Hi. I’m new to this forum, so please forgive if this message in posted at the incorrect discussion. My name is Ravi and I live in Cape Town, South Africa. I’m in the process of renovating an old house that been built with cement bricks and plastered. Due to weather conditions here in Cape Town, it’s become important to seal the walls against penetrating moisture. Now, I’ve opted to use a penetrating water repellent (instead of a sealant), but I’m not sure whether the repellent will work properly given that I’ll need to apply it onto the plaster. Logic tells me that it should repell water nonetheless, but I wouldn’t want to make the effort in vain. Any experiences out there that I could lean on for advice?
Regards
Ravi
Replies
Wouldn't it be better to apply the water repellent to the outside? Or is the outside plastered too? I've seen a product here in the States for concrete that paints on and dries as a sort of crystaline coating that supposedly waterproofs--seems like that might bond with plaster or stucco. If you post your question on Breaktime, those guys will have some ideas too.
I'm sure there may be some differences in the way the language is used between here and there, but I think of a sealant as a product that enters and binds withthe surface material and often makes it harder and more impervious from without while sealing components of the material within. It becomes a water repellant as a by-product of this action.
I think of a water repellant as merely a thin coating to skin the surface without much penetration and this thin surface layer is mostly impermeable to water. That is just my understanding, and the chemical people are always coming up with new products. The way you describe what you have sounds like it will work. I look for something that is acrylic or latex based. Vinyl might peel, and wax wears off in a few months, and silicone impedes future attempts at painting.
One common product for this sort of thing marketed in the US is Thompsons water seal, but it is mostly wax and lasts effectively no more than six months. An Acrylic product we have used is called Acril60, but I tend to question whether yu have the same name brands down there.
As I understand it, your walls are also plastered on the exterior as well as inside. Correct?
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Due to weather conditions here in Cape Town, it's become important to seal the walls against penetrating moisture.
Ravi--
tell us more about your weather conditions. and, is this plaster on the outside or inside?
Did you put up the plaster or are you dealing with stuff that was there already? How common is this construction where you live?
What is the plaster made of? Do you paint it? if so, with oil-based or latex?
those are all the questions i can think of for now!!
Megan
I am of the opinion that the only useful way is to seal the outside,the best product I think would be a silicon product.
You spray it on every few years,but easy with a napsack.
Hi Ravi:
I've worked on new, old and ancient plaster surfaces in Europe. Before doing anything, I think it is vital to know which type of plaster you are dealing with, and, has this plaster been treated (painted) before. The age of the building might give you an idea already. A wrong treatment can ruin the plaster and eventually the house. The plaster still has to be able to breathe as we call it because no matter what, you still have your heat transfer and humidity transfer going. The most common mistake is that people seal the plaster and therefore suffricate it. This can cause growth of mold between plaster and brick and the house will look sad very soon. I urge you - if you don't know what you are doing- to seek good onsite advise from an experienced tradesman.
Here are some basic ideas what to look for:
1. 2 layer lime based plaster (lime and sand); treat only with lime wash or so called mineral paints which interlock chemically with the sand. Plaster has to be cured for 4 weeks before painting (repair patches for example). Consult paint manufacturer if you want to use acrylic material.
2. 3 layer lime/cement based plaster (lime/cement/sand); like above
3. 1 layer resin based plaster also called machine plaster; after priming with acrylic emulsion you can paint with acrylic paint 2 times, first coat thinned with water about 10-20%, second coat original. This plaster has been in use only the last 15-20 years, if the house is older it might not apply.
These are just some basics I still would consult a knowlegable tradesman onsite!
Enjoy the work!
Dear Malemeister
Thanks for the excellent advice. I seem to have a lot of work ahead of me.
Cheers
Ravi