Help: Applying slate tiles to a concrete block retaining wall

FiFi_Mad_Mum

I have a raised flower bed built with breeze block, I picked up some 'bargain' slate tiles the other day but have since spent many hours on the web trying to work out how to apply said tiles. I saw that there are special adhesives suitable for exterior use and also that you have to seal the tiles as well, some say before fitting and some say after fitting but before grouting. I now realise I will have to render the wall before thinking about applying tiles. All advice gratefully received such as composition for render and best products for fitting tiles. As you can see bargain tiles are gonna cost a lot to fit.

FiFi

keystone

Do you really mean breeze or do you mean block?

Do you mean slate roofing tiles or;

do you mean slate floor tiles or;

do you mean slate coloured ceramic floor / wall tiles?

Cheers

FiFi_Mad_Mum

They are concrete blocks, the big rectangular shaped ones, sorry I thought that was what you called Breeze block.
The tiles are natural stone slate tiles suitable for floor or wall measuring 10cm x 10cm each.

FiFi

keystone

The problem with these blocks are that they are nicely porous and you'll get a build up of moisture if not downright wetness inside so that ultimately you could find the tiles being pushed off by a water sodden block freezing. Ideally you'd tank the inside of the wall but that might not be cost effective.

You can't tile straight onto the blocks without any preparation - they'll just suck all the water straight out of the addy with a "tiles all over the ground" scenario following shortly after. As a minimum you should prime them first but DO NOT use PVA. Use an acrylic primer like Mapei Primer G or BAL APD or SBR. Frankly I'd render first but still prime. For the addy use a single part flexible cementatious bagged adhesive suitable for external usage and if you use two part don't cross brand. I'd prolly be going for Mapei Keraflex or BAL SPF meself. Whatever you do don't use premixed tubbed stuff!

Fix the tiles using a solid bed (semi circular notched trowel) and don't spot fix them. If you spot fix water will get behind and then freeze and oops off it comes. If you have difficulty getting the tiles to stick then back butter as well as your solid bed to ensure 100% contact.

As regards sealing for slate I'd seal before grouting and seal again after grouting.

HTH

Cheers

FiFi_Mad_Mum

Hi Keystone, (tried to pm but your inbox is full)
Thanks again for the help on fixing our tiles to the wall. I hope I can pick your brains for a little bit more info, I bought the Mapei primer and the Keraflex as you advised and I think we may have mucked up, DH applied two coats of primer to the wall and then a coat of 2/1 render, we have just went to fix the tiles and the render started falling of the wall. DH now thinks that we shouldn't have primed first, is he correct?
Any advice for our predicament gratefully received.
FiFi

Alan_M_2

The idea was to render the blocks then use an acrylic primer on the render.

Now you've actually primed the concrete blocks I don't see an issue with tiling them directly, this is after all only an aesthetic finish, not a shower. So it doesn't matter if you don't create a completely impervious surface. Part of the purpose of the primer is to stop the 'draw' of the blocks pulling the moisture out of the adhesive too quickly and disrupting the designed drying process as well as stopping chemical reactions with cement.

I have to admit I don't have a great deal of experience of Mapei adhesives, when I ran my tile contracting business we used mostly Ardex and BAL.

For a job like this I'd use Ardex X7 (which can even be applied to wet surfaces) or mapei equivalent.

If you've got a reasonably flat surface just tile straight onto it. If it undulates enough that it needs flattening, then you may have to render it too a degree, I'm not actually sure how the primer will effect the bond of the render though - that's not actually something I ever came across.

keystone

Alan_M wrote: »

The idea was to render the blocks then use an acrylic primer on the render.

Thank you you - you are correct. I was just rereading my post in case I had been equivocal.

Now you've actually primed the concrete blocks I don't see an issue with tiling them directly, this is after all only an aesthetic finish, not a shower. So it doesn't matter if you don't create a completely impervious surface.

Yes that was one of the options I put forward.

I have to admit I don't have a great deal of experience of Mapei adhesives, when I ran my tile contracting business we used mostly Ardex and BAL.

I was unmoveably a BAL man until someone persuaded me to try Mapei out. If nothing else the pot life is phenomenal - you can mix a big batch up and work with it all morning (or afternoon)

... I'm not actually sure how the primer will effect the bond of the render though - that's not actually somethign I ever came across.

Me neither - never done it nor seen it.

Cheers

keystone

FiFi_Mad_Mum wrote: »

Hi Keystone, (tried to pm but your inbox is full)

Ooops - sorry I have made some deletions.

Thanks again for the help on fixing our tiles to the wall. I hope I can pick your brains for a little bit more info, I bought the Mapei primer and the Keraflex as you advised and I think we may have mucked up, DH applied two coats of primer to the wall and then a coat of 2/1 render, we have just went to fix the tiles and the render started falling of the wall. DH now thinks that we shouldn't have primed first, is he correct?

As Alan M has correctly surmised what I thought I'd said was either prime and then tile direct or render first, then prime, then tile.

Any advice for our predicament gratefully received.

I'd suggest to chop the render off that is still on there and then tile straight over the primer now. If you have some minor surface inconsistences these can easily be taken out with the tile addy first - allow to set then tile over. Like Alan I have no experience of trying to make render stick to an acrylic primed surface so am unable to comment immediately. I'll ask a couple of friends tomorrow but, as I say, I think the solution now is to skip the rendering element.

HTH

Cheers.

Alan_M_2

I agree, I'd straighten any areas up with a skim coat of adhesive and not bother with render unless the surface is in a shocking state.