Fix joist hangers into thermalite wall

[Draughtsman]

I'm assuming the blockwork should come up to the right height, sit these on the blocks, mortar over, and continue laying blocks...

This hasn't happened, and the top of block levels are now wrong for this anyway so I have to cut them into the thermalites somehow, without being too brutal (petrol stihl diamond disc, perhaps not). I was thinking of slicing slots in the thermalites with a 6mm masonry drill (not on hammer), blowing them out and setting the hangers in with a vinylester mortar (fischer)?

What do you think?

 

[jj4091]

If you are cutting slots then why would you need hangers, perhaps this will help http://www.johnnichollstrade.co.uk/assets/Hanson_Thermalite_Technical_Manual_2012.pdf

 

[Draughtsman]

I could have been clearer.

The slots would be narrow and horizontal, to take only the very top spades/flanges part of the hanger (in image) that would normally rest on top of a block.

I thought, cut some horiz, slots to a level, almost fill with vinylester mortar from a gun, push the hangers in, allow to set, carry on with floor.

This is a retro fit, the Thermalite inner skin is already there without gaps between the blocks to take joists. I thought that the vinyl mortar would allow some useful tolerance, be a good fix and provide a level bearing for a hanger.

Thank you,

Dain

 

[foxhole]

Thermolite will cut with a handsaw, hangers directly into it will not hold, you need a timber bolted to the thermolite and then hangers off the timber.With my build we ran threaded rod thru the blocks and washer and nut to both sides , even huge bolts don't hold well in thermalite, we tried some and could easily dislodge them.

 

[jj4091]

I agree with Foxhole but I would add Gripfix to the back of the timber as well as fixing with bolts or screws.

 

[foxhole]

I agree with Foxhole but I would add Gripfix to the back of the timber as well as fixing with bolts or screws.

Gripfix needs dust free background, hardly a description of thermolite blocks.

 

[Draughtsman]

I'm not thinking of using Gripfix, this Fischer mortar has a separate hardener and, I think, is much more robust.

I realise that you can cut thermalite with a saw, but I have no exposed edge to start cutting into.

A drill can be set to the right depth and be accurate enough (not on hammer action) given that I'll be cutting in an oversize slot. I'll just push it in an inch and then start working it sideways to cut a slot in the soft thermalite.

Apart from providing the fix; the resin mortar is to provide a more robust bearing surface than the block itself provides (those flanges go 3" into the block) and level out the bearing surface/evenly spread the load.

 

[Draughtsman]

I wouldn't put conc screws in, thermalites are far too soft.

Coarse thread drywall screws can be good in thermalite for light stuff like cavity closers but still not up to this.

 

[Doggit]

As Dain suggests, using a 2 part resin (after blowng out the dust and applying brick stabiliser) will bed the hangers in to the blocks in the same way that resting them on the top of the blocks would have (as show in page 75 of the brochure) so no bolts are needed, but he needs to find a way of getting as straight a line as possible. I'd use an angle grinder on top of a piece of wood to give you 2 straight cuts half an inch apart, and then maybe use a mortar rake to cut a deeper slot to work with.

 

[Draughtsman]

if Brick stabiliser used on a thermalite, I must look into that. I wasn't aware of brick stabiliser.

A mortar rake sounds a bit brutal on thermalite, the hangers aren't going in at an existing mortar course level.

Maybe using the disc to do just the centre of the slot (discs take out quite a lot more material at each end of each groove that they cut) and then carefully using the side of a drill bit to gradually carve out/finish the ends & depth of the groove, so the length of the groove would then not be much more than the width of the hanger.

I was thinking that an accurate line of flat bearing surfaces at exactly the right level might not be absolutely necessary because the 2 part will be providing take up/tolerance with the hangers inserted centrally into oversize horiz. slots (the hangers not actually sat on thermalite). The hangers will all go in at the same height tho, obvs.
I haven't checked what a min. required bed of 2 part underneath the hanger might be yet, any rough ideas (a half inch slot with hanger inserted approx. central would give 5mm)?

The cutting to a line provided by a piece of wood method sounds a lot quicker.

 

[Doggit]

A mortar rake fitted to an angle grinder will cut through the themalite dead easy, won't cause any vibration, but will need to be handled steadily, otherwise it'll wander everywhere. But it will be a lot more controlable than trying to use a drill. It might be worthwhile fitting a piece of wood underneath the hangers, and that would support them whilst the resin goes off.

 

[Draughtsman]

I have seen the rake thing on screwfix but forgot about it, carving it out with a drill bit may be only a little slower but give a more control.

It would be a blow if the hanger wandered before the resin set, I may put up a batten and sit them on it.

a weak pva mix might do the job of a stabiliser.

 

[Draughtsman]

Hangers are in, I used the masonry drill bit to carefully slice out the slots in the thermalites (plus an old 10mm wood chisel to rake out the centre of the slots). I had to take care to stop the slots from getting too big.

After the slots were marked out and cut I propped a joist up there to sit the hangers on so that I could get the 2 part gunned in, insert a hanger and move on to the next one before the mix in the nozzle cured. 10 joist hangers - 4 tubes of resin mortar, not cheap but very easy and it seems to be effective.

Thanks for any contributions guys.

 

[foxhole]

Have you offered in the timbers and knocked any nails in yet?

 

[Draughtsman]

The joists are sat in the hangers, I just used one screw to secure each joist down in each hanger before fixing noggins between the joists.

Why do you ask?