Acro’s on a scree

[Kilt]

Having an RSJ installed, SE’s been in and specified beam etc. 
 

however no one (SE or builder) seems to have taken into account the acro’s are going to have to sit on a ~70mm scree, UFH/70mm PIR floor. 
There’s currently around 30mm deflection (in joists above) to make up with the RSJ, with two bathrooms above. Quite a load to jack up. 
 

Anyone done this before.. cause for concern, or with decent prep no issue?

I cant see how else you could do it. 

 

[PeterW]

Acro’s are Acro Props, not Acro lifts - they are not designed to be used to lift loads.  How have you ended up with 30mm deflection as that will have left some pretty substantial gaps above if that is the case ..??

 

If you have to lift then it is much better to use a 10 or 20 tonne bottle jack on a platform to provide the lifting, and then support with an Acro as you go, working along each joist lifting no more than 5-10mm at a time. 

[ProDave]

Re the screed issue.  Long planks or large square blocks under each jack to spread the load.

[Danny68]

Plus worth clamping a piece of say 30mm ply on the underside of the beam once its in place above where you are going to put your acros, then coach screw the acros top to ply wood .Then when you jack up the joist the acro doesn't fall and crack someone on the head who's not paying attention . Plus it stops the across spinning metal on metal 

Edited March 28, 2021 by Danny68

[Kilt]

1 hour ago, PeterW said:

How have you ended up with 30mm deflection as that will have left some pretty substantial gaps above if that is the case ..?? 

Really long story, partly covered in other topics... but nutshell: original builder overloading spec’d joists, by installing wet UFH in a biscuit mix upstairs. 

They tried to fix issue with sistering, but did a bad/incomplete job due to 1st fix already occurring and didn’t want to re-do all services including 90% of house wiring. 
No chance of installing additional a joists as per above, so underslung rsj going in, to take out some of sag and stop further issues/dynamic deflection. 

No gaps upstairs, so either upstairs was built over the deflection, or the whole house has sagged over time or it’s been previously repaired, prior to our purchase. SE said it’ll be ok to prop joists and have rsj take out some of deflection, but obviously not the whole 30mm. 
 

I’m not doing this work myself, but want to ensure nothing’s been overlooked. Still waiting on builder to come and measure steel, so haven’t had full chance to iron out all the details. 

[PeterW]

Ok so you may want to pocket the RSJ into the wall and give yourself enough room to put a Jack under the end of the RSJ in the wall. Then insert it, Acros on boards under the beam and hold it tight and then it’s slow lift to raise the sag out of the joists using the RSJ, tightening the Acro’s as you go. Keep swapping ends, when it’s up as far as you dare then you set the padstones in and wedge with slate. Leave the Acro’s in for 48 hours til the mortar goes off.