Hi, all. I have an old (40 years?) concrete patio that is in good structural condition. It was poured with a red coloring agent or dye, but I can’t tell if it was added to the surface after the pour or added to the mix. If you sit on the patio, the color appears rather slightly on your clothes (and our white cat gets a slight reddish hue after sitting on the patio).
The patio was poured in 6 ft. x 6 ft. squares with 2 x 4 wood separating the squares. All the wood has now rotted away.
I want to cover the patio with a thin ashlar slate (maybe 1/2 inch thick).
Questions:
1. How should I fill the cracks left behind where the 2x4s were? Pack gravel into the bottom and then fill with concrete? Should I put an expansion strip into the slot first? Should I leave room on top to apply an elastomeric seal material to waterproof the joint?
2. How should I prep the patio surface for the slate?
3. The concrete patio slabs are independent and not connected structurally with rebar. I want to avoid cracking the ashlar slate tiles at these points, so I plan to align their joints over the existing gaps in the slabs. Also, I plan to fill the grout line over the old 2×4 gap with an elastic grout of some kind (like you see on top of commercial concrete expansion joints). Do you think this will work?
Thanks!
Steve
Replies
I'm gonne start throwing out some thoughts and see if anything makes sense.
Other than the rotted 2x4's, are the slabs in good shape and still where they started? I mean, have any of them shifted up or down. If they are all still level and even, I would clean out the gaps and fill them with sakrete, flush with the top of the slabs. Then I would overlay the entire patrio with Schluter Ditra and lay the slate on top of that. You probably want to clean the slabs weell to get the chalking paint off so the thinset will adhere.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Thanks, FE. Slabs are in good shape and there's no sign of movement. I removed three of them that had been uplifted by a huge blue spruce. The stump was ground out and the roots dug out. There are only minor hairline cracks in a couple of the slabs and the tops are all very even.I saw the article in FHB about making a non-cracking tile floor in a house with Schlüter-DITRA. Do you think it's really required with a 4" concrete slab underneath? Of course, that way, I could put down the slate tiles across the whole slab without concern for the gaps between the individual slabs.Do you know if Schlüter-DITRA is OK for outdoor use?
The reason I suggested Ditra is because of the wide joint lines in the patio slabs. You can fill them as flush as possible with a cement product, then the Ditra will help to span over the joints.
Outdoor use? Check the website.
Is the patio slab lower than the house slab? Maybe you should consider a mud bed, like a shower floor. It would allow you to raise the slate height, and it would be a good base.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
I checked the Ditra web site after your message. They make the point that the product is especially suited for outdoor use due to higher thermal movement caused by higher temperature swings. Makes a lot of sense. Thanks for thinking of that.How should I clean the patio? Weak muriatic acid wash?
Never used muriatic acid, so i can't say. Maybe a grinder?
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Your individual slabs will start or continue to move against each outher. So I would say that you need to maintaine the dormant space between your slabs with new clear all hart red wood.