One gallon of paint covers approximately 400 square feet. To estimate how much paint your project requires, enter your room measurements—rounded to the nearest foot—into our pop-up calculator. To ensure you will have enough paint, do not worry about excluding areas not to be painted, such as windows and doors. Additionally, a 10 percent waste allowance is automatically added to the total.
Before you begin, take the room measurements in the list below. If you have cathedral ceilings that create sloping walls, follow the special case instructions on how to derive this square footage.
Measure from floor to ceiling.
Wall perimeter for areas you plan to paint
Measure the length of each wall. Add all these figures together to obtain the total horizontal distance, or perimeter.
Ceiling width and length
Omit if you do not plan to paint your ceiling.
Sloping walls form a triangular wall space
To calculate a triangle’s square footage, multiply the length or base of the wall by the highest wall height and divide by 2.
Common paint problems —
how to prevent them
Usually it’s the paint itself that gets the blame for paint problems on your homes exterior. In most cases, the cause lies elsewhere. Here are some common problems and ways to prevent them. Blistering Es the earliest stage of peeling and is usually caused by moisture trapped under the new paint coat or by poor surface preparation. If blistering occurs within the first few weeks, it’s probably caused by rapped moisture. While latex paint can usually be applied, to many surfaces without any preparation. Alkyd and other oil-based Paints form ~‘.fl~istU~& barrier skin that traps the water inside The water then turns to vapor and forms dusters. To avoid this, never paint with alkyds after a rainstorm when the relative humidity is more than 85 percent. while dew’ Is on the siding. or too soon after you’ve washed the nEc surface. Also, never paint when the temperature is more than 90F degrees.
If the blisters appear after a month or so, the problem is probably poor surface preparation. If you washed the surface down with detergents, did you take the time to rinse completely? Unless such films are removed before painting, they can cause blistering. Also glossy surfaces must be given a light sanding, so the new paint will grip well.
Peeling is the curling of large pieces of dried paint and is merely a later manifestation at blistering. Severe peeling might also indicate use of a poor primer, or a hea film of dirt, grease or dust. Prevention involves sanding or wiping the old finish with a deglossing liquid. Then follow the manufacturer’s directions as to what primer might be required before applying the topcoat of paint.
Alligatoring is a cracking and flaking of the paint in a square pattern. It can result from applying paint over a previous coat that had a high gloss finish that was not sanded. Use of the wrong primer or use of old paint, particularly paint that’s been stored in an unheated space and allowed to freeze. To repair the condition, sand the surface smooth and apply the proper primer before applying a new topcoat.
Checking is a series of long lines, with shorter check marks crossing between isoaliv caused cv the wood underneath expanding and contraction, This can be a problem with exposed plywood siding regardless of the kind of paint used, Sanding and then applying a new coat of wood primer will usually solve d~e tcroh em. But if the new paint shows signs of coming loose, complete removal at the old Paint is required.
Wrinkling results in a crinkled surface that is caused by interfering with required drying time. Contributing factors are too-thick finish coat, building up of too many layers, undercoat that was not completely dry, wrong solvent or improperly stirred paint. Repair by sanding smooth and applying proper primer before painting topcoat.
Chalking or powdering characteristics are designed into some paints in order to keep the surface looking new. Chalking of old paint can interfere with proper bonding of a new coat. so scrub off as much as possible beforehand. In severe cases you might have to apply a bonding primer or sealer.
Mildew manifests itself as patches of black spots. Though most exterior paints contain mildew-inhibiting ingredients, none works under all circumstances. Remove mildew by washing down the affected area.
The ABCs to measuring paint
A. Measure length of all exterior sides of house to be painted.
B. Multiply the length of all sides (Answer A) by the height of the house. Note: Add two inches to he height for overhangs.
C. Divide he total square footage (Answer B) by the cove age ate displayed on the can, with a bleach solution. Use one-third cup powdered laundry detergent, two-thirds cup of household cleaner containing trisodium phosphate, and one quart of household bleach. Wear long pants, a long-sleeved shirt, gloves, goggles and an aspirator to avoid breathing the fumes.
Stains that bleed through the paint often are the result of sap from knots in the wood seeping through the surface, But it also can be caused by rust from nails and hardware. Many discolorations bleed through coat after coat of paint, so repainting alone is not the answer. Instead, apply a primary coat of stain-kill ~r, such as pigmented shellac-base sealer and then apply your paint.