Joist Levelling

[cm1375]

Hello, I need to level the joists.

The joists are about 2-3 mm out in places. I would like to level the joists using flexible tile adhesive to the highest point by ruling off using a long feather edge to reference points set in place.
The tops of the joists having been pre-cleaned and primed with bonding agent.

With the joists all level I would screw down 18mm ply over the leveled joists and then 12mm Hardiboard. The idea being that with the tops of all the joists level, the ply could be screwed down flat. A little adhesive to the back of the Hardiboard and it too could be screwed down flat to the ply. Which should result in a stable subfloor.

Then some levelling compound, adhesive and tile to hopefully exactly match the rest of adjacent floor.

For your info the 7" x 2 1/2" joists spans only 1.5 over the sleeper walls on 13 1/2" centers for the kitchen area in question.

I would prefer to use flexible tile adhesive to get a perfectly flat level on top of the joists rather than
faffing with cutting thin shims all over the place, which will go out of true after screwing down. Can anybody
see any problem with the leveling adhesive at the top of the joists, moving or degrading over the years, resulting
in gaps under the ply over the long haul?

Thanks in advance.

 

[Rae]

2 or 3 mm normal mate thats ok

 

[angrypirate]

I would use a polyurethane wood glue under the ply on the joists, this will expand to fill the gaps, I reckon tile adhesive would probably crumble over time.

Any deviation in the level once the ply has been laid could be lost in the backer board overlay either hardie or foam type..

 

[Dave]

Just board the floor and self level it. Don’t over complicate things.

 

[cm1375]

Thanks Rae, angrypirate and Dave. Agree with all.

Would always worry about the crumbling.

I do figure the flatter the stronger/stable the base. But am prone to over worrying.

Was not sure the polyurethane had enough compressive resilience, its a bit bubbly and squishy for quite some time but after a day or so it feels much tougher. Goes off a bit quick though, but should just about have enough time to quirt it along the joists in place beneath each of the two pieces of the 18mm.

Will create a few reference high points with the water level and adhesive. Next day when adhesive hard, will squirt between high points with polyurethane along joists, and roll out and screw down ply only at high points where adhesive will resist compression. The 18mm ply should resist the expansion of the polyurethane which will hopefully just fill the voids.

24hours later screw down between reference points.

Wish there was slow expansion polyurethane as opposed to the extra fast 1m stuff.

Best laid plans. Will all probably go belly up and end up in sticky mess. And realize that as all have said, I have overcomplicated things. And I made things worse. But more lessons learnt.

Thanks all again.

 

[angrypirate]

I normally use the 30 min stuff, and that's only really to stop any squeaking that may occur in the future. As Dave said don't over complicate it, its only 2-3mm, your going to be using SLC anyway.

 

[pink]

Hello, I need to level the joists.

The joists are about 2-3 mm out in places. I would like to level the joists using flexible tile adhesive to the highest point by ruling off using a long feather edge to reference points set in place.
The tops of the joists having been pre-cleaned and primed with bonding agent.

With the joists all level I would screw down 18mm ply over the leveled joists and then 12mm Hardiboard. The idea being that with the tops of all the joists level, the ply could be screwed down flat. A little adhesive to the back of the Hardiboard and it too could be screwed down flat to the ply. Which should result in a stable subfloor.

Then some levelling compound, adhesive and tile to hopefully exactly match the rest of adjacent floor.

For your info the 7" x 2 1/2" joists spans only 1.5 over the sleeper walls on 13 1/2" centers for the kitchen area in question.

I would prefer to use flexible tile adhesive to get a perfectly flat level on top of the joists rather than
faffing with cutting thin shims all over the place, which will go out of true after screwing down. Can anybody
see any problem with the leveling adhesive at the top of the joists, moving or degrading over the years, resulting
in gaps under the ply over the long haul?

Thanks in advance.

just self level afterwards its very strong any one with fibres

 

[cm1375]

just self level afterwards its very strong any one with fibres

Hi pink never used fibres. Have already bought the SLC with hired van. Found some 20mm fibre additives for screed which might do in SLC. So may well put some in, some mention on google about stiffening the mix which might worry though. Thanks

 

[cm1375]

I normally use the 30 min stuff, and that's only really to stop any squeaking that may occur in the future. As Dave said don't over complicate it, its only 2-3mm, your going to be using SLC anyway.

Hi angrypirate, yes just checked again, mine is Gator Wood Glue, its polyurethane 30 minute stuff, its looks fairly runny out of a bottle so should be ok. The other stuff I have been using till now has been out of a tube which has been going off a little quicker I think. Will pre trial the placement of one of the pieces of ply which needs to sort of slot under and into place (hard to explain). That piece of ply (the complicated one of course) includes where the washing machine will be, so want to tie together as much joisting as possible for maximum streangth there, its a large funny old shape which I am HOPING (once I've cut it) can be manipulated into place, with the screw locations pre marked out for speed. Thanks