Looking at the two methods: Hens versus incubators

Before you can choose the hatching method that’s right for you, you need to know a little bit about them. In this section, we explain each method.

Determining which method is best for you

Deciding whether to let a hen incubate your eggs or use an incubator depends on several factors:

• Whether you have room for an incubator: Incubators need to be placed in a heated room for best results. If you don’t have room for an incubator in a heated place, going the hen route is your best bet.

• The breed of your laying hen: If you have hens of a high-production layer breed, they’re not going to sit on their own eggs (check out Chapter 3 for breed information). The urge to do so has been bred out of them. If you have room for more hens, you can get a hen or two of a breed that’s known for sitting and put fertile eggs from the other hens under them (see the section “Understanding why some hens brood and others don’t,” later in this chapter, for more info). If you can’t have — or don’t want — more hens, you need an incubator.

  If you have breeds of chickens that will sit on their own eggs, you can wait until they feel broody and let them raise a family. We discuss broody behavior in more detail later in this chapter.

  Hens stop laying while they’re sitting on their eggs and while they’re caring for their chicks. So if you want to keep egg production high, or if you want to raise chicks at a time when the hens don’t feel broody, you need to use an incubator.

• Whether you want to see the hatching process: If you or the kids want to observe eggs hatching, use an incubator. You won’t be able to see much as a mother hen hatches chicks because they hatch beneath her, and too much disturbance will cause her great stress and may harm the chicks. You can, however, observe a mother hen caring for chicks and see their antics in a natural environment after the hatching is complete and she takes her babies into the world.

• What time of year you want the eggs to hatch: Left to nature, most chicks hatch in late spring through summer, and hens may not begin laying again until the following spring. If early laying is important, use an incubator to hatch eggs early in the spring.

  If you want chickens for meat, the time the hen picks to hatch the eggs may not be the best growing time for your climate. Of course, you can still eat the excess chickens from any type of hatching and rearing, but if you want consistent meat production at convenient times for you, use an incubator to hatch meat chicks.

  If you want show birds to be at a certain age for a show, you may need an incubator to plan hatching at the best times.

  If you want to sell chicks, it’s best to plan for them to hatch in spring and early summer, which can mean using an incubator to catch the highest demand period for chicks.

Sitting hens are great for the home flock owner who isn’t good at keeping track of things like turning eggs and who isn’t in any rush to have chicks at a certain time. Sitting hens are the green way to increase your flock, especially if you need only a few chicks at a time, because they don’t require any electricity to do their job.

Understanding why some hens brood and others don’t

Hormones affected by the lengthening daylight hours trigger the nesting instinct in hens. Hens have to be laying actively to get broody, so hens must also be in good health and must be receiving good nutrition. For about an hour before an egg is laid, and for 30 minutes afterward, a hen of any breed gets a bit broody, going to a nest and moving nesting material, sitting in it, and crooning. In some breeds at certain times of the year, the hormones that influence motherly behavior don’t go down after the egg is laid; instead, they intensify over a week or so until the hen is sitting firmly on a nest.

In certain breeds of chickens, man’s breeding practices have prompted them to produce fewer of the hormones that influence broody behavior. This selection process was done to keep them producing eggs because when a hen starts sitting on a clutch (group) of eggs, she stops laying. Table 13-1 shows some breeds of chickens, listed according to how often they get broody.

Note: This table doesn’t cover all breeds — just some of the common ones. Breed descriptions generally note whether the breed sits. See Chapter 3 for more breed descriptions.

In breeds that sit on their eggs, laying a certain number of eggs and having the right environmental conditions may trigger broody behavior. Still, even in these breeds, each hen is an individual, and some hens are better moms than others. Some people think hens that were naturally hatched and raised by their own mothers take better care of their nests. This trend has been proven true in other species, so it’s probably partly true in hens, too.

Hens of naturally sitting breeds seem to be influenced to some extent by the hens around them, and several hens may start sitting at one time. Several hens may actually sit on the same nest, although you want to discourage this behavior because it often results in broken eggs. Instead, have plenty of nests and enclose each hen as she settles down to sit firmly.

Encouraging your hens to brood

If you have a hen from a breed of chicken that’s known to sit on eggs, how do you encourage her to get started? Natural environmental conditions, such as long days and warm weather, seem to help. If you want a hen to sit in conditions other than these types, it helps to manipulate the light so that the length of the hen’s day gradually increases.

