What to do with this external wall/render?

delmonta

Hi, I noticed under my bay window outside it sounded hollow. Then I chopped off what you can see in the photo. But it doesn't seem like proper render, more like filler or something. It's white and a little bit soft/chalky.

It seems to be only under the bay window, the rest of the house is fine.

But I am planning to paint soon and need to sort this patch out. I've messaged quite a few renderers and most just said 'i don't do that kind of thing!'

One guy said it's not scratched so can't really just render over it. But he didn't suggest what I can do

So I'm a bit lost. Any ideas? The green underneath is solid but smooth, so mayb that can't be rendered

Thanks

FreeBear

If it isn't an external grade filler, it might be a lime based render/plaster... Chip off as much as you can with a hammer & scutch chisel. Paint over the area with something like Rendagrip and then finish off with a one coat render (https://tarmac.com/products/mortar/one-coat-render/ - Available from Wickes, B&Q, and others).

A plasterer or renderer won't be interested as it is only an hour or so of work, and the good ones will have plenty of day/week jobs on their books. If you don't want to tackle it yourself, a decent handyman should be able to sort it out.

delmonta

FreeBear said:

If it isn't an external grade filler, it might be a lime based render/plaster... Chip off as much as you can with a hammer & scutch chisel. Paint over the area with something like Rendagrip and then finish off with a one coat render (https://tarmac.com/products/mortar/one-coat-render/ - Available from Wickes, B&Q, and others).

A plasterer or renderer won't be interested as it is only an hour or so of work, and the good ones will have plenty of day/week jobs on their books. If you don't want to tackle it yourself, a decent handyman should be able to sort it out.

Ok Thanks. Yeah I was happy to patch it in, but I think most of the whole area under the window is useless, so it won't be just a few patches in the photo, but having to skim the whole thing, which I don't know if I have the skills to do a decent job!

A scutch chisel, I never heard of one. But if it helps get it off that will be very useful as a normal chisel and hammer isn't working so well

maisie_cat

I don't think you should go over lime render with a cement based product, you'll set your self up for a damp problem. Old buildings are designed to breathes so that if water gets in it can get out, newer buildings are designed to keep water out and cement render does not  breath.

FreeBear

maisie_cat said: I don't think you should go over lime render with a cement based product, you'll set your self up for a damp problem.

I would normally agree with you. However, this wall looks like it has had a coating of a green primer (possibly Bondit Pregrit) and the dreaded damp "treatments" as evidenced by the series of holes in the bricks one course up from the ground level - This probably means that a waterproof render has been applied internally thus ruining any chance of the wall breathing properly. The damage has already been done, so another layer of cement isn't going to make much of a difference.

delmonta

FreeBear said:

maisie_cat said: I don't think you should go over lime render with a cement based product, you'll set your self up for a damp problem.

I would normally agree with you. However, this wall looks like it has had a coating of a green primer (possibly Bondit Pregrit) and the dreaded damp "treatments" as evidenced by the series of holes in the bricks one course up from the ground level - This probably means that a waterproof render has been applied internally thus ruining any chance of the wall breathing properly. The damage has already been done, so another layer of cement isn't going to make much of a difference.

Thanks. I'm a bit worried now, I just got the Green Homes Grant to internally insulate the front, and externally insulate the back of the house. I guess doing this doesnt help the house to breathe at all either. I hope it doesnt cause any damp issues

That rendagrip stuff is expensive and only comes in huge tubs! I will only need a tiny bit. Is there anything else similar to that that comes in smaller amounts?

stuart45

You can use SBR mixed with cement as a bonding agent KA SBR Bond Co-Polymer Bonding Compound - 5L | Wickes.co.uk
Wickes also do a smaller tub for around a fiver.

delmonta

stuart45 said:

You can use SBR mixed with cement as a bonding agent KA SBR Bond Co-Polymer Bonding Compound - 5L | Wickes.co.uk
Wickes also do a smaller tub for around a fiver.

Ok, so just SBR and cement and it will have the same effect as rendagrip? What ratio? I already have some SBR and cement, so that would be ideal

stuart45

Just mix up so it's a paste you can brush on and it sticks to the wall. You need to get the render on before it goes off, which usually about 30 mins.
How thick is it?

delmonta

stuart45 said:

Just mix up so it's a paste you can brush on and it sticks to the wall. You need to get the render on before it goes off, which usually about 30 mins.
How thick is it?

Ok thanks, I'll do that. How thick is the area that needs rendering? Probably about 3mm

stuart45

You might struggle a bit with the one coat renders, as the aggregate size means they only down to about 5mm.
For a really tight coat you could get some fine silver sand and mix your own with cement.