Choose bales that barely dent when you push a fist against the side, that measure below 20% moisture content, that smell clean rather than musty, that are made of wheat, oat, rye or rice straw rather than hay, and that are all one size. Test a sample from every stack and from the middle of the bale as well as the surface, because wet bales hide moisture that the outside does not show.
Part of Straw Bale Construction
Bale selection is the field testing of straw bales for tightness, dryness, material and uniformity before they go into a wall.
A Bad Bale Costs You The Whole Wall
A wet bale built into a wall rots from the inside, and the wall can look sound for a long time before the damage shows. So the acceptance tests are strict and are done on every delivery. The parent article gives the criteria:
| Test | Accept | Reject |
|---|---|---|
| Fist push against the side | Barely dents | Sags, compresses unevenly |
| Moisture content | Below 20% | 20% or more |
| Smell | Clean | Musty |
| Material | Wheat, oat, rye or rice straw | Hay (grass) |
| Size | Consistent | Mixed sizes |
Hay is nutritious and attracts rodents, and rots; straw is nearly inert. The same logic applies to all natural-fibre building, but after the wall is built the moisture questions move to Bale Moisture Monitoring.
What You Need
- A moisture meter (the parent article suggests salvage from woodworking shops), or a reliable alternative; see the caution below on what a wood meter reads.
- Your own fist, nose and hands.
- A tape measure for bale dimensions: a standard two-string bale is about 90 x 45 x 35 cm and a three-string bale about 100 x 60 x 40 cm.
- A tarp, to keep accepted bales dry.
Method: Test Every Stack
Step 1: Sort by material. Reject hay; keep wheat, oat, rye and rice straw.
Step 2: Fist test. Push your fist against the side of the bale. It should barely dent. Loose bales sag, compress unevenly and perform poorly.
Step 3: Moisture reading. Insert the meter deep into the bale at several places, including the middle, and take several readings per stack. Moisture must be below 20%.
Step 4: Smell test. A musty smell means too wet. Smell the interior by opening a small gap, not just the surface.
Step 5: Look. Reject bales with dark patches, mould, white or grey fungal growth, or signs of rodent nesting.
Step 6: Measure. Pick bales of consistent size.
Step 7: Store the accepted bales under cover and off the ground.
A Wood Meter Gives A Comparison, Not An Absolute Reading
A meter built for timber is calibrated for wood, and straw reads differently, so a reading from a wood meter is a comparison tool rather than an absolute value: take readings in a bale you know is dry, such as one from the middle of a dry stack, and compare. A bale that reads clearly higher than your dry reference, or that is cool, damp or heavy for its size, deserves rejection even if the absolute number looks acceptable. When in doubt, reject; there is no repair for rot inside a finished wall.
Common Mistakes
- Testing only the surface. The middle can be wet while the outside is dry.
- Accepting bales with mixed sizes and then needing many custom bales.
- Using hay. It rots and draws rodents.
- Storing accepted bales on the ground or uncovered. They take moisture back.
Safety
Mould dust
Mouldy or musty straw releases spores that harm breathing. Wear a dust mask when opening or moving suspect bales, and do not stack them indoors.
What’s Next
- Learn next: Pinning and Strapping Methods
- Combine with: Bale Moisture Monitoring