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Building a Concrete Foundation for your Addition: Part Two

Welcome back! If you missed part one we covered how to size and form a foundation along with starting basics. Let’s keep moving!

  • AboltRebar reinforcement. Standard is two 1/2″ rebar laid horizontally in the footing and one every 18″ in the stem wall. Rebar ends are joined by overlapping 40 times the width of the rebar, or 20″ for 1/2″. These are tied together at two or three points with tie wire. Local codes and specific structural conditions may require a different program, such as adding vertical pieces with an “L” bottom in the footing placed every two feet. Rebar can be bent for corners by doing it over your knee (not always fun), using the ball hitch on the back of your truck or SUV, or ideally with a cutter/bender. You will usually want to lay the footing rebar in the trench before form ties cut off access, meaning before the opposing form is set.
  • Bracing and squaring. To check square you can use the aforementioned 3:4:5 method, but also want to compare the diagonals of any square section. If your addition is 20′ out and 16′wide, you would place a mark back 16′ on each side. Then compare the diagonal measurement of the created square. Ideally they are within an 1/8 or 1/4″. If it is too late to make an adjustment a larger descrepancy could be tolerated. If you are using form ties to hold the stem wall forming together, you only need to run a stake to the form top on each side to stabalize your formwork. Without ties lower sections of the forming must also be supported by stakes.
  • Pour day. We carefully measure and calculate the amount of concrete to order. Usually you will order a 5 sack mix with 3/4″ aggragate or what is equaivalent for your area. The dispatcher will ask you what slump you want, but you will confess what you don’t know and they will be happy to help you select. You need a plan for how you are getting the concrete to the forms. Can the truck drive right up? Will you carry it in wheelbarrows? Are you forced to bring it in 5 gallon buckets? You will want extra hands to help get your concrete placed quickly. Usually you will make one pass filling the footing and up into the stem wall to “seal it off.” A second pass will top off the forms. Sometimes you will add a little water to the mix (the driver will have water on the truck to mix in) for the walls after using a stiffer mix in the footing. To assure that the concrete mix is settling, you will work a stick up and down or rent an electric vibrator. You will want to tap the outside of the forms with a hammer to smooth out the concrete there. Don’t forget to put in your anchor bolts, closer together than code, for a good job.
  • After pour. When the concrete is in place and you are congratulating yourself, go around and look for any place concrete has fallen against forms and remove it. It is amazing how little amounts of concrete once hardened can make form removal difficult. If your pour was early enough, you might be able to remove form stakes after a couple hours, saving a harder job later. This depends on all the factors, such as air temperature and amount of moisture in concrete, that determine how much your concrete has set up. In any case this is just removing the vertical form stakes which now penetrate  the footing, while leaving the forms in place.
  • Stripping forms. The next day, remove all form stakes and bracing and all wall tie wedges first. Remove top cleats and any attachment of form to forms. Use a tool to “cut an edge” where form top meets concrete to make sure removal of forms doesn’t take some of your soft concrete with it. You will continue to gently break the suction grip the concrete has on the forms. You want to be very careful in any prying not to mar the soft concrete where you are leveraging. As the formwork is removed, you will want to clean it up before stacking.
  • Finishing. Look for places where concrete has built up too high such as around anchor bolts and remove with a concrete chisel. If there are any voids in the stemwall, where concrete didn’t fill in, fill these with redimix concrete if large (which would mean you didn’t tamp or vibrate well), or mortar mix if small. Clean everyything from inside the new structure. Backfill against stem walls and grade entire inside surface to a racked smooth level. You will also backfill against the outside forms and may want to do some grading for drainage now. If you are beginning construction immediately be careful, such as when tightening anchor bolt nuts and certainly when straightening an anchor bolt. Your concrete will be relatively soft for days.

If all of this overwhelms you, you may want to hire a recommended remodeling contractor or recommended professional concrete specialist for all or part of this vital process. Wasn’t this fun?


