External walls look shabby

[Behooven]

But to have a decorator paint them will cost about £4000! And then will need maintenance every few years.
They haven't been painted before. Anyone had Proteks (kind of silicon coating) which according to the ad lasts 25 years.

If they haven't been painted, don't paint them.

Are they brick or what?

How are they shabby? Dirt, water stains?

Are we talking about a detached 2-storey house?

can you post a photo?

It's a1950s bungalow with an upstairs loft conversion and an extension.
The original part of the house has roughcast which is in ok condition but the new bit at the back has a cream coloured render finish. This is the bit that looks dirty now. I thought getting it all painted was a solution but now I'm unsure.

it is bare mortar? usually somewhere between grey and yellowish depending on the sand used.

As long as it does not get damp, it will stay presentable for about 50 years, but if you paint it once, you will have to repeat it forever. Overspilling gutters and leaking drainpipes will cause mildew or lichen.

Don't think it's mortar? It's a thick creamy colour which was skimmed over the finished extension. It has a deliberate rough finish.
Tried to take a pic.

Oh and that's a reasonably clean bit as it's sheltered, the exposed bit on the front is manky.

Have you tried power washing it with a karcher?

a power washer will tend to take the "skin" off and leave it looking sandy or even pebbly, it will then shed dust and grit.

You can see the effect on concrete paving that has been powerwashed, which is usually harder and stronger than render.

Are you in an area where old cottages traditionally have a soft lime render, with rounded corners, often pink in for example Somerset or parts of Suffolk?

There are some foamed plastic coatings but I am not familiar with them. It might be described in your Planning Permission or Building Regulations plans, or on the builders quotation.

I'm in Scotland. Thanks both of you for answering. I think we are not getting the roughcast painted but are going to investigate the silicone based coating for the other surface.