Help!: Expansion joint / cold joint

[mercedism]

Finally got some ply down and am nearly ready for screeding.

Been reading up and i think what i may need is what is referred to as a cold joint.

The plan is to put something along the edges of the ply so we can screed upto it and then when this has gone off remove and fill with the same flexible adhesive i will be using for the tiles?

Screed will be 50mm depth, but what do i use to create the gap and what sort of width should it be? Or if i am heading down the wrong route please advise as would like to get the screeding down at the end of the week.

Pics can be found here as i can't seem to be able to get them on here.

kitchen

[Dave]

pics.....

[mercedism]

cheers Dave, if i am struggling with pics........

[Ajax123]

Not sure I understand what this is getting at. Why do you need a "cold joint".

Also what type of screed are you using as standard sand cement screed will not accept a great deal of deflection without cracking. On these type of old solid timber joists you need to be a bit carefull about this bit because you don't want the screed to crack. I would also put a polythene slip membrane under the screed on top of the ply first. This helps to prevent restraint and allows the screed to move "independently" of the ply which helps to reduce cracking. It will also prevent the need to prime the ply first.

Are you putting underfloor heating into the screed at all?

[Colour Republic]

Judging by the Pics Ajax, I think what he is planning on doing is screeding over the concrete area to bring it up to level with the insulation and ply and also the floor boards at the other end of the room, so he will be left with 3 different types of substrate

[Colour Republic]

oh no hang on... He's removed the floor boards, replaced with ply then injected the void with expanding foam. So maybe he's just planing on screeding the concrete area to bring up to level with the ply'd area?

[Ajax123]

oh no hang on... He's removed the floor boards, replaced with ply then injected the void with expanding foam. So maybe he's just planing on screeding the concrete area to bring up to level with the ply'd area?

Aaaah yes - you could well be right.

[mercedism]

Correct, because of the extension i have to have 50mm screed as per building regs. Due to height of back door i have removed old floorboards and replaced with 18mm ply (the thickest i could use). These are nice and tight and the foam was just to stop anything falling down as there was a small gap with dwarf wall there.

This will hopefully be all one level. Its just how to get the two to sit next to each other so this can be tiled. The plan was to start the tiles along the join of the two, but if you think i can straddle the join, 50/50 either side that would make life easier.

Note: Ply is the maximum height this can go allowing for thin coat of adhesive and my thin tiles.

[foxman]

Hi i always cut a bit of 6mm plyn to lenngth and place it between the new screed and new plywood and go back before its gone off properly take it out and your left with your expansion gap then silicone,cheers Mick

[mercedism]

Thanks, thats the advice i needed. Bet i haven't got any 6mm though!!!

Would you say its ok to bridge the join or should i lay the tiles either side?

[foxman]

If you want to bridge the joint you will need ditra matting or durabace ci or g matting you could put the tiles either side but in doing that your governed with your setting out and you will have to put a 5 mm silicone joint there might not look to good, cheers Mick

[mercedism]

Thanks again, just went and got some fibres for the mix and checked friends garage for some 6mm ply. (none there).

I will probably get the screed down and then start another thread on the tiling aspect of it. Only thing though is i really am limited for height so won't be able to put down anything like ditra matting as i need to be low profile. Can't spare even a few mm.

Will post some pics and hopefully get some help on the best plan to get them down.

[Ajax123]

I will leave the tilers on here to talk about the tiling aspect but from the point of vbiew of the screed you would be wise to either unbond the screed from the concrete using a poly membrane or make sure it is properly primed before you screed. The min depth you can use sand cement is 50mm. There is a potential issue of curling to take account of. To help minimise this you should cover your screed with a sheet of polythene for 7 days once installed in order to cure it. Then let it dry for 1mm per day before tiling. Prime the surface of the screed before placing any tiles on it.

You should not bridge the joint with tiles (even with uncoupling it could be a risk due to curling)

[mercedism]

The plan was that we are going for a dry mix with fibre. But we are going to prime it first and laying a cement slurry down for the bonding.

Once this is down, it will be a novelty not having a step in the middle of the room. I am happy to wait as long as it takes before tiling.

Some great advice, look forward to my next batch of pictures.

(hopefully might have found some decent software too, to aid in the design.)

[Colour Republic]

I am happy to wait as long as it takes before tiling.

Did you really just say that! Top marks Mercedism, almost unheard of! Hope it all goes well

[foxman]

I would let the screed dry first the way Ajax says but then you will be ok with a decoupling mat, it is what they are designed for alowing any moisture from new screeds to evaporate properly the way the mat is designed , looking at your photos your going to be pretty lucky if you put tiles either side of the two surfaces and for the setting out to be spot on especially as you have a sort of dog leg with your surfaces if you know what i mean. Mick

[mercedism]

I know i have the dog leg bit, so once screed is drying out i can start setting out on the ply to see what i have to play with and how it works out. The only slight advantage i have is the dogleg side will be where the kitchen units will sit.