patch render onto travertine

[GregM]

Hi Folks,
I have a bricked up doorway in a bathroom that I want to eventually tile over. The travertine bricks were standing proud but some work with a cold chisel took care of that.
After doing lots of reading here I'm wondering how far out this idea is.

1st coat 4-1 sharp sand - cement and plasticizer about 12mm thick
second coat 5-1 about 5mm thick.
Is this about right? I am going to give the travertine bricks a good drenching coz they look like they are going to soak up lots of water.

Anythoughts? How long between coats? Exactly how wet do I get them?
Any input appreciated
cheers
G

 

[GregM]

Let's try that again. I don't have travertine bricks in my wall. :mad2: I have Thermalite bricks. Breeze blocks. There's not too much difference is there?

 

[widler]

if they are thremalite,you can't render,render won't stick to that sort of block,if they are concrete block you can,but not thermalite. use bonding and skim it mate

 

[GregM]

I assume they are thermalite. They are very light, I can get a screwdriver to dig in fairly easily and a bolster chisel carves them up fairly easily, so they are very low density. I was hoping to dodge plastering it. It's only about 1m2 and i'm going to tile over it.
Basically I have done a bit of rendering before and have the bits. I haven't done any plastering and don't really want to go buy 2 bags of plaster for a little patch.
On the other hand there's no point doing it the easy way if it's going to crack and fall off.
Thanks for your reply.

 

[akinsontiles]

If its getting tiled onto just dot and dab it using plasterboard or a cement tile backer board for additional strength with dri-wall adhesive.

You don't mention the size and weight of the tile you are using so the max for plasterboard (un-skimmed) is 32kg per metre square in case you didn't know.

That way you can make sure its plumb and flush with the existing walls ready for tiling in about an hour you should be done.

 

[GregM]

I don't think tile weight will be a problem. Previously the bathroom had been covered in laminated, waterproof hardboard type stuff (Mermaid Board?) This covered all sorts of problems. One of which was a bricked up doorway. The top half is plastered and is sound. The bottom half is thermalite brick that stood proud of the wall. I hacked them back to about 15mm deeper than the wall. The first plan was to render it. I think now I should take it back a little further, even it out and use some cement backer board to fill it up. I'm using it elsewhere in the bathroom so i will have spare.
cheers

 

[Scott]

Just to clarify you cant dot and dab the cement boards, they will have to be mechancally fixed

 

[widler]

If its getting tiled onto just dot and dab it using plasterboard or a cement tile backer board for additional strength with dri-wall adhesive.

You don't mention the size and weight of the tile you are using so the max for plasterboard (un-skimmed) is 32kg per metre square in case you didn't know.

That way you can make sure its plumb and flush with the existing walls ready for tiling in about an hour you should be done.

duh,good thinking,drylining it,why dident i think of that:mad2:

 

[GregM]

Thanks to all that took the time to reply. I need to hack the breeze blocks back a little more - it's quite fun. I have a bit of adhesive left over that I can use and I will also drill and plug some cement board over the hole. cheers to all for averting potential disaster coz i really thought a cement render would be the way forwards.
A pint for you all

 

[White Room]

You can render on thermolite but it would need to be a weak mix and the way the blocks move it will crack anyway.

 

[GregM]

When I was trying to thin the blocks down a bit more they shattered so I removed them completely. I thought about removing the next layer so I could have a hatch into the bathroom.
'Honey I'm in the tub, could you get me a gin?'
maybe not.
I think it's going to make a very nice recessed set of shelves. I need to build the bottom up a little coz it's a bit too close to the bath height. I figure a few layers of cement board will do fine. Adhesive and mechanically fixed in place. Can I tile onto the edge of a few layers of cement board?

 

[White Room]

I would wipe over the edges with some addy just to fill any gaps, other than that should be fine.

 

[GregM]

That was quick. Thankyou