We are in the planning stages of a major spring renovation of our old home in BC, Canada. Over the last 110 years the house has settled and dropped and sagged (as we all do) and the floor is not so level. It is also a tad drafty on the feet and floors are old and worn. So, we are going to pour a 2" suspended slab on the first floor overtop radiant hydronic tubing. Being an old house, it has the typical layout of many rooms. I am working through the process of deciding if we should use conventional concrete or SCC (self-compacting concrete). The fellow I use here for concrete work has very limited experience with SCC. However, we both agree that if the floor is not too out of level that it might be the best way to go. However, if the floor is out by many inches then he suggests using traditional concrete so he can cheat from room to room and not allow the concrete to get too deep. The engineer has given us the green light for 2" of concrete on the floors. If we go the SCC route we were thinking of creating a dam at each door to each room to prevent the SCC from spilling out into the next room and changing the elevations of the already poured concrete. I am hoping someone here will have had more experience than my local contractor and I and be able to give me some direction: i.e., are we on track with our thinking or barking up the wrong tree?

I see very little advantage to spend the moneys on self consolidating concrete. If you have any leaks at all, it will continue to run until the leaks are full. You probably should put a poly break between the old and new both to stop damp rising and to prevent the new concrete from running away through cracks. Sorry, not sure if you are pouring over an old slab or if on a wood floor.

Much better would be to place 2 to 4" of eps foam and staple the pex to that but I don't know how that would effect the floor heights. (if over slab. If over floor you can insulate under the floor if needed.

I would use our standard thin slab mix, small agg., increased fly ash, 30 mPa concrete and about one litre per meter of super plasticizer.

FBBP, the existing floor is wood (1X8 fir planking) with lots of gaps between. Good idea on the eps foam, kill two birds with one stone, insulate and seal. Ceiling height is 9'6" so no issue there, just a few headache points with a change in the first step height on the stairs and the exterior doors. The interior doors will be removed along with kicks and baseboards so that will not be an issue. Would you please clarify why SCC, in your mind, would be not be necessary? Will the mix as you describe it be more flowable and easy to place given all the existing walls and tight spaces? For a conventional concrete finish my placer is thinking about $1500 while the SCC placement cost would be about $400. I need about 7 meters of material so it would cost me an extra $700 to go SCC and save me $1100 in placing. On purely a cost basis it makes more sense to use SCC. Perhaps the potential for leaking into cracks would make it more of a headache...I don't know.

we were thinking of creating a dam at each door

Doorways are natural places for expansion joints anyway.

Will there be insulation below that new slab?

Yes, I think I will put 1" foam under the slab for insulation and, if I use SCC, to seal the floor. If we go conventional concrete I will likely insulate from the bottom. On a different topic, I am having a hard time wrapping my head around adding 40,000 lbs of weight to the house. As I mentioned, the engineer said the floor can hold it…just seems like an enormous amount of weight.

I presume the engineer has actually inspected the home's structure and has actually run the calculations, right? 25 lbs per square foot is a lot to add to an older home.

Only 1" under the slab? I'm south of you and I would do at least two, plus additional insulation in the joist area.

What kind of a floor covering will go over the concrete slab?

You should look up a product called 'Bekotec' from Schluter if you really want to go through with this.

Zad - If your numbers are as you say, then it would make sense to use scc. Is your concrete guy expecting it to be self finishing too? $400.00? You are talking about scc and not gypcrete right?

What is underneath this floor that could get damaged if the are major leaks?

If placing foam, you might use different thickness to level the floor a bit.

The engineer and I only spoke on the phone and I gave him the spans, dimensions and type of lumber in the joists and he came up with a load carrying capacity of 150 lbs/sq ft, more than enough according to him. I will have to get him in to do a proper inspection for the permit which I will do soon. The joists are old growth fir 1.75" by 9.5" and the largest span is 11'4".

Having now looked at Bekotec the numbers change dramatically, down to 12 lbs/sq ft. (from 25 lbs at 2" depth) assuming I can get the floor reasonably level with foam before pouring. The Bekotec will work beautifully, serving as a partial seal (under the floor is basement so not a biggie if there is some leakage) and reducing load and amount of material.

