Flooring Joist Cradle

TiNcAn

So I am in a bit of pickle with my kitchen floor. I took up the tiles and grouting expecting there to be a decent concrete floor which I could pour on a leveling compound and finish with laminate flooring. The floor underneath is instead quite damp and I am not sure it is even concrete since it is fairly soft by concrete standards (see attached picture). There was a DPM applied ot the floor underneath the tiles as I expect that there is not a DPC (it's an old house).

I checked with a couple of manufacturers about applying and DPM and leveling compund but they stated that the subflor must be in good condition. So I think this rules out this option. The alternatives I am now considering are; a) DPC with concrete screed and b) Suspended wooden floor.
For otpion b) I am thinking if it would be possible to use something like joist cradles. I attached a picture below of such a cradle for reference. These would seperate the joists from the subfloor avoiding mositure travelling into the wood and would be relatively easy to install. Does anybody have an experience with using joist cradles and any advice in general on the approach to take?

Calahonda52

pictures of floor don't add much

are you proposing to dig out the sub floor for the cradles?

TiNcAn

I attached a picture below which should give you a better impression. In my opinion digging out the subfloor would be far too much effort. You can see in the picture that there are some striking outlines in the ground where they have laid some of the water pipes. So this would be tricky to dig out. 

Instead the idea would be to lay a wooden floor over it like described above or to pour a concrete slab on top. I could also seal the floor with a DPM before both methods to help any moisture passing through to the new floor.

fred funk }{

Would you not be raising the height of the floor if using the craddles? It would impact the doors as well.

TiNcAn

Good point. Either method would involve raising the floor unless the existing subfloor was excavated. Fortunately this is not an issue as there is already a step of around 16cm down to the kitchen.

Triboro

Is there any adjustment available up/down on the cradles themselves to counter high/low spots as you go?

listermint

What about sealing the floor with a Liquid DPM and then self leveling on top.

Then just floor it normally. I think there is alot of expense and possibly a poor result with the cradle system.

TiNcAn

The height of each cradle can be adjusted individually which is great because the floor is not flat and has a maximum difference of ~2cm. 

The liquid DPM with the self leveling was how I originally wanted to go, but the ground is not hard  and somewhat friable if you scrape it. I think the subfloor has more the properties of a lime mortar rather than cement. When I spoke with LAYDEX customer services they mentioned that if the ground is dusty or friable, the self leveling will pull the DPM when it sets causing it to unbond to the subfloor. This is why I am looking at other alternatives. 

What do you think would be the poor result of such a cradle system.

listermint

TiNcAn wrote: »

The height of each cradle can be adjusted individually which is great because the floor is not flat and has a maximum difference of ~2cm. 

The liquid DPM with the self leveling was how I originally wanted to go, but the ground is not hard  and somewhat friable if you scrape it. I think the subfloor has more the properties of a lime mortar rather than cement. When I spoke with LAYDEX customer services they mentioned that if the ground is dusty or friable, the self leveling will pull the DPM when it sets causing it to unbond to the subfloor. This is why I am looking at other alternatives. 

What do you think would be the poor result of such a cradle system.

If the liquid DPM is thick enough what would it matter if it was not bonded to the sub floor, Its roll is to prevent water ingress its not its roll to create adhesion between surfaces.


Other option is to self level first, DPM, the another layer of self level. I personally would knock that subfloor stuff on the head.

TiNcAn

Sorry I don't entirely follow by knocking the subfloor stuff on the head. Do you mean to just go ahead with DPM (or leveling before as well), leveling and leave it at that?

I don't know, but maybe the DPM must have a proper bond to work correctly. Just a guess here.

The DPM recommended to me by two manufacturers were Epoxy based. Any advice on whether this is the right tool for the job?

Dr_Colossus

TiNcAn wrote: »

The height of each cradle can be adjusted individually which is great because the floor is not flat and has a maximum difference of ~2cm. 

The liquid DPM with the self leveling was how I originally wanted to go, but the ground is not hard  and somewhat friable if you scrape it.
What do you think would be the poor result of such a cradle system.

If the ground is not hard and somewhat friable as is I can see the cradle system being a disaster since you're concentrating the floor weight and any movement above to the few pressure points of the cradle legs. I can envisage the cradle legs eventually sinking somewhat in the soft floor making your floor uneven again and likely to crack tile or damage laminate.

listermint

TiNcAn wrote: »

Sorry I don't entirely follow by knocking the subfloor stuff on the head. Do you mean to just go ahead with DPM (or leveling before as well), leveling and leave it at that?

I don't know, but maybe the DPM must have a proper bond to work correctly. Just a guess here.

The DPM recommended to me by two manufacturers were Epoxy based. Any advice on whether this is the right tool for the job?

level it first, this removes the uneven.

Apply DPM once the level has set.

You can then relevel on top. Or alternatively put some fibre board down prior to floor

TiNcAn

Thanks for the advice so far.

The floor itself is not soft, but I would say it is say relative to what concrete should be. That is still is a valid point that over time the cradle may sink in some places. My one other concern with the craddles is that they might lead to quite a hollow sound underneath kind of like a stage. This might be mitigated with some laminate underlay.

Is there any issue leveling a floor with with a self leveling compound if it doesn't contain any DPM. It would end reach a 100% RH overtime, particularly because the DPM above it would seal all the moisture into it. If you know any leveling and DPM products that would be suitable for this application please send me a PM.

Lumen

If you have 160mm to play with then some PIR insulation board (e.g. Kingspan Thermafloor TF70) would presumably be a good addition to the build up.

TiNcAn

I thought about doing that but it would take a good bit of the ceiling height. It is currently 2.66m high and this would be reduced to about 8 foot. That's not so bad but compared to the original part of the house which is 2.8m high it will feel a bit small. 

So for now I am trying to figure out if I can just level the floor without raising it.