On 19/02/2020 08:35, PeterC wrote:
On Tue, 18 Feb 2020 23:40:49 -0800 (PST), harry wrote:

On Tuesday, 18 February 2020 19:36:57 UTC, John wrote:
My house was built in 1988. The cavity walls are filled with slabs of
rockwool stuff - possibly not as well as I would have liked.

Occassionally I get salesmen trying to sell me the sort of injected cavity
wall insulation. They usually claim there is a grant toward it.

The only way you can tell if there are gaps is by use of an infrared camera.
[snip]

There is/was a grant for insulation at one time. Dunno what the current position is.

Is there such a thing as an infrared filter for a digital camera? If so, the
LCD should show the image same as a dedicated camera does.

Wrong waveband.

Near infrared is just off the end of the visible spectrum at 750-1000nm.
You can get IR pass filters but they mainly make trees look white.

Thermal infrared characteristic of objects at ambient temperatures on
Earth is in the 10um band with an order of magnitude longer wavelength.
You need special detectors and typically germanium lenses to make images
in thermal band IR. You can buy add-ons for mobile phones to do a crude
thermal IR camera for not that much (or hire real gear for a price):

https://www.amazon.co.uk/Thermal-Res...dp/B0728C7KND/

I think there is an Android one too. Don't expect too much as the sensor
is only 80x60 pixels interpolated up.

--
Regards,
Martin Brown