|Tradies and consumers regularly need good advice, whether it’s before installation or problem solving ‘peaking’ in a timber floor later on. Although a well planned, well installed and well finished timber floor will be the highlight of any building or renovation project, the opposite is also true, and poor planning, poor installation or poor finishing will ensure that a floor is a ‘feature’ for all the wrong reasons.|
What is ‘peaking’?
Peaking and cupping in boards can have a very similar appearance. Cupping can be present in the manufactured product or it can be the result of moisture beneath the floor. It occurs when an uneven distribution in moisture causes one face of the board to move (swell or shrink) more than the other. This difference in movement causes the board to take on a cupped shape. It relates to differences in moisture content through the board and drying stresses at the time of machining, or it can be the result of moisture being absorbed into the bottom of the boards.
Peaking, like cupping, may have the appearance of a floor that has become wet from beneath, but the moisture content in the lower surface of the board is not significantly higher.
Peaking in floor boards has two distinct characteristics: the floor has expanded a little after installation, and the profile is such that when the floor expands all the pressure occurs in the top shoulders of the boards.
Although the forces involved are sufficient to create the appearance of cupping, there is generally no gapping at the board edges or a reduction in the width of any intermediate expansion joints. Moisture meters will not indicate abnormally high readings that could be associated with moisture uptake.
What causes it?
Boards are often manufactured with undercut, which is where the top cover width is wider than the bottom cover width. If the undercut is too great and the floor expands then peaking can occur due to the expansion pressure being resisted by the top shoulder of the board only. Adhesives can also limit floor expansion and contribute to this problem.
As a part of their project planning, your customers will have to consider several factors. Firstly, some board profiles are more prone to peaking than others, and those boards with greater undercut will obviously be more prone to peaking (bottom cover width narrower than the top cover width by more than 0.4 mm).
Secondly, consider whether the floor is expected to undergo moderate to high expansion after installation. The key factor here is how close the timber’s average moisture content is to the expected average in-service moisture content.
If the floor is likely to expand because of locality (high humidity location), siting (eg a bushy gully) or flooring supplied at low moisture content (particularly with some imported materials), then there will be a greater risk of peaking.
Peaking can occur with product manufactured from anywhere around the world as well as related flooring products like bamboo.
How can peaking be avoided?|
Many problems in timber flooring can usually be avoided through sound planning before even laying the floor. It is important that your customers understand this and that they investigate where the floor is to be laid and its moisture content and profile in terms of undercut.
For many floors the risk will be minimal. For internal conditions you would expect the floor to shrink after installation because the gaps that develop in these floors close a little during moist times, although not to the extent that they place the floor under significant expansion pressure.
This includes floors laid in drier climates where the internal environment during the moist time of the year is modified by heating or cooling systems that dry the air. Upstairs floors also tend to remain a little drier than lower storey floors.
Where the risk of peaking is greater it is important to consider acclimatisation and to make an intermediate expansion allowance so as to account for the conditions that will induce expansion.
As for fixing the problem once it has set in, some tradies find that re-sanding and re-finishing solves the problem by producing a floor that remains flatter. However, the jury is still out as whether this is a remedy in all situations. Like all timber flooring issues, good planning and preparation limit the potential for expensive problems later on.
David Hayward is the Technical Manager from the Australian Timber Flooring Association. He is an engineer who has worked in the timber industry for more than 25 years. He has developed quality control programs specifically aimed at timber flooring and has served on the Australian Standards Committee that deals with the manufacture of solid timber flooring. He has also undertaken significant research in timber and timber flooring. He wrote the ‘Timber Flooring Manual’ and oversaw the ‘Timber Flooring Problems – Causes and Remedial Measures’ guidelines. Both titles are published by the AFTA.
The article is an edited extract from one a series of technical reports. Visit www.atfa.com.au or call 1300 361 693 for more information.