Exterior paint for damp outbuilding?

purplebutterfly

We're moving into a house with an outdoor toilet and utility room.  They're attached to the house and enclosed by a lean-to with roof and walls but no floor (there's decking onto garden slabs).

The utility room shows signs of previous damp and the toilet has some mildew on the back wall. 

What paint should we use?  I don't want to slap on watertight exterior masonry paint if I need to let the walls breathe.  I was going to wash it down with fungicidal wash first but should I also use a fungicidal paint?

I'm not doing anything fancy, just white paint to freshen things up. 

stuart45

Is it plastered or rendered inside? Lime wash is quite good for outhouses.

purplebutterfly

I think it is render but I can double check tomorrow when we get the keys.

I will look at limewash, thanks stuart45

I've also been looking at Snowcem if anyone has any opinions?

FreeBear

Lime wash - Get yourself a tub of lime putty, water it down to the consistence of double cream. With a good quality stiff brush, slap it on the walls and "brush out". If you want a bit of colour, add some pigment to the mix (raw earth pigments are good).

Home made lime wash is as cheap as chips, and one tub of putty will last a lifetime. Mix some sand in with the putty (2:1 or 3:1), and you have yourself some mortar/plaster which can be used for repairs. Kept in an air tight container, it will again, last a lifetime.

purplebutterfly

Can I use limewash over paint?  I don't know if it has previously been painted with masonry paint

FreeBear

You can get a primer to go over most surfaces before applying lime wash - The ones I've come across are usually an acrylic base, sometimes containing assorted sands. There are also silicate based primers, but they are darned expensive and I'm not sure how well they would work with lime wash..

A quick note about colours - Blues & greens will fade in lime wash until the stuff has dried. So they need to be used within days of being mixed.

NSG666

40 years ago Snowcem came as a powder, mix with water and paint it on, smelled lovely and lasted ages. Not sure whether it's ready mixed now but it's breathable

FreeBear

NSG666 said: 40 years ago Snowcem came as a powder, mix with water and paint it on, smelled lovely and lasted ages. Not sure whether it's ready mixed now but it's breathable

Just looked up the MSDS sheet for Snowcem - It is 80% white cement with a dash of antifoaming agents. So once mixed with water, it is going to have a short pot life, and breathability is no better than any other cementitious product.