DPM question

[RacingStripes]

Quick question if anyone done it before.
Im extending my garage and about to pour the new slab (well, when it warms up). Ive cut back the end of the old slab off as it sloped down at the old entrance and im sticking some 12mm rebar into the old slab to tie it to the new one.
What the best thing to do with the new DPM, have it coming part way up the old slab (at the minute theres loads of excess) or tuck it under the old slab?

Also, as I cut the old slab with a saw it has a completely smooth side, is it worth giving the side a "key" or am I overthinking that?

Wish it would be warm and dry up so I can actually pour it and get the door fitted.

[Chumley.mouse]

Tuck it under the old one and maybe tape it . Definitely try and rough it up to help key in, although it will still probably crack along the joint.

[paulwirral]

Drill a few holes at 45 degrees in the existing concrete face and hammer some re bar in , if you can form a semi circle hoop all the better, to tie it together , it’s not perfect but probably as good as you can do , it’s what I’ve always done when joining on to existing.

[RacingStripes]

Chumley.mouse said:

Tuck it under the old one and maybe tape it . Definitely try and rough it up to help key in, although it will still probably crack along the joint.

The old DPM sticks out by about 6" as thats what ive cut back so ill go for tucking it between that DPM and the slab.

Ive cut 6 lengths of rebar about 500mm and put them 200mm into the old slab. If it cracks it'll be under rubber tiles so I shouldn't notice, I just didnt want it to drop so there was a step appearing.

Its going from a 6m x 6m garage to a 9m x 6m. Ill finally have plenty of room to work on the car!