Don’t encourage sitting in the coldest months of the year unless you can heat the coop to about 40 degrees Fahrenheit. Hens don’t sit tightly for the first several eggs, so those eggs may get chilled enough to die. Plus, extreme cold may keep even the later eggs from hatching.

Hens also like dark, comfortable nests with plenty of nesting material. Just getting in one of these nests makes some hens ready for a family. You may want to set up some of these nests away from regular egg collection nests so you can enclose the hen to protect her as she sits.

Some people keep hens for sitting in their own special housing, especially when the hens are a different breed from the hens producing most of the eggs. Active breeds sometimes pick on sitting hens, and hens and chicks need special protection from predators that a regular coop may not be able to offer.

Hens don’t need roosters to get the broody feeling. They’ll sit on infertile eggs — or even on junk or rocks. But some home flock owners notice that when a rooster is around, he may encourage a hen to sit on a nest, even occasionally standing guard for her. On the other hand, some roosters may harass sitting hens, especially if few other hens are around.

Adding eggs to the nest

You may want to give a hen eggs that she didn’t lay because the hen that laid them isn’t a broody hen. If so, you’ll be glad to know that most hens readily accept eggs from other hens. Either remove the eggs that the hen laid and replace them with the ones you want to hatch, or just give her a few new eggs to sit on and remove a few of hers.

The eggs you add need to be very close to the same stage of development as the ones the hen laid. Don’t give a large hen more than 10 to 12 eggs, and give a bantam breed no more than 6 to 8 large eggs or 10 to 12 of her size if you want optimal hatching (see Chapter 3 for what constitutes a bantam breed).

If you want to save eggs to hatch from another hen, start collecting the desired eggs about the time you notice the broody hen starting to lay. Keep the collected eggs in a place between 45 and 65 degrees Fahrenheit and place them with the small ends down. Don’t shake them or subject them to rough handling. Turning them by tilting them one way one day and then the other way the next day is a good idea. Don’t store eggs more than ten days; after that, the eggs may not hatch as well. (See the section “Taking care of fertile eggs before incubation,” later in this chapter, for more on how to properly store fertile eggs.)

If you’re buying eggs to set under a hen, don’t order them until you have a sitting hen. Even if it takes a few extra days for her to hatch the new eggs, you’re better off using fresh fertile eggs than you are storing fertile eggs for a long time.

You can delay a hen’s sitting by leaving just one or two eggs in the nest. Remove those eggs before adding the new ones. Hens will remain sitting a few days beyond the original hatch date, but if one or two chicks hatch more than two days before the rest, the hen will probably abandon the late eggs so she can lead the chicks to food and water.

You can either replace each egg the sitting hen lays with a fake egg or leave the eggs in the nest until you’re ready to remove all of them. You can buy plastic, wood, and ceramic eggs from poultry supply catalogs (we list some hatcheries that sell supplies in Chapter 4); you can often find fake eggs in craft supply stores as well. Try to use natural-colored fake eggs. Don’t use Styrofoam eggs. If you just remove the eggs without replacing them with fakes, the hen may not settle down to brood the eggs right away and may even abandon the nest. You want a hen to be sitting firmly on the nest before you give her eggs you bought or saved to hatch. She will sit firmly when she thinks the clutch is big enough, and an empty nest gives her the wrong signals.

When you’re ready to set the eggs, reach carefully under the hen and remove the eggs she has. She may peck at you, grumble, and slap you with her wings. Then, protecting the new eggs in your closed hand, slide them under her carefully. That’s all it should take.

Occasionally, a hen throws out a new egg. Sometimes she does so when the egg is a different color or size from hers. If it isn’t cracked, put it back in the nest.

Giving a sitting hen what she needs

Isolate a sitting hen from the rest of the flock, or at least from nonsitting flock members. Chickens that aren’t protected may be picked on or disturbed by other hens, disturbed by the rooster, or picked off by predators because they won’t move off the nest. Other hens may crowd into the nest with the sitting hen, adding more eggs than she can sit on or breaking eggs in a shoving match.

If you find a free-ranging hen sitting somewhere, try to protect her from the environment and surround her with some kind of small mesh fencing to protect her from predators. Put a board or tarp on top, and she’ll be fairly well protected. If you have a hen sitting inside, also try to protect her from other flock members and predators.

