Repair Methods for Rendered Structures

Rak-43.3313 Repair Methods of Structures, exercise (4 cr)

Esko Sistonen

Anon. 2005: Rendering Book 2005. Helsinki. BY 46. 158 p. (inFinnish)

This kind of cracks in facade are usually a sign foruneven settling of the building foundations.

Repair methods• To do nothing

• Coating and patch repair methods– Light coating repair (minor patch repairs, coatings)

– Full patch and coating repair

• Covering repair methods– repair of entire facade, for instance, with an

– insulating rendering

• Demolition and reconstruction– Rendering removal and re-rendering

• Related repairs– Decreasing the level of exposure

– Repairs based on damaged underlayer

Different factors which has influence on decision ofrepair method

Lahdensivu, J. 2007. Selection of repair methods for rendered facades. In: Carpinteri et al. (eds.). Fracture Mechanics of Concrete and Concrete Structures. Vol. 3. High-Performance Concrete, Brick-Masonry and Environmental Aspects. Proceedings of the 6th International Conference on Fracture Mechanics of Concrete and Concrete Structures, Catania, Italy, 17-22 June 2007 pp. 1661-1666.

Selection of suitable repair alternative for each case

has several demands:• The repair must be cost effective• Aesthetic requirements• Degree of different deterioration mechanisms• Service life requirements of repair• Requirements concerning the reliability of the

repair

Repair methods of rendering damage

Anon. 1999: Rendering Book. Helsinki. BY 46. 90 p. (in Finnish)

Repair method Damage to be repaired Remark Cleaning of façade Aesthetic deficiencies

Preparation of maintenance painting

Wet cleaning is not possible for lime paint

Patch-coating of paintwork Aesthetic deficiencies Applies inorganic coatings

Maintenance painting Aesthetic deficiencies Painted at once Repainting Aesthetic deficiencies,

Paintwork damage The organic paint should usually be removed The number of coats of paint depends on the type of paint

Patch repair of rendering coat

Local rendering damage To be selected the patch repair mortar which corresponds to the old mortar

Local repair of underlayer Local damage at rendering and underlayer

Re-rendering of finnishing mortar and possible painting

Extensive damage at paintwork or finnishing coat

Re-rendering of rendering coat and possible painting

Extensive damage at paintwork and rendering coat

Exchange of façade material

Extensive damage at surface layer and underlayer, if necessary, to improve the thermal insulation

Related repairs (rainwater systems, eaves, flashings, etc.)

To be repaired for preventing recurrence of damage

Treatment methods for rendering surfaceMethod Objective Result 1. Mechanical removal of loose rendering

Removal of loose rendering Rendering already loose from the underlayer can be relatively easily removed.

2. Brushing the surface with a wire brush

Loose and easily unfastened removal of dust and paint

A commonly used hand applied method which does not damage rendering underlayer too much.

3. Surface grinding (tape or disc grinding, mechanical wire brushing)

Removal of the old coat of paint and easily detachable rendering

A good base for the renewal treatment

4. Chemical paint removal and pressure washing

Removal of the old coat of paint

Especially in decorative façades substrate damage are to be avoided

5. Sand blasting (dry, with water)

A thorough cleaning of the underlayer, removal of all loose material

A good base for the renewal treatment

6. Surface cleaning (water shower, washing solution, foam)

Removal of loose dust and paint dust

Cleaning the surface of the loose dirt. Strength of the solution, the water temperature and the spray pressure affect the result.

Different removal methods for old rendering

Removal method for rendering Applicability of the method Knocking down with the hammer Weak base off the rendering Demolition (mechanical) -compressed air hammer -electric hammer

Stronger removed renderings

Sand blasting, soft limestone sand Requires experience and skill, is suitable for the organic layer of paint and removal of finnishing mortar.

Rendering repair products

Lime mortarLime cement mortarCement mortar

Mortar is chosen depending on the case:-In patch repairs as same as the old-In re-rendering based on underlayer characteristics: rendering mortar layers should be weaken towards the surface, trowelled rendering should not be stronger than underlayer.

