Expert: Bill-C - 7/5/2011

Question
QUESTION: Hi Bill,

 As part of a landscape project i've taken on I'm going to be building a freestanding, straight run, full brick garden wall (using standard 215x65 scotch commons)
This wall will be 5.6m long and 1.6m high. It will be sealed and then painted white upon completion. using internet advice and calculators i've worked out the following:
5850x450x80mm hardcore sub-base
5815x415x150mm footing set 150mm below ground level with DPC 150mm above GL.

My dilemma is knowing which mortar to use, as ideally a lime mortar would be preferable for environmental benifits and experiences sake.

If  want to finish the wall in paint within a month of building it, would it be possible to use lime mortar and if so which type of lime is required and to what mix?

Could you also advise as to whether the footing is sufficient as i cant be sure from my own calculations.

regards,
      Robin.

ANSWER: Robin,

To fully answer your question I would need more information from you and therefore only answer based on the information you have given.

I presume the wall is 215mm thick if not you will require  intermediate brick piers to strengthen it.

Foundations should as a rule be 450mm to the top of the foundation , below adjacent ground level for frost protection which is a must in Scotland.
For a wall this height (215mm thick ) you should allow a minimum scarcement on the foundation of 150mm outwith the wall line. ie 5.6 + 150+150 = 5.9 long minimum. width 215 =150=150= 515 min
Normally this would be excavated to 600 deep and concrete poured to the excavation not on hardcore .It would also benefit from a single layer of reinforcement mesh A242 anti crack fabric laid with 40mm bottom cover.
You don't mention if this is retaining any ground or higher levels of earth adjacent to it .If it is then let me know.As the above will differ.
I would use class B engineering brick up to ground level then change to common brick. You also dont mention how this is being capped on top? Do not use a dpc at ground level on a garden wall it should be laid beneath the capping / cope or whatever your finishing it with. DPC'S used in garden walls always fail at ground level and create a slip plane for the wall to topple or move.
Always lay your dpc in a thin layer of mortar never lay it directly on dry.
As for mortar use a sand and cement mortar of 4-1 unless your doing historical work and insistant on lime then it would be a 6-1 5-1 lime but i wouldnt recommend it in Scotland .
Alternatively  use Hydraulic lime premixed 3.5 OR 5 for exposed areas
Contact me if you require clarification
regards
bill  

---------- FOLLOW-UP ----------

QUESTION: Hi Bill,

 Sorry, just as a quick followup Ive contacted my local builders merchants and they are not aware of an A242 fabric mesh. They did however tell me of an A252 reinforcement mesh, that 8mm bar at 200mm squares this comes in 3.6 x 2m sheets. Will this be sufficient instead of A242?

many thanks,
         Robin.

Answer
Robin,

Use the A252 MESH with 40mm spacers in the excavated trench supporting the mesh.
A242 may be rare now as it is 6mm and not readily stocked.
The use of a DPC at ground level can be omitted if you use the engineering brick up to 150 above ground level and fully grouted frogs in the brick.
I WOULD NOT RECOMMEND A DPC in a garden wall at ground level as it creates a slip plane for the wall to move.This is created by expansion and contraction and enevatibly will cause the wall to fail .
By all means use it if you are concerned  .

regards
Bill