nav[aria-label="Primary Navigation"] { padding: 0; & ul { list-style: none; width: 100%; display: flex; flex-direction: row; justify-content: start; align-items: start; gap: 30px; padding: 0; & li { margin: 0; } & ul li { list-style: none; } } }

Child Item

Suspended Floor - sunk sleeper wall question

mGrove

Hi,

I am in the process of insulation and levelling sagging floor downstairs. House is dormer type house.

After lifting floor boards, I see now that the biggest sag in the middle of the living room is due to sleeper walls in the middle being lower by 30mm.

What is best practice to fix this? If I start attaching sister joists, should I put shims under it so they don't side twist old joist? since sister joist is only attached to old joist.

Find more posts tagged with

Quick Links

Comments

10-10-20

Well done. You can tell it's a DIY job though... it's neater than a builder would ever have done it. 🤣 👍️

mGrove

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.

sliced floor plate timber and joist. Woodworm had a feast at some point.

mGrove

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

Excellent! Will read this.

10-10-20

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

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.

Bass Reeves

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.

The Continental Op

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.

mGrove

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.

Bass Reeves

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

10-10-20

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.

Doolittle51

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.

mGrove

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

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.

10-10-20

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!

mGrove

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

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

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

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.

10-10-20

I am not sure what deflection means in this case. Sleeper wall timber bowing?

Yes, the timber bowing following the release of downward pressure. Deflection is fine if that's what it is as long as you settle it or account for it before the floor is reassembled. Settling it would mean forcing it back into position and alignment with the rest of the floor using weight or fixings. Accounting for it would mean packing it and then ensuring that all other wallplate timbers are leveled off it. Settling is the simple option here, that's why I recommend you step on it and then run a laser level across the room and check whether they are all at the same level.

BTW OP, in the last photo the mortar under those blocks looks solid and it does appear to be a concrete floor, so that's a bonus. Any lifting of the mortar on the left of that photo is probably just deflection.

mGrove

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

ah beautiful! doesn't look too bad. this is actually giving me confidence in tackling sleeper walls. I am gonna digest this and make a decision.

Doolittle51

Here are some pictures to show what I did. In my case, the sub floor is concrete, and was sloping quite a bit. I levelled everything with concrete and mortar as shown, then put dpc on top, then fixed the floor plates.

I might not get a chance to post again here for a couple of days, so apologies in advance if you have any questions.

mGrove

https://www.boards.ie/discussion/comment/120354644#Comment_120354644

I have only notices the gap once floorboards were removed. before that the floor felt solid not bouncy, but you could tell it wasn't even. Sleeper wall in the middle has dropped. Sleeper walls are sitting on what seems like concrete foundation, I guess compacted stone. Not earth. But I think there is layer of mortar under them too.

I am not sure what deflection means in this case. Sleeper wall timber bowing?

Condition of mortar id say 65/35, some of it is solid while, some where there is a thin layer is crumbly. Definitely there are a number of spots where there are gaps between timber and mortar bed.

Would it be an option to remove joist, remove wallplate timber with mortar and dpc. Leave blocks alone.

Then put new Dpc, new mortar, and put new timber on top? I would have to make up for the lost height, especially the sleeper walls that are in the middle of room, in some cases 30mm lower than sleeper than sleeper walls which are beside a wall, with thicker layer of mortar. But that doesn't sound right. I assume big thick layer of mortar bed is not that stable as what I have now with packers?

10-10-20

ah japers - can of worms...

I hope that's just deflection. Did that gap open up because you took the floorboards off, or was it actually like that the whole time? Was the floor loose at this point? If you step on the joists at that spot, does it close up? The leading indicator here is going to be the condition of the mortar. Is the mortar on that section complete and still sitting on the blocks, or have the blocks dropped and is the mortar unevenly sitting on the blocks? If the answers to these questions indicate that the sleeper dropped, then you might need to get a laser level out and starting mapping this out with a view to replacing the sleeper.

As to whether you should pack-out and fill those gaps... that's TBD on the basis of above, but I would not be using a mortar repair as that's just a cosmetic filler.

