CharlieBangor

I have just come back from Chiclana where we have 2 houses there side by side. The first thing I noticed were green stains / marks on the walls near the base of the properties about 18 inches high. The marks were on both houses and faced the same way (north)

I know there has been loads of rain there recently and we have had some very high weeds but am obviously concerned that damp has set in

Is this something I sould be worried about?

Hillybilly

Hope you mean green stains on the outside walls rather than the inside?!

External green staining is usually due to a combination of lack of roof guttering (so the rain just runs down the outside walls) and lack of proper external drainage for the path/patio/terrace or whatever is against the walls in question. Being North facing any moisture will not get dried up by the sun. Dirt sticks to the walls and algae can grow there. If not dealt with it will eventually appear inside.

Clean it off with strong bleach but check inside too. Fit guttering if there is none and make sure water drains away from the area. You may need to use a sealant on the lower part of the wall if the problem persists.

EsuriJohn

Hi CharlieBangor,

Not really. Unless there is evidence of damp inside the property I would not be worried but some sensible precautions may be the order of the day.

Unlike UK most property in southern Spain does not come fitted with guttering and downspouts. This means that the rain sheds of the roof onto the ground at the foot of th external wall. if the ground is hard it will splash back up at least 18" carrying with it fine soil particles which are a fine bed for mould growth. In the damper but still warm winter months a verdant green hue will cover the North facing wall since it will not get direct sunlight to dry out the external face of the wall. The south facing walls receive enough sun to dry out at mid day and hence no growth.

Precaution 1. Make sure that the outside soil levels are no higher than when the property was built. It may not have formal "footings" so don't go digging away several feet of earth or removing hard surfaced paths without investigating in a small area first! Soil often accreted to the wall if the ground slopes up from the house or there has been a lot of gardening activity along the wall.

2. When you have got the level down to where it was or if there is a hard surface along the wall cut a shallow trench alongside the wall 150mm deep by 300mm wide line with a fabric drainage membrane and fill the trench with single size pea gravel to the level of the surrounding ground. This provides a drain outlet for rainwater and stops bounce back immediately adjacent to the wall.

3. Brush the wall at the bottom with a stiff brush and then treat with an anti fungal liquid according to the manufacturers instructions and repaint.

However if there is no sign of damp penetration and the ground is low enough there are those who would say that the green stain adds character and should be left well alone.

Regards,

John.

CharlieBangor

Thanks ever so much for this - it really has put our mind at rest!

John & Cath
Re the solar panels, I have your e-mail and will reply to you shortly - just at work at the mo!

Cheers

Andy