Measure Moisture in Caravans and Motorhomes

How to measure moisture within caravans and motorhomes is a common question which we receive all year round. After all, the purchase of a caravan is an investment for future holidays and owners want to keep them in their best condition.

Like a home, atmospheric moisture levels will increase in line with exterior moisture levels, too high and condensation occurs. Faulty seals and broken exterior shells will allow moisture to enter.

A caravans and motor homes are manufactured from a range of materials, including wood, foam and fabric which can absorb moisture. Where moisture enters the caravan through the exterior fabric, internal components will become damp, especially wood and fabrics, this is material based moisture. When moisture levels in the air reach to high, the water molecules will appear as condensation on cold surfaces, which in turn is absorbed by materials, this is airborne based moisture.

Some materials will be covered with a coating providing a durable surface and an enhance quality finish (cupboards and doors). If high moisture levels are present, the underlying materials like wood can absorb water molecules, but due to the exterior finish, the owner will be unaware of water damage until the coating peels off.

In fact, the only time an owner may be aware of potential moisture issues, is when the level is too high, causing damage to internal components. If you can see or feel moisture, then it’s too high!

Electronic moisture detectors can ‘detect’ moisture levels at a lower level than with touch and sight. The earlier moisture is detected, the easier it is to rectify. So it is prudent to check moisture levels with an electronic device.


Two Types of Moisture
As mentioned, there are two types of moisture, airborne and material based.

Airborne is the moisture contained within the air. This should not create a problem in normal conditions, but can lead to condensation, rot and corrosion especially if combined with low temperatures.

Material based moisture has been caused by water travelling from one material to another. Faulty seals or damage to the external structure is a common cause, along with damaged pipes under sinks or around the shower.


Measure the air humidity
Moisture in air is measured using Relative Humidity (RH). Below 75% RH is classed as dry, whilst anything over 75% RH will allow bacterial and fungal growth.

Electronic hygrometers like the Protimeter Hygromaster will provide an accurate reading of the humidity in air. Utilised by surveyors, both instruments record the measurements using %RH with temperature readings.

A simple method to test the air humidity within the caravan is to use a chemical reaction. Fugenex Damp Protect is a simple card incorporating a strip of paper which reacts to airborne moisture.


Moisture in the Caravan material and structure
There are two types of moisture meters than can detect and record the levels of damp within the caravan. The first instrument utilises two metal pins which provides a direct reading and the second instrument utilises a non-invasive radio mode.

Two-Pin Devices
A moisture meter featuring two metal pins at the top of the instrument will record the level of moisture by measuring the resistance between the pins. It is a direct reading and provides the best accuracy. Several models are available, Protimeter Mini and Protimeter Digital Mini.

However, most of the interior and exterior of the caravan contains surfaces that do not directly hold moisture, but provide a protective finish. The pins would therefore be required to push through the finished surface into the layer below.

This would leave a mark and is only advised to undertake from inside the unit and on surfaces that will not be directly seen by any future buyers.

Non Invasive Radio Mode
This method utilises moisture detection which sends a signal below the surface of the material to a nominal depth of 19mm. The instruments will not damage the surface so is ideal for all interior and exterior applications. The Protimeter Aquant2 features non-invasive moisture detection.

A major material found within a caravan is aluminium and steel which provides strength. All metals provide an excellent conductive material, so don’t be surprised if you receive a high signal around the metal structure.



Recommended Models
We would always recommend the Protimeter range due to their high standard of manufacture, outstanding performance and onsite durability. Plus they feature a two year warranty!

For direct readings, we would recommend the Protimeter Mini as it is the simplest instrument.

For a combination of two-pins and non-invasive we would recommend the Protimeter Surveymaster.

For air humidity readings, we would recommend the Protimeter Hygromaster which allows the user to interchange the sensor.

If you are employed by a caravan specialist, you may be best to purchase the Protimeter MMS2 which incorporates all functions into a single unit.


Further reading
Digital Moisture Meters
Dealing with damp in a caravan
Camping and Caravanning Club - Winter Caravan Checks