Plaster Repair Methods
How to Diagnose & Repair Plaster Ceilings, Plaster Walls & Stucco Damage

Types of Interior Plaster Damage

This section describes plaster damage types & causes at building interior walls and ceilings.

If you are concerned about the condition of exterior plaster or stucco surfaces, see

STUCCO, HARD COAT INSTALLATION, INSPECTION, REPAIR - repair stucco on masonry or on exterior surfaces

• Plaster cracked or loose due to structural or other building movement
  
  If the underlying structure of a ceiling or wall is bending or sagging or if you see gaps at the intersection of ceiling to wall or at wall corners, check first for underlying building movement. We need to understand the extent of movement and its cause before undertaking any repair.
  
  If plaster is cracked due to foundation settlement, frost heaves, expansive clay soil those conditions need to be addressed or we'll also find that our plaster repair will not be durable.
  
  Watch out: if an inspection of the building shows significant and ongoing settlement cracking like that in our photo above, no plaster repair will be successful until the settlement cause has been corrected.
  
  Below our photo shows a different type of movement that caused extensive plaster cracking: a suspended ceiling was hung from the framing of the building floor above, but without sufficient fasteners to remain rigid. Flexing in the ceiling caused the plaster ceiling to break and collapse, even though it was constructed using expanded metal lath.

Below: plaster fallen from the underside of the roof of a pre-1900 New York Home.

• Plaster cracked or loose due to failures of the supporting lath
  
  Wood lath, expanded metal lath, gypsum board lath, fiberboard underlayment may be loose due to building movement, leaks, rot, or simply inadequate fastening in the first place.
  
  Before repairing the plaster shown in our photo above, the missing wood lath would need to be replaced.

• Plaster cracked, loose, fallen due to broken plaster ears
  
  In our photo the author [DF] is gently pulling at loose plaster on the wall of a pre-1900 home in "the bleachery" in Wappingers Falls, New York.
  
  When plaster is applied to wood lath some of the plaster rough-coat mix is pushed between slots between the wood lath strips where it curls over, hardens, and thus forms a mechanical lock or key that holds the plaster in place .
  
  Building movement, mechanical impact, leaks, or other events can cause those "plaster ears" to break off. It may be possible to secure such plaster in place using plaster washers and repair screws provided that the plaster itself remains solid, not soft or crumbly.
  
  Our photo below shows plaster ears that are still intact and holding plaster securely against a wall.

• Plaster soft or crumbling due to water leaks
  
  If you see water stains where plaster is damaged or if you know that the building has had a history of leaks, you may have to remove the water-damaged plaster rather than trying to patch it in place.
  
  Water can change plaster such that it will not remain stable, in place, nor can it be secured by a few plaster ears or washers and screws. It's just too soft.
• Plaster soft or crumbling due to improper original mix
  
  If your plaster is soft and crumbly (so not repairable) and there is no history of water damage, the original mix may have been improper. If so, check the extent of soft plaster before planning your repair.
  
  More-extensive plaster replacement now may be wiser and ultimately less costly than having to repeat the plaster repair work every year or so.
  • Extent of plaster damage
    
    Except in cases of historic preservation, if you find that most of the plaster on a wall or ceiling is loose or badly damaged (photo below, it's probably less expensive and faster to remove it and replace the surfaces with drywall.

  

  Above: very extensive loose, damaged plaster in this Wappingers Falls NY Home (28 West St.) led us to simply remove all of the old plaster, replacing it with drywall fastened atop the remaining wood lath.

  Watch out: if sections of plaster on ceilings or high on walls are loose or if ornamental plaster trim or rosettes on ceilings or walls are loose, those surfaces may be unsafe, as we explain
  
  at PLASTER, LOOSE FALL HAZARDS but keep in mind that not all bulges in plaster walls and ceilings are from loose plaster. So also
  
  see PLASTER BULGES & PILLOWS

Plaster Repair Methods

Repair of Small Cracks in Plaster or Portland Cement Plaster

Pruter (1995) focusing on portland cement plaster cracks, gave an accounting of plaster cracks by crack width and possibly underlying cause, suggesting different repair methods depending on crack width. In our opinion those categories can be reasonably applied to traditional interior plaster cracking as well.

• Minuscule cracks
  
  less than 0.0005 in (0.127 mm) are "acceptable" and don't require treatment
• Hairline shrinkage cracks
  
  0.0005 in (0.127mm) to 0.10 in. (0.254 mm), also called crazing or checking cracks may expand or contract in response to temperature changes.
  