JR Mathwig Builders on HelpHive


 
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Building a Concrete Foundation for your Addition: Part One

Foundation 1You may have the perfect spot for a simple house addition and want to do it yourself, but wonder, “How do I build a solid foundation?” Proper plans include checking for any point loads requiring a larger foundation section as well as any hold downs required for shear strength. There is a reason that proper permitting makes sure these are done! Here we are discussing, across two articles, a basic foundation–here’s what is involved!:

  • Non basics: A point load is when weight from above is concentrated in one location such as a post supporting one end of a beam supporting floor joists. A widening of the footing may be required in this section. Holdowns will require specialized bolts to be embedded in the pour. An electrician may need to bury a ground wire or a plumber may need a hole blocked out in the pour for the passing of a pipe through the foundation.
  • Sizing: If you are forming for a poured in place concrete foundation, the stem wall is usually 6″ wide for a single story and 8″ for a two story. A single story footing is a minimum 7″ deep (high) and 12″ wide (better builders use a 15″ min.), while two story footings are a min 8″ deep and 18″ wide. National code specifies generically a minimum depth of  12″ for footing bottom  for one story and 18″ for two story houses. The 12″ depth is almost always too shallow though. The top 6″ of soil can easily get loose in a dry summer leaving your foundation almost on the surface. All foundations must be below the winter freeze depth. If your soil never freezes hard, the 12″ meets this requirement. Even if your soil only freezes every couple of years you want to go down at least 15.” I understand places in Minnesota have five foot depth requirements! Conversely Alaska builders building on permafrost must insulate the ground from the buildings heat so that the soil doesn’t thaw!
  • Digging: If you use a backhoe or power anything, understand that any disturbed soil must be removed so that your foundation always rests on undisturbed soil (There are exceptions where soil is professionally recompacted with a power tamper). Call the “before you dig” number to make sure power lines are not in danger as well as plotting any sewer or water lines. You will custom craft with a shovel for clean precise trenches or you may be going all manual anyhow. Slopes are dealt with by making a section level and then stepping down any needed amount to a new level to maintain footing depth. Trench width is not only what is required for footing, but wide enough to accomodate stem wall plus forming and stakes on both sides.
  • Batter boards: This horizontal board set on stakes and braced, holds a nail to which a stringline is attached. If setting a line for a wall coming out from the house, you can run another line parallel to the side of the house and then set accordingly. Conversely you can check for square using some math. You remember the Pythagorean therom don’t you! An easy adaptation is when one side (the form line) is 3 and another side (the house perpendicular to form line) is 4, then the diagonal (hypoteneus for math people) is 5. Applying that in ratio might be 15′, 20′ and 25′. The line parallel to house is set simply by measuring off house. You may set lines initially and discover you need to make an adjustment to make things square. When done mark form nails and nails for stake line (see below) to distinguish.
  • Forming: A common technique is to use 2 x’s to form the stem wall. These may be some of your floor joists. This allows for Simpson (or?) stem wall ties to be used to lock together your stem wall forming and also allows for easy adjustment of top height. You will also use some cleats , perhaps of plywood, to hold the form tops together. Some use plywood panels with 2 x 4 supports either flat or framed like a stud wall for forming. These can be built to suit, or an average size used and an additional board of dimensional lumber added at bottom as needed. The resulting slightly wider footing there should be underground. To set forms or boards you will first drive some stakes. Set a string line for the stakes, not the foundation line. Put your level on the stake as you line it up before driving it. If rocks throw if off too much, redrive it. While forms are set to top height, boards are set bottom first, maintaining minimum footing depth. You may want to rip the bottom board to a calculated width to make your top height come out where you want it. You can also rip the top board, or select a lumber width that is closest. Stem wall form top height is calculated by what is needed inside and out. Outside, code requires a minimum of 6″ from siding to soil, which will be higher after you grade for drainage. You are better off with more. Inside you need to maintain a minimum distance of 18″ from the bottom of floor joist to soil. You will want to attach forming to stakes and to other forming with duplex nails or screws to make removal easier.

As you can see this is a technical process, easier for some than for others, you may want the services of a quality recommended professional carpenter/contractor or a highly-rated concrete specialist. In part two of this article you will find information on rebar reinforcement, bracing and squaring, pouring, stripping,  and final finishing.


JR Mathwig Builders on HelpHive


 
Posted in Concrete & Paving, Excavation & Demolition, Remodels & Additions | 1 Comment »

Creating Paths and Patios with Pavers

pavers1Beautiful and usable yards are a blend of hardscapes and planted areas, of places to be and places to see. Defining areas is a process of creating outdoor rooms without walls and sometimes with borders that are intentionally fuzzy. Pavers can provide both natural looking patio areas and softer looking paths through a number of design options. Pavers are easier to conform to irregular terrain changes. They aren’t a choice you make to save money over a poured concrete slab, but rather for different looks and options possible.  Pavers are more eco-friendly as they allow rainwater to soak in rather than contribute to runoff.  Pavers also allow for later changes, redesigns, and access should you need to run a plumbing or electrical line.  So, what should you look for in a quality project?

