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Teddy in Troutdale
how to prep patio for slate tile
Teddy in Troutdale

This is my first time ever posting something, so I hope I am doing this alright. Here is my situation. I have a concrete patio with several (12) various sized slabs. They are well over 20 years old. The expansion joints are 1 inch and some still have the rotting wood in them. One slab has a crack. I bought slate tile about 5 years ago and want to lay it myself but can't get a straight answer on if I can fill the joints with concrete and then just tile without worrying about how the tile is placed across the joint.
Also, is pressure washing good enough before laying the slate or does other prep need to take place.

As of 8/22/15, I have watched/ tried to research what I should do with the expansion joints and have put in backer rod in all the joints. I am still not sure if I can cover the expansion joints with the slate tile I plan on installing. Any ideas?

Teddy in Troutdale
Re: how to prep patio for slate tile
Teddy in Troutdale

OK, so this is Teddi again and I have put in backer rod in all the expansion joints. While I have been trying to determine what to do next, I have noticed that the backer rod has shrunk in the joints (like pants getting short) so now there are some gaps.

Any ideas?

A. Spruce
Re: how to prep patio for slate tile
A. Spruce

Expansion joints are there to allow natural places for cracks to form, rather than the slab splitting across its midsection. In your case, with wood joints, same thing, just that the joint is full depth of the slab, rather than a "seam" line.

I cannot tell you specifics on putting down slate, however, you will need to fill those joints with mortar or concrete before you lay the slate. What you're likely going to find is that the individual slabs are always moving, which means that if you attach slate across those joints, it will crack along those joints. It is possible that an isolation barrier may do the trick, but you'll have to talk to someone more knowledgeable about it than I.

The John Bridge forum may be helpful, it is all about tile.

Mastercarpentry
Re: how to prep patio for slate tile
Mastercarpentry

What you probably have is separate slabs which will move individually. Any tiles (slate or other) which span the gaps between will crack and that may not take long. While you had the gaps open, did you notice any steel rods going between the slabs? If you're lucky enough to have that, then the joints can be filled with grout and you'll probably be OK. Most of these were not interconnected with doweling rods or rebar like I describe.

Used to see a lot of these kinds of patios, but you could get good treated lumber back then so I suppose they will never become common again.

Phil

dj1
Re: how to prep patio for slate tile
dj1

Teddy,

If you want nice slate tile patio, you will need a good sub tile, meaning: remove the slabs, prep (compact) the ground correctly and install a new slab.

Slate tiles are beautiful, but they also break easily - not the best choice. However, with the best support there is it might work. What you have now will not support them.

ed21
Re: how to prep patio for slate tile
ed21

Not sure why the backer rods shrunk, but they aren't made to be left exposed, but covered with sealant usually. The purpose is to shape the sealant properly so it can move with the joint. Thick at the edges to adhere to the material and thinner in the middle to allow stretching. Backer rod needs to be the right size. It needs to be compressed in the joint.
But covering the joints with tile will result in cracking. The joints need to extend through the tile. Matching a sealant to the grout might help to look better.

Teddy in Troutdale
Re: how to prep patio for slate tile
Teddy in Troutdale

Thanks for the info. I really was hoping to get this complete before all the rain, but not sure time will allow.

As for the slabs and rebar in the expansion joints, no, there was none. I do believe the backer rod was big enough, but maybe the sun exposure and heat we had this year was part of the cause of the shrinking of it.

I don't want the expense of taking out the concrete, my budget just isn't that big for this project. So, maybe a silicone sealant in the joints until I can get to the tile?

Also, I think I need to seal the slate before installing it. I would like the wet look. Any ideas of a good product?

Thanks so much,
Teddi

A. Spruce
Re: how to prep patio for slate tile
A. Spruce

Ask yourself this, if you can't afford to do this project right, can you afford to do it over when it fails miserably, and it will. Second question to ask yourself, does the patio look worse now than it will later covered in cracked, broken, and delaminating tile?

It will be better to save up the money to tackle this project correctly, than it will be to live with an eye sore that is made worse by attempting to do what should never be done. If I were you, I'd either replace the wood expansion joints or remove the wood completely and fill with mortar or matching cement. Pressure washing will make the slabs look nearly brand new. This will be your cheapest and easiest improvement to your patio. When you can afford to give your tile a proper base, then proceed with installing it.

ed21
Re: how to prep patio for slate tile
ed21

I'd be tempted to loose lay brick pavers on a sand bed so a little movement shouldn't telegraph through. Trying to get a grouted tile to not crack may be impossible in your situation.
I agree with Mr Spruce to wait until it can be done right or you're liable to have a worse mess.

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