Retaining wall mortar mix

[cmulley]

I am currently building a block retaining wall around 700mm high so that I can level my sloping lawn. I have set the footing and am now looking to start on the first course which will be using 7.3N 100mm concrete blocks laid flat. I need some advice on the best mortar mix to use and and some research has led me to a 3:1 mix of builders sand to cement with a plasticizer. Is this an ideal ratio and would the mix differ below ground to above?

I'm also planning to install a DPC and add weep holes every 500mm. Should the DPC be placed on the first course of bricks above ground and is it better to have the Weep holes above or below this?


Thanks in advance!

Chris

 

[Mike13]

3:1 is likely to be stronger than the concrete blocks, should also be quite waterproof. for an external wall where there is soil behind it, think long and hard about where the damp proof course should be, my 1.2m retaining wall has no damp-proof course, as they are usually polythene and could let the wall slip sideways.

 

[robinbanks]

Don't install a DPC

 

[matlob]

You also could do with some drainage behind the wall. Water in the grass/soil needs somewhere to go, either around the wall or through it

 

[cmulley]

Thanks for the suggestions guys and crisis averted with the dpc. My plan was also to apply 3 good coats of liquid dpm to the soil side of the wall, weep holes every 500mm, a perforated drain pipe behind for drainage, backfilled with gravel and filter fabric over the retained soil and around the pipe.

I'm going to render so was hoping the dpc would add some further protection to the wall finish. Is there anything else I could do to aid this? Options I have researched are a bellcast bead at the base of the render, a row of engineering bricks, as well as various waterproofing plasticisers that can be added to both the mortar and/or render. Have also read mixed things about waterproof paints because they do not allow the render to breathe. What would you recommend? I'd rather go belts and braces and do anything that helps the longevity of the wall where it's effective!

 

[Mike13]

gravel mixed with soil just behind the wall, the only sensible place for a dpc is above the highest soil line, and then it spoils the look of the wall. drain holes near the base are good, it would be a very clay soil to need every 500 mm. I have a sandy soil, and have never seen the drain holes release any water in quite a few years now.

 

[robinbanks]

Didn't get the soil mix thing, surely you mean drainage stone wrapped in teram, DPM against the wall, weep holes at the bottom, no DPC

 

[Mike13]

well where I live it is quite a free draining soil anyway, adding gravel in the 6" gap between wall and earth made sure it stayed that way.
Agreed DPC is absolutely not required for an external wall.

 

[Dereekoo]

Agreed DPC is absolutely not required for an external wall.

Unless you don't want ground water to work is way up the wall through capillary action and assist in blowing off you rendering over time, but as the wall will be attacked by the damp soil it's retaining I guess it's a mute point.

 

[lostinthelight]

Personall I wouldnt render it but instead would run wire supports along it and plant climbers to cover with vegetation to disguise and provide habitat for wildlife

 

[Mike13]

Unless you don't want ground water to work is way up the wall through capillary action and assist in blowing off you rendering over time, but as the wall will be attacked by the damp soil it's retaining I guess it's a mute point.