Mortar additives:-air-entraining agent-retarders-polymers-fibers-seal and hydrophobic substances-pigments

L (K) LimeHL (Kh) Hydrolic limeC (S) CementLC (KS) Lime and cemente.g. LC (KS) 35/65/600

External wall insulation

http://en.wikipedia.org/wiki/File:EWIS.jpg

Rendered Facades: Thick Rendering

Thick rendered facade with slab insulation Timber frame - thick rendering -solution

http://www.paroc.fi/solutions-and-products/solutions/walls/thick-rendering

Rendered Facades: Thin Rendering

Rendered facade with slab insulation Rendered facade with lamella insulation

http://www.paroc.fi/solutions-and-products/solutions/walls/thin-rendering

Rendered Facades: Thin Rendering

http://www.e-weber.fi/rapatut-julkisivut/weber-tuotteet/uudisrakentamisen-julkisivuratkaisut/serpotherm-eristerappaus-hienoroiskepinnalla.html

Tree coat rendering

•Mineral wool with lime- or limecement mortars •The tree coat rendering has been fasten with mechanical anchor to buildings framework. • Hot-dip galvanised welded wire mesh (f1 mm #19 mm)• Base plate etc.

Thin rendering

•Mineral wool or expanded polystyrene (EPS)• cement-based and usually polymer modificated mortars•Rendering is fixed to insulation with mortar and mechanical plastic fasteners. In some cases there are no mechanical anchors.• Plastic-coated glass fibre alkali-resistant reinforced mesh• Base plate etc.

Several internet links and publications…http://www.refina.co.uk/glossary_plastering.phphttp://www.betoniyhdistys.fi/index.php?__EVIA_WYSIWYG_FILE=2620&name=filehttp://www.betoniyhdistys.fi/index.php?__EVIA_WYSIWYG_FILE=2613&name=filehttp://www.julkisivuyhdistys.fi/julkkari2/juko/kansio.htmlhttp://www.buildingconservation.com/articles/articles.htmhttp://link.springer.com/content/pdf/10.1617%2Fs11527-012-9849-7http://publications.theseus.fi/bitstream/handle/10024/26698/NoviaUASS-LimeRen978-952-5839-21-0.pdf?sequence=1http://www.inca-ltd.org.uk/Perander Thorborg; Råman Tuula (1985) Ancient and modern mortars in the restoration of historical buildings. VTT, Espoo. 74 p. + app. 24 p. Tiedotteita 450 / Valtion teknillinen tutkimuskeskus.

Konow, von Thorborg (1989). Saltvittring i tegel – saltvittringsmekanismer. VTT, Espoo. 68 p. + app. 8 p. Tiedotteita 1003/ Valtion teknillinen tutkimuskeskus.

Several standards…

SFS-EN 998-1 (September 2010). Specification for mortar for masonry - Part 1: Rendering and plastering mortar.SFS-EN 1015-12 (February 2000). Methods of test for mortar for masonry - Part 12: Determination of adhesive strength of hardened rendering and plastering mortars on substrates.SFS-EN 1015-19 (September 1998). SFS-EN 1015-19/A1 (October 2004). Methods of tests for mortar for masonry – Part 19: Determination of water vapour permeability of hardened rendering and plastering mortars.SFS-EN 1015-21 (December 2002). Methods of test for mortar for masonry - Part 21: Determination of the compatibility of one-coat rendering mortars with substrates.SFS-EN 13658-2 (May 2005). Metal lath and beads - Definitions, requirements and test methods - Part 2: External rendering.

Several standards…SFS-EN 13914-1 (March 2005). Design, preparation and application of external rendering and internal plastering - External rendering.SFS-EN 13914-2 (May 2005). Design, preparation and application of external rendering and internal plastering - Part 2: Design considerations and essential principles for internal plastering.SFS-EN 15824 (July 2009). Specifications for external renders and internal plasters based on organic binders.