Just about to have a floor levelled and to my horror I’ve discovered that between the concrete screed that forms the base of the house and the course of bricks that the patio doors stand on, is…nothing. At least, not now that I’ve hoovered it out. It should be mortar but some invasive roots have turned it to sand…

So I need to fill it with something that will:
– bond to brick & concrete
– will stop the ingress of damp,
– that roots will not penetrate (offending plant to be treated to a systemic, then removed)
– fill a gap 15mm x 120mm x 3m
– sets rock hard, quickly and will last until the ends of time

Something like an epoxy adhesive seems like it would fit the bill…except I need it in a sensible size.

Am I thinking along the right lines? Any other products out there more suitable?

Yeah, I know a tube of frame sealant would probably do, but there has to be something better out there, right?

Ta!

I’d pack it with Slate and fill the gaps with mortar. You want something load bearing (not sure Expoxy is very good for that). Slate will be more resistant to the weeds and won’t crumble as quickly as mortar.

As above, slate and mortar.

You are trying to keep the two surfaces apart, not bond them together.

Load bearing is the most important part, adhesive isn’t the right substance for the job.

It’s not load bearing. Plants can grow through set concrete, so I feel the need for something more than slate & mortar.

I’d mix up a bit of concrete and put that in there

Molten iron poured straight in would do the job.

It’s not load bearing. Plants can grow through set concrete, so I feel the need for something more than slate & mortar.

Must have misunderstood your description above if its not load bearing.

Sounds like whatever was in there to start with was mixed wrong anyway if it turned to dust.

Lintels that hold up most of the holes in your house are held up with slate and mortar.
But if its not load bearing, then properly mixed mortar would do the job fine.

Bit of mortar and some membrane. Its only house

I’m rubbish at DIY etc – so ignore my advice.

But it’s a 15mm gap? Couldn’t you just leave it filled with air?

Epoxy mortar will solve your problem, pretty sure Jewsons sell it maybe even Wickes

Coldon

between the concrete screed that forms the base of the house and the course of bricks that the patio doors stand on

what is currently holding up the course of bricks? goodwill?

Must have misunderstood your description above if its not load bearing.

what is currently holding up the course of bricks? goodwill?

The slab is separate to the external wall, which stands on its own foundations.

Epoxy mortar will solve your problem, pretty sure Jewsons sell it maybe even Wickes

Cheers, I’ll look it up.

Need a photo. I have too many variables whirring around in my head each with a different recommendation.

is the gap vertical or horizontal?

is the gap vertical or horizontal?

Its a vertical gap.

Need a photo. I have too many variables whirring around in my head each with a different recommendation.

I can get a photo later today…this is the closest I’ve been able to find. It’s like the 1st image rather than the latter, there is a finger-sized gap between the wall and the slab. It’s a brick wall not a stone wall. House circa 1970, so built a bit (a lot) shit.

Grano/cement mix goes off like bell metal. You’ll get it at a builders merchant.

So is the gap on the inside or the outside? Floor leveled suggests inside, but why did it have plants growing in it?

It’s not a bad idea to have a gap round the basement floor slab, any temperature change will result in expansion or contraction and if it’s grouted solid it will just push the wall out when it expands, and leave a gap again when it contracts. Best with something flexible.

If your wall looks like either of those diagrams then you’ll have damp whatever you put in the gap, but then I’ve never seen a 1970’s house like that either.

So is the gap on the inside or the outside? Floor leveled suggests inside, but why did it have plants growing in it?

Gap is on the inside. Nature finds a way, I guess…

A little later than promised, but here are some photos:

Mix up a slurry of sand and cement and pour it into the gap. It will fill the void and seal any holes, if you pour in some roundup before it should help to kill any vegetation

Head hurts.

I assume its a ground bearing slab (Any air bricks around the perimeter)

I cant see any perimeter DPM / DPC detailing and the patio is relative high with the FFL.?

The spalling seems to indicate concrete and is that a day joint I can see?

I would probably go with a proprietary strong (cement ratio)pourable non shrinking grout which will provides a degree of water tightness.

I assume its a ground bearing slab (Any air bricks around the perimeter)

Nope.

I cant see any perimeter DPM / DPC detailing and the patio is relative high with the FFL.?

Patio is 2 brick courses below the bottom of the doors. There is a DPM visible over the top brick from the outside. I have no idea whether the base has a DPM. It ought to…I’m fairly sure the house was constructed after DPM became a mandatory part of building regs in ’65.

The spalling seems to indicate concrete and is that a day joint I can see?

Yes, it is a concrete base.

I would probably go with a proprietary strong (cement ratio)pourable non shrinking grout which will provides a degree of water tightness.

Cheers, I’ll look into this along with the epoxy cement mentioned above.

Another option would be to use a waterproof expanding foam, let it finish low (i.e don’t put too much in) and or rake it back once its dried. Then grout the top 20 to 30mm. It will reduce cold bridging.