Can I replace those bottom bricks and add a brand new rubber DPC? Or could this collapse?

[Matt723]

The previous rendered plinth was swollen and has been removed. It appears the ground has been raised with concrete by previous owners to create a slope away from the house and the original victorian DPC (some sort of tar) is now only about 2 inches above the ground.

There is no particular damp issue in the house (that I am aware of) however keen to do this right.

If those bottom bricks are rendered again at the same height we will be bridging the DPC again which I understand should always be avoided. But if it is not rendered at the same height I will end up with some badly damaged bricks visible.

Would it be good now that bricks are exposed to completely replace two or three rows with new bricks and make the plinth lower than before so that there is less bridge?

Or to avoid the bridging completely, should I look to have a brand new rubber DPC added (will be above and in addition to the original tar DPC) whilst the bricks are being replaced?

Or is it just too risky to mess with those low bricks?

Thanks!

 

[noseall]

The previous rendered plinth was swollen and has been removed. It appears the ground has been raised with concrete by previous owners to create a slope away from the house and the original victorian DPC (some sort of tar) is now only about 2 inches above the ground.

There is no particular damp issue in the house (that I am aware of) however keen to do this right.

If those bottom bricks are rendered again at the same height we will be bridging the DPC again which I understand should always be avoided. But if it is not rendered at the same height I will end up with some badly damaged bricks visible.

Would it be good now that bricks are exposed to completely replace two or three rows with new bricks and make the plinth lower than before so that there is less bridge?

Or to avoid the bridging completely, should I look to have a brand new rubber DPC added (will be above and in addition to the original tar DPC) whilst the bricks are being replaced?

Or is it just too risky to mess with those low bricks?

Thanks!

Point it up and forget.

 

[Matt723]

Thanks noseall. What do you mean by point it? Do you mean replace the damaged bricks and repoint without putting the plinth back?

 

[cdbe]

You could carefully rake out the (hopefully soft and loose) mortar above the dpc to a depth of 50mm, lay a length of 100mm pvc dpc on top of the existing and point in place, fix a temporary batten below the projecting dpc, render down to it, cut off the dpc flush then render up to it. Before rendering the lower section, remove the concrete 100mm out from the wall and subsequently infill with gravel to create a french drain.

I built a concrete block (above and below dpc) extension a few years ago and used a wider dpc in this way as I had to render above and below.

As it's a solid wall there will be no risk of collapse.

 

[Matt723]

Thank you @cdbe

Here is a sketch of what I understood you meant, did I get this right?

So I will have a second DPC (above the original TAR DPC which is now too low), and the plinth would be lower than before, bridging the original tar but being lower than the new rubber DPC?

 

[cdbe]

Not quite, the original dpc isn't too low, the ground is too high - if you raise the dpc you will get damp at the internal joist/floor level.

Like this, so you can render above and below the dpc without bridging it:

 

[Matt723]

Thank you this makes sense and I shall talk about this with the pointing guys next week. Couple of questions:

1. where does the french drain need to go? The soil under is compacted and removing everything to plow the soil would be quite the undertaking. On both sides there is no soil / greenery. Does the french drain need to go to the inspection chamber for the water going to the mains?

2. How deep the french drain needs to be?

3. Will I have a black line in the middle of the rendering where the new DPC sticks out?

 

[cdbe]

The french drain doesn't go anywhere, it's just a way of lowering the ground level against the wall - it should be 150mm below the dpc.

But if you're having "pointing guys" in and they're any good they may be able to repair the poor brickwork and it won't need rendering - see what they say.