One of our trade customers recently asked our team for advice regarding 2,152 sq. ft. of high quality engineered parquet floor he had recently installed into a Hollywood Hills’ home . The floor began to show signs of distress after the first season it was exposed to heating and some of the parquet panels had started bowing at the corners.
The installed floor was multilayer parquet with a 1/4 inch (6.5mm) thick top layer of white oiled oak with the grain direction diagonal to the panel edges. All panels had an 8mm deep 4 side groove and were installed using tongue and groove technique.
During the inspection in August 2014 one of our team members observed that the bowed corners were only on the flat grained top layers and only corners on the diagonal perpendicular (to the grain) were affected. This was because the panel core had split at the groove base.
There had been no failure or breakdown of the heating system in the house so excessive cold, moisture and over drying at extreme levels were unlikely causes. Also, the moisture level of the top layer of the panel at the time of bonding to the panel was estimated by cutting it away from the panel core. The top layer did not have an excessively high moisture level.
Design of the parquet floor did not appear out of ordinary. The only unusual feature was the grain direction of the top layer – Diagonal between two of the corners and perpendicular to the grain.
Several tests were carried out and revealed the following:
- Panels with the grain parallel to the panel edges showed little or no splitting.
- Panels with diagonal grain (to the panel edges) showed increased sensitivity to drying.
The ¼ inch (6.5mm) deep profile and rectangular groove of the panels had increased sensitivity of the floor to dry environmental conditions.
Consequentially the diagonal grain direction had concentrated most of the shrinkage stress at the upper edge of the angle in the groove’s base.
How to fix the problem?
Small holes can be drilled and panels can be glued down using epoxy resin though this might leave some minor imperfections or cause blemishes in the overall appearance of the floor. Another remedy is to remove the whole floor and install brand new panels with grooves that are as shallow as possible.
In future when planning a new parquet floor, especially an unusual design, it is essential to consider all aspects that may highlight vulnerabilities within the panels. Environmental factors such as location, extreme and continual heat or cold and excessive moisture or dryness are all issues that may cause stress to the floor.