Mundic Block

[ineedhelpplease]

Hi.

I believe Mundic block is made from old mining residues that contain sulphides that when come into
contact with moisture turn into sulphuric acid consequently making them unstable over a period of time.

I have an extension on my old Cornish cottage that was probably built about 1960 to 1970.

I've drilled a few holes in the extension wall and made sure they were damp inside and left them for an hour or so.

I then inserted pH Litmus papers inside and they did not show any signs of acidic substances according to the colour chart.

They did show up on the paper as being moderately alkaline.

Would this indicate they are not Mundic block ?

Many thanks in advance for any replies.

[redsturgeon]

You may have tested for acid but there are other issues according to this:

https://www.cornwall.gov.uk/housing/pri ... dic-block/

Sulphide Minerals

Often found in mine or quarried rock. These can oxidise under damp atmospheric conditions with the production of sulphuric acid. This attacks the cement causing weakness and expansion - commonly called 'Mundic Decay'.

Fine Grained Rocks

These are formed by sediments laid down on the floor of oceans and can be quite soft. They can change volume and delaminate under attack from moisture fracturing the cement of the concrete. This effect is called 'Killas'.

Furnace Residue

Clinker, Coking Breeze and Slag from metal smelters, gasworks and laundries. If the coal has not been adequately burnt it can expand when wet causing cracking.

Reactive Silica

Such as flint found in beach gravel generally found in mass concrete.

It may be that you need to hire a professional to carry out a full test.

John