Answers to Your Concrete Questions #3
A. Whenever you put something on a surface, remember the life will depend on the base you are putting it on. Make sure the base concrete is sound, all loose and cracked material is moved and the concrete is not bruised. Bruised concrete has a layer of dusty, partially crushed concrete that weakens the bond of the surfacing. There are many materials and methods. Something too strong and impervious could be lifted off by moisture freezing below if you are in a cold climate.
Q. My husband and I were going to have a landscape curb poured around our flowerbeds until we priced having it done. We have decided to do it ourselves. My husband is more than "handy" around the house. His concern is the "mix." He doesn’t want to use the regular QUIKRETE® because of cracking problems. Someone told him to use the QUIKRETE® sand, or the QUIKRETE® motor mix. We plan to dig down about 4" and leave about 4"exposed above ground, making the height 8". The width would be 4". Would you use 1/2 " rebar? Would you use a packed sand or pea gravel base to set the curb on?
A. Concrete shrinks when it cures. Because of this, you should break the entire length into lengths of about 12 feet or less to eliminate cracks. The rebar is a must. Do not run the normal rebar through the joints between sections. To prevent two adjacent sections from moving up and down relative to each other, use something that is used for highways. Connect the two sections with a plain (smooth) steel rod extending into each section about a foot. Put a liberal amount of grease on one end of this bar and wrap with a layer or two of paper. Then pour the concrete.
This will allow the sections to move slightly lengthwise because of the grease on one side, but prevent one side from raising or settling. It will look better for a long time with very little extra cost. This is very important if you are in a cold climate where the ground freezes.
Q. I'm not sure what the material is called, but that fiberboard stuff between the concrete slabs is sunken down and now it is filled with dirt and weeds are growing out of it. Should I clean it out and caulk?
A. The joints you are referring to are to allow the separate sections of concrete to expand and contract according to the conditions. Concrete shrinks when it cools or dries out and does the opposite when it gets warm. The is also a long-term shrinkage that takes place, but this is so small in a older driveway that it is not a factor.
You want a soft material to fill the joint so that the joint can shrink when the slabs expand. If you have a hard material, there is no give when the slab expands. If you have something like epoxy, this may cause the edges of the concrete along the joint to spill off. The same thing can happen if a open joint gets filled when as a joint opens up as the concrete dries and/or cools.
The soft material prevents the joint from filling and allows the concrete to expand. You should replace the joint with the same material (cheapest) or you can try to find an adhesive caulk that will hold under the dirty, moist conditions in a driveway.
If you do try to replace the black joint material with a caulk, you will probably have to put a backing material (foam backer rod) in the joint to caulk against otherwise the caulk will not adhere to the concrete properly. Caulk sounds good, but the application is too difficult without experience in knowing how to do it and what to use. It is best to replace what was there and periodically sprays the joints with grass killer and ant killer.
Q. Does anyone know how deep I have to get a pour of concrete if I want to put a car on it, and do I need re-enforcing mesh as well?
A. Normal is 4" concrete with a wire mesh over 2" of sand over a 6 mil visqueen membrane over 2" of sand. Recently, some have started using a fiberglass mesh in the concrete mix instead of the wire mesh. This seems to work better since it is uniformly spread throughout the concrete and unlike the wire mesh, it won't rust over time. Check with your local redi-mix company.
Q. Not sure if this is the correct term, but I've heard it thrown around by some friends of mine when referring to the smearing (for lack of a better word) of cement along their cmu walkway walls to make it more aesthetic. The foundation of my cottage is cmu, and I'd like to neaten it up a bit, using this method.
A. This is sometimes referred to as parging, similar to stucco. Here is a how-to on applying this. The loose material must be removed and the surface cleaned first. www.doityourself.com/stry/stuccoconcreteblock
Q. We had our steps repaired (3 years ago) and the job did not last. The limestone treads have loosened from the underlying mortar. What is the proper concrete for anchoring a stone step? Even the mortar between the joints became loose as well as the riser mortar. The steps are on the northeast side of the house and do not get a lot of sun. Did this play a part in the demise of the concrete?
A. If the stones were not seated properly in the bed of mortar, they would work loose from the action of walking on them. I would recommend removing the stones and cleaning off the old mortar prior to reinstalling them. If your environment were alternating wet and freezing, then this action would tend to work them loose if moisture was retained in the mortar during freezing.
Q. I would like to build a small shed in my backyard, say about 6' by 8' by 12'. I would like to know if I could use cement block and wood piers instead of pouring a slab, then build up from there using the piers as the foundation. Can I bury the block down into the dirt to keep it from being so high?
A. You can install pier blocks to use as the foundation, and yes, you can bury them in the ground a little to keep the floor of the shed closer to the ground. Just don't get too close to the ground with the wood portion of the floor. First, you are reducing the ventilation under the floor, which will shorten the life of the wood, and even pressure treated wood that is near or in contact with the ground is going to rot. Depending on where you're at, frost may be an issue as well.
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