Re-render or patch repair ground level external render?

[Paddiy]

Hi

I would like a couple of bits of advice on how to repair the render at the front of my Victorian property (see enclosed photos). I have removed the previous layers of paint and cement repairs to reveal the original render and intended to patch repair the cracks with a product like ‘patchcote lime plaster repair kit’ (as it says it’s for internal and external use) before painting over in limewash. However I’m not sure if the original render is cement or lime based? The house is an 1890’s build.

The previous repairs also covered the lower base layer of bricks (that protrude slightly from the wall) in cement render to keep water out but this has cracked and been keeping the damp in so I have removed it. Do I leave this lower layer of bricks free of render to allow it to breathe or recover it with a layer or lime render?

I was considering digging a French drain to allow the bricks below the slate DPC to breathe but am concerned that I might introduce moisture into the ground infront of the foundations that could cause movement as the previous owner laid crazy paving at the front of the property that has been displacing rainwater away from the property for a number of years. Is that a possibility if I change the moisture levels in the ground? Presumably the foundations won’t be affected, just the ground surrounding them? The area is clay but I understand the properties in our street sit on sandy riverbed being close to the Thames.

Thoughts/ advice most welcome!

 

[IHateDamp]

Where is the DPC?

Are the airbricks above internal ground level? In my property they are, so mine are some sort of periscope vent.

In your position I would get some of the render tested to be sure what you are dealing with and not do anything until then

Do you have any signs of damp in the room in the bay?

 

[Paddiy]

Thanks for responding. The airbricks are just below the surface of the floorboards inside the space for the joists, not quite periscope style, but close. The slate DPC is on top of first row of bricks in the external wall and under the row of bricks running below the air vent (you can just about see a section of slate DPC in the photo enclosed). There is a very slight smell of damp in the room with the bay but no sign of damp on the walls. I’ve had to prop up the flooring in the corners of the room as the timber had started to rot around the brick buttress that the floor joists sit on the internal side of the rendered wall. The bricks behinds the original render have started to deteriorate in patches so I suspected the render is largely cement based but when I tested a bit with white vinegar it started to very gently fizz. Should it fizz a lot more with fully lime render? (See photo)

 

[IHateDamp]

Whether the bricks were deteriorating before they were rendered or after is a question. I just watched a video where the presenter suggested in the old days rather than repoint brickwork, they would just slap on a lime render.
Apparently there is also a difference between portland cement ( very hard) and more natural victorian cements which are more forgiving.
I think you would need an expert / analysis to understand exactly what you're dealing with.

 

[IHateDamp]

Just been reading 'the warm dry home' by Peter Ward and it says that cement will fizz a bit, but lime will be a violent reaction fizz. Render is not meant to go to the ground; there should be an overhang so rain can drip off. The brick strap pointing higher up in your walls looks like cement.

 

[Cubist]

I wouldn't worry too much about whether the old render is lime or cement. Give the relatively small area and the fact that much of it is compromised one way or another it would be best in my opinion just to strip it all off and apply a new lime render coat - after giving the brickwork an opportunity to dry out a little perhaps.

 

[Paddiy]

Just been reading 'the warm dry home' by Peter Ward and it says that cement will fizz a bit, but lime will be a violent reaction fizz. Render is not meant to go to the ground; there should be an overhang so rain can drip off. The brick strap pointing higher up in your walls looks like cement.

Thanks for the info. Definitely not a violent reaction to the white vinegar so must be cement based render. The repointing was done last year replacing the old cement pointing that was added in the 80s. It’s now a lime based mix which is partly why I’d like to fix the render below it properly too. Will search for an example of render with a drip off overhang. I’ve not seen that on Victorian terraces/villas before.

 

[Paddiy]

I wouldn't worry too much about whether the old render is lime or cement. Give the relatively small area and the fact that much of it is compromised one way or another it would be best in my opinion just to strip it all off and apply a new lime render coat - after giving the brickwork an opportunity to dry out a little perhaps.

I’m inclined to strip it back and rerender in lime as you say as I think it will solve the slight smell of damp the bay room. My main challenge is finding a local plasterer that works with lime and wants to take on a relatively small job. I’m pretty good at DIY but think lime rendering without any practice may be a bit of a stretch. If the brick faces are blown I’m not sure what breathable product I would use to create stability and a key for the lime. I’ll do some more research on lime plasterers in the area. Thank you for your thoughts.

 

[IHateDamp]

Please update how the work goes !

 

[Stevers]

Render is not meant to go to the ground;

The brick damage visible means that ship's already sailed, but is that actually true for a rendered plinth anyway? Lime render is just what damp and damaged brickwork needs - nothing else required.

In your position I'd buy some NHL plus a bag of sharp sand and a bag of soft sand. I'd knock one of the faces off and have a go at putting it back with a 1:3 mix NHL to sand that's 50/50 sharp/soft. You haven't much to lose other than the time and materials. I've found NHL very easy to work with - both fairly sticky and easy to work. A scratch coat to get your eye in, then a finish coat. The scratch coat will need keying, and you will need to be ready to rub the finish coat with a wooden trowel as it starts to go off.

That should give you some idea of how good a job you could do, the quantity of materials required and how long it would take.