A hen doesn’t need a very big enclosure while sitting. She needs enough room to stand and stretch and flap her wings when she gets off the nest, and she needs room for small feed and water dishes. About 3 square feet for full-size hens and 2 square feet for bantams does the trick. You can make the enclosure with a circle of fencing with small openings that keeps chicks in, or you can use a cage with small wire openings.

Some hens don’t object to a careful move of the whole nest to a protected place, but it’s best to get the hen sitting in a place where she can be protected from the start of incubation.

If you need to move a hen, do it at dusk or at night. Try to slide something (such as a big cardboard box) under her and the eggs, and move the whole thing to the new spot.

Be careful: Wilder hens may fly off the nest as you move it and be hard to catch. The hen won’t know where you moved the eggs and won’t find them. Move slowly and quietly as you pick her up and confine her with the eggs.

By morning, a confined hen should’ve decided to stay put, but make sure she can’t get to the old area. Some hens may abandon the eggs and go sit where the nest once was. If you must move a hen quickly during the day, get a good nest area ready, move the eggs and the hen into it, try to darken the spot, and then leave — don’t fuss about her. Many hens will settle right down, but if yours doesn’t, you can’t do much about it.

Hens don’t carry eggs to a nest, although they may roll eggs a short distance back to a nest by reaching out from the nest with their beaks. If you see eggs out of the nest, mark them with a marker or pencil and put them back in the nest. If the marked egg turns up back outside the nest, the hen may be trying to discard it because she knows it’s no good, especially if no other eggs are out of the nest. Sometimes the hen is just clumsy. Other times, other chickens or predators may be disturbing the nest. If an egg comes out of the nest a third time, discard it.

If eggs crack or get dirty from manure or mud, don’t wash them. You can try to clean the egg with a soft, dry cloth, but washing it can cause bacteria to invade the shell. Don’t handle the hen’s eggs if you can avoid it. They will get chilled every time you remove them.

Make sure the hen always has food and water available. She won’t eat or drink very much — that’s normal; she isn’t active, and eating too much food creates the need to get off the nest more often. Place the food and water a little ways away from her so she has to get up to eat — getting up once in a while is good for her. Clean the pen area if it gets too dirty. Food, water, and a clean pen are all the care she needs.

Caring for a hen and chicks

Twenty-one days have passed, and the big day is at hand. If a hen has remained sitting firmly on the nest until now, you’ve got a very good chance that at least some of the eggs are going to hatch. Hens hear and respond to chicks peeping while the chicks are still in the shell. Now isn’t the time to disturb the hen frequently — you want her to stay on the nest until all the healthy eggs have hatched. So listen carefully and watch the hen for tiny heads popping out from under her, but don’t shoo her off the nest to look.

Choosing an incubator

You can find incubators for almost all budgets, and you can even build your own incubator with some parts you can purchase. Poultry supply catalogs, farm stores, and pet stores carry incubators — deluxe models that are almost “set and forget,” as well as some cheaper models that require more careful attention from you. Many secondhand incubators are for sale in newspapers, in magazines, and online.

Before you buy an incubator, you need to consider the following factors:

• How often you’ll likely be using an incubator
• How many eggs you want to hatch at a time
• What type of poultry, if any, besides chickens you want to raise
• What your budget can afford
• How much you want to be involved in the project

If you or your kids want to see the eggs hatching, you want to get an incubator with an observation window.

If you think the egg incubation project will be a one-time experience or something you do maybe once a year, buy a cheaper incubator or a good secondhand one. You can always upgrade later. If you’re already deep in the chicken hobby and you think you’ll be hatching eggs frequently, buy a better incubator. If you want to hatch eggs of turkeys, ducks, or geese in addition to chicken eggs, make sure the model you buy can accommodate the bigger eggs.

Most incubators require electricity (although you can buy gas-powered ones) and are meant to be used in a heated room.

The following list describes the three main categories of incubators (Figure 13-1 gives you a couple examples):

• Still-air incubators: Still-air incubators are the cheapest models of incubators. They’re usually made of Styrofoam or plastic. They range from models that can hatch just 4 eggs to models that can hatch 36 or more eggs, depending on egg size. Many of these have clear tops or observation windows.

