Uneven and bulging concrete floor. Sulphate attack? (with pictures)

[bigdrew]

I originally posted this in the flooring section but given the nature of it it is probably better in Building!.

Not sure how to handle this and its the first thing I need to decide on before doing anything else! I have recently acquired a 1960 Derby based house from my parents and understand that is has an issue with sulphate based hardcore / ground floor.

Underfoot the floor feels obviously un-even with some ridges and bulges, (it has been like this for the last 20 years with very little change according to my parents) I've not seen the actual concrete as there are still floor tiles down. There doesn't appear to be any problems with the walls. No cracking or bulging etc.

I've knocked on a few neighbours doors, they all seem aware of the problem and some have had it replaced. Any replacements were done in the 1980s, no one seems to have had it done more recently. The adjoining semi has been done.

The information online is fairly confusing, some people recommending core samples and others saying that they are a waste of time.

I guess my options are to have the floor dug out and replaced or leave it, level it off the best I can and hope there is no further reaction.

Anyone have any advice or dealt with this before?

Another point is the floors are different in the house, the white tiles (Lounge and dining room) are onto concrete with a thin bitumen glue.

The hall and kitchen look like there is a 15mm layer (asphalt?) so assuming some work has been done previously and it wasn't built like this..

The bit of wood is fairly straight. Finally are the tiles likely to contain asbestos (See tile picture)

 

[theprinceofdarkness]

From Wiki:- https://en.wikipedia.org/wiki/Sulfate_attack_in_concrete_and_mortar is it internal or external? i.e. is it the ground water carrying the sulphates or they within the concrete it self?
Asphalt covering sounds more like 1860 then 1960 and is a complete bodge. I would pull all the floors up and install a proper DPC + insulation + screed.
That last picture is of the suspect tile? I have never seen one like this how thick is it?
Frank

 

[bigdrew]

I'm not actually sure.. I guess I'd need to have the concrete tested. I'd assumed it was the hardcore that was the issue with a normal concrete slab above.

I'm going to knock on a few more neighbours doors this weekend.. see if anyone can shed more light.

Re digging it up. Are both internal and external walls likely to be on there own foundations and not resting on the slab?. Is the slab is just a slab with no structural use?

Would you say its a diy job?. Only thing that's sitting on it at the moment is the staircase.

 

[bigdrew]

Yes it is the Tile. They are quite thin.. maybe 5mm I'll measure one tonight They are fairly flexible.. they can bend a fair bit before they break

 

[^woody^]

Yes it looks like sulphate attack. The surest way to tell is with a core sample of the concrete, but the normal way is if the property is in a known area of a typical build and age then its just as good.

For remedy, the floor and about 700-1000mm of ground below (to the bottom of the foundations normally) needs to be removed.

This is normally associated with a broken drain or water pipe, so get those checked.

The work is notifiable to building control. And yes those tiles are asbestos, as is the bitumen backing

 

[bigdrew]

It is a known area. The floor has been this bad for 20+ years. If that makes any difference to the action taken. So not like a pipe bust and it's suddenly occurred or maybe it burst 20 years ago and no action was taken with the floor. But worth checking for piece of mind!
(House was brought new by my grandad so the floor isn't a surprise.)

Thought at the moment is I don't want to do the house up then have to unpick it to do the floor due to movement or wanting to sell andbit getting flagged on a survey.

That's seriously deep I !had more like 300mm in my head. 35m^3 @ 1m deep I'd guess.. so a lot of ground!

Thanks about the tiles. I'll leave them put till I decide on a solution!.

 

[wessex101]

I confess a lack of practical experience of sulphate attack on floors. But my understanding is that the characteristic of sulphate attack is doming of the floor, so as the contaminated fill expands and attacks the underside of the slab it creates an upward bowing in the floor. The OP's description does not seem to suggest that. I thought the remedy was to break up the slab and dig out the contaminated fill only.

I have seen asphalt covered floors where the asphalt has rippled causing ridges and bulges as described.

Looks like core samples are the only way to analyse the sub-floor fill.

 

[vinn]

What you've got as a topping on your floor is "The Blackstuff or Tarmacadam" crushed stones and asphalt, the same stuff that goes on the roads.
Your concrete surface doesn't seem to have been primed with hot liquid bitumen as a key for the Tarmacadam.
In my limited experience, I've never before seen Tarmacadam used indoors in a residence.

The odds are that you do have sulphate problems but you have nothing to lose if you remove all the topping down to the bare, cleaned concrete, & then use your straight edge on the exposed surface.
If the concrete is "flat" then a re-think might be needed?

 

[wessex101]

Tarmac???????? You're joking right?

It is paving asphalt or pitch mastic, quite a common floor finish in houses of a certain age.

Nearly forgot, the asphalt acts as the floor finish and the damp proof membrane so if you rip it up you will need a new waterproof covering to replace it. Obviously if you dig up the whole floor you put a polythene membrane under the new slab.

 

[Nige F]

www.masticasphaltcouncil.co.uk

 

[vinn]

Where in the masticasphaltcouncil site does it say use Tarmacadam on a domestic floor?

 

[vinn]

wessex 101,
No, I'm not joking wrong, not even smiling although I'm looking at a fool who claims various expertise but cant look at a simple photo without making a wrong claim for whats there.

Anyhow, I thought that you might like to know that:

"paving asphalt" is the same thing as "Tarmac" by another name.

"pitch mastic" is something different - it neither comes under "pitch asphalt" nor "Tarmac".

"paving asphalt" was never commonly used in houses of any age.

asphalt of any kind or mix has never been a "floor finish".

 

[vinn]

Nige F,

I'm still waiting for an answer?

 

[stuart45]

Paving asphalt is more of a USA term for Tarmacadam. The link below gives a better explanation of the terms.
Asphalt was used for floors, although it wasn't quite the finish as tiles etc would go over the top.
Good asphalters are harder to come by these days. Doing the vertical work is usually the most difficult.

http://www.pavingexpert.com/tarmac01.htm

 

[wessex101]

Well vinn it looks like asphalt to me but I defer to your clearly superior experience with tarmac.

Thanks for the link stuart45. In this country the term paving asphalt simply differentiates it from roofing asphalt, it just has a higher grit content to take foot traffic or furniture etc. and can even go up to take traffic on areas like car park decks with the right composition. Quite right about the floor finish, it often has tiles on it although I have seen plenty with lino or carpet, I saw one just the other week on a survey in Kent with carpet laid directly on the asphalt floor.