Where is this damp coming from? (with pics) 17 January at 4:13PM in In my home (includes DIY) MoneySaving 45 replies 1.8K views

MikeJXE

Doozergirl said:

MikeJXE said:

Doozergirl said:

silvercar said:

Would this work?

https://www.screwfix.com/p/no-nonsense-mortar-repair-grey-310ml/361jp

You need more than that.  You need to hack back the render slightly and install the render bead referred to by Section62, and then re-render.  

https://www.rendit.co.uk/renderplas-white-bellcast-bead-25m-renderplas-10mm-bellcast-bead-25m-white-2

Can you see how it brings the render away from the mortar joins of the brick and also tilts slightly down so water drips clear of the wall, it doesn't run into the mortar at all.  

 

That bead is only required when the render is flush with the brickwork

In the case of this job there is one course of brick set forward to whats below and that course is the drip 

Sort out any unfilled brick joints and stop the rain splashing up the wall 

I initially thought there was but I don't think there is.  I think the wire and the tape creates the illusion of one. 

I think it is flush.  

Yes I think you're right 

MikeJXE

Doozergirl said:

» show previous quotes

I initially thought there was but I don't think there is.  I think the wire and the tape creates the illusion of one. 

I think it is flush.  

Yes I think you're right however his hand sketch seems to show the brickwork protruding 

silvercar

MikeJXE said:

Doozergirl said:

» show previous quotes

I initially thought there was but I don't think there is.  I think the wire and the tape creates the illusion of one. 

I think it is flush.  

Yes I think you're right however his hand sketch seems to show the brickwork protruding 

*her

the render protrudes to the edge of the top row of bricks that protrudes over the lower rows,

Section62

silvercar said:

MikeJXE said:

Doozergirl said:

» show previous quotes

I initially thought there was but I don't think there is.  I think the wire and the tape creates the illusion of one. 

I think it is flush.  

Yes I think you're right however his hand sketch seems to show the brickwork protruding 

*her

the render protrudes to the edge of the top row of bricks that protrudes over the lower rows,

I don't think it is enough though.  The attached rough amendment to your sketch shows what I think may be happening - water running down the face of the render/roughcast is getting into the gap/crack between the render and the oversailing brick course and then penetrating down and through the bricks. (the bricks are just illustrative, not to scale, in reality your oversail is very small compared to the brick dimensions. In reality there is likely to be a narrow (and probably partially filled) cavity as well)

The bottom edge of the render/roughcast isn't sufficient to form a 'drip' - a combination of things like surface tension and capillary action will draw some of the water into any crack or gap, and with differential movement between the render and bricks it will be virtually impossible to seal the water out unless specific damp resistance measures were designed in.

For example, an apron of lead or zinc (see the second sketch) could have been formed above the oversailing course to form a 'drip' (roughly equivalent to modern render drip bead), or quite commonly sloping vitreous (or glazed) tiles would be built into the brickwork to cause any runoff water to drip well away from the face of the bricks. Another possible technique was the use of engineering bricks for the oversailing course, and the application of tar/bitumen to the joint and course above.

I think the flushness of your render/roughcast is at least part of the problem - it doesn't mean it is 'wrong', just that additional precautions would have been required to make sure water running down the face of the wall was kept out of the brickwork below.  I'd speculate it was possible something like that existed when the house was originally built, but repair work (possibly a long time ago) has removed that damp barrier, or made it ineffective.

You really need someone (like a surveyor) to inspect the walls and give you an opinion.  In cases like this photos aren't really a substitute for being able to look (and feel) first-hand what is going on.

silvercar

Section62 said:

silvercar said:

MikeJXE said:

Doozergirl said:

» show previous quotes

I initially thought there was but I don't think there is.  I think the wire and the tape creates the illusion of one. 

I think it is flush.  

Yes I think you're right however his hand sketch seems to show the brickwork protruding 

*her

the render protrudes to the edge of the top row of bricks that protrudes over the lower rows,

I don't think it is enough though.  The attached rough amendment to your sketch shows what I think may be happening - water running down the face of the render/roughcast is getting into the gap/crack between the render and the oversailing brick course and then penetrating down and through the bricks. (the bricks are just illustrative, not to scale, in reality your oversail is very small compared to the brick dimensions. In reality there is likely to be a narrow (and probably partially filled) cavity as well)

The bottom edge of the render/roughcast isn't sufficient to form a 'drip' - a combination of things like surface tension and capillary action will draw some of the water into any crack or gap, and with differential movement between the render and bricks it will be virtually impossible to seal the water out unless specific damp resistance measures were designed in.

For example, an apron of lead or zinc (see the second sketch) could have been formed above the oversailing course to form a 'drip' (roughly equivalent to modern render drip bead), or quite commonly sloping vitreous (or glazed) tiles would be built into the brickwork to cause any runoff water to drip well away from the face of the bricks. Another possible technique was the use of engineering bricks for the oversailing course, and the application of tar/bitumen to the joint and course above.

I think the flushness of your render/roughcast is at least part of the problem - it doesn't mean it is 'wrong', just that additional precautions would have been required to make sure water running down the face of the wall was kept out of the brickwork below.  I'd speculate it was possible something like that existed when the house was originally built, but repair work (possibly a long time ago) has removed that damp barrier, or made it ineffective.

You really need someone (like a surveyor) to inspect the walls and give you an opinion.  In cases like this photos aren't really a substitute for being able to look (and feel) first-hand what is going on.

That does make sense. In other areas of the wall (it extends all around the house) the render follows the line of your green arrow ie it protudes more over the brick and the white paint is unbroken between that and the bricks and more importantly there is no damp inside.