Reinstatement of render below DPC...?

[paulbandler]

A couple of months ago I removed a hard 'concrete' like skirting of render that bridged the DPC. In this process I did some damage to the face of some of the bricks, although in some areas it came away quite cleanly. I've asked the builder to repoint the exposed brickwork below the DPC but he's indicated that he thinks that as some of the bricks are in a poor condition it would be better to reinstate a hard 'sand-based' render up to, but of course not bridging the DPC which is just below a newly formed bell-cast.

Having sweated to remove the earlier render I'm hesitant about this as I'd hoped the couple of rows of exposed brickwork below the DPC would provide some ability for moisture to escape before relying on the integrity of the DPC to stop all moisture.

I appreciate that its difficult to make a value judgement without seeing the state of the brickwork but any suggestions would be most welcome. Of course its getting quite cold now for such external work but we hope to get whatever needs doing done in the coming week...

 

[mark_j_k]

How about replacing any damaged bricks? or removing them and turning them around.

 

[NT]

Rerendering in cement will much worsen their water content, which might lead to freeze/thaw damage. Cement will damage bricks when it finally comes off. If the bricks are so bad they need rendering, lime render will resolve visual issue and let them dry too.

NT

 

[essexbearhunter]

The problem breaks down in several ways:

1/ Does the builder believe that the poor condition of the bricks is an aesthetic or structural matter?
If it is aesthetic, the problem can wait and you can opt for turning round bricks or using the porous coating/refinishing that best suits the style of the place.
If structural (and he just wants to re-render the bricks) then it sounds like he is afraid of water being soaked up by the bricks and causing frost damage. The initial reaction should be to minimise prolonged water contact - perhaps using a French drain next to the wall and checking that water from the gutters is not discharged onto it.

2/ Is the method for drying the bricks working? Ultimately, it is the RETAINED water that causes the problem. Providing that the method for drying out the bricks is consistently more efficient than whatever is wetting them, then you have no problem.
If you have suspended floors then we are talking airflow/airbricks.
Solid floors are a different ballgame because the only drying opportunity (apart from the relative dryness of the ground beneath the house) is the exposed outer surface of the wall itself. Rendering (if perfect) would shed rainwater but would trap any water rising from the ground itself (e.g. from wet soil next to the wall that it below the rendering line).

My logical instinct would be to combine good drainage at the foot of the wall with a microporous coating that would shed most of the water but would still allow the wall to breathe ( the building equivalent of GoreTex).

 

[paulbandler]

Thanks for the responses.

Yes we've dug some channels beside the walls which are to be formed into french drains.

Regarding the use of a lime-based render below the DPC down to the ground, do we need to be careful to ensure the render doesn't actually come in contact with the ground? I mean as it is porous, could it act as a wick to enable moisture to climb up the outside of the brick whereas a hard cement based render skirt would tend to prevent this - is this the reason why such hard cement based skirts are so often found? Just asking ...

 

[paulbandler]

My builder just told me he's got some hydrated lime from Jewsons that he proposes to mix with water, wait a day then make into a render with some sand and a bit of cement. He was doubly pleased that his Polish workforce then turned around and said, oh yes, they use this stuff all the time in Poland!

Is this going to result in the breathable coating I require - doesn't quite sound like the '3-week slackened' specialst materials I see on some lime specialist sites... OTOH, we're only talking about a very most 1920's property here, so if it will achieve some basic breathability at most cost then that is fine...

 

[NT]

No cement! Adding cement causes premature failure. Otherwise it sounds just the trick.

Be aware this wont set unless it dries, so application must not quite touch the wet ground. Also that it may takes days to set, and this is the wrong time of year to be doing it.


NT

 

[biffvernon]

Definately no cement - but leave it till spring and the danger of frosts has gone.

 

[paulbandler]

I feared that the cement may have been a mistake - but the builder seemed very confident/insistent that it was needed, but, well, he always is...

Its happened now - and it did set hard. So, will i have a breathable skirk or have I just had the old problem reinstated...

 

[Gervase]

It depends how much cement he used. If he used the common building guage of 6:1:1 sand:lime:cement, then it will be as breathable as concrete and you'll be back to square one, I'm afraid.
Sadly builders are nearly always confident/insistent - and doubly so when faced with anything that goes against what they've always done.