  • First consider overall yard drainage and contours. You may need to change or improve paths for runoff of excess rain. You might want  to consider any needs for French drains. Are there any other changes in terrain that would be more aesthetically pleasing? If you are creating a paver patio you’ll want to end up with an area as flat as possible and in a way that integrates with the rest of the yard.
  • Excavation. Pavers involve sand over a base, so you will need to remove a lot of dirt. Recently a client of mine was able to have her huge 12 yard pile picked up for free through Craig’s List. Care needs to be taken to assure that the level of the dirt is a fairly consistent (plus or minus 1/4″ is standard, high or low by 1/2″ is still okay) plane that parallels your desired finish plane.
  • Base. You will want to install a 3″ base which should be compacted with a plate compacter. If you have very solid stable soil, 2 1/2″ will be fine. Less solid and stable can easily use 4 to 5″.  If your ground is wet from a spring or high water table you might need to invest in a geotech fabric designed to create buildable soils over near swamps. If you want to drive on your pavers you will want to add an additional 3 to 6″ to what you would otherwise need.
  • Sand. The sand layer is typically 1 1/2″. A lot of “paver sand” contains a lot of pebbles in the 1/8″, 3/16″ or even the occasional 1/4″ dimension. This makes placing pavers more difficult. As such, you may want to add a thin layer of fine, perhaps “playground” sand. You will also want fine sand to fill cracks between pavers after placement.
  • Pavers. The least expensive pavers are the 12″ x 12″ or 8″ x 16″, 1 1/2″ thick, concrete paver in grey or “red” (pink).  These can look great.  If you’re willing to spend more, you can get textured pavers that look almost stonelike, with a variety of colors, and ranging from rough to quite smooth on the feet. Smaller pavers can be placed more quickly. Larger pavers may need adjustment including pulling them up and adding sand. There will always be some edges or corners that are above or below the average plane of pavers. You may want to go over the pavers (gap fill-in sand in place) with a plate compacter to settle pavers into a nice plane. This will not crack your pavers :>}.
  • Patterns. Similar to creating patterns for tile, you can offset joint lines, or create a random looking  pattern that repeats every couple feet incorporating more than one paver size.
  • Joint size. Some opt for a tight, almost no joint design. One problem to be aware of is when an occasional joint is big in a no gap system it stands out more. The usual minimum gap is 1/8″ which allows fine sand to settle into cracks and makes for a more solid paver and it naturally hides larger joints that occur. Two reasons to use a larger joint is because you like the look with the pavers you have choosen, or in some cases to allow fill-in plants to grow in the gaps. On one project we used a 1″ gap pattern on pavers between a lawn and driveway and put sod in the gaps. This allowed the extra width we were trying to create for the driveway and a green look that blended with the yard.
  • Cutting pavers. Pavers are cut by a wet saw using a diamond blade. Cuts require a steady hand and the safety practices of a professional. Some homeowners can do this, but care should be taken in accurately assessing your ability.

Depending on the size of your project, the hardness of your soil, and the size of your pavers, this type of project can be quite large. You may want to hire a professional – find a Tile and Stone Professional or find a Concrete and Paving Professional to help.


JR Mathwig Builders on HelpHive


 
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Pouring a Concrete Patio

pouring-concrete-patioAdding a concrete patio can make a beautiful yard accessible and useful across the four seasons. For a yard to be truly inviting green plants and flowers need to be balanced with a place to be. In the Pacific Northwest grass is often too wet or the soil too moist for nine months out of the year. Concrete as a building material can be very economical if you can tackle the labor yourself and is still a very solid choice if you are paying for part or all of the physical work as well.

How do I begin planning?

  • Decide what you are going to do on your patio surface and how many people you would like to acommodate. You may want room for a BBQ, a table and chair set, other random chairs such as a chaise lounge, or maybe even a portable fire pit. Too small of a surface gives a crowded feel or may result in a chair leg slipping off the edge into soft ground. If your yard is very small you may want to limit the patio to devote more area to green space. You are balancing aesthetics with utility. You may find you are best served with two smaller hard surfaces. You may want a large area that can acommodate many guests.
  • Drainage. Consider the status of your yard’s overall drainage. If you need to change grading or add french drains, these should be considered first. Sometimes you have no choice but to let your yard drain onto your new patio, but ideally the patio drains away from the house and most or all of the yard drains away from the patio. Even in a yard lacking ideal grading and drainage the slab can still be elevated a bit and have a slight angle to clear water quickly.

