external DPC and soakaway

[untitled]

Hello all,

I wrote a question on the forum a few weeks ago but have not managed to get a definite answer thus far.

I have removed the external cement based render that bridges the slate DPC. Unfortunately I am unable to upload a photo as it says "sorry, the board attachment quota has been reached". I can send a photo but not on the forum. Anyway, this has damaged the brick surface so I need to re-render (I assume). If this is indeed the case would a lime based mortar help to reduce any potential damp that bridges this section? If so does anyone have an idea of how hydraulic or not it should be? Please note that I think the walls are now getting damper than before I removed the render (!)

The other part of my question is the concrete path that was abutting the property. This is angled towards the wall and led to rainwater being forced towards the cement render. I have cut a channel in this path forming a perimeter around the rear of the property 200mm wide and 150mm deep.

I am unsure as to the best course of action here. I plan to build a raised deck over the existing (remaining) path and put some gravel in this channel to act as natural drainage. Would this be advisable of should I be looking at diverting the water away using a french drain, guttering or similar?

If anyone has experience of this or just some plain common sense advice I would really appreciate it!

Many thanks in advance.

 

[Penners]

Hello untitled.

The usual way to prevent rendering from bridging the dpc is to stop it just above the dpc. Below the dpc the masonry is usually left naked. It's also helpful if your rendering stops with a short outward flare, known as a bellmouth. This helps to throw any drips running down the render clear of the brick plinth.

Yes, rendering with a lime mortar will definitely be helpful to the building. Others can give you better advice on your best choice of lime mortar.

Are you completely wedded to your concrete path? By far the best solution would be to lift it completely and replace it with a gravel path. If the soil against the walls is at or above interior floor level, dig a trench to expose the brick plinth down to a few inches below floor level, then lay your gravel path outside the trench. If necessary, you can backfill the trench with gravel, too. Just make sure that your trench does not go any deeper than the building's subsoil bricks - this is vital.

 

[untitled]

Thank you Penners. I've just picked up your reply.

I have now managed to upload some photos of the outside of the property and the state of the interior walls since I removed the cement render plinth outside.

The removal of the external cement rendered plinth and creating the 'soak away' have caused massive problems inside! Hopefully you can see in one image how the water is now 'beading' on the inside wall and causing black mould growth.

Given the state of the brick below the DPC and that the outer skin has now gone, would you still recommend only rendering only above the DPC? I can do the bell mouth detail up to the DPC from above but am worried that the lower bricks will just keep soaking up water like the sponges they have become.

Any advice would be fantastic (including how to deal with the soak away). I need to solve this problem rather pronto!

Thank you.

 

[Penners]

It looks to me as though the internal dampness on the brick plinth masonry is probably due to two things: porous bricks and failed pointing.

Renewing the pointing with lime mortar is a fairly straightforward procedure, and certainly needs doing. The possible porosity of the bricks is another matter. I can appreciate your wish to get the problem resolved as quickly as possible, but the problem is that damp is best approached in a step-by-step, "suck-it-and-see" manner.

So, rightly or wrong, here's what I would do if it were my house.

1. Repoint the plinth brickwork with lime mortar.
2. Protect the brick plinth from rainfall by leaning some sheet material against it on the outside (corrugated tin or similar) such that the air can circulate behind it freely, and dry out the bricks. I would leave this arrangement for several months - well into warmer weather if you can.
3. Render the house as planned, with a bellmouth above the plinth.
4. Once this has all been done, you need to see whether the plinth has dried out substantially. If it hasn't, then it may be that the porous bricks are wicking up damp from the ground. If it does dry out, then rain penetration can be suspected. Short of cutting out and replacing the plinth brickwork, I suspect that the only solution to this will be to lime-render the plinth, too. This is a controversial suggestion, but if it were my house, I don't think I could avoid it.

It may look a little odd to have the main rendering stop at plinth height with a bellmouth, and then to continue below (maybe a bit thinner?) but if you paint the plinth a different, perhaps darker colour, I don't think the effect would be unpleasant.

These are only my thoughts - a moderately experienced amateur. So please don't treat them as gospel! Others may have better ideas.

 

[untitled]

Thank you Penners.

Your suggestions make sense and I agree that time should prevail.

I will do this and report back late Spring 2015.

I Appreciate your response.

 

[Keithj]

I think Penners has it exactly. "Cover the plinth and wait till Spring" should reveal something.

There's no telling whether the damp you have now is old stuff drying out, or new water getting in. Shielding it from rain and letting air circulate should reveal more. It will go black for a while, but that's not necessarily proof of new damp.

Is the ground level outside lower than the ground level inside? That will be important when deciding about gravel, French drain, etc. We cut a French drain all round this house, since the floor level was below ground level. It took a while to dry out, but it seems our damp problems are solved. A previous owner had put a concrete path all the way round - that did NOT help, the surveyor assured us.

 

[MatthewC]

It looks from your last photo that there has been a concrete path up to the wall, and you have cut it back (which is a Good Thing). I would suggest that this might well have been the cause of the bricks' condition, as they would have been usually damp due to water coming out from under the concrete and also due to splashback when it rained.

I had exactly the same on an internal brick wall where there was "concrete plaster" on the lowest foot or so, and then lime plaster above. The lime plaster had blown and was falling off, and the bricks above the concrete were just like yours in the photo; where covered by the concrete they were perfectThe concrete had been applied as a fix for the dampness caused by (a) earth at floor level up to the stone wall outside, and (b) blocked gutters above causing water to flow down the wall. Problems now fixed, dry as a bone!

As Penners said, leave it and see!

 

[Matt Green]

Mould growth and beading water like that is a condensation issue, which means that suddenly that section of the wall has become very cold. Wet walls are more thermally conductive that dry ones so I also suggest drying that section out and seeing what happens.

 

[Roger H]

Hi. What direction does the water run in when the concrete path is wet?

Having cut out a channel (a move in the right direction) I suppose this lower section might actually be collecting water if the path inclines into it. Ideally I would remove the concrete path in its entirety and reduce its level as much as is practical when reinstating (or using a different porous path surface e.g. paviours). If the path is inclined away from the house and not presently encouraging water to enter your new exposed channel then this is less of an immediate issue.