Help!: Advice on tiling over bitumen concrete

[SLR]

Hi,

I would like some advice on the best way to go about prepping for tiling my kitchen floor.
Its ground floor concrete, i have removed the old vinyl tiles and the old asphalt/bitumen residue covers the whole floor. I have the underfloor heating kits needed and the porcelain tiles, but with regards to substrate prep I have been told different things by various tile suppliers in my area but all conflicting!

I was told to ply it with 6mm ply, then s.l.c! but in my mind i think it should be some sort of cement board and preferably with an insulation attached!
I have also been told to make a slurry mix with tilers primer and neat cement, paint it on then s.l.c. I just think that ply and heat is not the best idea even if i do screw and plug it every 250mm centre's! and with priming it what about the heat from the wires wont that just make the bitumen release more oil's and fail anyway!

Thankyou in advance for any help is appreciated

[Ken Bruty]

Hi SLR,

6mm ply is a definite no-no

I'm assuming that your house has a DPC under the concrete floor,if so, the method is as follows
Firstly if the bitumen is thin, get yourself a wire brush that will connect to an angle grinder and grind off the Bitumen, then use an SBR primer to prime the floor. If the floor is lumpy (more than a 5mm gap under a 2m straight edge) you will need to lay a slc suitable to cover bitumen. Next choose your insulation boards (Marmox is 1 example), the thicker the board, the more efficient your heating will be (the thinnest is 6mm). These will need to be laid brick bonded into a flexible tile adhesive with a 5mm bed (I tend to trowel the floor with an 8mm notch trowel and also trowel the back of the board this makes sure any small dips in the floor are filled), ensuring you get full coverage on the back of the board, then pressed and slid into the adhesive. Once this is dry, your floor is prepped for the heating mat/cable, which should be fitted according to your manufacturers instructions. As an additional process, I would recommend a covering of slc to encase the heater to protect it and allow the heat to be spread more eveny throughout the area. I hope that helps

[aph257]

Hi SLR,

6mm ply is a definite no-no

I'm assuming that your house has a DPC under the concrete floor,if so, the method is as follows
Firstly if the bitumen is thin, get yourself a wire brush that will connect to an angle grinder and grind off the Bitumen, then use an SBR primer to prime the floor. If the floor is lumpy (more than a 5mm gap under a 2m straight edge) you will need to lay a slc suitable to cover bitumen. Next choose your insulation boards (Marmox is 1 example), the thicker the board, the more efficient your heating will be (the thinnest is 6mm). These will need to be laid brick bonded into a flexible tile adhesive with a 5mm bed (I tend to trowel the floor with an 8mm notch trowel and also trowel the back of the board this makes sure any small dips in the floor are filled), ensuring you get full coverage on the back of the board, then pressed and slid into the adhesive. Once this is dry, your floor is prepped for the heating mat/cable, which should be fitted according to your manufacturers instructions. As an additional process, I would recommend a covering of slc to encase the heater to protect it and allow the heat to be spread more eveny throughout the area. I hope that helps

exactly

[Dave]

Top advice by Ken..

[SLR]

Hi Ken,
Firstly thank you very much for your advice, and thanks to all for conformation. The floor does have a d.p.c membrane under the existing concrete, you confirm my thoughts with the ply idea i thought as much! Is there any way of saving the amount of height gain with regards to bedding these boards down on 8mm adhesive! maybe another type of board say 6mm thick or the same board but fixed down with screws and plugs ( plenty of )! followed by the heating cable then a flexible levelling compound like you say to cover, then tile on to that? its just that the threshold on the French doors to the garden measures 30mm from my existing concrete base! I don't mean to question your expertise Ken, just trying to achieve the desired result within the limiting boundaries!
Regards.