  Air in these incubators moves through the incubator by cooler air being drawn in from the bottom and rising as it’s heated through some ventilation holes on the top of the incubator. Some models include fans to move air. Most models have a reservoir in the bottom that you add water to in order to provide humidity. Some models have automatic egg turners; otherwise, you need to turn the eggs by hand.

  These incubators require careful attention daily, and you need to follow the instructions exactly. They can provide a good hatch if you pay attention to details.

• Forced-air incubators: Forced-air incubators move heated air through the incubator with some kind of fan system. They’re more expensive than still-air incubators, but they generally provide for a better hatch because they eliminate the hot and cold spots that still-air incubators sometimes have.

  Many forced-air models also come with automatic humidifiers and egg turners, and some deluxe models have warning buzzers and other bells and whistles. Some attention is still needed, but it’s less than the still-air models require. Some come with observation windows. They range in capacity from 12 to 50 or so eggs.

  These models are probably the best type for most home chicken flock owners.

• Cabinet-style incubators: These incubators are large units with forced air, automatic humidifiers, and egg turners, and they have several shelves to accommodate eggs at different stages of hatching or of different sizes. They generally don’t have observation windows, and they cost you a considerable amount unless you find a good deal on a used model. These units are for the serious chicken hobbyist.

Automatic egg turners are standard in some incubator models but can be added to others. They work by tilting the eggs in a different direction every few hours — they don’t actually roll the eggs over. Automatic egg turners increase the number of eggs that hatch because the eggs are turned consistently and gently. They have to be turned off 3 days before the chicks hatch.

Accessorizing your incubator

You need to buy a few incubator accessories if the incubator itself doesn’t supply them. Some necessary accessories include the following:

• Thermometer: The thermometer needs to be at a level near the top of the eggs. You can place your thermometer on a stand or hang it to achieve this level. Make sure the thermometer has measurements large enough to read from the observation window, if you have one. Position it in the center of the incubation space so that it doesn’t touch the eggs or the walls of the incubator.

  Typically, when an incubator has a window, you read the thermometer remotely from outside the incubator because the minute you open the incubator, the temperature drops. Many remotely read thermometers are on the market — you place a probe or sensor in the incubator, and it transmits a reading to a device located outside the incubator. You can find such thermometers made specifically for incubators or for general household use.

  The correct temperature is critical to success with incubation, and the thermometer must show each degree. Even a difference of 1 degree can affect hatching. Buy a good thermometer and handle and store it carefully.

• Hygrometer: You can buy a hygrometer, which measures humidity, specifically for incubators or for household use. Many of the remote-style thermometers also measure humidity.

  Humidity is crucial to a good hatch, so make sure you buy a good instrument. Many of the better incubators have built-in hygrometers, some of which actually automatically add water from a reserve tank to adjust humidity.

You may also want an egg candler, a light that helps you look inside an egg to see whether it’s developing. You can buy or make these instruments. (See the section “Looking Inside the Egg,” later in this chapter, for more on candling.)

Setting up and caring for your incubator

After you buy an incubator, carefully read the directions that come with it, and then save those directions so that if you decide to use the incubator again in a year or so, you have the directions to refresh your memory.

Your next step is to find a place to set your incubator. It needs to be located near an electrical outlet, and it’ll be there for a month (so you probably don’t want to put it in the middle of a high-traffic area). Choose a room that’s heated to at least 60 degrees Fahrenheit and away from windows, heating vents, and doors that may cause wide fluctuations in room temperature. Also select a place where it won’t get knocked off or jostled too often.

If you have children or pets, you may want to put the incubator where it’s out of sight and out of mind. Children are prone to opening the incubator too often, handling eggs, or fooling with controls. Pets can hear the chicks peeping in the shells in the last days of incubation and may damage the incubator trying to get to the eggs. They may also jostle controls while inspecting the incubator or, in the case of cats, sleep on top of it, blocking the vent holes.

Have the incubator set up and running for at least 24 hours before you add eggs, to make sure it’s working correctly.

Finding and storing fertile eggs

When you have the incubator ready, your next step is to get fertile eggs. Finding fertile eggs may take a little time if you don’t have your own hens and a rooster, so start looking well before you want to hatch eggs. Even if you have your own hens and a rooster, you may not be getting fertile eggs. (In Chapter 12, we talk about how eggs are fertilized and how to make sure your own chickens are laying fertile eggs.)

