Packing a Steel on padstone

paulandfrodo · 10 Nov 2010

Am I correct in thinking that when placing a structural steel on a padstone, if the level of the steel is not correct (sometimes putting padstones in is awkward) and you need to raise the height (to make steel level) you should use metal shims and NOT mortar and a brick packer. This I base on the fact it's essentially like sitting the steel on bricks in the first place.

The possible effect is the steel could crush the much weaker brick packer.

Equally, I presume it's possible (based on a structural engineer's calc's) to use a steel padstone and put the steel (RSJ) on top of this. However, if you need to level the steel RSJ then you should not use mortar.

Pref. steel shims, perhaps a slither of padstone cut or slate. But not mortar and bricks....

Comments appreciated.

geraint · 10 Nov 2010

if it can crush the mortar.. i would be worried,,,, what is the padstone bedded on.....

Hitachimad · 10 Nov 2010

But the padstone is usually much stronger than mortar, and spreading over 4/5 time or more area than a steel bearing.

Ive only ever fitted with steel shims.

As for steel padstones, its quite popular to have a 300x100 flat (or bigger- depending on size of beam) to rest on, rather than padstones.

^woody^ · 10 Nov 2010

Why arn't the padstones put in at the correct level?

If you need a brick packer or slither of padstone, then you need a new level and tape

Yes you can bed the steel up, if you are confident that you are putting in a full bed of whatever - steel shims maybe just concentrating the load at a few points. A neat cement grout will do for thin beds or a strong mortar for a bit thicker beds

"Steel padstones" are called bearing plates

Here is a tip ... put the steel in first and then the padstone afterwards

Ossy · 10 Nov 2010

Maybe you're thinking of scaling common commercial building practice down to residential. It's the norm to position columns in a steel framed building on steel shims, then fill the gap beneath the baseplate with a free flowing grout. If it's a big baseplate you also need vent holes drilled in the plate to make sure you get full coverage of grout. The grout used is always equal to the cube strength of the concrete pad the column is sat on, so no 'weak link'.

For a residential job though, as has been asked before, is it really that hard to get the padstones at the right level?

paulandfrodo · 11 Nov 2010

Sorry just to make things clear. When I say "level" I mean on a vertical plane. i.e. the padstone is a little low. Thus it is needed to raise the steel a little to get it to the correct position.

geraint, I do see what your saying, but it's really down to the mix of the mortar... we've all seen "weak" mixes of mortar...

the point of a pre-stressed padstone is that is it's of a certain quality.

the padstones are sitting on 4" of a 9" party wall.

Thank's woody for letting me know steel padstones are called bearing plates - I'm happy as I've learned something - always a good thing !

Ossy, thanks.

Ossy/Woody, this is not my work I am querying. The first time I put padstones in (12 in all) I was no more than 2 mm out on ANY of my padstones, the steel supplier offered me a job on the spot !! I'm keeping an eye on a friends build for him... I'm just giving him my views on what I am seeing. I just wanted other peoples views on basically what I view as a **** poor job - oops... did I say that

RonnyRaygun · 11 Nov 2010

paulandfrodo said:
Am I correct in thinking that when placing a structural steel on a padstone, if the level of the steel is not correct (sometimes putting padstones in is awkward) and you need to raise the height (to make steel level) you should use metal shims and NOT mortar and a brick packer. This I base on the fact it's essentially like sitting the steel on bricks in the first place.

Can't see a problem with using steel shims as long as they are large enough. As Woody said, they will concentrate the load, but unless the beam is very heavily loaded and the shims very small, it's unlikely the bearing strength of the padstone will be exceeded.
Brick packers aren't a good idea as even though the brick itself may be strong enough, it's unlikely they will be cut tidily enough to get an even distribution of load into the brick.
I would use a strong mortar mix such as M12 (1:3) which should have a compressive strength of 12N/mm^2, and should be plenty strong enough for any domestic load. Mix Semi-dry to prevent shrinkage.

paulandfrodo said:
Equally, I presume it's possible (based on a structural engineer's calc's) to use a steel padstone and put the steel (RSJ) on top of this.

Yeah, bearing plates work in exactly the same way as a concrete padstones but have to be designed to deflect as little as possible otherwise the loads are concentrated in the centre.

paulandfrodo · 11 Nov 2010

Thanks ronny, the mix colour looks like it's prob. strong - but I only took a quick glance. But you can kinda tell pretty quick how much cement has been used. To be honest, the loading is not too great and as such should be fine. I'm just playing devils advocate in understanding what "should be" done. And so far, most people have confirmed what "should be" done and what you can "get away with"...

Mucho thanks... I'm off out into a very rainy day - full wet's on !

Hitachimad · 12 Nov 2010

We normaly use steel shims in 100mm squares for packing. Its instant as soon as the steel is placed ontop of the shims. Put whatever load you want on the steel straight away.

noseall · 13 Nov 2010

We use cement slates.

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Packing a Steel on padstone

geraint

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