How to Pour Concrete Ramp

There are times when a ramp is the way to go, rather than building stairs to get into and out of a building. One clear-cut case is for a gardening shed. Who wants to try and carry a lawn mower, or even worse, a lawn tractor, up and down stairs? In such a case, building a ramp is the only way to go. The only question is whether to make it out of wood or concrete.

I’ve had wood ramps, and they only last so long. A pressure-treated wood ramp will last longer, but even then, it will eventually weaken and break. While you’ll get a lot more years out of a pressure-treated plywood ramp than you will out of just plain construction-grade plywood, concrete makes much more sense if you want something permanent. Yet many do-it-yourselves avoid it because they’ve never done concrete work.

However, working with concrete isn’t all that hard, other than dealing with the physical weight of the concrete. You will get a workout, mixing, pouring, and finishing the concrete. But if you’re reading this, I’m guessing you’re ready for that part.

Some Considerations for a Concrete Ramp

Before building a ramp, you need to plan out your project. Unlike working with wood, you can’t make changes mid-project with concrete. You must decide what to do and set up your project to reach that goal.

The maximum ratio of length and slope you want on any ramp is one inch of drop for every 12 inches of run. This is a requirement of the American Disabilities Act (ADA), something you must consider for a wheelchair ramp. But it’s also a practical consideration for other things. If you have a ramp any steeper than that, you’ll find it hard to go up and down, especially when wet or icy. Better to run your ramp out a little farther, than to have a dangerous ramp to contend with.

The concrete should be a minimum of four inches thick, although, for light use, you can get by with only two inches. This means that you’ll need to dig out the earth at the ground level so that the bottom edge of the concrete ramp goes down into the world.

On the other hand, you really don’t want to be pouring concrete that’s any thicker than 12 inches. If your situation requires that the uphill end of the ramp is more than 12 inches thick, fill the space with rock, gravel, or compacted dirt so that you don’t need to use as much concrete. Keep this filler at least four inches away from the edges, so that your ramp doesn’t lose any structural integrity.

Calculating Your Concrete Usage

The easiest way to calculate how much concrete is needed, in cubic feet, is a simple mathematical calculation. First, calculate the volume as if you were making a rectangular slab, not a triangular cross-section. To get this volume, multiply length x width x height (or thickens). Be sure that you are doing this all in inches or feet and not a combination thereof.

This will actually give you a volume double that of your finished ramp. So simply divide that answer in two, and you will know the volume of your ramp. If you have done your calculation in inches, divide by 1,728 to get cubic feet. To get cubic yards, divide the cubic feet by 27.

Concrete comes in 60 and 80 pound bags, depending on where you get it and what type you buy. It should give you a mixed volume on the bag as well. Keep in mind that this is an approximate volume, as how you mix it will affect the final volume. So buy a couple of extra bags, just to be sure.

Ramp Over Existing Stairs

In the case of pouring a ramp over an existing staircase, the volume of the stairs can be subtracted from the total amount of concrete needed. However, other than this, the process is no different, as the ramp cannot be made at the slope of the stairs. It must still maintain the same rise and run as otherwise.

Building the Concrete Form

You will need a form to pour the concrete into. This basically consists of plywood sides for the form, which are held in place by wood stakes. The form keeps the concrete in place while it is setting, allowing you to do a neat job, rather than something that looks like your kids did it out of mud.

Before setting your form, you’ll have to dig out the downhill end slightly to allow your ramp to go four inches into the ground. The idea here is that the top surface of the ramp will come down exactly to ground level, making a smooth transition for you and anything that you have to take up and down the ramp. If you try to do this without digging into the ground, the bottom end of your ramp will break.

As you are digging out the ground for the bottom end of your ramp, remove the sod. Don’t just remove the grass, as the roots of the grass will die, leaving a void. You want solid ground under your ramp, not a void.

Cut the plywood sides of the ramp to match the exact height you want. You will use this as a guide for leveling and smoothing the ramp, so cut it accordingly. Set the plywood form in place and pound wood stakes into the ground to support it. These stakes need to be solid, as the weight of the concrete will try to push the forms outwards. Nail the plywood to the stakes.

If you need to, partially fill the space inside the form with a compactable gravel or rock subbase to take up some of the space and reduce the amount of concrete needed. Remember to leave space for four inches of concrete on all sides and the top.

Not everyone does it, but it is a good idea to brush oil on the inside surface and edges of your plywood form, so as to prevent the concrete from sticking to it. This will make it easier to remove the form, when the time comes.

