Can You Pour Concrete Over Existing Concrete

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Information about Can You Pour Concrete Over Existing Concrete

Phil Puccio

Can you pour concrete over existing concrete?I am pouring new concrete directly over the old concrete terrace.

can you pour new concrete over old concrete?

The simple answer is YES, you can pour new concrete directly over the existing concrete.

However, there are a few things that you need to consider before making a final decision.

Is the existing concrete stable?

How you determine that might be the most important part in answering this question.

When I look at old concrete, the first thing I do is look for subsidence and uplift. When the plate has settled, I try to figure out why and if I think it does settle more.

If it cracked and cracked, why did it? After lifting, did the plate return to its original level or did it stay in that position?

If you can’t come up with a conclusive answer to these questions, it’s probably a better idea to remove the old concrete and find out why it settled or raised, and then fix the problem so it doesn’t happen again.

If you just pour new concrete over it and don’t fix the problem, there is a good chance that the same thing will happen to the new concrete.

If it’s a solid piece of concrete maybe a few small cracks and the surface is worn, ugly or pitted, you can pour new concrete right over it.

I suggest pouring at least 2 “over the old concrete so you need to be able to accommodate the new slab height whether it’s a floor, patio, driveway, or sidewalk.

How thin can you pour concrete over existing concrete?

You can pour over the old concrete up to 1.5 inches thin.

Remember, concrete contains aggregates (rocks). The smallest rock size is about 3/8 of an inch. If you pour thinner than 1.5 inches, you won’t have enough cement paste over and around the aggregate to make strong concrete.

It will crack and break in the end if you pour it too thin.

The old concrete was over 20 years old. It was originally cast in several sections, so some of the seams looked like cracks.

The surface was badly worn and pitted, but the slab was structurally fine and there was enough height to pour a new slab directly over the old one.

I had to tilt the new concrete away from the house because the old concrete was sloped towards the house.

I ended up pouring the new concrete 4 inches thick on the house and 1.5 inches (thin) on the lawn. This allowed me to get a 1.5 inch slope on the new concrete away from the house.

Pouring over the old concrete instead of showing it off and removing it saved the customer hundreds of dollars.

how to pour concrete over existing concrete

Step 1. I started this project by pressure rinsing the old concrete to remove any mold, dirt, and loose concrete.

Step 2. I let it dry for 24 hours then I brushed on a light coat with a concrete primer. My favorite adhesive for this is Welding Crete. It basically glues the two concrete slabs together.

This decking slab was 4 “thick on the house and 1.5-2” thick towards the lawn, so I decided to glue everything onto the existing concrete.

If all of the new concrete was 3 inches thick or more, I wouldn’t have to glue them both together.

Step 3. I made the perimeter with 2×4 and set it for degrees with my self-leveling laser.

I like Topcon RL-H5B, it’s so easy to set up and learn. I just put it on the stand, hit ON, and it levels itself and starts the rotating laser.

Then I check my level with my incline stick and the receiver and set my inclines. Very easy!

Step 4. After the shapes are set, I install the wire mesh and call for concrete.

I’m using a 4000 psi concrete mix with 3/8 in. Pea stone because I’m stamping this slab.

This would also be a good mix for a broom finish. I like the 3/8 stone because it stamps a little easier than the 3/4 stone.

The tools I will need to pour the new concrete are:

This new concrete deck was 9 ‘x 12’ and took up 1.5 cubic meters of concrete.

This is more than what I wanted to mix by hand so I just called my ready mix supplier.

Step 5. I poured and leveled the concrete, let it float, then let it cure until it was ready for stamping.

Can you pour concrete over painted concrete?

Yes you can if the new concrete is 3 inches thick or more.

When pouring concrete over concrete, it is best to join the new concrete to the old concrete if the new concrete is less than 3 inches thick.

When the concrete is painted and you’re pouring less than 3 inches of new concrete over it, you’ll need to remove the paint (high pressure wash or sand) and then apply a binder to “glue” the new concrete to the old one. .

If the new concrete is 3 inches or more thick, you’ll want them to move (expand and contract) independently. This is when we use a “bond breaker” between the old and new platters.

You can leave the paint on the concrete, put some plastic on top, and pour the new concrete over both the paint and the plastic.

Pouring concrete over an existing concrete driveway or sidewalk

The same principles as above apply to pouring concrete over an existing concrete driveway or walkway.

You can do this if the concrete is solid (solid) with small cracks, pitting, debris, surface damage, or just plain ugly.

You just have to consider the extra height. How does another 2, 3, or 4 inches in height affect doorways, stairs, adjacent walkways, or garage floor heights?

If there is extensive subsidence, uplift, or cracking, I want to investigate why it was in the first place and fix that problem before I pour new concrete over it.

Will the new concrete hold up on the old concrete?

Freshly poured concrete sticks to old concrete if you called a bonding agent. use Welding Crete.

Weld-Crete is a “glue-like” binder specially formulated to bond new concrete to old concrete.

My rule of thumb is, if your new concrete is less than 3 inches thick, you’ll want to make sure it sticks (or sticks) to the old concrete.

If your new concrete is 3 inches thick or more, you don’t want it to stick to the old concrete.

You want it to expand and contract on its own to reduce the chance of an accidental crack.

To prevent the new and old panels from sticking together, you’ll need to install a bonding agent such as plastic, Typar, Tyvek, roofing paper, or an inch of sand between the two panels.

If you’re gluing the two panels with Weld-Crete, the best way to do this is to apply it with a soft brush and brush it into the old concrete.

I demonstrate how to do this in the video.

Finally:

The simple answer to the question “Can I pour concrete over existing concrete?” is YES SIR.

You just need to understand the limitations and reasons why this might not be a good idea.

Here’s another video that shows you how I poured a new garage floor over an old garage floor.


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