If you are a homeowner or maybe you live on a small farm and you need a concrete pad but you feel limited in your ability and can’t hire the work out because of the cost or other reason then you are likely to look at alternative methods of getting what you need done. You might need a concrete slab to go under a shed for its floor, maybe for a patio sitting area or maybe inside your barn so you have a clean area for your animals. This slab will never see a lot of traffic or heavy objects placed on it and won’t be used to store vehicles or farm equipment. Well then you might consider dry pouring concrete instead of hand mixing or having yards of concrete delivered. Only select this method with the understanding that results are not guaranteed and knowing the slab is not likely to last as long as premixed concrete.
Warning Before You Start
The first thing you need to understand is this really is not the right way to do things and although you might have a reasonable immediate outcome the future of that slab is not set in stone. It would always be better to hand mix in a wheel barrow than to dry pour and the best method is when large batches can be mixed in a concrete truck. The reason is the concrete will be uniformly mixed with the correct amount of water to let it cure evenly.
A Better Alternative To Dry Pouring Concrete
A better method would be to pile the concrete in the center of your form and form a volcano shape and then mix it with a hoe or shovel by taking dry concrete from the outside and putting it into the center and then using a hoe to distribute it in the form. This way the concrete is evenly mixed and you would use the same amount of water per bag of concrete. You could do the half pour and then add rebar mesh and then your second pour. Water is a very important aspect of concrete most people don’t understand and it can change the PSI pounds per square inch level of the pad dramatically. Too much water is as bad as not enough and with dry pouring you pretty much have no control of the percentage of water in the mix.
How To Dry Pour Concrete For A Light Duty Slab
So, now that you have been warned a couple of times that this is not the best method how do you actually do it.
The first thing you want to do is prepare the area by digging out any organic material and topsoil. You want to remove all the grass, debris, manure if you’re in a barn and dig down until you reach a gravely clay mixture. Anything organic even tree roots will break down over time and cause the slab to crack.
A layer of gravel and a plate compactor would be useful at this point to reinforce the soil before you pour your concrete but it will require extra work and expense. At the very least you want to make sure the base is even and not spongy.
The next thing to do is use 2×4 material to layout the perimeter of your slab. Use stakes on the outside of the boards to set their heights and hold them in place. A string line will tell you if your boards are straight or bowed and need to be adjusted. Backfill on the outside of the boards with dirt to prevent the concrete from getting under the board.
The ground should then be moistened with a garden hose. You don’t want to create dust but you want the dirt to be very moist so it doesn’t suck moisture out of the concrete as it cures. It is best to do this the night before especially on very hot days. Starting the pad in the morning is also best so the dirt won’t dry in the sun.
Pouring the concrete is as simple as dumping bags into the pad area and raking with a heavy steel rake to a level height. If the slab is over 6×6 feet then you should consider pouring out half of the dry concrete and moistening it well and then adding rebar or rebar wire mesh in the center and then adding the remaining half of the dry concrete to complete the finished height.
Moisten the concrete slowly over the next couple hours to let the water drain through the slab. Doing this is likely to wash away much of the concrete on the surface so don’t be aggressive.
The concrete should surface cure within 24 hours but it won’t fully cure for maybe 7 days or much longer. It is good to cover it with plastic and keep it most for at least the first week.
Final Note
Like was said a few times there are better ways to do this even if it means you piling the concrete in a volcano shape and working it within the form area but keeping track of the amount of water and concrete you use so the entire slab is evenly mixed and hydrated.
Your results will vary and if you are in an area that sees frosts and snow then its likely this slab will eventually crack and need to be replaced even if you never drive a car or even a heavy riding mower on it.
The real reason we are covering this method is to give you alternatives that are just as easy. Hand mixing in a wheel barrow or other large steel mixing tray is also a consideration but even mixing it on the ground in a cone or volcano shape is going to be better than spraying water on dry concrete and hoping it cures evenly and strongly. However sometimes you have to do what you have to do and we understand that. Do your best but do it with knowledge.