Cost effective finish for outbuilding exterior walls

Hi all,

I have a number of outbuildings with exterior walls that are cement plastered and painted with commercial exterior paint. The paint is now in poor condition and needs to be removed back to the plaster, with some cracks also needing repair.

Rather than repainting with commercial paint, I’m wondering what alternatives there are.

I was thinking about some kind of cement- or lime-based finish that could be brushed or applied over the plaster, perhaps something that could also be coloured.

What alternatives have you used, and what would you recommend?

Thanks!

I lime wash. All my house rooms, barn, gate, oven with the same mix.
I use high calcium (more reactive) lime putty that I prepared a few days earlier. I mix it with water using a mixing paddle on a drill.

Three important advices:
1. The consistency should be full fat milk-like, not a creamer. If it's thick, it will flake off. It will seem that it's too thin and application process will be very messy, but this is what works for me. I use a large, natural hair brush 20 cm/8" wide. Since it's messy, please protect the areas/objects that you don't want to paint, as the wash will be dripping from the brush.
2. Do not try to make it perfect with the first coat. Thin mix will not cover everything perfectly. The succeeding touch-up will cover inperfections. For this I use 5 cm/2" brush.
3. Do it when it's cooler, overcast and humid after the rain. 15 C/60 F would be perfect. Shaded interior can be done on a warm, even hot day, but it may need water misting throughout the day. I lime washed interiors on hot, dry days and they also turned out great, but for the outside I would never risk it to do it in full sun on a warm day. If I had to, I would wait for the night.

If it's done properly, it does not flake, nor dust. It looks gorgeous.
I lime washed following surfaces: lime plaster, clay plaster, fired clay bricks, compressed earth blocks, concrete.

I never used any colorants, because the super bright white finish is my favorite and also, because I live in a place that gets 3500 hours of sunshine that needs to be reflected off the buildings.
Mineral colorants would probably work great.

Regarding cost. I do not remember exactly, but half to full 5 Gal bucket of lime putty will do 30 m2/330 sq ft of area. One $25 bag of lime makes 2 such buckets, so $25 per 60 to 120 m2.

I know South Africa is a huge country with some warm areas, cool mountains,  and  unique penguins around Capetown.... what is your home climate ?  
Cristo speaks with wisdom, I saw his oven and it is worthy of an art museum.  I thought I could quickly find a photo, but alas......

With his recommendations,  you save countless hours using lime plaster over the existing plaster.  Limewash also has almost magical qualities: antibacterial, antifungal to name a couple

As a kid, I spent a lot of time white washing buildings which was made of lime so probably the same as Cristo speaks of.

Thank you for the helpful responses thus far.

Pretoria is situated at a high altitude of roughly 1,300 meters, its unique valley topography acts as a natural heat trap. This results in long, hot, wet summers balanced by short, dry, and cool winters.

What do I need to keep in mind when prepping existing painted walls, except for removing old flaky paint, sanding remaining painted surfaces and washing with a pressure washer to remove all dust.

Internet search for local recipes suggest using hydrated lime, with us also called builders lime, is that correct?

I always white wash on raw surfaces, that never had any paint before, so I would recommend that you really strip it well, because if synthetic/acrylic paint was used, the lime will not create bond with plastic.

I use high calcium hydrated lime (made by Lhoist) with at least 95% of CaOH. Regular lime available in popular stores in US is always dolomitic and MgOH is less reactive than pure CaOH. Quicklime CaO could be also used (with care) but would need to be hydrated for a longer time.

I always prepare the putty first, so some CaO that was not hydrated will have time to hydrate thoroughly and will be ready to absorb CO2 either in plaster or in lime wash. To make putty, just mix the powdered hydrated lime with water in a bucket, using powerful drill with a paddle till cream cheese/dense sour cream consistency is achieved. Smooth the top and cover with 3 cm of water and cover with a lid, plastic bag or even plywood. It will stay good for years as long as it's ALWAYS covered with water, which will prevent drying and reacting with CO2. In hot climates, 3 cm o water may evaporate in a day, so it's good to store it really tightly covered in shaded area. Like I said before, one 25 kg bag of hydrated lime will make two 20 l buckets of putty. I usually start using it after 2-3 days. I have a barrel of putty, that is 4 months old and when i need to plaster I mix it with sand and some water and straw and when I need to lime wash I just mix with water.