Advice needed on laying porcelain tiles

[Alan]

Hi All, I will be laying 9m2 of 600x300 rectified polished porcelain tiles in my bathroom. It will be over green chipboard and I know all the advice is against this but I have tiled over chipboard before and not had a problem. It is new chipboard, well screwed down at 5” centres with no bounce in the floor.

Question 1. Should I prime the floor with something like Mapei Primer G?

I plan to use Mapei Keraquick with Latex Plus (recommended by Mapei for laying on chipboard)

Question 2. What size and type of trowel. I have read lots on the subject and I am more confused than ever. I would think a 10-12mm square notched trowel on this size of tile, giving a 5-6mm bed. But there are many recommendations for round notched trowels on floor tiles as it gives better total coverage. The problem is it also says that whereas a square notched trowel will result in a bed half the depth of the notch, with a round notch trowel, the bed would only be a third of the depth of the notch, so 3mm for a 10mm notch. Surely this isn’t enough.

Question 3. Tile spacers. As these are rectified tiles, I plan on using a 2mm spacer, is this OK? I am planning to use Mapei Ultracolour Plus which has a minimum grout line of 2mm.

 

[Waluigi]

Very difficult to answer your questions when what you are suggesting from the offset is doomed for failure. Just because you’ve got away with tiling onto chipboard once, doesn’t mean you will be so lucky again.

 

[Dumbo]

In not going to get into chipboard argument as you have made your mind up .A 10 mm square notch trowel gives you a bed depth of about 3mm because you use it at an angle of approximately 45 degrees . Also minimum of 3mm grout joint .

 

[Flintstone]

Just don’t tile on it simple as that, there no reason to. Is it cost or laziness ? Overboard with 6mm hardiebacker, easily available.

 

[Just Rizzle]

i dont give advice to those who dont listen

 

[On one]

How can the chipboard be screwed at 5'' centres,if (probably) the joists are at 450mm to 600mm spacing?

 

[Alan]

How can the chipboard be screwed at 5'' centres,if (probably) the joists are at 450mm to 600mm spacing?

The joists are at 400 centres and there are 5 screws to each joist at 125mm centres. The floor is level to within 1mm ( I levelled it with packers on the joists where required). There is very little bounce which I verified by filling a glass to the brim placing it on the floor and jumping up and down. No water spilled out (I saw that test on a website and thought I would try it). I know it is not advisable but adding another 8mm for Hardibacker and the cement adds too much height. It is not a wetroom, there is a shower tray for the shower so water on the floor will be minimal. I understand why professionals would not want to do it because of the comeback if there are failures, but for DIY, if the floor is solid, providing the right adhesive is used I can't see the problem

 

[Cranbrook]

I don't do it anymore admittedly but in the past I used to tile straight on to chipboard to keep height to a minimum, and I must admit I've never had any comebacks, this included two bathrooms in a house I lived in for ten years, so if you are certain there's minimal movement and you're doing it for yourself, then I don't see a problem really, if it fails, you redo it and say sorry on this forum for not listening

 

[Wishiwasatoptiler]

Just spend the £100 on hardie, screws and Flexi addy and crack on, why waste the £30 plus on tiles m2 and addy and effect for it to chance to fail.

 

[Waluigi]

It may well be absolutely fine but all it takes is a tiny leak from the shower, kids splashing a little too much in the Bath, a leaking pan connector or some other plumbing leak in the dozens of joints in a Bathroom for there to be a failure when water hits the chipboard. Personally I try not to use chipboard at all, I’ll use ply and then overboard it.

Obviously you can counter the argument by suggesting that no water will ever reach the substrate but I don’t believe anyone can be in control of something like that.