Different floors one room

[temptedtojoin]

Hello, I am hoping somebody can give me some advice. I have had an extension built on my kitchen. This is nearly ready for tiling.

On one half of the room i have joists with old floorboards on, they have been removed and replaced with 18mm moisture resistant tounge & groove chipboard which is glued and heavily screwed down. The other half is 50mm screed layed over 100mm concrete with insulation under.

The screed is flush with the chipboard so at the moment the floor is all one level. This cannot be altered in any way as there is not enough door clearance, so tiles will need to be laid onto these 2 floors.

What i would like to know is would i need to use 2 different adhesives?
Where the surfaces meet can i overlap or do i need 2 keep the surfaces seperate? (there is one bit that is an l-shape which would make not overlapping difficult.)

One final question, the doorway to the room is about a 45 deg. Do i tile to the inside edge, outside, or middle of the threshold. This leads to the hallway which eventually will have carpet. Door opens into the kitchen.

(other information: tiles 333x333x8mm, porcelain. South facing room with 2 windows. Washing machine will be on chipboard end.)

 

[grumpygrouter]

First thing to say is that you will need an expansion joint where the 2 substrates meet. Screed and timber with expand and contract at different rates giving rise to stresses in your tiles which would resulting in cracking. Secondly, if there is no room to overboard,the chipboard really needs to be replaced with 18mm wbp ply instead. Chipboard is not the best substrate for tiling onto!!! If you have ply instead of the chipboard, you will usually be able to use the same flexible adhesive all the way through, but this depends on who's make of adhesive you use. If you HAVE to stay with the chipboard then I recommend that you check out Ardexflex 7001 adhesive for the timber side. It is excellent stuff but isn't a cure all for your potential problems.
I normally tile to halfway into the threshold where the door shut line hides tile edge.

 

[Ajax123]

I think this one sounds fraught with danger. As grumpy says chip board is not great for tiling too and if the washing machine is on this area and it leaks there are likley to be long term issues.
Overplying is a great option. Would a decoupling mat be a thinner option if clearance is an issue. If you must keep the current levels then it is worth considering taking the chip board up and replacing it with Ply. Also is the ply screwed down or nailed.
You deffinietly need a joint where the 2 substrates meets. Overlapping is not a sensible option I'm afraid.

 

[meagain]

The old floorboards are not removed yet, so i could still save this then with ply.
The only reason i opted for the chipboard was because it was moisture resistant, so if there was a leak it would be no different to the ply. Also i thought it would make the strongest level flooring compared to ply because of the tounge and groove so would flex less. Also because it was chipboard i thought the gap between that and the screed would be fine because chipboard would be unlikely to expand due to it being manmade.
The original floor was 19mm, i have to change this to 18mm so that 50mm of screed can be laid and would give me a level playing field. This is very tight to the back door opening which can only be raised a little, which i am allowing for adhesive and the 8mm tiles.
I don't even know how thick adhesive i need to use, i am hoping that is quite low, as height is a real big issue.
I will have to look up a decoupling mat, but i need 18mm on the joists to give me enough room to get 50mm screed down which was building regs. requirement.
Fully open to suggestions, also joists run length ways and just sit on dwarf walls, that was another reason for going for chipboard as i wouldn't have to put a lot of noggins in where boards join. Room is 8ft wide though.
We can do this.......

 

[Ajax123]

The old floorboards are not removed yet, so i could still save this then with ply.
The only reason i opted for the chipboard was because it was moisture resistant, so if there was a leak it would be no different to the ply. Also i thought it would make the strongest level flooring compared to ply because of the tounge and groove so would flex less. Also because it was chipboard i thought the gap between that and the screed would be fine because chipboard would be unlikely to expand due to it being manmade.
The original floor was 19mm, i have to change this to 18mm so that 50mm of screed can be laid and would give me a level playing field. This is very tight to the back door opening which can only be raised a little, which i am allowing for adhesive and the 8mm tiles.
I don't even know how thick adhesive i need to use, i am hoping that is quite low, as height is a real big issue.
I will have to look up a decoupling mat, but i need 18mm on the joists to give me enough room to get 50mm screed down which was building regs. requirement.
Fully open to suggestions, also joists run length ways and just sit on dwarf walls, that was another reason for going for chipboard as i wouldn't have to put a lot of noggins in where boards join. Room is 8ft wide though.
We can do this.......