  Repair: apply 15-18 dry mil thickness of a good elastomeric coating over the whole surface
• Minor structural movement cracks
  
  0.125 in - 0.250 in in width are usually structural in origin, opening and closing with building movement in the structure or in the finished surface materials.
  
  Repair: as above for hairline shrinkage cracks + the addition of a crown of 1/16" of elastomeric coating centered over the crack - remarkably he approves this treatment for cracks up to 1/4" in width!

• Serious structural movement cracks
  
  0.250" to 0.5 inch in width
  
  Repair: after reviewing the cause of building movement and making any required repairs, fill the crack with plaster, masonry or concrete patch material improved with an additive of latex or acrylic to add flexibility and adhesion.
  
  Some repairs may begin with a urethane sealant or high grade acrylic caulk - both flexible sealant materials.
  
  We used this method to repair the drywall corner crack shown here and traced to minor seasonal frost heave of a building's footing, after inspecting the building to convince ourselves that there was no more-serious damage to the building's structure. We think this same approach can work with plaster crack repairs.
  
  Repairing the corner crack above we cleaned out all loose material, injected a flexible urethane sealant, then applied a heavy duty mesh tape, and finished the corner with a corner trowel and gypsum based joint compound.

Repair Mesh Tape or Screen for Small Holes in Plaster Surfaces

Sold also for drywall repair are a wide range of plastic or fiberglass mesh tape and aluminum screen that can be used to repair small holes in plaster (or drywall) surfaces.

Above: we use mesh tape or heavy-duty self-adhesive backed mesh tape for small plaster hole repairs and we may use it across cracks in plaster as well. But when patching plaster over expanded metal lath use paper tape.

The surface is cleaned, sanded lightly, and the patch mesh is applied, then top-coated with plaster patch compound or with joint compound.

Shown here, plaster (or drywall) screen patch from Tuzazo.

Plaster Washers & Screws for Small Areas of Loose Plaster

Photo above: minor plaster damage can usually be repaired with plaster patch compound or even by cutting a small section of drywall that is screwed in place and top coated with plaster or joint compound.

For the area of damage shown (57 South Grand Ave., Poughkeepsie New York) we also used a few plaster repair washers and screws to be sure that the surrounding plaster remained firmly attached to the wood lath above.

Below: One of several manufacturers, Hillman Group produces 1.6" diameter zinc-plated plaster repair countersunk washers that are used with 1-inch screws that are driven through the washer center and into the wood lath backing the plaster ceiling or wall.

Plaster repair washers are also sold in 1-inch diameter but in my OPINON I prefer the larger diameter as more-secure.

If your wall is much thicker, perhaps having had more than one generation of plaster repair, you may need to use longer screws.

The countersunk washer center means that using a proper bugle-headed repair screw will find the screw head set flush with the washer surface. The holes in the washer help assure that the top coat of plaster or joint compound will adhere to cover the repair washer and screw.

...

Watch out: be sure to use zinc-plated, stainless or other coated, non-corroding, coarse-threaded metal screws for this repair. (Coarse-threaded anti-corrosion coated drywall screws can work.) Otherwise you may find rust stains bleeding through the repaired plaster surface.

Plaster Repair Compound for Small Plaster Damage Areas

For very small holes in plaster or if you want to try your skill at smoothing a larger patch directly onto exposed wood or metal lath, use a premixed plaster patch compound, or try our old favorite, Dash Patch or an equivalent wall/ceiling patching product. These are gypsum based patching compounds that set and dry quickly to a smooth, hard surface.

You can apply this patching compound in thicknesses up to 1/2" in one pass.

Dash Patch does not shrink and has good adhesive properties.

You'll find the Dash Patch technical data sheet below from more than one manufacturer who claim that name.

Similar patching products are made by a blizzard of companies including Dap's ElastoPatch, Dap FastPatch, DAP Presto Patch, Por-Rok's "Dash Patch" floor and wall leveler, RapidSet Wall Repair.

Cut & Fill Drywall Patches for Larger Areas of Plaster Damage

For a homeowner or less-experienced handywoman/handyman who needs to repair a larger area of lost or loose plaster (loose to be removed first) our opinion is that it's probably easier to simply cut a rectangle of drywall to fit the area where you've removed loose, damaged plaster, then screw the damaged drywall to the wood lath or to wall studs or ceiling joists.

