Inside wall bricks below window sill crumbled

[Bea1711]

Hi there,

I am in the midst of redecorating my victorian flat - I took off my radiators with the intention of filling the crack and then painting behind the radiator when behind one of the radiators (below a upvc window) I discovered the huge crack behind the radiator where the mortar between the bricks seem to be missing. What then happened it that when I knocked the wall above the crack and below the windowsill was that the wall had crumbled and the bricks and mortar behind had crumbled too. I took to just remove the loose crumbled bricks and mortar. As I now don’t have bricks below my window sill, I need to lay bricks but as this is a period property, I wanted to get advice on next steps from this forum? What bricks, mortar and plaster should I use?

 

[Stevers]

That looks like modern gypsum plaster/cement render; these finishes are very rigid and do not respond well to movement. Whatever it is, it clearly isn't very well attached to whatever is behind. The bricks shouldn't be loose like that and there shouldn't be a void behind that crack. It looks like someone has moved the radiator bracket because the previous fastenings have failed being so close to what could be a significant vertical crack.

I've gone over to using Natural Hydraulic Lime mortars usually 1:3 with 50/50 building sand and sharp grit. It's nice to use and better for period buildings as it is more tolerant of damp, movement and salts. I'd use an NHL render for scratch and levelling coats, and as you already have gypsum plaster I'd finish that with Thistle One Coat - unless there is a possibility of damp. Many DIY stores will sell you a 12.5kg plastic bag. I store NHL and Thistle One Coat in plastic fertiliser or paint tubs, and that way it lasts forever.

I'd take a little more plaster off to explore the state of the brickwork near that crack, which may need to be made good, or any patch plastering will be a waste of time and effort. A bit of background would help us. If this is a conversion (I think it must be); is this an original opening, perhaps once a door? What does this window look like outside, and is there another flat below you to consider?

 

[Bea1711]

Thanks very much for your reply.

This flat is in a conversion and is on the first floor. Based on the houses on the street that have not been converted, I think it has always been a window. As it has been raining a little over, i’ve been checking the gap where the bricks have been removed and it seems dry. When I bought the place a couple years ago, the survey told me that the building has been affected by structural movement. It is considered likely that the affects are more significant due to the bookend effect whereby longitudinal expansion of the terrace pushes the end of terrace properties sideways. The result is the distortion at the top of the front wall and on the side wall of the property. Repairs to the brickwork are evident and there are no signs of current ongoing structural movement. Over the time that I’ve slowly redecorating and uncovering things in this flat i’ve found that modern materials have been used for patches when they maybe shouldn’t have. I’ll open up the plaster near the crack a little more.

Attaching photos of what it looks like from the outside. What is below the window is the shared entrance to the building.

It seems like the bricks that were loose (that i’ve subsequently removed) are different to the bricks below it. What bricks are needed to replace them?

 

[stuart45]

The bricks are different because they used a cheaper type inside.

 

[Stevers]

The 'book end effect' on terraces is new to me, but then I only look after one very detached house. Internal bricks are often underfired and not suitable for outside, so a random selection of salvage bricks put together with hard cement mortar for any garden feature, is pretty much doomed. With nothing to hold them down, and nothing much for them to do, it might not be unusual for the top row of bricks (or stones) under a window cill to be be odds and ends, and poorly bonded. I've noticed that sort of thing here, but from a small sample.

I suspect that the original 'stone' window cill is visible through the gap. It doesn't look like it's a cavity wall, but a row of stretchers wouldn't rule that out. Such a row of stretchers might suggest English Bond, but the limited outside bonding visible doesn't seem consistent with that. A bit more plaster off would reveal any bonding and if bricks have broken where the crack is.

 

[Bea1711]

I managed to pull off a bit of plaster on the top.

I’ll open up the crack to get more plaster off over the weekend.

But here are some close up pics of the top below the sill and the cavity

 

[malcolm]

It's possible the window is a replacement and the size was a bit different and the window fitters weren't all that concerned about your historic fabric and did the infill badly. The chasm surely must be missing a piece from the middle otherwise the house would be at an alarming angle on one side.

I would tend to put bricks back in where there is space for bricks. Lime mortar is always best as it's easier to use and will protect the sill above. Lime plaster is best too. Though outside has been done in cement and inside you'll have emulsion paints and you are above ground level so it probably won't matter very much what you use for mortar or plaster.

 

[Bea1711]

Thanks for all the responses.

What bricks, lime mortar and lime plaster should I use?