliminate any further problems and restore the appearance of the flooring

It is imperative though, that the stabilization is undertaken gradually over a period, and that thorough moisture readings are taken on both sides of the timber before sanding If the floor is sanded before the wood has stabilized, the edges of the board will be lower than the centre of the boards

How To Avoid The Cupping

If you are about to lay a floor using a stick down method, take thorough moisture checks of the sub-floor and the humidity of the room that is to be fitted

The sub-floor should be ideally below 12% moisture content and the humidity of the room should be between 40% and 60%

If there is any doubt regarding the integrity of sub-floor, it may be necessary to applyan epoxy resin damp proof membrane to the sub-floor

If you are installing using the secret nailing technique, then an impervious layer should be laid over the sub-floor or battens -e g foil, polythene membrane or builders paper

Make sure that an adequate acclimatization period is allowed for This is normally achieved by storing the flooring in the room for at least two weeks prior to installation The room should be heated and ventilated in the same conditions that the floor will be used i e temperature and relative humidity

Further Points To Consider

1 Tangential cut hardwoods always have greater movement than radial cut or quarter sawn hardwoods

2 Narrow width solid hardwoods are always more stable and less prone to movement than wider width flooring

3 Engineered flooring will always cope better with fluctuations in moisture, and climate

4 Wood floors will always move depending on the season- e g in winter months slight opening of joints and cracks are to be expected

Allan is technical manager of Birbek Floors Ltd, a UK distributor of European oak wood flooring and American walnut flooring http://www.birbek.com

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Filed under: Healthy Home

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