Doolittle's post is to do with whether those blocks are provided with a compacted stone foundation and mortar or whether they were put sitting on the compacted earth with just mortar underneath to allow leveling. If it's just soil, it may have compacted further over time if there was organic matter within. The threaded rod which he then installed would have securely tied the wall plates to the blocks, preventing deflection. Whether that's needed or not here is hard to know, but I'm thinking not.

Laying a new sleeper isn't rocket-science - but you need to know that the base is solid and not going to give way in 10 years.

mGrove

Thanks again for all the replies lads! I really appreciate the input!

This is a classic case of scope creep. I just wanted to insulate the floor, but then also need a level floor for new flooring so here we are.

For shims under the joist I might make them out of treated joist timber if hardwood cracks. I ll test both of them out. For joists that are sistered, noggins should provide support.

I am confident enough to sister joists, replace old one etc. However I think my limit would stop at wallplates, mortar etc. As I understand it's not a simple case of putting dpc, slapping some pre mixed mortar and adding a piece of timber on top. Are there bedding in and levelling procedures? I read Doolittle51 reply and that info was lost on me.

Wall plates look 50/50, some spots are grands, some spots are worse off. Mortar is cracked and crumbly in some areas. I know in ideal world, wall plates would be redone. However I am gonna leave them alone. What are the real risks? Floor won't shift that drastically and if it will, joists are 1-2 mm from walls.

There is a spot where sleeper wall timber lifted. My plan is this. Plastic packers and fill the gaps with this. (This is different room to above pic)

10-10-20

Good info Doolittle.

OP, if you do end up replacing the sleeper wall-timbers, coat the timbers with SBR and that should reduce the suck from the mortar bed and reduce the chances of it weakening from rapid moisture-loss into the timber.

Doolittle51

I did something similar a couple of years ago, but replaced all the joists and floor plates too. My sleeper walls weren't in great condition so I had to replace some bricks etc. House is a similar age as yours. Just bear in mind that the floor plates on the sleeper walls are probably just laid on a bed of mortar and not secured at all. In my case, the mortar was really dry and crumbly, so the floor plates were essentially just sitting on top of crumbling mortar. Before installing new floor plates, I levelled the top of all the sleeper walls with concrete and/or mortar, using the old floor boards for shuttering. I also bedded in threaded rod so I could bolt down the new floor plates.

I'd recommend replacing all the joists and floor plates too. It'll take a lot longer to complete, but might actually be easier than what you propose. Laying the new joists is easy once you've got nice new level floor plates. And you can choose a thicker floor plate to make up for the difference in joist height to achieve your desired finished floor height.

10-10-20

The overview photo helped a bit as I could see the bigger picture. It's a much larger room than I had imagined and it's a more modern house, and that changed my considerations significantly. I must also add that it looks like a significant DIY job, so well done for taking it on.

I think that packing/shimming is the way to go and replace any joists which are out of spec (define a spec for yourself). The one comment that I'll make is that I think that hardwood might crack when skew-nailed, but I know that builders used to prefer slow-grown soft woods such as pine or cedar with good ring density. Maybe ask in a builders-providers for such.

Last point from me is: this is also now your only chance to check the existing joists for flex (at the midpoint) and you might also consider reviewing the joist interval in case you want to strengthen the floor. I know that's asking a lot of "a simple DIY project", but none of mine have ever not suffered from scope-creep to the point of doubling. ;)

The Continental Op

Hardwood packer is fine but if your new joist is fixed to your old one a few noggins will have a similar effect. Rather than nails I'd use screws but I always use screws. I'd clamp the old and the new together then fire in a few 6 x 100mm part thread screws with an impact driver. Probably not room to easily put them in square so they'd probably end up at an angle which is why I'd clamp the joists together (so the joists don't move as the pull together as the screw tightens).

Unless is was just one or two joists that needed replacing I think I'd do all of them so the spacing between the the load bearing areas remain the same? Again thats just me.

mGrove

old joists are 110mm, and new joist I have are 100mm. I need to replace couple joist.

In order make new joist same height, I was thinking of adding a hardwood packer underneath the joist with wood adhesive. Then skew nailing it to sleeper timber.

Would this be sound enough approach?

Calahonda52

so is the sag only in the "bay"?

Sister joist will make insulating/fitting membrane much more difficult