I need to make a cement ramp for the purpose of channelling rainwater down to the sidewalk. (it is pooling up in a bad way, and flooding the basement apt. currently)
So, I am wondering whether the best way to direct the flow would be with a smooth surface which would simply sluice the water down; or with shallow grooves in the cement like you might make with a broadtooth comb? I know the grooves would be less slippery – would they also better handle a downpour?
Also, I’ve never worked with cement before – is there a particular type I want to get for this purpose? How long to I have to get it smooth and possibly put in the grooves before it is unworkable?
you can place a broom finish (after smoothed and sloped then a push broom on the surface, leave small grooves in the direction you want the water to run) on it to keep it from becoming a slip hazard when wet.
read an article or two or a book chapter on concrete. there are a number of things to do right.
I don’t quite understand what you are trying to do.
Is the water running from the sidewalk under your foundation and you want to channel it into the gutter? Or do you need to actually channel it along the sidewalk for some reason?
You also need to supply a bit more information, like what the fall is across your proposed slab, and what sort of flows you are expecting to have to move. The replies are going to depend entirely on the specifics.
In general, if you are only moving small volumes such as rainwater the smoother the concrete the better. While that’s counterintuiive, essentially when the surface is flat the whole surface acts as one big channel with water moving downhill from the moment it hits the surface. If you add smaller channels the water has to move *sideways *to those before it can start moving downhill, and that impedes flow. For shallow flows any irregularities, even in the direction of flow, also break down the smooth flow of water through turbulence and decrease flow rates.
You only want to add channels if the flow rate is at least periodically high, such as when the guttering from the building is draining on to the slab, or else when you have insufficient fall across the slab to sheet the water rapidly enough.
For a job like this you don’t need any particular mix. There are no structural or cosmetic issues, so go with whatever meets your needs in terms of working time and cost. The exact amount of time you’ve got for working depends on mix, but you can allow at least half an hour unless you use a rapid set mix.
I will second the recommendation that you reed some how-to manuals before doing this, especially since you have never worked with concrete before. There are a lot of ways that you can screw up a job like this if you don’t know what you are doing. There are manuals available online.
Yes, I’d read up some manuals or how-tos before trying the concrete thing. It does happen that professional contractors don’t always get it right the first time, and sometimes even they need break out what they’ve placed and try again.
All things equal, go with the flat surface, maybe sloped a little into the middle. The “broom finish” (literally produced with a broom) will provide traction for anyone walking across it, especially when it’s got water on it - if there’s any chance that someone might. The biggest problem with the grooves is that they’ll trap any dirt, leaves, blown trash, et cetera, and they’ll be a constant hassle to keep clean.
Read the books concerning the right amount of water to add to the concrete mix and follow the recommendation - it’ll work out that much better. Read the books concerning score lines to put into the concrete and take care with them. The concrete is probably going to crack - it will crack just from the thermal stresses of setting - but if you do it right, it cracks along the score lines, and you can’t actually see the cracks.