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PostPosted: Tue May 02, 2017 7:54 pm 
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Hi there,

I have just ripped out a 1st floor bathroom in our 1930s semi and found the floorboards and joists are rotten. The damage is directly underneath where the previous owners bath was.

Having done some reading it looks like I might need to replace the joist ends using joist end repair plates. Is there any way I can support the joist from above whilst I cut the bad end off, instead of using an Acrow Prop from underneath?

Alternatively could I just 'sister' new joists along side and leave the old ones?

Any help or suggestions would be much appreciated!


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PostPosted: Tue May 02, 2017 8:00 pm 
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I can't see how you are going to replace those without taking the ceiling down tbh.
It's lathe and plaster and they are attached to the rotten joists that need taking out.



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PostPosted: Tue May 02, 2017 8:08 pm 
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:withstupid: As Stevie says not much else you can realistically do here IMHO.



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PostPosted: Tue May 02, 2017 8:15 pm 
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You can't sister them since there is no support on the ends and the important part of the current joist is rotten. If you were able to remove and replace one at a time then eventually the ceiling would have no fixing to the joists. As other have said, you need to do it properly and take down the ceiling. If it is any consolation, at least you found the damage now while it is still safe (I hope), better than have it give way under a new bathroom a few years down the line.



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PostPosted: Tue May 02, 2017 10:40 pm 
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Might I ask why you don't wish to place acrows underneath?
It is possible to do it without removing the ceiling and I've done such a thing but really unless the ceiling is something special then it's a lot of work and hassle for no great benefit and to be honest it's still better to put some support underneath.
For what it's worth the way I've done it I never the past on heritage sites is to work on one joist at a time cutting away the rot and splicing in a new piece with steel plates on the sides. As others have pointed out removing the joist will also remove any support to the lathes meaning the plaster is in effect just floating. To provide new support wires were fixed to the joists and bent so they laid on the top surface of the exsisting plaster ( think a large flat u shape) , then a mix of plaster of Paris and hessian was put on to Bond the exsisting to the wires . As I say frankly a lot of work , a lot of time and unless the ceiling has some historical worth , which I would doubt in a bog standard '30's semi really not worth it.



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PostPosted: Wed May 03, 2017 7:37 am 
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Hi everyone, thanks for the quick replys.

The reason I was trying to avoid propping underneath is that there is a shower cubicle and a partition wall below. Although joist 5 looks the worst in the photos, Joist 4 is actually in worse shape (and it's thicker - more of a supporting roll?). I was worried I wouldn't be able to get a prop underneath far enough from the wall.

How much rotten wood do I need to remove? Also joists 2 and 3 are a bit crunch too, I don't think I can get to 2.


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PostPosted: Wed May 03, 2017 7:53 am 
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As I said it's possible to remove the joists without removing the ceiling but as has been said by Steve you lose the fixing between the two which unfortunately means it really still needs supporting during the operation. I find it common for the snots ( where the plaster has squeezed through the lathes) also tend to break off during work too which only makes the integrity worse. Couple that with at that age it's more than likely lime sand plaster which has little structural strength and it becomes increasingly likely that an unsupported span would fall anyway.


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PostPosted: Wed May 03, 2017 9:44 am 
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You have to bite the bullet and take out that ceiling. Okay it will be an awful mess but if you prepare for it you can get it done and out in a morning. Buy a load of plastic sheets and cover everything. Put some ply or chipboard over the sink, loo and shower cubicle. Get one of those all on one forensic overall suits, a decent mask, eye mask and gloves. Work from above and smash it downwards, at least you have that advantage. Have a garden sprayer handy to spray the dust down. Shovel all the spoil up into rubble sack and get it cleared. That is the hard part done, the rest will be so much easier with a clear working space top and bottom.

Good luck with it :thumbright:

DWD



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PostPosted: Wed May 03, 2017 7:44 pm 
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Thanks again for your continuing help guys. Ok, so I'll take the ceiling down, I can hire Acrow Props from Jewsons. In terms of the splicing is it best to remove about 500mm of the joist and replace, and use splice plates-

https://www.amazon.co.uk/Splice-Plates-Joist-Connecting-Repair/dp/B0078LRPKW/ref=pd_sbs_60_4?_encoding=UTF8&psc=1&refRID=7WAGQCXFAZ1FNZ9F1NBM

or

Use these end plates which sit into the wall pockets?-

https://www.amazon.co.uk/d/Nails-Screws-Fasteners/Joist-Repair-Plates-1000mm-Fixings-DELIVERY-MAINLAND/B0078L5XV0/ref=pd_sbs_60_4?_encoding=UTF8&psc=1&refRID=PHA7BW0H2K1SJ38ZMM2S

or

Can I just run another length of joist along side the old joist and new end and coach bolt them together?


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PostPosted: Wed May 03, 2017 8:17 pm 
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You could save yourself quite a few bob by doing the job traditionally rather than using end plates.
By traditionally, I mean to cut out the rotten joist end and splice in a new section of joist (length of cut out piece + 60cm)
& bolted to the original using corrugated timber connectors & 12.5mm threaded rod/nuts & washers (4 No bolted connections per splice)
You would prop the existing joists from below and probably work on them one at a time.
It would also involve chopping out the joist holes in the brickwork to accommodate the offset joist ends + making good the brickwork after.
You might also consider wrapping the joist ends in dpc & nailed on (just the section in the wall) before fitting.

Cheers.


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PostPosted: Wed May 03, 2017 10:27 pm 
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you can cut an bolt-on the joists tails like davy1 says. you coulduse a tempory binder roughly supporting across the tops like the copper pipes at right angles. the binder could pull the joists level no acrows needed
cutting out the rotted wood in short sectionsyou could pare down to the plaserlaths and lift the last bits and snip the fixing nails

cut and bolt-on one joist at a time and cap the ends in dpc wrap



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PostPosted: Thu May 04, 2017 7:27 am 
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Thanks for the suggestions. So instead of using metal plates I can bolt on new timber like this.. With two different options for support?


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PostPosted: Thu May 04, 2017 9:24 am 
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CoxHQ wrote:
Thanks for the suggestions. So instead of using metal plates I can bolt on new timber like this.. With two different options for support?



First I would like to say that I agree with Stevie in that I personally would take down the ceiling.
I would also prop from below.
I would probably work on two joists at a time, completing those before going on to the next two.


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PostPosted: Thu May 04, 2017 9:49 am 
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Thanks Davyp1,

I'm going to bite the bullet and take down the ceiling and prop from below as you all recommend, although I will still only be able to support joist number 2 from above. Thank you for your sketch, is there any disadvantage to bolting on another piece of timber inline with the cut joist (as in my diagram) in order to use the same hole in the brick?


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PostPosted: Thu May 04, 2017 10:14 am 
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CoxHQ wrote:
Thanks Davyp1,

I'm going to bite the bullet and take down the ceiling and prop from below as you all recommend, although I will still only be able to support joist number 2 from above. Thank you for your sketch, is there any disadvantage to bolting on another piece of timber inline with the cut joist (as in my diagram) in order to use the same hole in the brick?


You don't need an acrow for each joist (as in your diagram) - two acrows with a scaffold board on top will allow you to support all the joists from below, (there's no need to put the acrows at the very ends of the scaffold board).

If you're bolting new sections to old joists allow for a 1200mm overlap.

If this will be used as a bathroom again the joists should be doubled up.

_________________
One day it will all be firewood.



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