# Forum Home Renovation Brickwork  Horizontal Cracks in Internal Single Brick Wall

## Comments

Hi All,  Am new here and thank you for reading and helping.  Our house was built in 1955. It is double brick, with single bricks inside (between rooms). The walls are rendered and have a cement rough finish.   We have a few cracks in internal walls. A few vertical ones and 45deg ones round the window lintels. We also have a few horizontal cracks (1mm wide) which expands to 2mm when it rains after long dry periods.  We thinking of just chipping out the vertical cracks and 45deg ones and filling it with cement render. However, am a bit concerned about the horizontal cracks. We had a brick layer out and had a look at the sub-floor area as we thought we may need under-pinning. He said it looks fine and should seek assistance how to repair the horizontal cracks. These cracks seem to be following the brick mortar. Below some picks. Any advice on how to repair this would be appreciated.  Pic 1 shows horizontal cracks (ignore the horizontal purple mark as it is just paint). Pic 2 (ignore the vertical line as sparky put a new light switch) is on the other side of the same wall showing the crack is right through the wall (and is in the brick mortar).

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## PeteV

kind of hard to tell what the problem is... assuming underneath is fine, could there be something above pulling it up? eg. a top plate fixing? is the wall built from concrete blocks/bricks or clay bricks, or maybe a mixture? maybe some photos of walls adjacent could help...

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## johnc

You most likely have some seasonal movement possibly caused by the long dry followed by the recent damp weather. If the cracks don't close or continue to grow look for a leaky outside down pipe or water pipe either under the house or running nearby. Also look for trees near the house that are getting a bit large. 
With solid plaster if the cracks become to large you need a metal bridging material and then plaster over that, similar effect to the mesh used in bridging joins in modern plaster sheet only tougher. However those cracks look minor and you should follow Rods plaster tips on veeing out and refilling. 
I doubt you have a major problem but you are getting movement and if it is a result of either a shift in moisture around the footings or tree roots it may well get worse. Have the neightbours or yourselves done any major excavation work recently?

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## Comments

Thank you for the kind replies.  Any major excavation work recently? nope. This is an internal wall (room) and in the middle of the house  see pic C It is a single story house built in 1955.  Think it is just red bricks (not sure if concrete blocks/bricks or clay bricks, or maybe a mixture).  As mentioned the builder looked under the house and it was fine.  But after this recent rain I had a look in sub-floor and saw a puddle of water underneath where the cracks are.  Must be natural water seepage or something.  I need to sort that (another topic not for this thread).  The cracks have not moved at all with the recent rain.    I chipped it away to the bricks and some of the mortar (between the bricks) was just powder (sand running out!).  Some of the other ones I just opened the crack a bit and did not chip past the render/plaster.  (My texture on the wall seems rough - as per picture - and thinks I only need to use sand&cement&bonding agent as plaster --- I hope)?  A few questions please: Am hoping to first stitch these cracks back up and see if they re-appear.  I will have to sort the water seepage later. For now I am not going to use any mesh  Chipped way cracks (to bricks and mortar holes) - pic A:  Can I use sand&sement mix to fill the or do I have to use a mortar mix? Cracks that I just opened (not past the render/plaster) pic B: Can I just use a flexible sealer, and then put sand&cement (with a bonding agent = bondcrete) as render/plaster. Where do I find Rods plaster tips?

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## PeteV

a mortar mix is a sand and cement mix. you want your ratio to be around 6:1 sand:cement. good idea to add bondcrete into the mix as this will help it adhere and also acts as a sealer. i recommend removing all debri from the cracks and dampening the area before "stuffing" new mortar mix into the gap.
hope this helps!

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## johnc

At 6:1 you are getting a pretty weak mix. Shouldn't it be 6 sand, 1 cement and 1 lime, or if a cement only product as a filler of gaps perhaps go for 3:1 or 4:1 at weakest.

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## jago

I was under the impression that Portland didn't need lime although I agree 6:1 is a skinny mix I was taught 5:1:0.3 Sand, cement, Fire Clay for mud (mortar) and not too much water use a plasticiser.

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## PeteV

portland cement does contain limil, i guess it is still recommended for use in mortar, but not when your using bondcrete. overuse of plasticiser can weaken the cement so i be a little hesitant in using so much. there are some plasticisers that claim they don't break down the cement, but i don't really trust them, particularly with the likes of mortarlocks where i have seen the result of too much of it...

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## Comments

I am planning on using a pre-mix of sand & cement.  Sand and Cement - Cement Australia 
Can I use this for both filling as mortar (between the bricks) and as render/plaster (for top "coat" on internal wals)?  Maybe I need to add some bondcrete only for the render/plaster job? 
thanks for replies.

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