damp internal walls - possible solutions?

I guess - without seeing some photos - IMO feels like 3 possibilities:
a) The damp is an internal wall problem only, stuff bridging the dampcourse under the floor, in which case clearing out the underfloor may fix the problem;
b) DPC failure somewhere, either inside or out
c) Bridging of the external DPC, though digging 60 cm (must have been painful) should have resolved that.

Maybe a couple of photos, any solution will only fix the problem to which it was addressed.

Gents, what kind of DPC was used in the 40's, and could it be prone to failure?

Compleat Amateu is on the money in with the possible causes, good chance a 1940s house had a bitumen damp course. Look around, you should find a course of bricks with a black rubbery compound. I went through the same problem with my 1920s place. There are plenty of rising damp tradesmen around which should be able to come out and offer solutions and go over all your walls with a moisture meter to determine where the dampness is and how high up the wall is. The proper way to fix the problem is to fix the damp course issue, in my case the bitumen damp course has failed, there are 2 popular methods to fix which involves removing all the render (if rendered) 400mm above the highest water mark on the affected wall and apply either method:

1) Chemical injection - On your damp course level, 2 x 100mm holes are drilled into the brick work and chemicals are pumped into the brickwork under pressure to create a chemical damp course. Completed by a tradesman
2) Cream Solution - The solution I went with (DIY), every 110mm in the mortar a 10mm hole is drilled on your damp course level. Push in a cream solution (Dryzone HEAD OFFICE - Rising Salt Damp Treatment | mould prevention | water proofing | what is damp proofing | damp in walls | water damage | damp proofing | mould cure | damp walls), the cream will spread through the mortar to create a damp course barrier.

Have the render re-applied using a salt retarder additive, Allow at least 3 months for the brickwork to dry out before painting.

Originally Posted by barney118

You mentioned digging down 60cm is there backfill up against these walls? That's a fair way.

Whoops, that was a typo... It should have read 20cm.
The dirt in the ground is fairly sandy

Originally Posted by Craigoss

Compleat Amateu is on the money in with the possible causes, good chance a 1940s house had a bitumen damp course. Look around, you should find a course of bricks with a black rubbery compound. I went through the same problem with my 1920s place. There are plenty of rising damp tradesmen around which should be able to come out and offer solutions and go over all your walls with a moisture meter to determine where the dampness is and how high up the wall is. The proper way to fix the problem is to fix the damp course issue, in my case the bitumen damp course has failed, there are 2 popular methods to fix which involves removing all the render (if rendered) 400mm above the highest water mark on the affected wall and apply either method:

1) Chemical injection - On your damp course level, 2 x 100mm holes are drilled into the brick work and chemicals are pumped into the brickwork under pressure to create a chemical damp course. Completed by a tradesman
2) Cream Solution - The solution I went with (DIY), every 110mm in the mortar a 10mm hole is drilled on your damp course level. Push in a cream solution (Dryzone HEAD OFFICE - Rising Salt Damp Treatment | mould prevention | water proofing | what is damp proofing | damp in walls | water damage | damp proofing | mould cure | damp walls), the cream will spread through the mortar to create a damp course barrier.

Have the render re-applied using a salt retarder additive, Allow at least 3 months for the brickwork to dry out before painting.

Thanks, that's really helpful. I will check both of these options out. No sign of any damp proof course, bitumen or otherwise.
Can anyone recommend any good rising damp tradesmen in bayside Melbourne area?

Thanks again