TECHNICAL BULLETIN 4 JOINTS

INTRODUCTION C. Powdering mortar joints: When be performed to determine the mortar has deficient integral compatibility of the repointing This bulletin is intended to provide a characteristics, resulting in mortar chosen. guideline for the conditions relevant component separation or loss to repointing of mortar joints between of aggregate typically caused by C. Chemical: Chemical analysis units. freezing or extreme weathering of modern cements can be of mortar. performed to determine the binder (cement/lime) content. DEFINITIONS D. Loss of inappropriate joint Placing a crushed mortar sample Pointing: To fill or refill and finish the profile: When joint profile has into diluted hydrochloric acid joints eroded or otherwise lost its does this. If a reaction (bubbling) weatherproofing capabilities or occurs, most of the binder was Repointing: The process of removing desired aesthetics. lime. Cement will leave a murky deteriorated mortar from the joints liquid that dissolves over a of masonry and replacing with new E. Inappropriate mix/material: few days. By rinsing remaining mortar. When existing joint composition aggregate, examination is has an inappropriate mix design possible to visually determine Tuckpointing: A special kind of joint or incompatible replacement size, range of color and overall used to make wide, irregular joints materials (i.e. sealant, too high granulation of aggregate. The resemble thinner and more regular compressive strength, etc.) most accurate testing requires joints. laboratory analysis. 2. VERIFICATION OF EXISTING APPLICATION CONSIDERATIONS CONDITIONS D. Proposition: By a combination of the physical and chemical analysis 1. When to repoint A. Visual: Visually inspect joint for results, the proportional mix of original profile, color, fooling and materials in a mortar can be A. Missing, void or deteriorated texture characteristics. calculated. mortar joints between masonry units. Missing or B. Physical: Physical analysis of E. Petrographic Visual analysis deteriorated to the extent mortar is compiled by removing (using a high—powered moisture penetration and/ existing sample that can be microscope) by specially trained or facade integrity has been tested using sieve analysis to technicians of prepared mortar compromised. identify size, type and color samples can assist in determining of aggregate. Compression or confirming the composition and B. Debonded or cracked mortar strength testing should also be proportions of mortar materials joints: When bondline separation completed on existing mortar in a sample. This is particularly occurs between masonry and sample to determine hardness of helpful when evaluating samples mortar to a degree that allows original mortar. In no case should from historic properties. moisture penetration. Typically replacement mortar be harder this is 1/52 inch or greater. (higher cement content) than Mortar Joint Removal (Refer to SWR original mortar. Testing of the Institute Technical Bulletin #3 Mortar substrate to be pointed should Joint Removal)

A RESOURCE FROM THE SEALANT, WATERPROOFING & RESTORATION INSTITUTE DESIGN CONSIDERATIONS FIGURE 1 Parts by volume Mortar Mix Parts by Aggregate, of portland Parts by volume of measured Mortar cement, cement, volume of After determining original hydrated in a damp, Type or portland blast- masonry composition of mortar by methods lime or loose furnace slag cement described above, the appropriate lime putty condition mortar mix can be designed. Mix cement ingredients typically consists of lime, cement, aggregate, water Not less than and possibly pigments. The relative 2 ¼ and not proportion of lime to cement more than 3 1 1 -- to aggregate will determine the M times the sum 1 -- ¼ compressive strength, workability, of the volumes bonding strength, joint texture, of the cements elasticity and color characteristics and lime used of the mortar. ½ 1 -- S See Figure 1 for standard modern 1 -- Over ¼ to ½ mortar mix designs. -- -- 1 N Over ½ to 1 -- See Figure 2 for historic mortar 1 ¼ mix designs. -- -- 1 O Over 1 ¼ to Consideration should be given not 1 -- only to existing mortar conditions 2 ½ (hardness, color, porosity, texture), but also to existing substrate; building location relative to elevation exposure (N, W, S, Lime: "Lime" is a burned FIGURE 2 HISTORIC MORTAR TYPES N), extraneous (adjacent structures, form of lime derived from the pollutants, etc.) and climate conditions. calcificafion of sedimentary Hydrated In all applications, the replacement limestone. Lime is an essential Designation Cement Lime or Sand mortar should not be harder than the ingredient in mortar because Lime Putty adjacent substrate or original mortar. it adds plasticity, improves Testing of the original substrate to workability, and provides 3 - 3 water retention attributes for M 1 1/4 determine existing physical properties 3/4 is recommended to verify compatibility. effective bonding, decreases shrinkage in mortar and reduces S 1 1/2 4–4 1/2 Cement: Portland cement has been efflorescence potential due to its used since the mid 1800s. It is a purity. Hydrated lime, type S, is N 1 1 5–6 combination of lime, silica, alumna and typically used for mortar mixes. O 1 2 8–9 iron oxide that is ground up, burned in Lime putty, or fully slaked and a kiln and mixed with gypsum to form a screened dolomitic lime in putty K 1 3 10–12 fine powder. Natural cement, consisting form, is also available today. “L” 0 1 2 1/4–3 of high-clay-content limestone burned Aggregate: Aggregate typically in a kiln and ground into a fine powder, consists of clean sand obtained was used widely between 1850 and naturally from and Color: Mortar pigments are typically 1920. Masonry cement consists of a riverbeds. Aggregate acts as filler and inorganic mineral oxides from specific mixture of Portland cement or blended helps in the workability of the mortar. materials that, when added to the dry hydraulic cement and plasticizing A siltation test should be performed aggregate portion of the mix, provide materials such as limestone, hydrated on aggregates to ensure aggregates a range of colors for the mortar. or hydraulic lime together with other are suitable for mortar mix – (refer to Pigments should not exceed 10 materials introduced to enhance one or technical manual to be sent separately). percent of the weight of the portland more properties. Masonry cements are cement to avoid excessive strength primarily used for the laying or relaying Water: Water should be clean, potable reduction of the mortar. Pigments of masonry units. water. should be used in the smallest amounts

