| Dry sandblast cleaning is a relatively new method of | | | | him to remove by blasting. |
| cleaning block machine newly built masonry, although | | | | 3.Provide adequate protection for all non-masonry |
| the system has been used for many years in | | | | surfaces adjacent to work areas, Use plastic sheeting |
| masonry restoration work. | | | | and duct tape to protect windows, doors, etc. If |
| Many architect/engineers prefer sandblast cleaning | | | | possible, painting, caulking, etc. should be done after |
| over conventional wet (acid) cleaning because of | | | | sandblast operation is completed. |
| possible adverse acid reactions with certain types of | | | | 4.When all surfaces are prepared and protected, the |
| brick. Other designers are reluctant to permit | | | | operator can begin a first test cleaning. |
| sandblast cleaning from fear the blasting will erode | | | | Operator should clean a small area with the nozzle |
| the face of the brick and mortar joints. | | | | first close to wall, and then at varying distances from |
| Sandblast operators can be compared with other | | | | the wall, trying to select a working distance that will |
| construction tradesmen: some are artisans and others | | | | give the best cleaning job with the least damage to |
| are incompetent. However, with a qualified operator, | | | | brick and mortar work. |
| proper specifications and good job inspection, | | | | Job superintendent and architectural inspector should |
| sandblast cleaning is as good as any other system | | | | be present at this time to confirm acceptable |
| and is sometimes superior in many ways. | | | | practice. Approved areas should be marked and |
| Basically, sandblast cleaning involves the following | | | | identified as acceptable standard for the entire job. |
| equipment: Portable air compressor, blasting tank, | | | | Specifications for Sandblast Cleaning |
| blasting nozzle, operators' protective clothing and | | | | Scope |
| hood. | | | | This section includes cleaning of newly constructed |
| Air pressure delivered by compressor to blasting tank | | | | clay masonry with dry abrasive material forced by |
| may range from 40 lbs. to 100 lbs. per square inch. | | | | compressed air from tank through hose and nozzle. |
| Blasting tank is charged with the specified abrasive | | | | Material |
| material and pressurized to force the mixture of | | | | Cleaning material must be dust-free and abrasive. |
| abrasive material and air into blasting hose and to | | | | Hardness should be approximately 6 on Mohs' Scale. |
| nozzle. | | | | Material size shall conform to one of the two |
| Blasting pattern is determined by nozzle size, type | | | | categories listed below according to acceptable finish |
| and air pressure. Speed of cleaning is determined by | | | | of masonry surface. |
| type of abrasive used, nozzle size, type, air pressure, | | | | Equipment |
| nozzle-to-wall distance and of course, condition of | | | | Air compressor must be capable of producing |
| surface to be cleaned. | | | | pressure between 60 pounds and 100 pounds per |
| Abrasive material used in brick cleaning is usually sand, | | | | square inch at the machine and should have a |
| quartz, or granite and must be clean and finely | | | | minimum air flow capacity of 125 cu. ft. per minute. |
| graded. | | | | Nozzle inside orifice or bore size may vary from 3/16" |
| Sandblast cleaning material should conform to one of | | | | diameter to 5/16" diameter. |
| two particle size graduations outlined in the | | | | Sandblast machine (or tank) must be equipped with |
| specifications below. | | | | controls to regulate flow of abrasive materials to |
| Type "A" gradation is to be used when the masonry | | | | nozzle, and shall be capable of supplying sand at a |
| is very lightly soiled or when only a very light or fine | | | | minimum rate of 300 pounds per hour. |
| texturing of the brickwork is permitted. | | | | Operator must wear O.S.H.A.- approved hood and |
| Type "B" gradation is used for cleaning heavy mortar | | | | protective clothing. |
| stains from brickwork and where medium texturing | | | | Workmanship |
| of the masonry is permitted. | | | | 1.Brickwork must be dry and at least seven days old, |
| Sandblast cleaning may be used for cleaning all hard | | | | preferably 14 days. |
| burned, non-glazed, smooth or textured brick. | | | | 2.Before blasting, all large mortar particles must be |
| Included in this category are reds, buffs, whites, | | | | removed with hand tools. Use wooden paddles, metal |
| grays, chocolates, etc. | | | | scrape hoes or chisels if necessary to remove |
| Lightly sanded, coated, slurry, or sandbox brick should | | | | hardened mortar. |
| not be cleaned by sandblasting, unless cleaning cannot | | | | 3.Provide adequate protection for all non-masonry |
| be accomplished by any other method, as the brick | | | | surfaces adjacent to work area. Use plastic sheeting |
| face can be permanently damaged. | | | | and duct tape to protect windows, doors, etc. |
| Handmade or reclaimed brick may also be | | | | 4.Sandblast operation may begin if representatives of |
| permanently disfigured by sandblasting. | | | | architect and/or prime contractor are present to |
| As a further precaution, approval of the brick | | | | inspect trial cleaning areas. Operators must test clean |
| manufacturer must be obtained before permitting | | | | several areas, with nozzle trained at varying distances |
| sandblast cleaning. | | | | from wall, finally select-ing working distance that |
| The following procedure is recommended for | | | | affords best cleaning job with least damage to brick |
| Sandblast Cleaning: | | | | and joints. Test areas approved by representative of |
| 1.Wait for mortar to harden. Brickwork should be | | | | architect and/or prime contractor must be marked |
| completely dry and at least seven days old, | | | | and identified as acceptable standard for entire job. |
| preferably 14 days. | | | | 5.All brick and mortar joint areas considered by the |
| 2.Remove all large mortar particles with hand tools | | | | architect to be severely damaged by the cleaning |
| before blasting. Use wooden paddle, the rough edge | | | | operation must be replaced at the expense of the |
| of a brick, or metal scrape hoe. Chisels may be used | | | | cleaning contractor. |
| if necessary to remove hardened mortar or concrete. | | | | 6.If directed by the architect or engineer all concrete |
| This "pre-cleaning" is a very important part of | | | | brick machine cleaned by sandblasting shall be |
| sandblast cleaning. Sandblast operator would | | | | waterproofed with an approved clear coating as |
| irreparably damage wall if large droppings are left for | | | | designated by architect or engineer. |