Am I really able to do this myself? The work is very physical and you will want some help. At each stage you may find you want to hire others for that part or do some yourself. Here is the process:

  • Excavation. How much soil needs to be removed? The minimum concrete slab thickness you will want is 3 1/2″ over a minimum of 3″ of base. If you decided on a 12′ x 18′ patio that means you must remove about 4 1/3 yards of soil or about 10,000 lbs and 5 trips in your neighbor’s truck. Though the 3 1/2″ slab thickness is adequate, your project will benefit from a thicker base, such as 5″. This provides a stable surface for your slab. Consider if you can use the soil somewhere in your yard such as in a landscaping mound. Use a 4′ level on a long straight 2 x 4 to check if your slab will drain as planned. Use the 2 x 4 to check for excessive mounds or dips in your plane. I prefer to dig down an extra 2 to 4″ around the perimeter for a thick border, either 6″ wide or just using shovel width.
  • Forming. Should I hire a carpenter? After excavating out your patio shape plus an additional 3″ for forming, set perimeter forms by securing 2 x 4s with wood or metal stakes. Usually stakes are set about 3′ apart, closer if soil is loose. Screws driven with a cordless drill is the easiest choice, but make sure screws or nails are from the outside so that you can remove them after slab is poured. On the outside form parallel with your house, check to see that you have uniform distance from your house and that the 2 x 4 forms a straight line. You can use string, but you can trust your eyeball. After selecting end points for your side forms, check that your forms are square by measuring and comparing the two diagonals that would form an X across your square or rectangle. Adjust forms until these are very close. I like 1/4″. Some are happy with 1/2″ to 3/4″ since you probably won’t notice at that discrepancy. You will probably want a 2 x 4 running through the center of your pour to screed concrete to, and which will be removed after concrete is placed. Supporting stakes should not be driven as deeply and you will place them farther apart, like 5′ to 7′ to aid removal. Remember to have a 2 x 4 precut for screeding concrete to level of forming.
  • Base. Think of how proud your 8th grade math teacher would be. The amount of base to have delivered is the total cubic area less the area for the slab. Any dimension in inches must be divided by 12 to convert to feet. Total cubic footage is divided by 27 to convert to cubic yards which is how base is ordered. For example: I have a 10′ x 17′ slab, and upon placing my screed systematically in various places I find that my excavation depth varies from 7 to 71/2″. I want my slab to be 3 1/2″. My base thickness will be the 71/4″ average less the 3 1/2″ slab for 3 3/4″. So, 10 x 17 x (3.75/12)= 53.125. Then dividing by 27 I find I need 1.97 or two yards of base. Similarly I will need (1.84) two yards of concrete. Sometimes it takes a little more than you think. I like to prepare a few stepping stone forms to use extra concrete. Some cut a 2 x 4 an inch shorter than the space ebtween forms, and attach stakes to the top side of each end, extending them out about 4″. This is used to screed your base to a consistent depth.
  • Reinforcing. What was that ZZ top song Concrete and Steel about anyhow? While many redi-mix concrete suppliers offer reinforcing fiber as a mix option, most reinforcing is in the form of rolled wire mesh which is pulled up into concrete as you pour or a rebar grid which is elevated on concrete “dobies,” or on rocks. I prefer a tighter grid, say from 20″ to 30″ on center, with #3 (3/8″) rebar rather than wider spacing with #4. If you don’t have access to a rebar bender, #3 is easily bent around a hitch ball on a truck and can be bent over your knee. This is to have a continuous band around the perimeter, though not an absolute necessity. Overlaps are traditionally 40 diameters (16″ for 3/8″). Rebar is tied at overlaps and intersections using tie wire and lineman’s pliers. With practice you can get ties tight without breaking them. If you don’t have access to that bender/cutter you’ll need a metal blade in a circular saw.
  • Pour day. Even if you’ve gotten this far by yourself, you will want help. Though with lots of experience under my belt I have poured and finished large slabs by myself, it is never fun and even less smart. You will want two other helpers and if they are free don’t chase away a third. If the truck can’t reach your pour site, you will want at least one construction grade wheelbarrow with the tire inflated to proper pressure. Homeowner garden wheelbarrows are not strong enough. You will need a bullfloat of wood or magnesium, usually 36 to 42″ in length with necessary poles, a fresno metal finish float with poles, hand wood trowels, hand metal finish trowels, a magnesium trowel, a metal edger, and plastic buckets to keep hand tools in water. Tell the concrete company what you are pouring and confide that you are new to this and they will set you up with the right mix. If not too hot a day they might suggest 5 sack, 3/4″ minus aggregate, in a 5″ slump, with water on the truck to add if necessary. It isn’t important that this makes sense.
