Render directly to old block work

Hi,

Firstly I’m not a plasterer of any description!

I have an old very damp farm shed/worshop which I want to make more water proof. The shed walls are block work with a rough face. It was suggested to me that rendering the block work inside and out would waterproof the walls. As I mentioned I’m not a plasterer and have no skills that I’m aware of with trowelling floating etc.

So, my idea was to use a hopper spray gun, like a Marshalltown, to apply a tyrolean or rough cast type render directly to the block work. Reading about this I believe the correct procedure is to apply a scratch coat first but I’d like to avoid this due the afore mentioned lack of skill.

Would it be ok to apply an SBR/cement slurry then apply the render to this? It doesn’t need to be pretty, it’s only a shed, just waterproof and not fall off!

Thanks in advance for any advice.

yes

when it comes to dealing with water, there are currently two schools of thought:

1. try to keep water out of the walls (rarely works and even it if it does, it will fail in the long run)
2. design an assembly that promotes drying capacity of your wall

First question you need to ask yourself: where does the water come from? Do you have a leak in the roof? Do your walls get wet due to cross wind and rain? Is it rising damp from the ground and a lack of damp course?

Second question: what about ventilation? Is the shed adequately ventilated? If not, find the highest point of your roof and install a little cupola or a ventilation turbine or a louvered roof vent. Make sure there's adequate air intake as well, perhaps install a louver on the bottom side of the door. You don't need massive amounts of ventilation, but just enough.

If your moisture problem is rising damp, rendering it with waterproofed sand/cement is not going to work. All you'll do is trap the moisture inside the wall and your render will turn green quick and likely crack/delaminate within a couple of years.
If you have a roof leak, fix it. If it's only cross wind and rain then yes, cement render might actually be productive, although I personally still wouldn't advise it anyway.

What I would suggest is that you render it the walls with lime/earth or lime/sand mortar (not hydraulic lime, pure lime) and finish it with either a hot mixed lime wash or a lime/chaulk or lime/fine sand skim coat.

Your render is extremely capillary active: it will suck the moisture out of your wall to the outer surface because the limewash/lime plaster on the outside promotes drying. If you want to better understand how this works; watch this:

This is how traditionally for ages, houses have been kept dry. Ever since the Technological Revolution, paper pushers, architects and engineers thought they knew better than ages worth of proven practice. They pushed cement and NHL onto the public and the results have been disastrous.

Hope that helps

Oldhens said:

Hi,

Firstly I’m not a plasterer of any description!

I have an old very damp farm shed/worshop which I want to make more water proof. The shed walls are block work with a rough face. It was suggested to me that rendering the block work inside and out would waterproof the walls. As I mentioned I’m not a plasterer and have no skills that I’m aware of with trowelling floating etc.

So, my idea was to use a hopper spray gun, like a Marshalltown, to apply a tyrolean or rough cast type render directly to the block work. Reading about this I believe the correct procedure is to apply a scratch coat first but I’d like to avoid this due the afore mentioned lack of skill.

Would it be ok to apply an SBR/cement slurry then apply the render to this? It doesn’t need to be pretty, it’s only a shed, just waterproof and not fall off!

Thanks in advance for any advice.

Click to expand...

Any pics of the inside and outside walls.