Then finish the job with drywall tape and a wide 18" skim coat across the perimeter of the patch.

Tip: mark the location of wall studs or ceiling joists in pencil on the edges around the plaster hole that you're patching. That makes it easy to see where to drive plaster or drywall screws when installing a drywall segment patch to fill large holes.

Plaster Repair Method Guides, Manuals, Standards

• Amico, METAL LATH SPECIFICATIONS, SPECIFICATION FOR METAL LATH AND ACCESSORIES, LATH AND PLASTER [PDF] Amico, 3245 Fayette Ave. P.O. Box 3928, Birmingham, AL 35208, (205) 787-2611, (800) 366-2642 and in Canada: 1080 Corporate Drive, Burlington, Ontario L7L 5R6, Canada, (905) 335-4474, (800) 663-4474. Amico is the largest metal lath producer in North America. Website: http://amico-lath.com/
  
  Amico is lath and plaster accessory producer.
• Ashurst, John and Ashurst, Nicola. Practical Building Conservation, English Heritage Technical Handbook, Volume 3. Mortars, Plasters and Renders. New York: Halsted Press, 1988.
• ASTM C 842
• ASTM C 841 Metal Lath or gypsum lath installation

• CGM Por-Rok DASH PATCH PRODUCT SPECIFICATIONS [PDF] CGM Inc., 1445 Ford Rd., Bensalem, PA 19020 USA, Tel: 215-638-4400 - aka Por-Rok, Novatek, retrieved 2023/12/23, original source: http://www.homasote.com/assets/files/installation/dash_patch.pdf
  
  Excerpt:
  DASH PATCH is a gypsum based powder which, when mixed with water forms a plastic composition that can be troweled onto most surfaces to provide a smooth base for resilient or hard surfaces. DASH PATCH is designed to have rapid setting, high strength, adhesion and workability. DASH PATCH will not shrink or expand.
• CMP, DASH PATCH PRODUCT SPECIFICATIONS [PDF] CMP Specialty Products, 1445 Ford Road Bensalem, PA 19020 USA, Tel: 267.522.8000 Web: www.cmpsp.com
• Flaharty, David, PRESERVING HISTORIC ORNAMENTAL PLASTER (Updated) [PDF] (1990)
• Grimmer, Anne E., The PRESERVATION & REPAIR of HISTORIC STUCCO [PDF], (current version) National Park Service Preservation Brief No. 22., retrieved 2018/06/18, original source: https://www.nps.gov/tps/how-to-preserve/briefs/22-stucco.htm
• Grimmer, Anne, DETERIORATED PLASTER FINISHES - REPAIR STANDARDS [PDF], U.S. National Park Services, ITS No. 19, retrieved 2018/06/18, original source: https://www.nps.gov/tps/standards/applying-rehabilitation/its-bulletins/ITS19-DeterioratedPlaster.pdf
  
  Interpreting the secretary of the interior's standards for rehabilitation, applicable standards.
  
  Excerpt:
  Issue: Finished plaster walls and ceilings are important in defining the character of many historic buildings.
  
  But deteriorated plaster surfaces are not character-defining and they are not representative of the historical appearance of a building.
  
  Just as removing plaster to reveal brick which was never exposed historically does not meet the Standards, leaving a historic plaster wall in a deteriorated condition also does not meet the Standards.
  
  Deteriorated plaster should always be repaired, or replaced with gypsum board, in a rehabilitation project.
• Isham: "An Example of Colonial Paneling", Norman Morrison Isham, The Metropolitan Museum of Art Bulletin, Vol. 6, No. 5 (May, 1911), pp. 112-116, available by JSTOR
• Jowers, Walter. "Plaster Patching, Part Il." Restoration Primer. New England Builder, November, 1987, pp. 4143.
• Leeke, John. "Problems with Plaster, Part One." Landmarks Observer, Vol. 12. March/April, 1985., pp. 10,14. Also "Problems with Plaster, Part Two." Vol. 12., May/June, 1985, p. 12.
• Leeke, John. "Saving Irreplaceable Plaster." Old House Journal. Vol. XV, No. 6, November/December, 1987, pp. 5155.
• MacDonald, Mary Lee, REPAIRING HISTORIC FLAT PLASTER WALLS & CEILINGS [PDF] (1989) [Print Version - we recommend this copy] U.S. National Park Service, Preservation Briefs, No. 21, Flat Plaster
  
  This plaster repair guide focuses on plaster repair methods for historic (and thus older) homes, particularly where plaster is based on wood lath, metal lath, or rock lath.
  
