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RE: Welding against concrete

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Even the best of welders will tend to go through on a B-P1c weld.  You would
have less tendency for damage with a full pen P-L1a and a backer bar.  The
problem is that a B-P1c weld will require an 1/8" root opening.  The
tolerance on the concrete surface will almost assure you of having concrete
in direct contact with the weld metal in certain locations, and the concrete
will be damaged.  You might also want to consider a BTC-P4 which allows a 0
root opening, but requires a groove.  The BTC-P4 will also decrease the burn
through tendency but give you the same effective throat as the B-P1-c weld.
You will use less weld metal on the BTC-P4 but probably not enough to offset
the groove prep cost.

The damaged concrete will be highly localized and not very deep depending on
the actual process used.  If you have allot of weld like this, the iron
workers will set up an automatic or semi-automatic wire fed welder which
will minimize heat input, and decrease the burn through tendency.

I would revisit the choice of the B-P1c weld.  Once you've made the weld
choice, go to a local steel fab shop and weld up a couple of pieces of 1/4"
plate on the slab on grade, and check the concrete for damage (borrow a
chipping hammer).  A shop experiment will be telling, because the iron
workers in the field will be better.  The field will also be using a fast
freeze electrode.  The shop will be using a mud rod (fast flow) that is
hotter and will have more of a tendency for burn through.  

Shop experiments are fun.  It gets you out of the office for about an hour.
You get your hands dirty.  You can make sparks.  ....I'm starting to tear

Harold Sprague

> -----Original Message-----
> From:	Polhemus, Bill [SMTP:wlpolhemus(--nospam--at)]
> Sent:	Wednesday, February 09, 2000 1:16 PM
> To:	'seaint(--nospam--at)'
> Subject:	RE: Welding against concrete
> To clarify:
> I'm not talking about an EMBEDDED steel plate, but about butt-welding TWO
> 1/4" plates together, where if you look through the joint before welding,
> you can see the concrete underneath. I'm worried that, even with partial
> pen
> welds where theoretically the weld metal won't quite contact the concrete
> surface--though it would stop short a mere couple of sixteenths away--the
> radiant heat might damage the concrete in some way.
> -----Original Message-----
> From: Sprague, Harold O. [mailto:SpragueHO(--nospam--at)]
> Sent: Wednesday, February 09, 2000 12:57 PM
> To: seaint(--nospam--at)
> Subject: RE: Welding against concrete
> Bill, 
> It is a common detail.  I have not seen any failures in the field due to
> the
> local high heat on an embedded steel weld plate.