Having read a post on the SF forum, I was just wondering if any chemists or addmix manufacturers actually know and could please explain to the layman what waterproofer actually does to finished render when added 
What does waterproofer ACTUALLY achieve??
- Thread starter dougalhouse
- Start date
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Waterproofer in render is an all round bad idea. Of course what it claims is to make the render waterproof, but this is really impossible because render will inevitable crack and craze and water will get in anyway. But then you are in a worse position because the waterproofer prevents (or at least reduces) evaporation so that the water in the render cannot now freely escape. The other bad effect is that rainwater falling on the wall, instead of being absorbed evenly over the whole wall surface, now runs down the wall and concentrates at the bottom.
There are sealers that claim to be waterproof but at the same time highly permeable so they allow water to evaporate. These work because the pores in the sealer are smaller than the water molucules but are large enough for water vapour to pass through. Personally I feel that these are still restrictive and must reduce evaporation, but I guess there will be other views on this.
Bottom line is that good quality breathable lime render has kept most solid wall houses dry for hundreds of years, whereas I have seen hundreds of houses riddled with damp due to hard sand cement render and dreaded sealers.
There are sealers that claim to be waterproof but at the same time highly permeable so they allow water to evaporate. These work because the pores in the sealer are smaller than the water molucules but are large enough for water vapour to pass through. Personally I feel that these are still restrictive and must reduce evaporation, but I guess there will be other views on this.
Bottom line is that good quality breathable lime render has kept most solid wall houses dry for hundreds of years, whereas I have seen hundreds of houses riddled with damp due to hard sand cement render and dreaded sealers.
There are many types of waterproofer - all of which work in different ways. Many of the admixes that are added to renders basically reduce the amount of water that is required to make the render workable. This has the benefit of reducing shrinkage during curing and therefore reducing the number and size of cracks through which water can pass. Other admixtures include polymers or silicates which block the pores in the render - also reducing opportunities for water to pass through the render.
Jeds is correct in that hard renders tend to reduce breathability - especially when waterproofers are added. However, this is only really a problem when they are used inappropriately - e.g. on period properties.
Jeds is correct in that hard renders tend to reduce breathability - especially when waterproofers are added. However, this is only really a problem when they are used inappropriately - e.g. on period properties.
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Wow
Thanks
That clears that up a bit
Thanks
That clears that up a bit
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