One of the tools that conservators can use when evaluating the condition of wooden objects or structures is a moisture meter. Not all meters are created equally and they only provide what could be considered a semi-quantitative indication of the percent of moisture. Please talk with a conservator before using a meter as it may not provide the right answer for the problem. Read on to find out more…
What are moisture meters?
Moisture meters are small handheld electronic units that can be used to detect the percentage of moisture in materials. Those designed for wood use two metal electrode pins that are inserted into the surface of the wood. The electrical resistance between them is influenced by the moisture present in the wood (more moisture, less resistance) and the result is a numerical value expressed as a percentage.
Do they cause damage to the object?
There are wood moisture meters that are considered non-destructive, but they are not as accurate as those that you insert. Because you do have to insert the pins into the wood, this can cause a small amount of damage. Generally the pins are similar in size to a sewing machine needle and the damage is minimal. On the majority of objects or sites that we work with, the result is not noticeable, but it can be filled for aesthetic purposes. The conservator will discuss where best to sample if this is a concern and options for alternatives. In general, this tool is considered to be a non-destructive technique for measurement.
How exactly will this help me understand the condition of the wood?
Conservators use a variety of tools and techniques to assess the condition of materials. Part of our ethos is to minimise interaction and damage to an object and the research question must be clear before sampling or analysis takes place. Likely, the conservator will start with a visual inspection of the material which will give clues as to why it is experiencing deterioration. The next step would be minimally invasive techniques such as pin testing and moisture level testing.
Understanding the amount of moisture in a wooden object can provide insight into:
- Whether moisture levels are high enough to encourage biodeterioration (soft rot, brown rot, fungi, mould);
- If certain areas of the object have higher levels of moisture than others. For example, perhaps one end of a waka is experiencing higher decay than another. It may be that there is a leak in the building or increased moisture levels nearby.
- If a conservator is treating a waterlogged wooden object and it is undergoing a slow drying process, a moisture meter can provide insight into how quickly the wood is drying or at what stage in the treatment it is.
What type of moisture meter should I get?
The meters from home improvement places are helpful, but are limited. They all operate on the same premise, but the professional grade can be:
- more sturdy (not such flimsy plastic so they last longer)
- more accurate
- more range in their measurements
Some of the professional grade meters can be calibrated for the wood species based on the density. Above all, look for an instrument that measures over 40% and has a small error range.
Can I get any locally in New Zealand?
The suggestions below can all be ordered in Aotearoa New Zealand.
Good mid-range units, very accurate, nice feature to select wood species:
Upper low range instrument: