Cob and concrete

[CumminsandGoings]

I’ve recently taken ownership of a 500yo cob farmhouse covered in many sins. Its going to take a few years to tackle everything so I’m trying to prioritise tasks and get easy wins.

On one back corner I have this:



Two drainpipes sending water all over this concrete which goes just round the corner.

Inside this is where the worst damp meter readings are at around 30%.

My first task was going to be to run the drainpipes along the wall and into a drain and see what impact that has.

Or should I just dig up the concrete and then I can extend the drain? I will only be able to do the half nearest the house as I think the rest supports the retaining wall.

The reason I’m reluctant to dig up the concrete and extend the drain now is because I don’t know why it was put down or what’s under it and don’t want to get into a bigger job I don’t currently have time for.

In these situations is it best to make changes one at a time and assess impact or just go the whole hog?

 

[Cubist]

This is a KISS job. Cut the drain pipe and extend it around the corner to enter the drain there. Keep an eye on things for 2-5 years and then think about digging up the concrete - well or year of so say.

 

[Flyfisher]

Agreed. I did something similar when we first moved in and were faced with overflowing surface water drains due to the soakaways being clogged up.
We were fortunate that the land on the affected side of the house sloped away so I bought some lengths of 4-inch flexible pipe (the sort of thing used for underground conduit), cut back the affected downpipes, slid the flexible pipe up the downpipes and pointed them away from the house by about 3-4m onto grass. This immediately allowed the areas near the house to start drying out and solved a number of damp related problems.

As pointed out above, allow plenty of time for things to reach a new equilibrium. In my case, I rarely have a problem with delaying things though I did eventually get around to digging some trenches and laying new surface water drainage pipework, but that was really just a cosmetic job because the 'quick and dirty' approach actually solved the real problem.

 

[CumminsandGoings]

I was hoping you would say not to dig it up. Have enough on my plate this winter. I'll sort it out and see what happens to the damp readings.

Does anybody know what counts as a damp wall internally? There doesn't seem to be too much sign of mould on the inside but the lowest moisture levels in the walls are single digit so there is definitely a difference

 

[Kearn]

As you’re presumably pressing the two pronged damp meter into something other than timber, then whatever it’s spits out is meaningless. It’s conductivity…

Cob covered in cement can be a horrible can of worms, the damp bit in the middle of the impermeable sandwich can turn to mush. Presumably you’re south west, there’s more decent cob specialist down there at least to help out. What is often the case is a slow and steady approach to investigating and removal, as the skins of rigid cement take on a more structural role once the cob has inside has rotted away.

You’re right to shift any water away from the building, as it will find its way through cracks in the cement and get trapped inside to do its damage. But that’s just stopping things getting worse, I’m afraid it’s not the only solution if it’s cob encased in cement.

 

[CumminsandGoings]

Yes the damp meter is a two pronged although has a masonry setting. The meter readings may not be accurate but they do seem to correlate with where I think the worst of the damp is and also when I test a skirting boards the read out is different but correlates the same with the other areas.

Yes I've had a cob specialist out before we bought it and he thought everything looked ok. Recently we had water coming in above one of the windows, there's a small crack running up the face of the property so think that might be the cause. Every time I walk round the outside I seem to find more I didn't spot before.

Cob guy suggested one option is to remove the render up to near the top of the stone plinth which we think is about 1.5m high. He said that will help the water get out and is apparently a fairly traditional finish. It will help things whilst we continue to figure everything out.