Pavers Over Concrete --In The Dusty Desert


(Surprise, AZ)

Here is a question regarding laying pavers over concrete where the area is very dusty.



We have a concrete patio slab and would like to put pavers on it. The slab is large, with expansion joints and each half tips towards the middle, where there is a long, one inch drain dumping water out to the edge of the patio. We have no problems with hard freezes and get only 7 in. of rain each year.

This is the question: if we use sand under the pavers, I'm concerned that washing off the pavers with a hose will cause us to lose the sand underneath it and the pavers will become 'rocky' to walk on. If we use thinset underneath, the pavers will be harder to hose off since the dirt will not slip between the pavers. This might not be a big deal except that this area is really, really, dusty. Thoughts?

ANSWER

First of all, I assume you realize that you will have to address the trench drain that is in the middle of the existing concrete patio. The first thing that comes to mind is raising it to the new height. I am not sure what should be under it now as the new base. Also, The area where it empties the water off the patio will be higher, unless you add some fill and regrade.

If you are doing a lot of hosing off, probably setting the pavers on sand and also filling the joints with sand is not the best option. You might consider polymeric sand, which is applied and then wet down. After a very short while, it hardens.

I don't see a problem with mortaring the pavers over concrete for your existing concrete patio. When you hose off the pavers set this way, you should use a hard flow and force the water off the patio, not hose it so that it will go into the joints. There are many types of patios either of concrete or stone set in concrete. Once it is built correctly, hosing off is not a problem. This will be a much more stable hardscape for your situation.

The last option is to remove the concrete patio and start over with pavers, using polymeric sand. I would price it out both ways since setting pavers in concrete is more costly than using the dry laid method with polymeric sand. You also have the cost of digging up the drain and installing a new one. Just installing a new one is less expensive.

Comments for Pavers Over Concrete --In The Dusty Desert

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Mar 08, 2011
 Fewer Choices
by: Herenotthar

Thanks for all the good advice. The patio is about 20 feet wide so I get what you're saying: I'd need to have another 4 inches in height at the house side of it for it to drain properly. Since I have a door there, that won't work. I also have a wall around the patio and ruled out destroying the existing concrete since it might/would destroy the wall in the process. So, I think I'm thinking raising the existing narrow drain, keeping the elevation as it is on the existing concrete patio, but would need to decide between the poly sand or just using a thinset base.
Mar 08, 2011
 Drain In Patio
by: Susan

There are two issues here.

1. The first is "filling" the drain area. The most important thing for the stability of a patio is the structure beneath it. The drain area would have to be filled with concrete and/or stone so that it becomes a stable base for whatever is going on top of it. So when you fill this "drain" area it must go down deep enough to create that stability. I don't know what is beneath the drain, but in the link I provided Building a Patio, you can see just what the bases should be and also how thick they should be too. That being said, one inch in width is very narrow and might almost be called a large joint. You might consider having a professional assess the situation.

2. The second is the re-grading of the patio entirely. I believe this can be done. However, it all depends on your surrounding grades and elevations. A patio should pitch for at least 1/4" per foot. So based on how your patio is now graded with the drain in the middle, your existing patio edge is not at the correct elevation for the new grading pattern. The elevations are changing due to the raised patio height from laying pavers on top. You have to make sure all elevations work properly so no water drainage problems are created...last thing you want!

See Landscape Grading. The same or similar concepts would apply to a patio.

Getting back to what type of construction would be best...

How large is this patio? Sometimes it is not worth it to try to save some money when spending some more will create a better and more long lasting landscape project.

Consider this:
1. Remove the patio. I understand it's concrete. However, I'll bet it is less expensive than you think.

2. If you go this route, you can start all over and have everything built correctly, pitched properly, have no problems arising from beneath from an existing patio and old drain area.

3. You can modify the shape if you like.

4. You can build it dry laid with polymeric sand if you want to use pavers. But...you can also use regular sand, not polymeric, now that you have no concrete underneath. I know many people use polymeric sand, it's very popular, and it can be very successful. However, it can also crack if not done correctly or the weather is not cooperating. I also think about the fact that the beauty of a dry laid application is that if anything were ever to happen, you can easily remove the pavers and replace them. With polymeric sand, it's not quite as easy.

You don't have to use concrete at all.

I have an old house. I understand the expenses in home ownership! However, I also know that sometimes it pays to spend a bit more to do something right.



Mar 07, 2011
 Patio Drain Clarification
by: herenotthar

Thanks for your wonderful comments. I should have been clearer in describing the drain which runs down the center of our concrete patio. It's an inch wide, about 20 feet long, BUT it's only about 1-2 inches deep. My thinking was I could just leave it alone if I go with either the polymetric sand or the concrete, or I could have it filled and instead of allowing the 'new' paver patio to be essentially two parts, as it is now, with each sloping towards the center, I could have it built as a more conventional patio with the entire patio sloping away from the house. Would this change any views? From what y'all are saying, either the polymetric sand or concrete are the options.
Mar 07, 2011
 Other Responses to Pavers Over Cocnrete
by: Susan

Here is another response regarding laying pavers over concrete, which was posted on my Facebook Page. To paraphrase....

You also have to consider the thickness of the pavers and that you will now be at a higher level once the pavers are placed. The concrete must be in good condition or easily repaired with a patch. Lay the pavers on the concrete slab and use a construction adhesive at the edge. Sand can then be placed (swept) into the joints.

My Response!
Brian,
Thanks for your thoughts. However... I am not sure about the stability of a patch. I feel the concrete should be in excellent condition without need for any repair at all.

Also, I know laying pavers over concrete can be done and in certain situations I have recommended this myself. However, I often wonder about the long term when it is done with sand. In extremely heavy rains, the water can percolate through the sand joints and then cannont continue into the ground due to the concrete. There might be water collection on the patio and the sand might need some re-doing.

I understand the homeowner here does not get a lot of rain, but continuously hosing off the patio also creates excess water.

Here are some simple drawings showing some of the typical ways to build a patio, including dry laid, pavers or stone set in concrete and a concrete patio itself.

Building a Patio

I would venture to say that a better solution would be to use polymeric sand in the joints, which hardens. And of course, not the point of pavers at all, but setting the pavers in concrete is an option too.

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