Render below DPC

[clairelouisecook]

Our house is made of soft old bricks which do take in water and blow,due to the age of the house we have no foundations; the house is build on chalk with a slate damp course. The previous owner pebbledashed the building which we have taken off and intend to re-render to the old slate damp course with a smooth finish. I have a small amount of damp on one wall ie inside of the wall we are intending to render. Previously on the outside of this wall (where the damp is showing inside) the earth was piled above the damp course which we have dug out and this may have been the cause of the damp inside. However I have a conundrum I want to protect the soft bricks below the damp course from blowing but understand that rendering below the damp course is unwise as it may allow damp to progress up the building. One suggestion is to paint below the damp course with something like 'Black Jack' twice, on the second coat put sand on it for good adhesion then leave a 5mm gaps below the damp course (to stop damp) and render the brick below the damp course. What do people think? Any other ideas? Anyone know the rate for rendering currently including the cost of guys who knock up the cement or anyone good with fair rates?

 

[RonnyRaygun]

If you've got solid walls rendering below the DPC will allow water to be drawn up from the ground, past the existing DPC and into the masonry above. This can then not only rise up the wall but also go through the wall causing problems to plastering and finishes.
But worse than this, if you have timber floors it can lead to dry rot, and I know from experience what a job that is to get rid of

(The house I renovated had exactly this problem due to a bridged DPC. Replacing the timber floor with concrete was the easy part; little did I realise the dry rot had made it all the way to the kitchen window lintel, the first floor wall plate, and the bathroom joists

It sounds like the earth is probably what was causing your damp issue so hopefully removing that will solve your problem.

Black Jack won't stop water getting into the bricks as the water is being drawn up from the ground, so painting that on won't make a lot of difference to whether the bricks blow.
If you render the bricks, you need to make sure that the DPC isn't bridged, so leave a gap as suggested just below the bell bead and this could even filled with a compressible material.

 

[jeds]

Please be careful with re-rendering Claire. The mix needs to be a suitable lime mortar. Don't let a plasterer talk you into using cement.

Do you have good drainage around the base of the wall? i.e. a french drain or similar. If not I would consider that before you do anything else.

Personally I have no issue with adding a plinth render but I would use a specially formulated product rather than just a render mix. The purpose of the plinth is to protect the bricks from splash back so it does need to be a bit harder than the main render but should still be highly breathable. It is usually a very thin coat rather than built up layers.

There are several products on the market - Marmorit comes to mind.

 

[gregers]

how about also installing a bell drip at dpc height and then render almost up to the drip,leaving a gap so not to bridge the dpc,this is what we used to do when installing a chemical dpc and rerendering jobs.