sm_jamieson
wibbled on Tuesday 20 April 2010 09:25

I have an existing floor slab (poured last year) and will be pouring a
new one to butt up against it. Do I need to join the new slab to the
old in any way? Yes I could have put rebar sticking out of the
original slab, but it was not really convenient at the time.
Cheers,
Simon.

I won't answer whether you *need* to (depends on the base).

If you do - this trick is fairly easy:

Drill into the side of the old slab at foot intervals and resin-mortar in
some heavy studs (M10-M12), say 4" into the old slab and 4" protruding.
That should provide a good mechanical lock.

I've seen this done on a much larger scale when they widened the M25 bridge
decks near Jnc 7-8 - bloody great big bars where set into the sides of the
original deck and then the new slabs were poured incorporating these bars.
Couldn't see the details of how they tied the rebars to the mortared in
bars as the shuttering was up at that point - I assume they were well tied.

What was interesting is how long the shuttering and scaffold frame stayed
up - many months IIRC.

Probably not necessary to be too fussy with a floor slab, but if the mesh in
the new section rests on these studs it should be a pretty strong bond and
will assure there's no way either slab will slip vertically relative to the
other.

Anyway, the method I mentioned up top is exactly what I did when I had to
backfill a new bit of concrete to repair excessive hackery to my concrete
strip house foundation and I wanted to be sure the new concrete would stay
attached to the existing strip.

--
Tim Watts

Managers, politicians and environmentalists: Nature's carbon buffer.