Support under joists

[rick]

I have built 4 stone pillars (only 2 course each) on top of 18x18x4" concrete pads. The pillars are to provide support under joists on a decking area .....

Additional supports in readiness for HotTub going on the decking.

The joists are already in place ... so I can't remove, just need to 'fill the gap' to provide load bearing.

There is a gap of about 1.5"-2" between top of pillars and underside of joist ...... which I need to fill with a mix.

I had thought about Grano (3:1) but can't find it anywhere local to me.

So I could use builders sand (3:1) or go buy some sharp sand

or even some 10mm pea gravel and do a 1:2:3 stiff concrete mix

Thoughts ?

[Jim Stewart ...]

slate

[alan_m]

Use a cut down concrete paving slab? They come in various thicknesses.

Install a secondary wooden frame pillar to pillar to provide more than a point load support.

[Colin Bignell]

I would have though folding wedges would do the trick. That is folding wedges as in this definition, rather than some sort of sleep aid, which Google seems to throw up for the term:

[rick]

you mean cement & slate or just dry slate ?

[rick]

You mean put in a paving slab with mortar top & bottom ? ....... just pitting in dry would likely be not 100% supporting

To difficult to add any framing, no room to work

[Jim Stewart ...]

dry late...hammer it in tight

[Jim Stewart ...]

makes a good DPC as well

[rick]

In case description not clear this sketch may help (quick rough sketch

- no CAD masterpiece)

[Andrew]

There are some slabs (intended for council use) that are

2 inches thick. Or possibly some 40mm block paviours. Anything that is not compressible and fits snuggly.

[Andrew]

Or use a car jack to lift the joist slightly to avoid hammering it in

[John Rumm]

A strongish fine concrete. If you want do it all in one fill, then don't make the mix too wet. That should reduce the shrinkage.

The traditional way would be to fill close to depth, and then pack the last bit with slate (it slides in nicely, and is very strong in compression).

If you want a "dry" solution, the pairs of large folding wedges:

[Chris Hogg]

Jack up the decking *very slightly* at each pillar with a car jack and appropriate length of 2x4; slide into the gap bits of slab and/or slate until snug (they don't have to be neatly trimmed - any old bits will do); remove jack; repeat on next pillar. The weight of the hot tub will ensure the packing doesn't go anywhere.

[rick]

Thnx

[rick]

Fill close to joist, and push slate is after its set or while 'wet' (agree it would be a dry mix)

[Andy Burns]

No travis perkins? They sell grano as well as grano&dust

[rick]

Don't have any slate, years ago it was being ripped of roofs everywhere ..... will ask around

[John Rumm]

After it is set, that way you can get a good interference fit - plus you can "tune" the amount of packing to suit the gap and or the sag of the joist.

[Brian Gaff]

Yes because the joists will flex, and warp, anymix will sooner or later crack away. Then you get the bouncing back and a clunk when it hits the pillars. Brian

[Tricky Dicky]

You can get adjustable supports to help level decking. Wickes sell these but there are plenty of others available to suit all kinds of gaps

Richard