Suspended Floor - sunk sleeper wall question

10-10-20 · 13-03-2023 11:01PM

https://www.boards.ie/discussion/comment/120355254#Comment_120355254

High-bar set there alright. As you mentioned, you used shuttering to create the sleeper-wall bedding. I get the impression that builders just place about three large dabs of mortar down on the wall, then set the timber into this and level it off before lifting the timber and filling in the remainder of the mortar and checking for level again.

mGrove · 14-03-2023 09:03AM

https://www.boards.ie/discussion/comment/120355522#Comment_120355522

Ok I get you now. if you have floor plate that's deflecting - essentially separated from mortar bed then you have issues right? since I understand floor plate not resting on mortar bed is a no no.

Here is another pic of the gap, I spot various degrees of gaps on different sleepers. maybe due to floor, and then old floorboards being removed.

Here is some one previously, inserted shims. Not sure at what stage this was done but looks like old work.

After some thinking I have decided to rip all timber out and rebuild sleeper walls using Doolittle51 pic as refs. Since I have all the tools anyway, just need to get some general purpose mortar and threaded rods.

My main reasons are not the gaps as such as I am still not convinced they pose big risk. (maybe bouncy floor?)

But in the living room, two sleeper walls there run in the middle along the room, have sunk so I would have to essentially sister every joist. Then do the same in one half of the kitchen... hallway that separates the two is ok.

Since I am sistering every joist, I would be just installing new suspended floor along old one, doubling weight on sleeper walls. Don't like that idea. I might as well delete old timber. Some old timber has signs of previous woodworm.

Sistering joist takes some amount of work too, plus installing m12 bolts with plates is not cheap.

If adding all of the above in terms of effort + money, it makes more sense to start fresh. As it was mentioned, it might take longer, but it should be easier.

10-10-20 · 14-03-2023 12:30PM

I'm presuming that any of the wooden shims are original installations (unless you tell us otherwise) and the plastic are yours? If so these wooden shims were originally inserted to account for the differences between each of the sleeper-walls at the point where they were laid and they should be providing a level surface over-all, to which you can take an offset from (using a laser) and validate the overall levelness of the floor.

The point which I was trying to make earlier was that if you have a floor which is laid level 30 years ago and you then strip it back by unloading it mechanically and also remove the floor-boards, that floor will try to recover from the settling, deflection and changes in humidity which it was under for that 30 year duration with the result that some parts will lift slightly. That small amount of lifting is natural and will (or should) recover as you refloor the room, but you have to decide whether the gaps now observed were the results of either: recovery from loading/deflection/humidity OR settling/failure of the sleeper-wall.

I'm suggesting for that reason that you take time to map out the room with a laser level to define these differences as you may find that the floor is 95% level, but just with work needed in that one corner. I hope that this is clearer.

mGrove · 14-03-2023 03:18PM

from this picture you can see how far middle sleepers have sunk. so even if close the gaps I am still not level.

10-10-20 · 14-03-2023 03:22PM

https://www.boards.ie/discussion/comment/120357741#Comment_120357741

Ok, clear. I just didn't want the point to be left hanging. Good luck with the work and I think we all do look forward to updates!

Doolittle51 · 14-03-2023 07:46PM

You'll find 20kg bags of ready mix cement in most builders providers. I mix up about a third or half a bucket at a time, just using an old garden trowel. Same for mixing mortar. Have a look for tarmac brand ready mixed mortar. It's the only one i found thats actually pre-mixed. Most other ready mix bags have the cement in a seperate bag and you need to mix it with the sand yourself.

mGrove · 14-03-2023 09:28PM

https://www.boards.ie/discussion/comment/120358874#Comment_120358874

Yea I am planning on using this, K mix general purpose mortar for creating bed / level layer. and maybe slap some of it at the bottom of blocks to secure them in case some are loose. I don't really need cement, since I am not putting new blocks right?

https://www.goodwins.ie/products/k-mix-instant-mortar-render-25kg-just-add-water.html?name=%20k%20mix&type=simple

Doolittle51 · 14-03-2023 09:31PM

You'll probably be ok with mortar. I had to make up a couple of inches or more in some places, so concrete was a better option for me.

10-10-20 · 14-03-2023 09:34PM

Yes, those mortar bags are fine. You should try add a plasticiser with the mix water. It helps to make the mortar more "plastic", workable and lessens the need for water.

https://www.goodwins.ie/products/mortar-plasticiser-5lt.html?filter_set%5B%5D=1,1056,1083

A bucket trowel (or garden trowel) and a medium sized brick trowel - then you're sorted.

https://www.goodwins.ie/products/draper-soft-grip-bucket-trowel-140mm-81237.html?filter_set%5B%5D=5,1785,1790

https://www.goodwins.ie/products/brick-trowel-soft-grip-275mm-by-draper-81233.html?filter_set%5B%5D=5,1785,1790

Generally if putting mortar on existing concrete/block, wet it beforehand to reduce the suck (rapid removal of water) by the dry concrete.