Yes, I am talking SCC and not gypcrete. We can't get gypcrete where I live so it is either conventional or SCC for me. Good idea on using foam to do some of the levelling (if needed) under the Bekotec. The $400 price is finished as he describes it. I have never used the product so I am going on what a local installer who has used it before is telling me. He sais that he places, jiggles it a couple times with a 4' tube float to get the aggregates down and then comes back after it has set up to grind off any stones as needed. Does this sound about right?

I plan to install a glue down engineered hardwood that is guaranteed for glue down over radiant concrete.

Regarding the insulation, I agree on adding more and planned to use the foam as a sealer/insulation and then add foil backed batts under the floor to an R value of 10 or so. If I use Bekotec I will likely just insulate under the floor except where I use xps foam to fill in the low spots.

Hey ICFHybrid,
From what I read about Bekotec, it sounds like they recommend tile, carpet and parquet and make no mention of glue down hardwood. Have you seen this done with success?

The Bekotec will work beautifully, serving as a partial seal (under the floor is basement so not a biggie if there is some leakage)

You can lay down a plastic layer under the Bekotec and any amount of rigid foam.

I have only done Ditra and tile over the Bekotec, but if you call the Schluter technical line, they will put you in touch with one of their regional experts who should be able to help with that question.

I just called Schluter and glueing down engineered hardwood is fine, as long as you use the proper glue. Thank you so much for turning me onto this product, it will cost an extra $1000 even with the savings in concrete but it will dramatically reduce the floor loading and take a huge worry off me…even if the engineered numbers say it would be ok to use as high as 25 lbs/sq ft. Will keep you posted on progress with the engineer who is crunching numbers now and as the project starts in just over a month.

Zad - something to consider. SCC is very dense and very fluid. If it gets under the foam or the Betotec, it will probably FLOAT them so everything will have to be glued down. You might also consider filling the pex with water to prevent floatation.

Also it is important to make sure you wet cure the SCC.

Bekotec fits together very tightly and Schluter even has an adhesive loaded edge seal sort of thing that can be used. You would have to be incompetent to float the Bekotec as pretty much anything on top of it holds it down even more, including the PEX. There was quite a bit of advance whining about placing the PEX on the Bekotec knobs, and how that was going to lift the panels, but that fear went away once work commenced, too.

At 230 lbs, I'm not a Northern European skinny mini and could not walk directly on the Bekotec without crushing the edges of the knobs a bit over time. I cut some 1/2' ply panels at about 18" X 36" in order to move around on the surface and that worked fine. No one else had any trouble walking directly on it.

I heard back from the engineer today and using the existing structure (without adding one more beam in one location) with max span of 14'4" and using a floor load of 15 lbs/sq ft of concrete plus the live and dead loads required for the building code of Canada our floor will be at 73% capacity. Good enough for the engineer to sign off on. I could easily add one more beam to reduce the max span to 11'3" which would significantly drop this percentage and increase my peace of mind (so I probably will) but it is nice to know the existing structure has what it takes to hold this load. Looks like we are a go with the project as planned. I am sure there will be plenty of low areas so I will figure all that out and use 1/2" or 1" xps foam to fill in some space and keep the concrete thickness down. My concrete placer is a big guy too so I will be sure to have some plywood panels around for him. It is going to take some time to seal the perimeter up as this house has the old cast iron grates for heat and cold air returns…lots of small forming to do. I am going to use a Noritz nrc1111 tankless heater to heat the floor and I am very happy to be saying goodbye to cold floors. We start March 3 when a fellow who is building a new place here is coming in to salvage all the existing hardwood flooring for his build…nice to know the flooring will get used more after 110 years of use. To wet cure the SCC I will have to use plastic as I won't be able to dam it and keep it under water. Even so, I think I will have to caulk all the edges to keep water from draining down the floor-wall joint.

Very good news. The engineer did a site visit today and he was really happy with the structure of the house. He is a few months away from retirement and has been in practice for 48 years and seeing the fir joists in our home reminded him of how homes used to be built. He had absolutely no issues with the support under the main floor and provided me with stamped load carrying capacity giving me the green light to put up to 2" of concrete down as it stands now. I am still considering using Bekotec to reduce the overall load but now having the engineer tell me the structure is more than strong enough I might just go ahead and pour 1.5" without the Bekotec and save myself the time and expense of putting the Bekotec down. Thoughts?