  • Concrete placement. Accuracy now saves time. Whether by concrete truck chute, wheelbarrow, or eight workers with 5 gallon buckets, place the concrete quickly starting the farthest away, and in shady spots before direct sun spots. Make sure you continuously screed the concrete level with form tops and fill in holes as you go along. Screeding is done with one person on each end of your 2 x 4 screed moving it back and forth in coordinated fashion as they each also pull excess concrete toward them. If another person is available they should pull back excess with a shovel or concrete rake, so that the load isn’t too hard on screeders, and fill in low spots in anticipation of screeders reaching that point. This process makes the surface uniformly level and knocks larger rocks down into the pour.
  • Finishing. If you hired a pro, now is when you are really glad you did! Immediately after all concrete is placed and screeded, begin removing concrete off form tops and overspills from outsides. You can gentle tap the sides of the forms to provide a smooth surfaces when forms are later removed. If placement went quickly and it hasn’t been hot, you will need to let the concrete set up for a little while. Though concrete is science it becomes art at this point.  For decades the next step has been to use a jitterbug to knock the rocks down. This is the process of pounding down on the slab with a mesh tool when the slab is wet but will support your weight with your sinking only about 1/2″. Some use a rolling jitterbug cage on an extension pole. Very nice. Some use an electric screed after placement and then skip the jitterbig phase. Some use the wood float mentioned below.The next step will be to begin going over the surface with the bullfloat. If done too early you will lose the uniform level surface you have created and bring up too much cream. If done too late you will discover rocks that are not sufficiently below the surface and now don’t want to go down and you will also find it hard to work up enough cream. Magnesium, whether in bull float or handtrowel, will work up cream when needed over a wood float. For this reason some finishers will use a wood bullfloat early and a magnesium bullfloat later, though most stick to a single step here. There needs to be enough cream to produce a smooth surface but not so much that you are just pushing it around. The technique is like spreading peanut butter. If surface stops being spreadable and you are starting to drag up material, you are going past bullfloat stage. If necessary spray water over a section as needed to allow this process. If sufficiently smooth for the bullfloat phase it is time to wait again.I like to go around the perimeter with the edger early to knock down rocks. This is a finish tool that will be used later when concrete is hard enough to metal trowel, but a preliminary pass will save you headaches.Concrete is ready for the fresno hard metal finish trowel when there is enough cream to smooth out but the tool does not produce an excess. At the right stage the fresno will work, whereas if you tried to use the bullfloat you would drag up material and have a problem to fix. If you are going to use a broom finish, you may do usually all your final smoothing with the fresno. After it dries to the point where a broom produces fine lines without making deep lines and dragging up material it is ready for the broom finish. If opting for a smooth finish, you can be satisfied with what the fresno can produce, but traditionally the hand finish process is added. This is done by going out onto the slab on plywood squares with 2 x 4 handles you have made for this purpose. The slab has to be hard enough to support this without sinking and you work backwards from your starting point finishing over any marks made. The lead edge of the trowel is lifted slightly to smooth out the work and avoid digging in. Alternatively, like peanut butter, you lift one edge then the other as you go back and forth. Additionally you will often add sweeping circular motions. Invariably you will have to use a magnesium trowel to work up some cream in a trouble spot before refinishing with the metal trowel. Remember to use your edging tool again.

Do it yourself and hire a contractor?

As you can see there is a lot of work and planning involved. If you hire this done, your builder is earning his keep. If you decide to tackle something like this yourself you can save a lot of money because you are taking on a lot of work. Perhaps neighbors can form some teams to complete projects in each others yards. For some this is a very sensible option and at times the only affordable one. For probably most, this is beyond their scope, and they will want to hire the labor and expertise of professionals for at least some of this.

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