Filling cracks in external rendered walls

[MisterBoy]

Our house is about 150 years old and at some point the red brick was variously painted or rendered on different walls.
There are quite a few cracks... the widest you might just get your finger-nail in, most are hairline. Stone window lintels/sills nearly all cracked too but seemingly old cracks.

I'm going to be monitoring them (fitting crack guages) before we eventually get around to re-painting the house but in the interim I'd like to fill some of them, rain can get through pretty small cracks if the wind is the right direction. Plus it makes it easier to see if the crack opens at all.

Would the panel recommend simple exterior grade filler, or something else? I know you would normally grind the cracks but for a quick cosmetic fix can I avoid that?

Not sure how well you can see but there's a couple on the wall and above/below the window:

 

[MisterBoy]

A saw a guy on YouTube using gap sealer on a skeleton gun, which I assume is just outdoor grade caulk of some sort.

 

[opps]

Assuming that the cracks are not structural, I use an angle grinder to open the crack and then use Toupret Fibacryl. It is like a caulk but is also has micro fibres in it. I gun it in and let it dry. It shrinks back, so once dry I fill over it with Toupret TOUPRELITH F and sand that back when dry.

If you don't care about being able to see where the crack is but just want to make it water tight- don't bother with the angle grinder and just gun some CT1, Stixall, SikaFlex over the top and smooth it off. They are MS polymers, almost as flexible as silicone but unlike silicone, they can be over painted.

 

[MisterBoy]

Cheers @opps. I hope they're not structural - or if they are that they are stable, old cracks! You see new ones sometimes but then it's easy to get paranoid, it can just be the angle of the sun or that you never happened to look closely before
You can see the sill is clearly cracked, and I think the lintel above is too but they look very old problems. The paint is at least 10 years old (we think) and of course telling if a crack is in the wall or just the render is not easy.

I figure filling them will be another way to easily see if there is movement, though I hope to fit some guages too. It's getting to the point of needing repainting but I would be annoyed to go to all that work/cost and then find there are cracks that need sorting. Rather monitor the cracks for a couple of years (?) then paint once we're sure it's all fine.

BTW do cracked sills and window lintels matter? They are surely stone and it seems a classic thing on older properties, but they are supposed to be structural. I assume the cracks mean they are held in place strongly through compression using the arch principle?

 

[opps]

With cracked sills and lintels, I just go ahead and use heli-bars to distribute the load. I use a wall chaser with diamond blades to create a channel to accept the stainless steel heli-bar.

If, for example, the sill had a crack half way along, I cut an 8mm wide, 8 inch long channel in to the front face of the sill and then another in the top of the sill. I then seal the channels with dilute SBR (not sure how necessary the SBR is but it means I don't have to worry about dusty surfaces). I then cut the heli-bar to length and "glue" it in with anchor-fix resin. Then the next day face fill it with 2 pack filler.

It works very well but if the house is subsiding, the crack will just move elsewhere.

 

[MisterBoy]

That's interesting, thanks @opps. Not come across heli-bar before but makes a lot of sense. Is that the sort of thing you might use if - heaven forbid - you did have structural issues in the wall? I've seen buildings with metal strips like a set of stiches up the side but it's very ugly.

Out of interest how long does it take to do one piece? I wonder if I should put it on my long-term list when we come to repaint the whole house, to fit it in every sill/lintel that has a crack since it can be easily covered up.

 

[opps]

Have a look at the following

https://www.helifix.co.uk/products/remedial-products/the-helibeam-system/

Additionally hit the home page and look at the other options.

Each window sill would take about 30 to 40 minutes (assuming that you are working off scaffolding rather than a ladder). If you don't have a wall chaser you can use an angle grinder with a diamond blade. A cheap wall chaser (with two diamond blades) will cost about £80 from the likes of screwfix or Toolstation. A big advantage of the wall chaser is that you can connect it to a dust extractor (read: vacuum) and both cuts will be parallel and the same depth.

Cost wise? £20 for 5L of SBR- you will have loads left over, smaller quantities are available via Amazon. 4mm helibar 1m long, approx £5 ( I use a diamond blade in an angle grinder to cut them but you can use a hack saw). The anchor-fix- about £8 per tube (note: unless you use a hole tube within 10/15 minutes you will need to buy extra nozzles. The stuff goes hard really quickly). 2 pack filler- 3L of Upol Easy deep fill for for about £20 on ebay.

Each sill will cost about £10 in materials.

 

[MisterBoy]

GReat, thanks very much