  The author guides us through first identifying the type of plaster problem being addressed, then suggests a range of plaster patch or repair methodsds, and for historic buildings, she discusses plaster replacement options when the original plaster is beyond repair.
• MacDonald, Mary Lee, REPAIRING HISTORIC FLAT PLASTER WALLS & CEILINGS [PDF] (1989) [Web version] U.S. National Park Service, Preservation Briefs National Park Service, U.S. Department of Interior, Preservation Brief No. 21, retrieved 2018/06/17, original source: https://www.nps.gov/tps/how-to-preserve/briefs/21-flat-plaster.htm

• National Gypsum Co., LATH & PLASTER SYSTEMS, [PDF] 092300/NGC, National Gypsum Lath and Plaster Systems, National Gypsum Corporation, 800-628-4662 describing National Gypsum's Kal-Kore brand plaster base
• National Gypsum Corporation, Gypsum Construction Guide, NG, 2001 Rexford Road, Charlotte, North Carolina 28211, Tel: 704-365-7300, Email: ng@nationalgypsum.com, Website: http://www.nationalgypsum.com
• National Gypsuym Co., MSDS: GOLD BOND® BRAND GYPSUM BOARD PRODUCTS, [PDF] plaster base, National Gypsum Corporation. Other drywall MSDS sheets are found
  
  at Drywall MSDS.
• Poore, Patricia. "The Basics of Plaster Repair." Old House Journal, Vol. 16, No. 2, March/April, 1988, pp. 2935
• Pruter, Walter F, PORTLAND CEMENT PLASTER CRACK ANALYSIS & REPAIR [PDF] Building Standards, September/October 1995 pp. 22-24
  Note: This article appeared originally in Walls and Celilings Magazine, June 1993.
  
• US Gypsum, PLASTERING PRODUCT & SYSTEMS TECHNOLOGY - VENEER PLASTER JOINT REINFORCEMENT SYSTEMS, [PDF] PM 5, Product & Systems Technology, US Gypsum, May 1998, retrieved 10.5.2010, original source: http://www.usg.com/rc/technical-articles/plaster/
  plastering-technical-guide-veneer-plaster-joint-reinforcement-systems-en-PM5.pdf United States Gypsum Company, 125 South Franklin ST., PO Box 806278, Chicago, IL 60680-4124,
  
  Excerpt:
  Two methods of joint reinforcement are utilized in USG vbeneer plaster suystems>
  
  Where normal drying conditions exist and the systemn framing provides high rigidity (I.e. wood framing and 16" o.c. spacing) a glass fiber tape reinforcement system is suitable and most expedient.
  
  However, where rapid drying conditions exist, a paper tape and setting-type joint compound system is recommended.
  
  Also note that a paper tape and setting type joint compund must also be used with steel framing systems and with certain specific systems on 24" o.c. framing spacing.
  
  Paraphrasing from this document:
  
  USG uses the term shadowing in this document in describing the visual effect over gypsum board joints caused by the lower moisture absorption rate (take-up) and lower capacity than gypsum base face paper.
  
  Shadowing at joints occurs where veneer plaster is applied over tape joints, requiring a second coat to completely hide the tape, providing a visually uniform surface. USG Advises: "This [second] cover coat must be allowed to harden and dry before plaster application is started.
• US Gypsum, Gypsum Construction Handbook [purchase at Amazon.com] H17, Technical Folder SA920 and PM2, PM3 and PM4, United States Gypsum Company, 125 South Franklin ST., PO Box 806278, Chicago, IL 60680-4124,
• Van Den Branden, F., Thomas L. Hartsell, Plastering Skills [purchase at Amazon.com]Amer Technical Pub (July 1, 1985), ISBN-10: 0826906575, ISBN-13: 978-0826906571 [purchase at Amazon.com]
• Weaver, Martin. "Nuts and Bolts: Properly Plastered." Canadian Heritage. Aug./Sept., 1981, pp. 3436. Also "Nuts and Bolts: Fixing Plaster." Oct., 1981, pp. 3335.
• Worsham, Gibson. "Exterior Plaster Restoration at the Lord Morton House, Lexington, Kentucky." Association for Preservation Technology Bulletin. Vol. XIII, No. 4 (1981), pp. 2733