Bass Reeves · 14-03-2023 09:58PM

OP another option is to get 150X50mm to use as sister joists. Notch them for the end and for sleeper walls to bring to the exact level you require. You can probable buy them treated. Brace or screw them onto existing joists. Its a different approch. I would not be a fan of depending on an 30mm of mortor cased onto the top of blocks to make up the difference it could crack down the line. I would much perfer to make up the difference with a thicker wallplate

mGrove · 14-03-2023 10:22PM

https://www.boards.ie/discussion/comment/120359411#Comment_120359411

You can read through the thread as I discussed why I don't think it would be a good option. Sister was considered but due to the amount of sistering I would have to do, it doesn't makes sense in this case. Plus other issues.

I am not going to put thick level of mortar. Difference will be made up with thicker sleeper or doubling.

The Continental Op · 14-03-2023 10:48PM

https://www.boards.ie/discussion/comment/120359502#Comment_120359502

You want a reasonable thickness of mortar. If its too thin it won't do that much good and probably crumble, particularly if you don't wet the top of the blocks before putting the mortar on them. What happens is dry blocks (could be bone dry in your case) suck the moisture out of the mortar before it has time to cure properly.

Bass Reeves · 14-03-2023 11:28PM

https://www.boards.ie/discussion/comment/120359411#Comment_120359411

The weight of the new timber would not actually add weight to the sleeper walls. It would actually reduce the load weight on any particular point on the sleeper wall. It the action on the floor above that put weight on the bearing points the greater the area of the transfer of that weight the lower the weight on the bearing point.

Only reason I was recommended using sistering is it makes it relatively easy to install for someone who may not be a carpenter. The new joists will carry the majority of the load you only need to brace or attach to existing joists to firm the structure as what should have been done originally. I only have used the old joist to position the new ones.

The woodworm may be an issue if the woodworm is still active. It virtually impossible to eliminate even with wood preservatives. You would only want to bolt where there is a gap and a 32mm spacer ( metal) would solve that issue.

Having said all that a complete new floor is the best solution.

mGrove · 15-03-2023 08:48AM

https://www.boards.ie/discussion/comment/120359595#Comment_120359595

that's good tip! ill make sure to mist some water on blocks. I am aiming for 20mm thickness as that what it was before and roughly will be give same height. Obviously it'll vary as blocks are not even.

https://www.boards.ie/discussion/comment/120359789#Comment_120359789

Ok that make sense. My thinking was, if I have to sister every joists, I might as well just have only new joists.

In addition, mortar was missing or crumbling in a number of places and I understand that putting shims between floor pate and dpc is not good solution as floor plate is not attached.

I may still sister few joist in the hallway.

10-10-20 · 15-03-2023 01:07PM

Just on the mortar discussion, not to be pedantic, but a couple of general points which I have learned:

You're not supposed to work with wet blocks as the excess water causes the bond at the interface between the mortar and block to fail (dilutes it, effectively), but you do need a minimum of moisture within the block to complete curing process as well as keep that suck to a minimum. Old blocks which have been indoors for years are going to be dryer than new or outdoor blocks.

So what I do is just wet the block about 10 mins prior and let it soak in. No need to wet it again, just apply the mortar and tap the block down into place.

Joints should be 10mm in depth. When making up the mortar and especially when using thin joints (less than 10mm), watch out for stones in the mix. You may on occasion need to sieve the material if you need a thin joint. 🙄

Mr AJ McCormack has some very good info on the topic of mortar here:

https://www.pavingexpert.com/mortars

mGrove · 15-03-2023 01:12PM

https://www.boards.ie/discussion/comment/120361247#Comment_120361247

Excellent! Will read this.

mGrove · 01-04-2023 06:43PM

Thought I would update this thread with the work I ve done. Was busy doing living room and kitchen. Going through my phone I realised I didn't take many pictures at all unfortunatly.

First of all, BIG shout out to everyone who gave me advice on how to approach this. Especially to Doolittle51 for providing photos! Massive help. Thank you.

This may not be perfect but I am happy with the result. Installed subfloor is level, solid, not bouncing. I had to buy a used refurbished nail gun but otherwise only cost was material.

definitely not as daunting as it sounds, if you have time. You spend more time making sure everything is level and waiting for mortar to dry than actually doing work.

Here are few photos anyway. I had to double stack some floor plates in the middle to make up the height.