I have to tie together my existing garage foundation with the new foundation
of the garage extension. I have drilled holes in the concrete at the base of
the existing garage and can insert steel rods into these and the other end
of the rods will be embedded in the new foundation. The rods are a very snug
fit in the holes. Should I use anything in particular (besides cement) to
fix them in place in the holes?
I think the correct method of doing this type of thing, is to break some of
the existing concrete away to expose the reinforcing bars. Then you tie the
new rods to the existing rods to form one complete unit again. When the new
pour of concrete is done, it fills the space that has been broken away on
the existing footing, so forms a whole new section to the new section you're
Just sticking the rods in holes doesn't hold the new section firmly enough
once the weight of the new blockwork is complete. This can cause the whole
thing to separate at the joint. This is why the rods much actually be
Interesting point, though the structural engineer specified T20 500mm long
dowels - I won't be bending that anytime soon!
You're probably thinking of a solid slab but the existing foundation is a
strip foundation (and I doubt there is any reinforcing mesh - I certainly
can't find out - there's a wall on top!) and the new foundation is a
trench - far, far deeper and the new slab is far, far thicker..
I also have to insert dowels into the existing slab to tie the base
together. The structural engineer has shown similar use of dowels to tie
together garden wall sections across expansion joints.
Thanks for the suggestion though.
Although BW's method is probably best practice, I think yours is a good
second best, try polyester resin, used to make rock solid connection into
stone, concrete etc. For a good bond, make sure all the dust is blown out
of the holes - a bent flexible drinking straw is ideal:
That's 150ml cartridge, they have a 380ml one too but that uses a non
In a similar vein, what do builders do when filling trench foundations for a
house/large project when they can't pour the complete trench in one go?
Presumably they have to tie the separately poured sections together?
They'll just leave a section with reinforcement poking out and the next pour
will join in from there. There's not really a need to shutter the join as the
concrete will slump a little but not spread out to nothing, you should
shutter if you have steps though. Level founds make for a happy bricky so
it pays to tap in pegs every couple of metres to indicate the level required
for the pour. Have just used the spotmix type people on a job (the ones
who barrow to the hole) and although it costs more it is worth it for a
hassle free life.
The concrete people couldn't reach the far trench for my garage, so I built
a wooden slide (with sides) to carry the cement to the furthest trench. The
highest end of the slide resting on a workmate, the lowest end on some
bricks. Worked like a dream - 5m3 of cement poured in less than 40 minutes,
no wheelbarrows required!
Great, 5cubes is quite a lot so you'll have saved a bit over spotmix prices.
Glad the slide stayed together and in place :-)
ps: have you ventured over to uk.d-i-y , it has a bit more traffic/viewers than
here so useful for obscure questions although the noise level has been
creeping up quite a bit lately. Good luck with the build.
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