Levelling/ sealing concrete floor for tiling

[robertoi]

Hi,

I guess this a question for Matty really - you gave me some advice a while ago about wooden flooring over a (potentially!) damp concrete floor with no DPM.

Anyway, I have now decided against wood, and am planning to tile the floor with underfloor heating.

Currently, the floor has crappy ceramic floor tiles stuck down with pretty minimal adhesive onto the concrete, which in turn has had a thin layer of bitunimous liquid DPM poured onto it in the past. After removing 6 of the tiles, I can see that this bituminous stuff is peeling away with some of the tile adhsive, and so Im guessing its gonna have to go. The floor is also a little uneven in places, particularly where I believe an old load bearing wall was removed (what is now the kitchen used to be the scullery plus an outdoor loo/ coal scuttle before being knocked through). So I reckon Im going to have to atempt to level the floor aswell.

You may remember that I was quite worried about the knock on effect on the walls of sealing in any moisture that may be in the floor with a DPM. I have now decided to chance it and use a liquid DPM, simply because I cant afford the alternatives, it seems to be what most other people with older properties end up doing, and I dont want the floor covering to be ruined in future. The bits of the floor Ive exposed so far seem to be fairly dry, and where is some dampness still, im pretty sure this is because of a pipe leak we had a while ago.

SO! with all that in mind, I'd be really grateful if you could tell me whether you think the following is a reasonable course of action:

1) remove old floor tiles and knock off any loose bits of old DPM and adhesive
2) use a floor scrabbler to remove the rest of the old DPM, and to level off any gross uneven areas in the floor (can a scrabbler be used for this, or do I need to grind it?)
3) seal/prime the subfloor - is this necessary, and what should I use?
5) apply self levelling compound - Im guessing I'll need a latex product due to possible moisture in the floor
4) apply liquid DPM - any chance you could recommend one? Is it worth adding kiln sand etc to produce a good surface for tiling adhesive to bond to?
5) Stick insulation boards onto floor with flexible tile adhesive
6) Lay underfloor heating element
7) Tile and grout the floor

Reckon that sounds about right? How long would I need to leave the self levelling compound/ DPM stuff before going onto the next step?

Many thanks in advance

Rob

PS - having done all this floor prep, reckon I could use wood safely after all?

 

[robertoi]

What does anyone think of my plan? Im on tenter-hooks!

 

[mattysupra]

your answers are here. //www.diynot.com/forums/viewtopic.php?t=80131

Dont worry about sharp grit. Also you really should forget the underfloor heating unless you use water system. The cost of running electric heating is stupid. Also it is another item that can cause floors to fail, pushing your luck really when laying screed, dpm, floor coverings ect.
Also a scrabbler takes off the top surface of concrete. Shot/bead blasting may be your best bet.
Have a look here for products http://www.f-ball.co.uk/

 

[robertoi]

Thanks for that - I had a look at that post before. Guess I just wanted a bit of reassurance! Will look into hiring a shot blaster.

 

[robertoi]

Should have said -

I wont be installing the UF heating straight away, I will leave the self levelling compound a good few weeks to dry out properly before installing it. Surely heating is only likely to cause problems with very 'young' floors, as the continuous expansion/ contraction and more rapid drying as a result would be the thing likely to cause probs below? Besides, there will be insulation boards between the heating element and the compound.

BTW - in your sticky - is there any particular reason why you recommend F75 rather than F76 for the DPM?

 

[robertoi]

Sorry for the multiple posts to my own question.

Shot blasting machines appear to cost a fortune to hire and are bloody huge to boot.....any alternatives - aside from alot of manual labour that is?

 

[mattysupra]

the two coat system dpm is better than one coat. There is to much room for error with one coat, like a pin hole in the first coat or the floor sucking the epoxy in leaving bare patch. If you dont use these products every day then always go with two coat. As for shot blasting, you can do it by hand with a scrapper ect. But it is going to be down to your own judgement on weather the floor will be o.k to use the products over. The dpm has to bond properly and if the old glue ect lets go 6 months down the line then the floor will fail. Try ringing the fball tech line, they keep bringing out new products all the time and may advice a better system for you?

 

[robertoi]

Cheers,
I'll give them a ring on Monday.

How about using a diamond cup disc on an angle grinder to get rid of the crap? Its fairly loose in places anyway, and its only an area of about 4 square metres.

 

[mattysupra]

ye that will do.

 

[robertoi]

Thanks for your advice Matt

Got all my materials now for this job and just about ready to get on with it - but after removing all old floor tiles Im beginning to suspect that the floor has a slight slope to it. This isnt something Id anticipated.

I bought two bags of Stopgap 900 for the first layer of self levelling, which I worked out should give 4mm depth over 7 sq. metres. However if theres a slope of a few mm, this means the compound will run from one side of the room to the other, making the compound thinner on one side, and possibly less than the recommended min depth of 3mm.

Do you reckon this is likely to be a problem or should I get one more bag to make it 6mm to be on the safe side?? The floor on the higher side is in much better nick than on the lower side, so presumably I could feather the edge of the first levelling layer down to the wall, apply dpm, then add my 4mm top layer of compound.

Many thanks

 

[mattysupra]

dont worry about the slope. The compound dont run that much. Start at the deep end and work to the higher level of floor. You should end up with correct depth.

 

[robertoi]

Thanks -
This may sound like an incredibly thick question, but when mixing the compound, I should mix all 3 bottles of 900 liquid with all 3 bags of 900 powder at the same time right? And then shoull I just pour the whole lot onto the floor in one go before troweling?

Thanks

 

[mattysupra]

i mix 3 at a time but i do this everyday! all depends on how fast you can lay the stuff! i would go for 1 at a time unless a small area. 6sqm or so.

 

[robertoi]

Cheers matt - youre a legend.

Have laid the 900 - great fun! will wait 24 hrs (or do I need more time since I laid approx 6mm thick?) before applying dpm. Got alot of pinholes in the 900 - presumably these will just be filled with the dpm liquid as I apply it?

My fault for not getting a spiked roller I suppose.

 

[mattysupra]

alot of pinholes?? You did prime the subfloor first before laying the compound? And give in 2 days before you put the dpm down. You have the 2 coat system dont you?