TECHNICALBULLETIN 4 REPOINTING MORTAR JOINTS FIGURE 3

possible to provide the desired color. used in the mortar depends on the panel should serve as the standard for Color should match original joint color, composition of the dry ingredients, the balance of the work on the rest of not the soiled existing color. It should moisture content of the aggregate, the building. be noted that the proper use of local types of masonry units being installed aggregates in the mortar mix could be and desired consistency for the 2. Mortar Installation another successful method to control technician. Climate conditions: Repointing should color, especially when attempting to be performed only when the outside air match older historic mortars. Joint Profile temperature and substrate temperature Mixing Procedure There are a variety of joint profiles meets or exceeds 40 degrees and common today. Figure 2 illustrates the wall is given proper protection All components (lime, cement, typical mortar joint profiles. from the elements. Masonry shall be aggregate and coloring) should be protected from freezing for 72 hours volume measured for precise mix The most effective and watertight joints after placement. High lime content ratios. Measuring devices should are the concave and “v” tooled joints. mixes require extended protection from Flush joints are used when other finish consist of scales or appropriate volume freezing conditions. Straight lime mixes materials (stucco or coatings) are to containers and not used soda cans, may need protection for up to 90 days. be applied over masonry. Existing coffee cups, etc. Mix proportions joint profile should determine the should be available at jobsite for Joint condition: The prepared appropriate replacement joint used in production control purposes. mortar joint (as per Technical Bulletin historic projects. #3 - Mortar Joint Removal) should Dry mix should be thoroughly mixed be flushed clean with potable water, to ensure proper blending of lime APPLICATION CONSIDERATIONS resulting in a damp condition free of and cement and complete coating of standing water often referred to as aggregate. Acceptable means of mixing 1. Mock-up Panel SSD (saturated surface dry). are manual (hoc and mortar box) or mechanical (mortar mixer or paddle An important consideration for a Joint placement: Pack mortar into mixer). Most mixers cannot dry mix successful repointing project and the prepared joint in three equal, the components prior to adding water. mutual understanding between successive layers (1/4 inch thick). Each The mixers will bind and not run if this contractor and owner/architect is the layer should be fully compacted and procedure is followed. Enough water installation of a mock-up panel. Usually thumbprint hard prior to the installation should be added to produce a damp a 5-foot-by-5-foot panel is sufficient to of the next layer. The final layer is to be mix, which will retain its form when demonstrate the joint profile, mortar tooled to match the prepared mock up compressed into a ball. color and overall appearance within panel. If the joint is more than 1 inch the surrounding masonry. Typically, the deep, placements of first and second Fully mixed mortar should be used contractor would install a panel at an layers should be 2/5 each of joint within 50 minutes and should not be inconspicuous but representative area depth with final layer the remaining 1/5 retempered. Percentage of water of the building. Once approved, the inch (not to exceed 3/8 inch).

TECHNICAL BULLETIN 4 REPOINTING MORTAR JOINTS A. Curing of mortar: Upon such as face shields, eye and completion of installation of fresh hearing protection. It is also mortar, area should be mist cured incumbent on the contractor periodically to maintain a damp to ensure that pedestrians and condition for approximately 72 building occupants are protected hours. This promotes desired from the dust created by the bonding between mortar and operation. Protective tarping masonry and ensures consistent and mesh have proven to be full-depth curing of mortar. effective in controlling the dust to the work area directly. The B. Clean up: After mortar is fully use of vacuum attachments to hardened, thoroughly clean the equipment housing is also exposed masonry sufaces of effective in collecting dust. Some excess mortar failings, smear stains and efflorescence using attachments prevent workers from stiff nylon bristle brushes or wet having a clear view of the mortar burlap. The surface should be joint and should not be used. rinsed down with clean, potable D. References: The able guidelines water applied at low pressure. are developed primarily for C. Environmental impact: reprinting of masonry units. Consideration must be given to Repointing for stone, terra cotta, the impact that mixing mortar block, etc., will vary joints have on the health and due to substrate materials and safety of the workers and the conditions. Refer also to USIM environment of the surrounding Standards C144 ( Aggregate for project site. Workers must wear Masonry Mortar), C150 (Portland and be properly trained in the Cement), G2o7 (Hydrated Lime), use of respirators and other C270 (Mortar for Unit Masonry) personal protective equipment, for additional information.

DISCLAIMER These materials have been prepared by industry representatives as an aid to provide interested parties with general information concerning the subject matter addressed herein. The Sealant, Waterproofing & Restoration Institute (“SWR Institute”) has merely compiled information from industry representatives and, accordingly, the SWR Institute, its members, employees and agents expressly disclaim any responsibility whatsoever for the accuracy of the terms, product listing, methods, procedures, specifications, views and opinions discussed herein. SWR Institute does not necessarily approve, disprove, or guarantee the validity or accuracy of any data, claim or opinion including, but not limited to, comparisons of the physical properties and characteristics of any product, procedure or application. SWR Institute, its members, employees and agents expressly disclaim any responsibility whatsoever for damages arising from the use, application or reliance on the recommendations and information contained herein. COPYRIGHT NOTICE © Copyright 2019 by the Sealant, Waterproofing & Restoration Institute. All rights reserved. This work may not be reproduced or transmitted in any form or by any means, electronically or mechanically, including photocopying, recording, or by an information storage and retrieval system without the prior written permission from the Sealant, Waterproofing & Restoration Institute.

TECHNICAL BULLETIN 4 REPOINTING MORTAR JOINTS