Fertile eggs are usually available in the spring and summer, but they may be hard to find at other times if you’re not producing your own.

Caring for eggs in the incubator

A mother hen seems to know instinctively what her eggs need. If it’s very hot, she gets off the eggs to let them cool a little; if it’s cold, she sits tightly. Her body provides the perfect humidity, and she fills it with water herself. When you take over the job of incubation, you can never be as good as a hen, but with careful attention to details, you can have a successful hatch from an incubator.

Egg ultrasound: Candling an egg

Candling is a way to look inside an egg without opening it and killing the embryo. Candling involves shining a bright light on the egg in a darkened room and seeing a shadow inside. You can see the size of the air cell, veins in an egg with an embryo, and the dark mass that indicates the yolk and the embryo.

Candling works best with light-colored eggs, but you can candle brown eggs, too. If you do so quickly in a warm room, you won’t harm the developing chick. You can buy candlers from poultry supply places, but they’re also relatively easy to make (see Chapter 4 for a list of reliable poultry supply places).

To make a candler, follow these steps and refer to Figure 13-2:

1. Line a cardboard box with aluminum foil.

   The aluminum foil makes the light stronger.

2. Place any good, strong source of light inside the box.

   An LED flashlight or reading lamp works, as does a 60- to 75-watt incandescent light bulb.

3. On one side of the box, make a ½-inch hole.

To candle an egg, follow these steps:

1. Wash your hands.
2. Turn off the lights in the room.
3. Quickly remove an egg from the incubator and hold it outside the box against the hole in your candler box.

The beam of light will shine into the egg, allowing you to see shadows inside the egg. You’re looking for the size of the air cell, dark embryo masses, and blood veins inside the egg.

Don’t keep the egg out of the incubator too long — no more than 5 minutes. Mark the egg before you put it back in the incubator so you know which eggs you’ve looked at. If you intend to candle a few eggs more than once, you may want to number or otherwise identify each egg. You can candle an egg as many times as you want, but the more you handle the egg, the less likely it is to hatch.

Knowing what to look for: Stages of embryonic growth

A tiny chick develops very quickly. Almost as soon as the sperm penetrates the female reproductive cell, called the blastodisk or true egg, which is a small white spot on the yolk, the cells begin dividing to produce a chick. (For more information on fertilization, see Chapter 12.) By the time the egg is laid 26 hours or so later, a ring of cells has already begun to form. If the egg is incubated by the hen or put in an incubator, cell growth rapidly continues. But most eggs cool and go into a state of suspended growth for at least a few days.

As a chick develops, the air space in the egg enlarges, and the egg actually loses weight. Looking at the egg’s air cell changes during candling is one way to see whether a chick is developing (see Figure 13-3).

After 24 hours of incubation at 100 to 102 degrees Fahrenheit, the chick’s head, eyes, digestive system, and backbone have begun to form. They’re still quite small — you need a magnifying glass to see these structures well, but rest assured that they’re there (see Figure 13-4).

After 44 hours of incubation, the heart begins beating. Two circulation systems begin to function — one in the embryo and one in the vitelline membrane, which surrounds the embryo and acts something like a placenta in mammals, absorbing food and oxygen from the egg white and transferring it to the chick.

By the end of the third day, the beak has begun to form, limb buds are present, and temporary “gills” appear on the embryo.

By the end of the fourth day, the embryo has begun flexing and moving and generally rotates 90 degrees to lie on its left side. All the internal organs have formed by the end of that day.

By the end of the fifth day, the reproductive system has formed and begins to differentiate into male or female, although you can’t tell the sex by looking at the embryo.

By the end of the seventh day, digits appear on the wings and feet that will make toes and wing sections.

By the end of the tenth day, the tracts where feathers will grow have formed, and the beak hardens.

By the end of the 14th day, the toenails have formed.

By the end of the 16th day, the embryo occupies much of the space inside the egg and has begun to use the egg yolk as a food supply because the egg white has been used up.

By the end of the 19th day, the yolk has been drawn up into the chick’s body in preparation to hatch.

Playing doctor: Helping a chick hatch

Sometimes people feel sorry for a chick that appears to be having trouble getting out of an egg. It may have pipped (made a tiny hole) and have its beak out, but it may seem unable to proceed any farther.

