Agenda - 10-05-2010 - 4g - Laserfiche WebLink

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J; �,.'".i%, 1 Masonry products, particularly brick, have a harder (weather protecting) layer on 2 the exterior from the firing process. When repairing or cleaning masonry surfaces 3 use care to ensure the protection of that exterior surface. Abrasive treatments, 4 such as sandblasting and using grinders can erode the outer layer, leaving the 5 masonry unit much more vulnerable to exterior elements, particularly wind and 6 rain, and deterioration. 7 s The selection of mortar for masonry work is equally 4 � - T �}� 9 important. Traditionally, mortar was designed as ��§� �# '�`` ��R'°'� ' � lo the "soft" binding agent that provided adhesion and �: . ��t� �� 11 cushion to the masonry unit. Mortar was designed ��,;�� 12 to fail and be replaced regularly through repointing. �� � �. 13 Repairs to historic masonry, brick in particular, �� -�� 14 should involve the use of a mortar with a high : � ,r,:..,-�"� � � 15 concentration of hydrated lime to ensure that the N�� ,�� ` s 16 new mortar is softer than the historic brick. - �� -� �. ��. 1� Contemporary Portland Cement products are much � �"" 1s harder than lime-based mortar. Repairs to historic �Kr� t� � � �� 19 masonry using mortar with a high Portland Cement � �� 2o content will create a masonry wall where the mortar • � �,} 21 is harder than the brick—a situation that will cause 22 the bricks to fail rather than the mortar. 23 24 25 DESIGN STANDARDS for Masonry 26 2� III-B-7. Retain and preserve masonry features such as brick, stone, concrete, terracotta, 28 and stucco that are significant in defining the overall historic character of a local 29 landmark building structure or site. 30 31 III-B-8. Maintain and protect masonry features and surfaces by appropriate methods. 32 Test any proposed cleaning or paint-removing technique well in advance on an 33 inconspicuous sample area. It is not appropriate to use destructive cleaning 34 techniques such as sandblasting, power washing, or high-pressure water blasting 35 on historic masonry surfaces. Only use chemical cleaners if gentler methods like 36 low-pressure washing are ineffective, and then only under the supervision of the 37 HPC. 38 39 tll-B-9. It is not appropriate to parge, paint or coat an unpainted masonry surface if it was 4o not parged, painted or coated historically. Repaint previously painted masonry 4i surfaces in traditional colors--appropriate to the historic character of the property. 42 43 III-B-10. Repair deteriorated or damaged masonry surfaces and features through 44 traditional methods for consolidating, piecing-in, or patching. Repoint masonry 45 mortar joints if the mortar is cracked, deteriorated, or missing or if moisture 46 penetration of the masonry surface is evident. Prior to repointing, use hand tools 47 to carefully remove loose and deteriorated mortar. Do not use grinders or circular 4s saw blades for joint removal. Replace mortar with new mortar to match the 49 original in composition, strength, color, and texture. Duplicate the width and 5o profile of the original mortar joints. It is not appropriate to substitute modern 51 coatings such as water repellents for repointing or repairing historic masonry. 52 Consider such coatings only if traditional repair techniques fail to eliminate 53 moisture problems. 54 9/27/2010 Draft Orange County Design Standards 28