Outdoor tiling

[AndyH]

Hi everybody,

I have a outdoor garage that is being converted to a laundry and storage area - it is totally covered, enclosed and approximately 6 meters by 4 meters. It has an existing concrete slab that is probably 10-15 years old. The temperate ranges from 5degrees celsius to 40 degrees celsius - there isnt any snow or freezing temperates.

Our builder has said that we need to raise this slab approximately 40mm so that the doorway is higher than the outside so water doesnt come in. We will then tile ontop of this with porcelain tiles.

Id like to have a go at this myself, - am i right in assuming that a sand/cement screed should be used to achieve this level, applied directly ontop of the existing slab? And then tile directly on top of this? Or is this the wrong way to go about it?

Should a sealer or membrane of some sort be applied to the exisiting concrete slab or screed before tiling to prevent the tiles cracking?

Thanks! :)

[Honorary Bloke]

By rights, there should be a water barrier underneath the old slab. But since you can't know if there is, I suggest a further barrier under the new.

Tiles are laid directly on flat concrete every day, no worries. But it must be FLAT! Tiles want flat, period.

How to achieve the 40mm rise is another issue and maybe someone else will recommend a solution. I would tend to want the whole slab hammered out and re-poured, but that is an expensive alternative.

[mic-d]

The 40mm rise is very easily done with a mortar bed. You use a 4:1 mix of medium river sand (bedding sand or sharp sand - not beach sand) and cement. Mix the sand/cement dry and then add only just enough water to allow a fistfull of mix to retain its shape but not leave moisture on the hand. It will seem much too dry, but any wetter makes it hard to work and will shrink and crack when dry. It helps to have an offsider mix while you lay it. Unless you are fit, I wouldn't try more than about 4x3m on your own in a wheelbarrow. You can use a cement-based tile adhesive to bond the cement to the mortar or a diluted bondcrete mix. Use 40mm alum angle at the doorways. Throw the mix around the wall first to build a ledger at the right height. Use a wooden float to compress the mix down hard. Once the ledger is complete start filling the rest of the void and compress it down by bashing it with the float or stomping on it. use a straight edge across the ledgers to carve off high spots or fill low spots. Aim to finish it all in one day. You will be able to walk on it immediately and even tile immediately if it is done right. After you have trimmed the surface flat and true, you can also run a steel float over it to bring a bit of moisture up and consolidate the surface, making it less dusty when dry. It is quite normal however for the surface to be a bit dusty and easily scuffed up, don't worry if this is the case. Small imperfections like boot/knee marks are irrelevant.
Goodluck.

Cheers
Michael

[AndyH]

thanks for the replies, much appreciated, esp Michael for being so detailed!

Michael, is the cement-based tile adhesive/diluted bondcrete mix added together with the sand and cement when mixing the mortar? Or do you put the adhesive down, then put the sand/cement mortar over it? Apologies if its a stupid question, im a bit new to this!

Cheers

Andy

[mic-d]

G'day Andy, I should say that you don't really need to do much prep on the concrete with this type of mortar floor. If the concrete doesn't move then your bed can't go anywhere even if it doesn't bond to the concrete. However if it doesn't bond it might sound a bit drummy if you tap it. If that bothers you then you can apply tile adhesive to the concrete as you go. Or you can brush the concrete with bondcrete. I wouldn't add any additive to the mortar - makes it too hard to screed. Forgot to mention that you should probably acid wash first too if its a used, old concrete surface.

Cheers
Michael

[AndyH]

Great! Could i pick your brain for one last thing? The outside of this garage is concrete slab, and im thinking of tiling this with sandstone tiles (400x400x15mm thick). However, the slab is very uneven from the builder jackhammering out the existing slate. its exposded to the elements, but nothing crazy.

Can the same method be applied to level this outdoor slab and then tile ontop of it? its probably about 4x8 metres. Ie would i acid wash > mortar mix with adhesive > tile?

What would you recommend for the tile adhesive - the guy said i could use sand and cement to stick it down. What would you recommend the mix to sand and cement be? Or should i use a cement base adhesive?

Thanks again, much appreciated. :)

[mic-d]

Great! Could i pick your brain for one last thing? The outside of this garage is concrete slab, and im thinking of tiling this with sandstone tiles (400x400x15mm thick). However, the slab is very uneven from the builder jackhammering out the existing slate. its exposded to the elements, but nothing crazy.

Can the same method be applied to level this outdoor slab and then tile ontop of it? its probably about 4x8 metres. Ie would i acid wash > mortar mix with adhesive > tile?

What would you recommend for the tile adhesive - the guy said i could use sand and cement to stick it down. What would you recommend the mix to sand and cement be? Or should i use a cement base adhesive?

Thanks again, much appreciated. :)
Hi Andy, you could use the same method but it would be overkill and you need a surround to contain it at the edges. A better way to go (assuming its pock-marked with holes from the jackhammer but reasonably flat) is to make up a mix of 3 parts plasters sand and one part cement using a latex additive such as Davlastic to wet it rather than just water. Prep the concrete as you've said and screed the mix across it making sure to fill all the low spots. You're not aiming to build the entire surface just smooth out the irregularities. Lay some plastic over it so it dries slowly. Ardex has a range of premixed screeds if you prefer to buy some bags of product. Avoid using a SLC with gypsum in it - not good outside. You should be right to tile next day with a tile adhesive. You could lay it into a wettish motar mix if you're prepared to do all that mixing, but I reckon tile adhesive applied with a 10-12mm notched trowel is the way to go.
Cheers
Michael

[AndyH]

Thanks so much for you help, im much more confident in tackling it now! i think i would have made quite a few mistakes without your advice haha :)

Cheers!

Andy