This does not sound right. Buidling Regs don't usually stipulate screed depths. These are generally set by British Standards. If it is floating it should be Minimum 65mm if Sand Cement and Minimum 35mm if Flowing Proprietary Screed. If Unbonded (i.e. on a solid substrate over a sheet of polythene) then 50mm Sand Cement and 30mm Flowing is appropriate. You could reduce the depths perhaps by using a flowing screed. For such a small area thoug you would be best looking at a bagged material. There are a few of these about but availability of some depends on where you are in the country. This would give you a bit more room to play with in terms of heights.

 

[tellmenow]

Looking at building regs. spec. sheet. floor: 50mm screed on concrete slab on 1,200g damp proof course on 70mm celotex tuffr insulation batts.

I have 50mm gap to screed, this cannot be lower because it has to be level with existing floor. It cannot be higher as i don't have the clearance at doors. Even if i wanted to put down 40mm it won't level off with the original floor. I don't want to put anything less than 18mm on the joists as it won't match the 50mm that i have to lay.

Just to confirm i have to lay 50mm. As i also have pipework to be covered. But i also want to tile the whole room, which will span across 2 substances. Screed & chipboard or ply.

I am following the regulations and everything upto now has been done to level this out.

 

[Ajax123]

Looking at building regs. spec. sheet. floor: 50mm screed on concrete slab on 1,200g damp proof course on 70mm celotex tuffr insulation batts.

I have 50mm gap to screed, this cannot be lower because it has to be level with existing floor. It cannot be higher as i don't have the clearance at doors. Even if i wanted to put down 40mm it won't level off with the original floor. I don't want to put anything less than 18mm on the joists as it won't match the 50mm that i have to lay.

Just to confirm i have to lay 50mm. As i also have pipework to be covered. But i also want to tile the whole room, which will span across 2 substances. Screed & chipboard or ply.

I am following the regulations and everything upto now has been done to level this out.

This sounds highly suspect in terms of the expected performance of a screed in these curcumstances. Not saying that your spec sheet does not say what you say it says but if it does say that it does not meet the minimum requirements for floating screed under BS8204 part 1. The fact you have pipes to cover makes it even worse because burying these in a screed of this depth they will simply act as crack inducers. I strongly suggest that you review this if possible because my gut feeling if you use a hand compacted cement based screed in this way you will have problems with cracking due to shrinkage, curling and due to the induced cracks from the pipes. Are they copper or plastic pipes. If copper hey also must be lagged. The nominal depth of floating hand compacted screeds should allow a minimum depth of cover to conduits of 50mm so if it is a 15mm pipe the overall depth of screed should be 65mm.

Which part of the building regs is this trying to acheive (my guess Part L - Thermal) I suspect they have come up with a plan to meet the thermal requirements and simply filled the other 50mm up with screed witout very much thought (sounds a bit harsh reading it back but not meant that way).

If you were to use a self compacting screed you would be able to use this at 50mm depth without any of these risks provided you can acheive 25mm cover to the pipes you mention.

 

[Perry]

put a mat well at the door which can be lower

 

[fromtheprojects]

Either way, i have to lay 50mm now. The whole extension has been built around these measurements.

I will have screed and ply or chipboard.

Is chipboard really that bad to lay tiles on? would it not be the better choice in my situation.

If its moisture resistant green chipboard why would that cause a problem by washing machine if things leaked???

 

[yourkillingme]

It has to be laid.

I am now going for 18mm wbp plywood. To make sure this is down strongest, would you suggest full size boards?, half boards? or have just seen they do 18mm ply planks so could be laid like floorboards????

 

[White Room]

Full boards, you want the least amount of joints as possible

 

[DHTiling]

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