Paint rendered plinth or not?

[jv12]

I have polished my foundation base (lime-based fiber-reinforced plaster on styrofoam). I have no issues with the color of the unpainted surface and can imagine leaving it as is, but are there other reasons to paint it? Does the paint possibly protect the plaster in some way? What type of paint is most suitable if one still wants to paint?

 

[Martin_B]

Yes, I'm wondering about this too, if the color in some way has any protective property on plaster. Like, does it prevent moisture from getting in as much or so? Anyone know?

 

[Helioz]

The paint protects against water intrusion, discoloration, algae/mold attack, frost damage, salt precipitation, thereby increasing the longevity of the plaster. Personally, I think silicate paint/lime paint is too sensitive for a ground-level plinth, but if you are prepared to repaint every 5 years, they are absolutely the most diffusion-open. Therefore, the more expensive silicone emulsion paint remains, which provides the best wear protection (if painted with a 3-step treatment) and is the most diffusion-open, or the cheaper and more easily painted acrylic-based plinth paint (often requires no primer).

I think both of Jotun's paints are excellent, here is a product sheet with painting instructions:
http://www.lovelyhome.se/pub_docs/files/jotun/Jotun_Mur_fargkarta.pdf

Otherwise, there is Saku Plinth Paint (no primer, can be painted over after 2 hours):
http://www.ac.teknos.se/?pageid=H3817&lang=20

Flugger also has its system:
http://flugger.se/Faerg/Utomhus/Fasadfaerg/Fasadfaerg_Facade_impredur_vit(FACADE IMP).aspx

 

[Martin_B]

Then there's also Nordsjö Murtex V Silikat. I don't know how good it is compared to the ones you recommended.

 

[Helioz]

Then there's also Nordsjö Murtex V Silikat. Don't know how good it is compared to the ones you recommended.

Silicate paints (there are no major differences between manufacturers) are excellent on facades because they are so diffusion-open. The paint is also beautiful because it is completely matte and wears nicely as it gradually washes away from the surface like a distemper. But on a plinth that takes a lot of wear from rain, snow, dirt splashes, plants, etc., I think a silicone emulsion paint is better as you don't need to repaint as often and you also have a better chance to pressure wash away dirt. The etching properties of silicate paints (glass, ceramic, natural stone, tile, metal) mean you have to protect with masking a lot before painting as well.

 

[Martin_B]

The etching properties of silicate paint (glass, ceramics, natural stone, clinker, metal) mean that a lot of protective masking is required before painting as well.

This was more than I actually knew. But you also mention natural stone. Rough concrete, for example, contains gravel, which is stone. So silicate paints corrode concrete?

 

[Helioz]

This was more than I actually knew. But you also mention natural stone. Concrete with gravel, for instance, contains stone. So, do silicate paints corrode concrete?

Yes, the paint etches the concrete until the water has evaporated and the paint has cured. Presumably, this only increases the paint's adhesion. However, you should protect concrete slabs against paint splatters as it can otherwise cause unsightly stains.

 

[Sommartorparn]

If the plinth is plastered with pure lime plaster, then the paint should also be lime-based. Or? Perhaps reinforced lime paint, so-called hydraulic?

 

[Helioz]

If the plinth is plastered with a pure lime plaster, then the paint should probably also be lime-based. Right? Perhaps reinforced lime paint, so-called hydraulic?

If it's pure lime plaster then it should be pure lime paint. If you have hydraulic lime plaster, Hydraulit is better.

 

[Sommartorparn]

Well, hydraulic lime plaster is pure lime plaster. No additives. It is usually used for the base coat. However, I was wrong about the hydraulic paint. It is only used for kc-plaster. However, there is lime paint suitable for hydraulic plaster, if that's what it's about.

I recommend that the original poster contacts the company that manufactured the plaster to get advice on which paint is suitable. Better to leave it unpainted than to use the wrong paint!

 

[Helioz]

Mnjaaa, hydraulic lime plaster is pure lime plaster. No additives. Usually used for base plastering. However, I was wrong about the hydraulic paint. It is only used for kc plaster. There is, however, lime paint suitable for hydraulic plaster, if that is what you are dealing with.

I recommend that the original poster contact the company that manufactured the plaster to get advice on which paint is suitable. Better to leave unpainted than use the wrong paint.!

By pure lime plaster, I mean air-hardening lime plaster which differs from hydraulic lime plaster. Hydraulic goes well with hydraulic lime plaster, especially on baseboards and exposed areas, as you can see in the product sheet from Målarkalk here:
http://dokument.malarkalk.se/1101_1905/pb1420-1427.pdf