Re-doing a bad job of levelling floor

[Ninemill]

Hi everyone,

I have a problem with the floor in my terraced house that I’m hoping someone can advise me on. When I moved in to the house 3 years ago I levelled the very uneven concrete floor in the front room and then put carpet down but have had problems with it ever since.

I used a cement screed to fill in the big dips in the floor and then used self-levelling compound as a final layer to bring it level and flat, but over time it’s become evident that the layers I put down have not bonded with the original concrete below at all - this has manifested itself in a ‘crunchy’ feeling under foot as the top layer cracks and breaks up as you walk on it.

I’ve put off the inevitable for a while but now I’ve decided to take up the carpet, thoroughly level the floor and put down some wooden flooring instead. Can anyone offer advice about how to avoid a repeat of the above with suggestions on materials or techniques?

The room is around 3.5 – 4 sq.m with an undulating floor, maximum height difference of about an inch in places. I’ve taken up the very loose pieces of levelling compound now and found that I laid this very (too?) thick in places, some pieces are over 15mm in thickness.

I've read the main article in flooring and am I right in thinking I need to bring the floor within about 3mm of level with 400 repair mortar, prime with p131 neoprene primer then use a water-based self-leveller to finish it off? I'm assuming the repair mortar will stick well to the floor below it when applied thinly?

Many thanks in advance for your advice.

Tom.

 

[mattysupra]

no you dont need to bring the subfloor within 3mm with repair compound. Use the repair compound/ mortar to take out any bad dips/holes.

I would use an agrylic compound like balls 200. I think (from memory) that it can go 12 or 15 mm in one go. But it may be cheaper to do a filled mix with agregate and then one full skim when dry at say 3mm.

Always prime between coats and the concrete subfloor.

 

[Ninemill]

Thanks very much for taking the time to reply Matt, do you have any links to suplliers of the products you mention, or are they commonly available from builders merchants?

Just a couple more questions if I may?

You say in other posts that the acrylic compounds don't flow very well, is this just relative to water-based or are they particularly difficult to work with?

Also, there's a large part of the floor, maybe 40%, where the levelling compound I put down has not cracked and has bonded well to the concrete below. Is it OK to bring the rest of the floor roughly up to this level and apply a thin layer of acrylic compound over the whole floor, or should I take out all exisiting compound down already?

Many thanks again,

Tom.

 

[Ninemill]

Went to the local F Balls dealer today and spoke with the counter staff. They didn't have 200 so instead we've gone with a filled mix of green bag so get the level and then a finishing coat of 300.

The datasheets say a 3mm drying time of 12 hours before proceeding with the top layer. Any ideas what this will increase to with patches of 20mm application? What are the consequences of applying the top finish to soon? My girlfriends father is coming over to help with the top layer on Sunday and I'm worried it wont be dry enough.

 

[mattysupra]

who advised you this ? whats there name/company please! send me that in a P.m, you may have to add me as a friend to do that in my profile.


First off, the green bag will be o.k, but i would of preferred to see 200 go down due to it strength over a deep fill. You wont have a problem tho.

The next problem is that your using 300 to smooth off. Its water based so will flow well (easy to use) but is moister sensitive. Basically- if you have a moister problem in your subfloor (damaged/non working dpm) which is possible due to your last screed failing but still bonded! Then this 300 will fail also. Acrylic 200 would cope with moister problems.

However- 300 is fast set so can be a pain to use unless your super fast at putting the stuff down. As you dont do this for a living, Red bag water based would of been a better option for yourself if water based is what you wanted.


Now lets hope there is no moister problem in your subfloor. If so then there will be no problem with using the water based 300 providing the compression strength of the green bag is the same or equal. i don't know the answer to this as they have changed the spec of green bag and i have not had time to play with it. Again tho- red bag has less compression strength so would of been the better choice for yourself.

You will however need to allow the green bag to dry out properly before using the 300 due to being moister sensitive. At your thickness i would like to see at least a week with good ventilation/fans in place.


I still cant belive they dont have 200 in stock where you are! You must live in cowboy/latex city !

 

[Ninemill]

Could have well been a case of poor explanation by me. Originally over the phone I asked for a price on 200 and they said they didn't stock it but they did do 300. I looked it up on the Balls website and to my untrained eye it seemed to be very similar in it's intended use.

It's difficult to recall the exact conversation I had at the shop, but I explained I wanted to do a deep fill of around 20mm with 300 (thinking it was similar to 200) and then finish off with straight 300. They said green bag would be better for the thick first layer.

Anyway, I put the green bag layer down today so I'm glad it wasn't the complete wrong choice! It went down extremely well on top of the primed floor. According to your guess I have a week to sort out the top layer so I'll have chance to ring the shop again and have another, better informed chat about the top layer. I can always take the 300 back and get them to order in some 200 for me.

Thanks again for your input, I'll have a more concise chat with the shop on Tuesday and let you know if their opinion seems to differ from yours or whether I just didn't express myself very well and got bamboozled with data sheets!