Extra-large Ramps

In the case that you are making an extra-large ramp, such as making a wheelchair ramp from ground level to a raised porch, you will need to pour sidewalls, and then pour the top slab for the walkway. In this case, build a double set of forms, leaving six inches between them. These will become your sidewalls for the ramp and will be poured first.

In this case, the rebar must hold the sidewalls and ramp surface together. Continuous pieces of rebar will need to be bent so that they form a squared-off U, then placed with the opening down so that the legs of the U are in the sidewalls and the bottom of the U is embedded in the ramp’s surface.

Once the sidewalls are poured and have a chance to set, the forms can be removed from between the walls and the space between the sidewalls filled with rock, compactable gravel or compacted dirt. The top can then be poured.

Prepping and Pouring the Concrete

Before mixing and pouring your concrete, you’ll want to add some mesh (wire mesh) across the entire area of your ramp. Concrete, like rock, is strong under compression, but it is not really strong in tension (pulling), comparatively speaking. That’s why rebar and remesh are used in all concrete projects. Should you end up with a void under your ramp for some reason, then every time you put weight on it, it would be under tension. That could cause cracking in the concrete, but the mesh would strengthen it against breaking.

Before pouring the concrete, put in a layer of roofing felt or tar paper on any permanent wood structures with which the concrete will come into contact. This will act as a moisture barrier. For example, if you are building a ramp for a garden shed, you’ll want to put a layer of tar paper on the front of the shed’s structure, where the concrete ramp will meet it.

For a small ramp, such as one you would need for a tool shed or garden shed, you can mix the concrete in five-gallon buckets or a wheelbarrow. For larger ramps, like a wheelchair ramp, you may want to rent a towable concrete mixer or even have the concrete delivered by truck.

The easiest way to buy your concrete for small projects of this type is to use ready-mix concrete. This will already have the proper sand-to-concrete mix ratio, saving you from having to measure it. All you need to do to mix it is add water.

It is possible to add gravel to your ready-mix concrete as you mix it, to reduce cost. While this slightly lowers the concrete’s strength, it won’t be a problem, as normal ready-mix is stronger than what you need for a garden shed anyway.

Mix the concrete using slightly less water than recommended. You don’t want a runny concrete mix for sloped surfaces, such as ramps, so it won’t tend to try and run downhill. We’re only talking about a little bit of difference in water here, like a drinking glass’ worth, but that’s enough to make a difference.

You might use a mixing paddle mounted in a drill to mix your concrete rather than trying to do it by hand or with a shovel. You can get tired quickly mixing concrete, so anything you can do to make the job easier is worth it.

Once you start your pour, you want to finish it. What I mean by that is to continue mixing more concrete and pouring it until you have enough concrete for the whole ramp. Don’t stop in the middle of your pour for lunch, and come back later. Not only will you create a stress point that could crack, but you may also have a high point that goes above the level of your plywood forms, causing problems.

As you are pouring the concrete in, use a trowel or shovel to puncture the concrete slurry, breaking up any possible air bubbles. For the area near the forms, have someone tap on the plywood with a rubber mallet. This will help bring air bubbles to the surface, rather than allowing them to remain trapped in the concrete, causing voids.

When you get the plywood form filled, use a 1”x 4” or 2” x 4” to level the top, allowing it to ride on the plywood’s edges and push excess concrete towards the bottom. You’ll need some help for this part, with one of you on either side of the ramp. Slide the bar back and forth as if cutting through the concrete, just above the level of the form. If you find any low points, add more concrete to them, and then go back over them with your wood bar to smooth them out.

Finishing the Concrete

Once you have completed the form and removed any extra concrete, you need to use a hand trowel to smooth the surface even more than you accomplished with the 1”x 4.” As you do this, you will notice that water or “cream” will rise to the surface. This is good, showing that you have troweled the concrete sufficiently.

Allow the concrete to cure to the point where the cream evaporates off, and then broom the surface. This is nothing more than dragging a stiff broom across the surface, to give it a slip-resistant texture. You want this perpendicular to the fall line, so go across the ramp with the broom, not down its length.

If you are going to radius the edges of the concrete, it is done at this time, with a special tool, called a steel hand edger. This is not required, but will help prevent you from having a sharp edge to scrape shins on. Besides, it makes your job look more professional.

Once your concrete has reached the point where it can no longer run, you can remove the plywood form. This should be roughly one hour after completing the pour. You’re usually better off going a little longer, rather than removing it prematurely, especially if you have oiled your boards.

The concrete doesn’t actually dry, it cures by a chemical reaction. It is necessary to keep the concrete wet while it is curing. Continue to wet it down for a few days, after your pour. If you encounter any voids in your ramp, they can be filled with a concrete patch material.