Prep for Engineered wood or laminate floor on 1962 concrete slab & screed

Hello. I'm planning to lay either an 16-18mm thick wood flooring or an 8-12mm thick laminate flooring. I'm a fairly competent DIYer with some engineering, building & construction knowledge (i.e. I'm an officer based civil engineer). I've been reading various discussions on various forums about subfloor preparation and am left very confused as none of them seem to hit my concerns squarely on the head. So here goes...

The situation in my house is:

1. I want to lay an engineered wood or laminate flooring (depending partly on the outcome of this discussion and partly on price) through the lounge, hall and dining room.
2. The floor is approx 30mm of screed on top of a concrete floor slab (see photo)
3. My house was built in 1962.
4. I'm not sure it was built with a DPM (I've read it wasn't a requirement back then). HOWEVER, I broke some cracked & heaving screed up which was causing a high spot in a corner of the lounge and can see what might be a DPM (see photo) - possibly not very affective. The plastic sheet is very thin (e.g. more free coroner shop plastic carrier bag than what we'd used as DPM plastic sheet today).
5. The screws for the gripper rods around the rooms were rusty and snapped with a tap or two of the hammer, so I'm assuming some damp gets in. I've not noticed any other signs of damp.
6. On top of the screed are Marley tiles. The tiles are fixed with a bitumen adhesive (see photos).
7. I had a friend in the abestos business test the tiles and they confirmed the tiles contain asbestos. The bitumen may also, but I didn't have that tested, although I think it unlikely.
8. Besides the Marley tiles, across the three rooms I also have areas:
   • Where the Marley tiles have been lifted and the bitumen is exposed (see photos)
   • Original screed (rough in places) (see photo)
9. The Marley tiles seem securely fixed, although I'm sure it wouldn't take much to lift them with a little heat and a scraper as the bitumen adhesive was obviously applied sparingly (see photo)
10. I've removed the broken bits around the edges the room where the gripper boards are.
11. I've been over the floor with an 1800mm spirit level and it looks pretty level. However there are small hollows of around 2mm of, say, approx 750mm to 1500mm diameter.
12. I'd like to avoid removing the Marley tiles both because it's extra work and because of the asbestos. I definitely won't be getting into removing the bitumen.

I feel my options are:

1. Leave the Marley tiles down and pour a Self Levelling Compound (SLC) where the tiles are missing to bring it up to the same surface level as the tiles (so approx 2 to 3mm of SLC. Then lay the new floor on a DPM from the builder's merchants (300 microns / 1200 gauge)
2. Cover the whole floor with SLC to even it out and encapsulate the Marley tiles. This will be approx 2 to 3mm over the tiles and 5 or 6mm where there are none. Then lay the new floor on a 1200 gauge DPM.
3. Remove the Marley tiles and lay fibreboards on a 1200 gauge DPM.

What I hoping for in any replies are the pros and cons of each option and suggestions on what products I should use, layer by layer, to level the floor and protect the engineered wood or laminate.

Sorry it's long, but I all the detail may save further questions.

Many thanks.
Steve

 

Bad news that’s a full rip up grind down screed and surface dpm job, you’ll need to test the compression strength and Rh% of the screed to find out what products you need to use. Wood needs bonding to the floor not floating like a laminate so you will need a high compression strength high flexural strength screed for that, you’ll get away with Ardex NA for the laminate. I wouldn’t touch it with a barge pole unless it was a belt and braces prep on that it’s absolutely going to fail otherwise.


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Agree with above, out with the old and in with the new...

 

Latex over it all and float a engineered wood with built in dpm underlay. Job done. V4 t and g pva all edges. Don’t use a clic system. They crack constantly.
Stuck done floor is nicer but you won’t get any guarantee sticking to a old subfloor like that. You should really have it dug out and have a new screed put in. Depends how much work and money you want to throw at it


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Thank you all for your replies. That all sound very expensive and way too much work.

Was it clear I was considering Engineered Wood and not solid hardwood fixed to the subfloor? I thought floating Engineered Wood would be fine if I lifted the marly tiles, laid a 2mm layer of Ardex NX, plus their liquid DPM and then another 2mm layer of NX?

Ardex say the NX will bond well to the bitumen adhesive residue and suggested the above approach.

 

Floated floor is fine


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Use an underlay with a built in DPM

 

We always use a underlay with a built in dpm over old slabs. Howdens 4 in 1 is very good


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If the floors flat you only need to fill in where the tiles are missing


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Thanks all.

I'm still in two minds about whether to lift the tiles or not. I think I'll have a go and see how easy it is on mass - probably this weekend. I've lifted a few around the edges and they came up easy if I heated them first , so I may just do a few a night and hopefully get through it without much difficulty.

The alternative is laying Arditex NA over the tiles, but for some reason, I feel the better job would be to lift them.

I was thinking of a floating floor on a plastic DMP. But I do see that if I keep the tiles down that would be overkill and if I lift them it wouldn't take much to lay a liquid DPM (although I don't know how much that is, but I think it'd be worth it if it's £100 or so).

The very last thing I want to to have problems in the future because I tried to save a bit of time or money now.

 

A liquid dpm is not cheap


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Just an update and to close out, I lifted the tiles (respirators used, tiles lifted easy) and laid a smoothing layer of Stopgap 1200 followed by Stopgap F77 and another layer of Stopgap 1200. I'm pretty happy with the results and it's a huge improvement on what was there before, which was a mess.

Cost about £600 in total, but happy I can now lay the new flooring without any worries further down the line.

Thank you all responses and food for thought.

 

I would not remove the Marley tiles this should only be done by a contractor who specialises in removal of asbestos. Damp test
, screed the floor for level fit a floating floor with a dpm and underlay.

 

You can remove the tiles yourself. You will be fine. Very small amount of asbestos in the tiles.