Leaching on outside wall - advice please

[PThomas]

Hi all

We have an outside wall that we built 3 years ago. It's 6" concrete block and rendered by a professional. We painted it with a latex paint suitable for outside.
The side walls are fine, which have soil and plants behind them.
The rear wall is partly soil and partly hollow.
Each year we have had to rep ain't the bits that have gone white, typically it's the same places. Some of these have now had 7 or 8 coats!

Is there anything we can paint the wall with to stop it leaching?

Thanks in advance for advice and suggestions

 

[misterhelpful]

If it's blistering and powdery it is likely to be efflorescence, caused by salts in the walls. It's harder to control outdoors, as moisture is always more prevalent, but an alkali resistant primer may help. Some stabilising solutions do the job as well, but you will need to check the manufacturer's instructions.

The other reason could be surfactant leaching, which is when moisture causes the soaps in paint (especially darker ones like yours), to bleed through the surface. Surfactants usually leach out very slowly and disappear without being noticed, but if there is a temperature change soon after fresh paint is applied, such as warm days to cold nights in spring and autumn, they will appear much more quickly and heavily. If this is the problem, you need to ensure the fresh paint is only applied when temperatures are relatively stable.

In either case, the wall to be totally dry when painting, so if the part of the wall with the problem is a regularly damp area, you will need to resolve that issue first.