Help!: Do i have a magnesite topping

[dan121]

Hi, First time poster, usually can find answers through previous posts, but i need help on this one. I have to tile approx 40sqm of a ground floor with travertine tiles, i have ordered mapei marble and stone cement adhesive on the basis that i had a cement screed (checked utility room) unfortionately after removing the rest of the laminate flooring i have found something which i suspect is the dreaded magnesite topping. Beneath is a discription of what i found:

A smooth almost polished yellow to brown screed at around 20mm deep

It had damp areas, my house was built in the 1950's and therefore i believe there is no dpm, also the floor was covered with a polythene membrane then foam then laminate so it would have trapped moisture.

The damp patches i could scratch lines out with my fingernails

The solid a bolster was needed to chip it

small fragments would disintegrate between two fingers but not a dust/sand like substance

I took a blow torch to a sample and it did not catch fire

The edges, only the thinnest possible part would burn the colour of a lit cigarette, not a lot of smoke, not much heat retention and it had a faint smell of rubber.

finally i took a volt meter (don't have damp reader) and tested the floor, on contact + - it would go to 2 oclock max - half an hour dry spots (12hour clock face)

Nails rusted and internal beads rusted to approx 4 inches up, not everyone though.


I made the above points as through reading previous posts these were the questions asked. One of my main hopes about the possibility of it not being magnesite is that i have read that it is a cork like substance and a good underlay. My floor is hard and polished and smooth, if snapped in half it does have slight bubbles but nothing extreme, same as mortar.

Your opinions would be really appreciated, i dont want to rush ahead and rip it up if it is an alternative topping that is acceptable as a bond.

[jay]

pictures might help
and welcome to the forum

[Ajax123]

Magnesite would show up as being saturated on an electronic damp meter whether or not it was damp because it is conductive. Not sure what reading you should get on a volt meter. Also the smell of rubber is slightly odd as I am not sure Magnesite would smell so. However an SBR modified screed would and these can be laid remarkably thin. Colour wise Magneste tended to be pinky red, or green. Not usually brown or yellow. They are pretty colour stable so would not tend to fade. It also tends not to pulverise too easily and remains blooming hard throughout. From your description I don't think you have magnesite. Do you have any ideas as to when it was laid?

[dan121]

CIMG0066.jpgCIMG1434.jpg

[dan121]

The house was built in the 1950's but between then and around 1990 it could have had renovation work, one part that makes me think this is that one piece of skirting is below the screed. Also up to the skirting its perfectly flat then in pillows out i.e not troweled to the wall, i guess its trowelled rather then poured as it must have been pretty firm not to fill the outside edges to the max.

[dan121]

I've just had a plasterer with over 40 years experience take a look at my floor, he said it was a dyed sand cement, polished to a high standard to be a finishesed floor. The thickness dictates the smell of rubber i.e. additives added. Probably done in the 70's. I'm very confident now to move forward but would appreciate any conflicting ideas.

As for the dampness i believe i should put a liquid dpm down on top of the screed with a suitable upstand. Few questions
will it bond to the tile adhesive, do i need to prime it, thinking of using a cement based tanking slurry from antel (trade). Does this sound appropriate or are there more suitable products/ easier to obtain (not trade).

Thankyou please advise if i should ask this in a seperate thread