Is mastic/deck o seal needed if.....

[Aquaholic1]

Good afternoon! I'm hoping that y'all can provide me with the correct answer...

We are currently in the process of having our existing patio installed with large porcelain tiles (not pavers). The guys are floating/placing cement underneath the porcelain tiles. Is mastic/deal o seal needed since the initial spray decking under already had mastic?

 

[ajw22]

Yes.

Will there be an expansion joint between the tiles and the coping?

There should be, it should match up with the expansion joint for the spray decking, and it should be filled with flexible mastic.

 

[Aquaholic1]

ajw22 (Allen) - So, what you're saying.... is that even though there was already mastic between the existing spray decking and old coping that there still needs to be mastic added between the new porcelain tiles and new coping? If so, can you explain why? Thank you!

 

[ajw22]

ajw22 (Allen) - So, what you're saying.... is that even though there was already mastic between the existing spray decking and old coping that there still needs to be mastic added between the new porcelain tiles and new coping? If so, can you explain why? Thank you!

Because the cement couples the tile to the deck. And if there is not an expansion joint between the tiles and coping the deck movement will cause tile movement and put pressure on the coping and bond beam and something will crack. Either the bond beam, coping, or tile.

You need a continuous expansion joint along the coping so nothing will put pressure on the bond beam.

 

[Aquaholic1]

Because the cement couples the tile to the deck. And if there is not an expansion joint between the tiles and coping the deck movement will cause tile movement and put pressure on the coping and bond beam and something will crack. Either the bond beam, coping, or tile.

You need a continuous expansion joint along the coping so nothing will put pressure on the bond beam.

Allen,
Just so I'm understanding you clearly....So, we have the initial cement that is spray deck, then the guys are floating new cement on top of that to make it level to the coping, then the large porcelain tiles will be placed on top of the new cement. So, definitely mastic and NOT grout - correct?

 

[ajw22]

Allen,
Just so I'm understanding you clearly....So, we have the initial cement that is spray deck, then the guys are floating new cement on top of that to make it level to the coping, then the large porcelain tiles will be placed on top of the new cement. So, definitely mastic and NOT grout - correct?

Mastic and NOT grout where? Along the joint with the coping should be mastic, other joints can be grout.

 

[Aquaholic1]

Allen,
I'm talked about the space between where the new coping and new porcelain tiles meet. How many mm/inches of a gap for mastic? When I asked the Hispanic guy about mastic last week he said it wasn't necessary since this is on top and not the initial cement. That's why I'm asking PRIOR to them grouting. They haven't gotten to the grout part yet.

 

[ajw22]

What is the space on the deck expansion joint?

What will be the gap for the grout joints between the tiles?

Around 3/8”.

 

[Aquaholic1]

Allen,

Sorry for my delayed reply. I cooked dinner then we ate. I just went out back and found the bag of white tabs they're using in between the porcelain tiles and they are 1/4"/6mm. Then I went to look at the new coping that meets up to the porcelain tiles and there might be room for two playing cards.

 

[ajw22]

Then I went to look at the new coping that meets up to the porcelain tiles and there might be room for two playing cards.

A bit wider would be better. You can't get foam backing rod or mastic into a space that thin. And over time dirt will fill that space and compromise any expansion joint the two playing card space is giving now.

 

[Aquaholic1]

A bit wider would be better. You can't get foam backing rod or mastic into a space that thin. And over time dirt will fill that space and compromise any expansion joint the two playing card space is giving now.

Allen,
Good morning! I appreciate all your knowledge and help. So, we definetly need MASTIC between the new coping and new porcelain pavers regardless if there is initial underlayment of spray deck - correct? So, the solution would be.... before they place grout then they need to cut some of the porcelain tile that's located between the new coping and porcelain tiles?

 

[ajw22]

So, we definetly need MASTIC between the new coping and new porcelain pavers regardless if there is initial underlayment of spray deck - correct?

Definitely no, recommended yes.

No one can say what type of movement you will get. The expansion joint is an insurance policy against problems.

Maybe things will be fine with what you have. There is no way to know.

We see a few folks here every year asking why are things cracking around their pool and they don't have an expansion joint.

So, the solution would be.... before they place grout then they need to cut some of the porcelain tile that's located between the new coping and porcelain tiles?

Yes, if that is the way the tile layout works and you want the insurance of an expansion joint..

 

[Aquaholic1]

Allen,
Thank you VERY much. I shouldn't be, but I'm so hestiant to address this to the tile guy.

 

[ajw22]

How many tiles need to be trimmed?

Post pics of the tile to coping joint and if you can lift a tile post pics of the expansion joint in the deck the tile is on.