[Ken Bruty]

I think you're thinking that an 8mm trowel will trowel 8mm thick of adhesive, but that's not the case. Forgive me if I'm reading you wrong, an 8mm notch trowel will give you 3mm of solid bed, the 8mm notch creates a ridge 8mm high but when flattened reduces to 3mm, so if you trowel on the back of the board and the floor, effectively you will get 6mm of solid bed which is the maximum thickness for a thin bed adhesive. The reason the boards are stuck rather than screwed is becuase you will get a flatter and more solid surface on which to stick your ufh to, so you're only raising your floor level by 12mm (if you use a 6mm board), then 4mm with the cable + slc, then 4mm bed of adhesive + your tile thickness. Incidentally you will need a minimum 10mm notch trowel to fix your tiles if they are 30x30 or over, and back skim your tiles with tile adhesive as well as trowelling the floor if the tiles are heavily studded (embossed) on the back, to ensure 100% coverage over the ufh, and trowelling the adhesive in straight ribs will ensure all air is expelled from underneath, therefore making the tiles bed easier and with minimum or ideally no lippage.

[Gazzatile]

Very good advice Ken

[SLR]

Hi Ken,
Well that should work out great, all that roughly amounts to 30mm with 10mm thick tiles! I have a rounded 10 x 20mm notched trowel for my 600 x 400mm tiles, I will source some 6mm boards to lay and an 8mm notched trowel. If the wire brush on angle grinder proves to labour intensive on my 23m2 floor then I can always see my friend at the hire centre and pick up a concrete planner! either way i WILL get that nasty bitumen adhesive off!!

Thank you very much for your help and patience Ken.

[SLR]

Hi,
My floor does need leveling up, and in places is more than 5mm over 2m straight edge! Does this mean that the SBR is not used and instead use a levelling compound to go over bitumen! I have been recommended these two products from a local supplier! Firstly is Palace tilers primer SBR and Palace fast flex floor leveller! Does anyone know if either of these products are suitable for my flooring situation or even if they are any good at all? I am at the moment removing the bitumen as best i can with a 9" grinder with a wire brush attachment! Its a monotonous job and whilst doing this today I was thinking why not put the diamond blade back in and criss cross groove the whole floor creating a scarified surface similar to a scratch coat like you do when rendering!! I didn't, but the thought was there!
Thankyou in advance any help is much appreciated.

[Dave]

The wire brush is the best way.. but you can get the SBR and mix it with some cement or adhesive and cover the floor in a slurry coat ( brush or flat trowel applied) and this will create a strong bond..

Then you can Self level onto this to get it flat ready for tiling.

[SLR]

Hi Dave,
Thankyou for the advice mate and clearing that up for me, I have struggled getting the bitumen up with a wire brush its quite thick in places and the brush just seems to burnish it and heats it up! so i have put the diamond blade back in and am removing it with that, its alot quicker going and its providing a really good key to the surface! dusty job but so much better than a wire brush! I am holding the disc at about 40 degrees to the floor in an arcing motion so as not to put grooves in the floor, ive found that the trick is to keep the tool moving ( as you would with a belt sander!) At this rate i will have the 22m2 done by the end of the day. The wire brush attachment works ok on the really thin stuff and i have used it where i can then swapped over to the blade!
Thanks again Dave and to everyone thats posted here I really do appreciate it

[Dave]

No probs.. let us know how you get on.. maybe a few pics of work in progress and the finished result..

[SLR]

No probs.. let us know how you get on.. maybe a few pics of work in progress and the finished result..

Will do Dave.

[SLR]

I have been recommended these two products from a local supplier! Firstly is Palace tilers primer SBR and Palace fast flex floor leveller! Does anyone know if either of these products are suitable for my flooring situation or even if they are any good at all?

[Ken Bruty]

Hi SLR,

I've not used those products myself as Palace isn't widely available in my area, but if I were you, I would read the application section of the bag, if it doesn't say ok over bitumen and ufh, I would give the technical department a bell and ask for advice on this particular product, there may be someone else on here that has used the product to say yes or no, if you can't get the info from Palace.