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Old question but still confused....

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Discuss Old question but still confused.... in the Tile Adhesive / Grout Advice area at TilersForums.com.

J

JimboD

I’m tiling a 90m2 area with 600x600 limestone tiles, 12mm thick.

The base is a poured screed (very level) which also contains the underfloor heating pipework.

I appreciate I need a 100% coverage with the adhesive.

I appreciate that the round notched trowels give better coverage (primarily as they leave more adhesive on the floor)

From what I read, some folks state you need a 20mm round notch.

What I am confused with is the size of the notches required to achieve a solid bed. I watched a really interesting video that highlighted how what is more important is the orientation of the adhesive ridges and how having straight lines are important rather than having wavy lines – if you bed the tiles in by moving from side to side perpendicular to the ridge lines they close up and create a solid bed (and don’t if you have wavy lines or grooves running parallel to the bedding motion)

So, with this in mind, why does the bed need to be so deep? 20mm round ridges must compress down to about a 10mm bed so uses a huge amount of adhesive.

In my situation, I have to ensure the tile bed is not too deep as they run up to a bifold door (ideally I need 3-4mm).

So, my question is… Why wouldn’t a 10mm round (or square) notch, with grooves laid perpendicular to the tile bedding movement suffice in creating 100% coverage (especially if back buttered)?

Second question…. In my mind, there seems to be a disconnect associated with the thickness of the bed that is left vs what people are claiming. The maths doesn’t make sense. For example, a 10mm notched trowel is claimed to leave a 3-4mm bed, but how is that possible? Imaging cutting the top 5mm off the top of each 10mm ridge and laying it in the 10mm deep groove next to it. You’d end up with a 5mm level base. So where does 3-4mm come from?

The rounded trowels leave more material behind so would be even deeper, say 6mm for a 10mm trowel.

Can anyone please help clarify things for me so I know what the best approach is.

It would be much appreciated!

Cheers
 
J

JimboD

Aha! of course. makes perfect sense :)

So a 10mm rounded notch will give me the 3-4mm depth i am looking for but will i get 100% coverage? I'm hoping yes if i apply the straight line and perpendicular bedding motion. That video i eluded to was awesome - they bedded in clear glass tiles so you could see the impact on the grooves underneath and how they only close up properly if you use that technique.
 
O

One Day

You could use a 4mm mosaic trowel and achieve 100% coverage.
IF (big IF) the floor is perfectly flat and the back of your stone is like glass, and the adhesive has the correct consistency, and you trowel, back-skim and bed them perfectly.
I think guys shout about large notches because our floors are so bad, you have a better chance of good coverage.
Personally, I won't use more than a 12mm trowel on floors. If it's so bad I need a 20mm round notch, I would prefer to straighten the floor.
 
J

JimboD

Arh yes, "laitance". I noticed the dusty film when the screed was first poured (didnt know the technical name) but over the past few months had assumed it had all come away with all the coming and goings, sweeping and hoovering. Will check tomorrow if its still there. Hopefully wont need to attack it with a rotary sander but knowing my luck....Better to check now though and sand if necessary, than have 5k of tiles lifting in a years time!

NB: The screed came from SouthernScreed and on their website they show a video of someone sweeping the laitance off with a broom!

So many steps - laitance removal - UFH cycle - moisture level - sealing - possible membrane - adhesive choice - tile sealing - expansion gaps etc etc etc. ALL of which many DIYers will have overlooked or got wrong :)
 

Albert

TF
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Just looked into membranes on Impish's suggestion. A few rolls of durabase seems the best bet but adds 3mm to the depth. Hmmm, need to do come careful measurements tomorrow as i think 3mm membrane +4mm adhesive + 12mm tile might be too high for then being able to run the tiles flush into the bifold door edging strip.

Thanks everyone for the speedy replies!
Ball and Mapei do 1mm mats
 
you have to back butter porcelain anyhow ,whatever you decide ,screed the floor and put 6mm on back of the tile
I've got 59cmx59cm porcelain tiles. Floor is flat enough, maybe the odd minor discrepancy here and there but nothing major. Tile shop said will be fine with a 20mm round notch trowel (has a depth of 15mm).

I was planning on back buttering the tiles with the flat edge of the trowel - are you suggesting to use a smaller notch trowel to add to back of tile or will I be OK with my buttering plan and is 6mm a general target or too much for my smaller tile?

If I have a total adhesive depth of c8 to 10mm and as near to 100% coverage as possible the odd minor floor discrepancy (2mm her and there) should not be an issue?
 
F

Flintstone

Your trying to run before you can walk here. What is the screed made of, have you got a hygrometer to test it and have you got floor sanding equipment? It's a none starter if you can't answer those with a yes. A membrane isn't an option if you fancy it, it's a must. Also 10mm trowel is too small, it's hard work trying to get coverage with that size trowel. Why are you getting a professional out if you are doing the job your self ?
 

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