Gaps between joists and RSJ

[Kilt]

I have a RSJ supporting several joists that clearly suffered from bad deflection (bananas spring to mind). 
 

the worst joists are fully supported on the RSJ, but closer to wall plates there’s 1-7mm gaps between joist and rsj. Clearly these joists have less issues, so rsj isn’t needed. But to avoid any future deflection im thinking these gaps should be filled, whilst there’s access. 
 

If so…

whats best way to fill these gaps? Wooded wedges, glued and whacked in?

Kemfix Resin squeezed in?

[markc]

@Kilt any pics? I’m struggling to get my head around this

[Dave Jones]

do you mean the joists are into the web of the RSJ ? Whats above ?

[Kilt]

15 minutes ago, markc said:

@Kilt any pics? I’m struggling to get my head around this

Can’t really get any photos…

 

but Hope drawing makes more sense.
Rsj runs across centre of room with joists flying over. 

it’s clearly been installed after joists became bananas, hence the worst offending ones are resting on the beam. 

[markc]

Now I see, I would go with double wedges - one from inch side sliding on each other, this creates a parallel pack that does not push the joist over

just noticed it’s only 5mm at max. Plastic shims from screw fix etc.

Edited August 13, 2021 by markc

[Kilt]

6 minutes ago, markc said:

Now I see, I would go with double wedges - one from inch side sliding on each other, this creates a parallel pack that does not push the joist over

Thanks. Makes sense, I’ll give them a go. 

Access might be bit of a nightmare, which is why I thought something I could inject, fill gap, but sets rock hard. Hence thinking chemfix or some injectable mortar. 

[Dave Jones]

turn the ones on the left and right that are not sitting on the rsj upside down so they are. crown up if you like.

[markc]

23 minutes ago, Kilt said:

Thanks. Makes sense, I’ll give them a go. 

Access might be bit of a nightmare, which is why I thought something I could inject, fill gap, but sets rock hard. Hence thinking chemfix or some injectable mortar. 

There are “gun-able” expanding grout materials out there but you really need something to contain the spill until it starts to go off, very messy, quite expensive and a pain to get right.

if access is difficult and the floor is staying put then cut some long low and timber wedges and these can be knocked into place by sliding a hammer or flat bar across the top flange of the RSJ

Edited August 13, 2021 by markc

[James Newport]

Try https://www.epoxy-info.co.uk/resins_shop.htm

 

The mouldable epoxy putty can be pushed into the gaps. The thixatropic resin can be injected and has the consistency of vaseline so it doesn't run everywhere. If you try it, get the slow set stuff, otherwise you risk it setting in the tube. Both of these have excellent compressive strengths. 

 

The trouble is the 1-2mm gaps - neither is really suitable because the gap is so small. 

 

Any chance of bolting timbers to the RSJ and then packing up off that?

[Temp]

I think I would jack them up a few mm and insert one or two shims/plates cut from 1mm mild steel. Perhaps do the middle ones as well if they will move.

 

One way to lift them a bit would be to cut a length of say 4x4 that is a few mm longer than the distance from underside of joist to the floor. Perhaps put down some plywood to protect the floor first. Then hammer it upright like a pit prop.

Edited August 14, 2021 by Temp

[Kilt]

On 13/08/2021 at 15:49, markc said:

Now I see, I would go with double wedges - one from inch side sliding on each other, this creates a parallel pack that does not push the joist over

just noticed it’s only 5mm at max. Plastic shims from screw fix etc.

double slip wedges and some polyurethane glue has been working a treat. Thanks!

[Kilt]

On 13/08/2021 at 16:12, Dave Jones said:

turn the ones on the left and right that are not sitting on the rsj upside down so they are. crown up if you like.

thanks, but it's a retrofit, so there's floors, UFH and carpet on top of the sagging joists.

[Kilt]

On 13/08/2021 at 16:44, James Newport said:

Try https://www.epoxy-info.co.uk/resins_shop.htm

 

The mouldable epoxy putty can be pushed into the gaps. The thixatropic resin can be injected and has the consistency of vaseline so it doesn't run everywhere. If you try it, get the slow set stuff, otherwise you risk it setting in the tube. Both of these have excellent compressive strengths. 

 

The trouble is the 1-2mm gaps - neither is really suitable because the gap is so small. 

 

Any chance of bolting timbers to the RSJ and then packing up off that?

thanks for the Link, that's a goldmine of stuff!!

[Kilt]

On 14/08/2021 at 01:59, Temp said:

I think I would jack them up a few mm and insert one or two shims/plates cut from 1mm mild steel. Perhaps do the middle ones as well if they will move.

 

One way to lift them a bit would be to cut a length of say 4x4 that is a few mm longer than the distance from underside of joist to the floor. Perhaps put down some plywood to protect the floor first. Then hammer it upright like a pit prop.

Thanks, I might try this for the smaller gaps... but there's some weight on the joists (hence the bowing joists).