unsupported joists below extension

12 Feb 2014
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United Kingdom
Hello all,

We had an extension done last year and the builders weren't great. They temporarily supported the new floor joists with a bit of 4 x 2 to get their levels right and left it in when they finished.

I've just come to remove this today and it seems like it's been supporting the joists all along! No wonder the floors are creaking!

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I've been and got some slate for packing out the underside and have propped up each joist in the mean time.

What's the best way of packing out underneath? Slate slips and mortar? Just mortar? Anything else I would need to do other than temp support whilst it dries?

Is it usual practice to have that much mortar at the sides of the joists?

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No benefit with slate. Just poke the mortar in with a thin piece of timber or suchlike to ensure its full. Dry and strong means it wont shrink.
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Got half of the joists finished and am happy with the results. The other half of he joists extend though into to the downstairs toilet and have a breeze block wall at half span which the builders have used as a support albeit not very well.

Should I remove this mortar and replace it with a brick slip or a timber support or should I place more mortar around it to help things? Ive put noggins between the joists to stop movement and try and seal the toilet area.

The joists into the house are appalling. They've put some bits of rubble in and most of it has come loose whilst the other joist isn't vertical and has some slate wedged in.
Can I support the floor again and remove the rubble and slate or shall I just enforce with mortar again? will be tricky to get a dry mix however.

I can't straighten the joist as it's been glued and screwed to the floor above, it's annoying but there's not a lot I can do with it.



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If its a solid chunk of mortar it can be left and just fill in around it.
If its a bit crumbly, just push it out and re do it and make a better job of it. Is the joist likely to drop if you do that?

If you are going to push the mortar out and if you have a timber block tiles or slates or whatever to hand then that's probably a simpler option.

In fact, if you use a block of wood, and measure it right, you could potentially just place it against the mortar and hit it in and the mortar will come out the other side - no need for propping the joist.
Much appreciated, good solid advice as always woody.

I shall prop the joists temporarily until it's all set and good.

Sorted the joists and the bounciness has gone.

However I've now discovered this!

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The RSJ that supports the corner of the house from the first floor up has a smashed up rosemary tile and a bit of slate wedged underneath it and only a small section is actually doing anything!

There is a engineering brick pillar beneath the RSJ and one of the bricks isn't brilliant either. I don't know why they didn't order a slightly longer steel so that it could have been supported by the entire pillar!

Should I Acro the RSJ and remove the tile and slate or can I apply the same method as before with dry mix?

Thanks woody,

Shall I just leave the rosemary tile in situe then and fill the rest of the void with semi dry mix?

Just a little worried as this is considerably more load bearing than individual floor joists.

Woody, any chance you could confirm if I should leave the rosemary in place? Just worried about it turning to dust one day.


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