Mastfuyi FY8870 · ball probe on top
Damp
Touch the metal ball to a wall or floor and read how wet it is, 5 to 40 mm deep. No pins, no holes, no phone.
Works with
How it works
- Hold it in the air and press ZERO to calibrate.
- Touch the ball to the surface.
- Move along the wall — the number rises towards the leak.
Specs (from the manufacturer)
| Method | pinless, spherical probe |
| Depth | 5–40 mm |
| Range · accuracy | 0.1–99.9 % · ±2.5 % |
| Materials | plaster, cement, wood, paper |
| Extras | colour screen, torch, alarm, auto-calibration |
| Size · weight | 220 × 40 × 31 mm · 119 g |
| Power | 2 × AAA (not included) |
In the box
- Moisture meter
- Cloth bag
- User manual
- Retail box
Questions about Damp
Does it need a phone?
No. It has its own color screen and runs on 2 × AAA batteries (not included).
Will it leave holes?
No. It's pinless: you touch the ball to the surface and it reads moisture 5 to 40 mm (0.2 to 1.6 in) deep.
What can it measure?
Plaster, cement, wood and paper, from 0.1 to 99.9 %, accurate to ±2.5 %.
Why does the reading jump?
Metal behind the surface — nails, pipes, mesh — throws the reading off. Check a few spots around it.
Can I return it?
Yes, within 30 days of delivery if it's unused and in its original packaging. If it doesn't work with a phone this page says it works with, we refund you in full, including return shipping.
Guides that use Damp
Spark or Spark Pro? How to choose a phone thermal camera
Both plug into a USB-C phone and use the same app. The difference is how many temperature points they measure, and that decides how far back you can stand and still see the pipe.
October 22, 2026
Can a thermal camera find termites? What it shows, and what it can't
A thermal camera can't see termites, but it can show the moisture and warmth a colony leaves in a wall. How to scan for termite risk between inspections, and what to do when you find something.
October 22, 2026
How to find a hidden water leak behind a wall (without opening it up)
A stain on the plaster tells you there's water in the wall, not where it's coming from. Six steps to narrow it down to one spot before anyone cuts the wall open.
October 22, 2026Buying guides
- Home check before you buy or rentWhat to check in a house or apartment before you sign: water and damp, drafts and insulation, wiring, the roof, pests — and a free printable checklist.