DIY Network

Bedroom Repair: Plaster Cracks From "Restoration Realities" episode DRTR-106

	The cracked plaster BEFORE the repair.

In this episode of DIY's Restoration Realities, we visit Knoxville, Tennessee and the home of Sean and Jennifer Bolen. The restoration of the Old-North Knoxville home is already well underway. Restoration specialists Bill Click and Chris Babcock join the Bolens to help them with a couple of projects. In this segment, they address cracked and damaged plaster in an upstairs bedroom.

Materials and tools:

For plaster repair

five-way tool or other scraping device
3-4" taping knife
utility knife
6" wide taping knife
10"-12" wide taping knife
cordless screw gun or drywall gun
ladder and walk Boards
drill with paint mixing paddle
drywall screws
plaster washers
large cellulose sponge
rubber base grout-float
trowel
5-Gallon Bucket
2-3 Gallons of room-temperature water
box of perlited plaster
1-Gallon of bonding primer
drop cloths
150-grit sandpaper
spray bottle
gypsum wall compound
safety glasses and dust mask

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Repairing Cracks in Plaster Walls

It's a certain rule of thumb: With old houses comes cracked plaster. The Bolens have already patched some of the plaster in the downstairs foyer and dining room. They might have opted for the cheaper alternative -- covering the damaged plaster with drywall -- but the Bolens wanted to retain the historical integrity of the house by using materials that are period-authentic to the time when the house was built. In addition, for a cost just slightly more than that of installing drywall, the plaster will be more durable.

Following are the basic steps our restoration specialists followed in the plaster repair.

	Figure A
	Figure B

Begin by assessing the cracks and trying to determine possible causes (figure A). The plaster cracks in this old house appear to be settling cracks and are fairly common in a house of this age. In this case, there are large cracks that have been repaired previously (figure B), as well as mid-sized and tiny "spider cracks." There's also a drywall patch that was put there previously when an electrician had to gain access behind the wall when the house was re-wired.

Settlement over time is one cause of cracked plaster, but another is key disintegration. This is where the plaster protrudes through the wood lath to create a bond. It can also be caused by poor-quality plaster, water damage or normal wear and tear. The first step in repairing cracks is cleaning them out.

• Using a five-way tool or other scraping device, clean out loose plaster from inside cracks (figure C).

• In the case of larger cracks with plaster falling out, remove the damaged plaster to reveal the binding course.

• Knock old plaster through keys in the lath to establish a better binding course for the new plaster to adhere to (figure D).

  Figure C

  Figure D

  
  

• Restoration Terminology: A five-way tool is a single tool a variety of uses -- including scraping, cleaning, opening paint-cans, etc. The binding course is the area or surface that the plaster binds onto -- in this case, the wood lath. The key way is the term that refers to the spaces between the slats of the wooden lath.
  

• Large cracks, where the lath and plaster have been pulled away from the wall, can be re-secured using metal plaster washers and ordinary 1-1/2" or 2" drywall screws (figure E). This secures the existing plaster to the wood lath.

• Secure screws and washers diagonally on either side of loose plaster, about 1-1/2" to 2" from the crack (figure F).

  Figure E

  Figure F

  
  

  Figure G

This plaster repair consists of two coats: a base-coat plaster for re-establishing the key-ways for a binding layer, and a top-coat finish layer to provide a smooth surface. Our base-coat is a lime-based plaster, also called "brown coat," that is heavily sand- or silicate-based.

• Combine base-coat plaster using room-temperature water, following the manufacturers instructions. (Hot water can cause the plaster to set up too quickly.)

• Using an electric drill with paint-paddle, mix the plaster to about a sour-cream consistency and allow mixture to sit for a few minutes as it starts to thicken -- or slake.

• Mist the lath with water lightly (figure G), being careful to avoid over-saturating the wood. This will help to prevent the lath from wicking moisture out of the plaster, causing it to dry too quickly and possibly result in more cracking.
  

• Using a trowel, squeeze base-coat into the cracks (figure H), making sure to get it into the keys of the lath.

• Smooth over crack and angle off excess (figure I).

• Depending on humidity, the base coat can take from 2 to 24 hours to set up completely. Allow a couple of days for it to dry completely.

• Once the base coat has dried, sand to a smooth finish.

  Figure H

  Figure I

  
  

  Figure J

A previous repair to the plaster was made with a drywall patch and gypsum. However, we used a lime-based plaster for repairing the cracks. Those two materials cannot be mixed since gypsum and lime create a negative reaction. To smooth out the rough patch, we skim-coat the area with more gypsum compound and smoothed down our finish-coat even with the patch, feathering it in for a smooth appearance. The compound was applied using a 12" knife and spread smooth (figure J). Once the job is done and the surface has been painted, it the two surfaces should be essentially identical.

Figure K

Apply Finish-Coat

The final step is to apply the finish coat. The finish coat is much finer than the base coat, and has a high lime and talk content that gives the plaster a sheen.

• Spread the finish coat evenly over dried base coat.

• The finish coat can also be used alone to cover small, hair-line cracks.

• Polish the plaster repairs by lightly spraying with water and smoothing over with grout float (figure K).

• Once the finish coat has dried, the newly repaired plaster can be given a fresh coat of paint or wallpapered.
  

Restoring old plaster walls with lath backing is a wonderful gift to give an old home. But there are a few things you need to keep in mind before you start. Water is sometimes the culprit that makes plaster crack in the first place, so you need to be sure to fix any leaks or causes of moisture several weeks in advance. Temperature also plays an important role as well. It's best to maintain a room temperature of 55 degrees to 70 degrees while plastering. The room you're working in will need to be at this temperature at least 24 hours before plastering to ensure that the walls are completely dry. It must stay at this temperature during plastering and until the plaster has completely set.

In the segment that follows, the second portion of this project is -- the dress-up of the house's entry-hall stairway using anaglypta wall-covering and a wood chair-rail.

Note: This is a summary of steps included in the procedures shown in this episode of Restoration Realities. There may be variations in procedures for your particular restoration project based on the types of materials you select and the nature or extent of your particular project. Always follow proper safety precautions, and read and follow manufacturer's guidelines, diagrams and safety notices that come with materials or products that you select.

RESOURCES :

Renovating Old Houses: Bringing New Life to Vintage Homes
Author: George Nash
Publisher: Taunton Press
ISBN: 1561585351
Order this title from Amazon.com.

Renovating and Restyling Older Homes: The Professional's Guide to Maximum Value Remodeling
Author: Lawrence Dworin
Publisher: Craftsman Book Company
ISBN: 1572180293
Order this title from Amazon.com.

Selecting and Renovating an Old House: A Complete Guide
Author: United States Department of Agriculture
July 2000
Publisher: Dover Publications
ISBN: 0486409562
Order this title from Amazon.com.