The temptation is great to help these chicks, but doing so can cause more harm than good. You can’t just pull off the shell. Hatching is a slow process even in ideal conditions — you have to be patient.

Generally, when eggs pip but then fail to hatch, the temperature, oxygen level, or humidity is too low. The temperature may drop because someone is constantly opening the incubator to check on the chicks’ progress. Poor ventilation may cause the chicks to become weak because of a lack of oxygen. And humidity can get too high and actually drown hatching chicks because they can’t breathe. These problems may be correctable and the chicks then will finish hatching. But even if conditions seem to be fine, many experienced chicken owners believe that chicks that can’t hatch on their own are doomed to either die anyway or live a weak, unhealthy life and so don’t help them. New chicken owners usually want to help the chicks and it doesn’t hurt to try. Just don’t be too upset if they don’t make it.

Sometimes the membrane has dried out too much around the chick, or the chick is in a bad position for hatching. If the pipped hole isn’t in the large end of the egg, the chick is in the wrong position. If you see no hole but you hear peeping inside, the chick also may be in the wrong position. If you see a hole in the right area but the chick can’t seem to finish hatching, the membranes may be dried out.

In these cases, helping — slowly and carefully — can save a healthy chick. Make sure the chick is still alive — it will move or peep if it is. If you’ve decided to try to help the chick, start by making a warm operating area with a padded, clean surface. Sterilize a small pair of nail scissors and a pair of tweezers with rubbing alcohol, or boil them for a few minutes. Have some clean, warm water nearby.

Under the shell is a thick membrane loaded with blood veins. The chick has already pierced the membrane in one spot if it has started to hatch. If you tear the membrane too early, it will bleed profusely and either weaken the chick or kill it.

With the scissors and tweezers, carefully pick little pieces of shell off the membrane, around the hole in the egg. Ideally, you work like the chick would, circling the large end of the egg and removing half the shell. Around the air cell, there may be no membrane, allowing you to remove shell pieces easily. If the chick has started a hole in the side or small end of the egg, the chick is in the wrong position, which is why it’s having difficulty hatching. You need to be even more careful in this case.

Be careful not to cut the chick. If you cut a vein in the membrane and it bleeds, stop at once and put the chick in the incubator. You can’t do anything to stop the bleeding. The bleeding will probably stop, but it weakens the chick. You can start again in an hour or so if the chick is still alive and not free.

If half the shell is removed and the head and neck are exposed, the chick should become active and wiggle out of the rest of the membrane and the egg. Moisten the membrane that’s left with a little warm water and place the chick, with some shell still attached, back in the incubator. It will probably just lay there for a while. If the chick isn’t up and walking within an hour or so, it’s probably too weak to survive.

Handling the bad hatch: When things go wrong

If eggs hatch early, either the temperature was too high in your incubator or you counted the days wrong. If the eggs hatch late, the incubator was a little cold or you counted the days wrong. If the eggs are hatching over a wide time span (more than 18 hours), your incubator may have had hot or cold spots, or you may have improperly stored the eggs before you put them in the incubator.

If many eggs don’t hatch by the 22nd day, pull some out and open them. If no embryo is inside, they probably weren’t fertile or they were stored too long or improperly. If embryos started forming and then died, the temperature or humidity of the incubator wasn’t right, the incubator didn’t have adequate ventilation, or the chicks died from bacterial contamination or a disease. Not turning the eggs enough or handling them roughly can also cause embryos to die.

If you open eggs and find some living embryos, put the unopened eggs back and give them some more time. If many eggs don’t seem to be hatching, always check a few eggs before you discard all of them.

If chicks hatch but they appear “sticky,” with egg goo on them, the humidity may have been too high, the temperature may have been slightly low, the ventilation at hatching may have been poor, or they may have an inherited condition that causes this symptom.

Malformed or crippled chicks can be caused by slightly high temperatures during incubation, disease, chemical contamination of the incubator, or failure to turn eggs enough during incubation. Bad legs can also be caused by hatching chicks on slippery surfaces.

If hatched chicks have large, bloody, or mushy naval areas when hatched, the incubator temperature may have been slightly low, the humidity may have been too high, or the chicks may have a disease called omphalitis, which is caused by bacteria invading the naval area. For this reason, chicks should hatch on a dry, clean surface.