Asphalt like substrate under old tiles.

[teo]

Hello everyone.
After my experiment with travertine tiles in my house (which turned out to be quite difficult) my sister asked me to tile her kitchen.
She got some polished textured porcelain, 600*400, for the whole area.
I ripped up the old ceramic tiles, and on certain areas they sounded hollows...
After stripping all up i noticed why they were making a funny noise....under the adhesive,that went up very easily, was a black screed....looks like asphalt, hard but if knocked with a chisel it come off easily.
Theres nearly an inch of that stuff; under that theres the usual very brittle screed, with cement sand and aggregates.
Since i never tiled on that stuff before i was wondering whats the best thing to do.
I have got some 2 part leveling compound to level everything up, and s1 adhesive to fix the porcelain.
My instinct tells me to dig it up, its not that much, probably 3 square metres, and put down new sand cement screed.
Is it the best thing to do?
Also that black stuff smells like that spray for insects (to kill them..) is it normal?
The other half of kitchen doesnt have that black screed, but normal one...but noticed the old adhesive didnt stick either cause was bit brownish and not clean ( i guess was old vinyl adhesive not taken up).
Is it ok to scratch that surface and then SBR the whole lot, put down new leveling compound, then tile?
Also do i have to prime again the leveling compound prior to tile?
Thanks for any help!

[GirlRacerRed]

Hi teo

my first question is, do you know how old your sister's house is? Does she know why there's a black screed on one half of her kitchen floor and not the other?

My concern here is that the black screed was put down for a reason but is now starting to fall apart. You need to find out why the black screed is down if you can, then you can decide whether the whole floor needs to be looked at and repaired before you tile over it.

[floora]

Inch thick, is probably grade 1 asphalt easist to remove it and bring the surface back to level,as for the other adhesive better check it is not water sofenable before considering where to go.

[teo]

Thank you for reply.
After a more careful look, it seems the asphalt screed is being used as a leveling compound over the concrete, then combed to stick vinyl on top (i can see the combing patterns).
The other half is normal cause is an extension built later.
No more info available cause she doesn't know...shes been there for just 2 years.
After pulling away a bit of the black compound, like i said before, i found the original screed, the typical sand and cement one.it seems dry to the touch.
Its nearly 1 inch, probably less (more likely 20 mm).
I think it will be safe to pull up.
As for the other adhesive it seems there are just few traces of solvent based adhesive, already removed (was easy, it wasnt much!).
As for the new screed...if i do the sand and cement screed, is it allright to tile over it as soon as its dry?
I have worked on site with tilers that tiled over screed just the day after (or as soon as it was walkable), but dont know if its the right thing to do or were just rushing...

[Gall.B]

surely not sand cement if they are tiling it next day, depend's on depth of screed normally a fortnight's curing time.

[teo]

I had another idea....since i think the house has been built in the 1980 it might be a damp proof of some sort...
What about if i cover the whole lot with sbr, then 2 part leveling compound it ?
It will be around 3 mm of leveling compound, plus the adhesive...maybe that would do the trick?
We dont really want to wait weeks just for 3 square metres of kitchen...

[GirlRacerRed]

Teo

I have a black tar like damp proof membrane all throughout the ground floor of my house, which was built by Barratts in 2003. Apparently, according to Barratts, the DPM isn't supposed to be there and was an addition to my house after they sold it part-finished. My DPM is in fine condition so I had no problems just priming and tiling straight over the top.

If you can take some pictures of the 2 parts of the kitchen that you're trying to tile, it might help the guys on here understand a bit more what you're up against.

GRR

[floora]

If you wish to do it fast then smooth it, and fit Ditra mat then it can be tiled the next day.

[teo]

Hopefully those photos will help.
The black substrate has few cracks,not deep, like superficial, and in random places (not a huge ones around walls and things like that).
It doesnt sound hollow, but in few places sound like the concrete underneath is brittle or debonded.
In few places i had problems ripping the old adhesive up, had to use a very sharp chisel.
The old ceramic tiles didnt have any cracks at all, and the grout was fine.
Just where the extension met the old screed there was a huge crack, as you can see from the photo...but i think thats cause the extension "settled" in place....otherwise no crack in the old tiles (but they were smaller...330*330).
The black screed is 20 mm sometimes 19 mm though..not an inch deep like i said before.
To summarize...is it possible to level the whole lot (after having repaired the hole in the black screed) with 2 part leveling compound? (maybe i need a slurry coat with sbr and cement before that?) then tile after its dry?
The only crack there was before was were the extension floor met not the black screed, but the bit after that( as you can see from photo, the one at the bottom not the one at the top, tiles were fine there) so i dont know if ditra is required (it cost a bomb sob..).
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