Large Format Outdoor tiles advice.

[cdbe11]

Hi, I'm new to the forum and fairly new to tiling, my only previous "proper" job was my recent bathroom (600x600 porcelain, about 25m walls and floors) which went pretty well.

I'm now having a go at the patio - it's 30m, a concrete slab laid last year. It was laid in 3 bays, between screeds (rows of cut down paving slabs) so there is a bit of hairline expansion/contraction between the materials - I don't know how accommodating tile adhesives are so I want to use a flexible, with a standard set. I've yet to put a line across the slab but I'm hoping it's +- less than 10mm. The tiles are 750mm 10m rak porcelain. I'll be using shmox twister 2mm levellers.

I want a thick bed 15mm? - I think it'll be easier and I could do with gaining a bit of height. I've tried to read and understand the square Vs round notched trowel business - I get that a 20mm square will make a 10 mm bed etc but can't grasp how different shaped beds behave so I'll stick with square as that's what I've used before.

My questions are -
adhesive - coverage for 30m with a 15mm bed?

type - I've been advised that Pro Flex SPES Ultra Tile Fix Standard Set Flexible Adhesive would be ok, I don't have access to trade prices but can get 10 bags locally for £134 so this is my starting point?

priming - I've previously used SBR, should I prime tiles, concrete or neither?

trowel - I think I need a 30mm square notched, but they don't seem to exist - I suspect I'm missing something here?

back buttering - is this just a thin smear on the back of the tiles and should I do it

anything else? I'm ok with cutting and grouting and using the shmox but I'm sure there's plenty more.

any tips or suggestions would be greatly appreciated

 

[gamer1]

For your patio tiling project, here are some answers to your questions:

Adhesive Coverage: To calculate adhesive coverage, you'll need to consider both the tile size and the notch size of your trowel. In your case, with 750mm x 750mm tiles and a 15mm bed, you'll likely need a significant amount of adhesive. It's essential to follow the manufacturer's recommendations on coverage for the specific adhesive you choose.

Adhesive Type: The Pro Flex SPES Ultra Tile Fix Standard Set Flexible Adhesive you mentioned should work well for your project. It's essential to use a flexible adhesive given the potential for expansion and contraction in an outdoor setting.

Priming: While SBR (Styrene Butadiene Rubber) is commonly used as a bonding agent for concrete, it's not typically used as a primer for tiles. For priming, you can use a specific tile primer suitable for the substrate (concrete, in this case). Priming the concrete surface before tiling can improve adhesion.

Trowel Size: A 30mm square-notched trowel may not be a standard size, but you can achieve a 15mm bed with a smaller notched trowel by using a technique called "back-buttering" (applying adhesive to the back of the tile). This compensates for the smaller notch size and ensures proper coverage.

Back Buttering: Yes, back buttering involves applying a thin, even layer of adhesive to the back of each tile before setting it. This helps ensure good adhesion and coverage, especially when dealing with larger tiles or uneven surfaces.

Additional Tips:

Make sure your concrete substrate is clean, level, and free from any contaminants.
Consider using an uncoupling membrane like Schluter-DITRA under the tiles, which can help with movement and provide a waterproofing layer.
Use a rubber mallet to gently tap the tiles into place, ensuring they are level and evenly set.

 

[Alan tiler]

Hi,i laid a porcelain patio last year on a cement bed,i also slurry coated(SBR mixed with some of the cement,30-40mm cement then a 5 mm spacer.For the grouting i used Sika fastfix compound,sets solid.

 

[cdbe11]

Thanks. It's done - pretty much as I planned but I made a 15mm notched trowel from an old float. I back buttered the tiles and the bed thickness was just about ok to get over the high areas, took 15 bags of adhesive. Killed me in the heat last week and wasn't really keeping the joints clear so had to spend a day clearing them all out - a lesson learned. Now it's all ready for grouting but it seems rain forecast forever! Grout is mapei ultracolour plus, the issue is water in the joints, I guess they need to be bone dry - so I'll need fair weather before and some time after I apply the grout?