Surface Grouting to Repair Mortar Joints

Surface grouting to repair mortar joints

When joints are weathered but not badly deteriorated, this technique can stop leaks more economically than repointing

By Kenneth A. Hooker

ase #1: Your turn-of-the-cen- c ar e co m m e n d s a tury brick building has de- m i x t u r eo f 1 p a r t 1 veloped leaks. The brick it- p o r tland cement, ⁄3 1 C part lime, and 1 ⁄3 self is fairly dense and smooth; mortar joints are narrow. An in- parts fine silica sand vestigation shows no large (Ref. 1). Premixed, cracks, severe spalling, or exten- proprietary surface sive deterioration of the mortar, grouting mortars al- but erosion caused by decades of so are available. e x p o sure to the weather has Manufacturers opened small gaps at the inter- say that glazed or face of brick and mortar. very smooth brick Case #2: Your new brick build- can be left un- ing, completed six months ago, masked and any ex- has begun to leak in rainy weath- cess grout removed er. An investigation shows no ma- from the face of the jor flaws in design or construc- brick w i t h a d a m p tion, but it does reveal a s p o n g eo r c l o t h . network of tiny cracks between M o r e often, though, the units and the shallow raked the brick are care- mortar joints. These apparently fully covered with were caused by shrinkage of the masking tape before mortar as it set, followed by grout is applied. chemical cleaning. In one study, In both cases, repointing would walls known to leak be one option likely to solve the were tested for wa- leakage problem. But properly ter permeance before Surface grouting has helped stop leaks in older brick d o n e , r e p o i n t i n g i s e x p e n s i v e , and after the joints buildings such as Bowman Hall at the University of Wis- and the condition of the mortar were mask-grouted. consin at Stoughton, where mortars joints are weathered joints described doesn’t seem to The tested walls av- but generally sound. warrant full repointing jobs. Fur- eraged a 93% reduc- joints aren’t badly damaged, just tion i n w a t e r p e r m e a n c e a f t e r 1 t h e r m o r e ,w h e n j o i n t sa r el e s st h a n eroded ⁄8 inch or so from normal 3 the typical ⁄8 inch wide, chipping t h e treatment (Ref. 2). weathering. The special grouts or grinding out the old mortar is Lynn Lauersdorf, chief of the designed for the process bond very hard to accomplish without building technology team for the well and seal the interface be- damaging the brick as well. Wisconsin Facilities Manage- tween the mortar and brick to ment Division, has overseen sev- stop leaks,” Lauersdorf says. Try surface grouting eral m a s k g r o u t i n g p r o j e c t s i n Before planning such work on In situations like these, sur- t h e past 20 to 25 years. Lauers- a historically significant build- face (or mask) grouting is anoth- dorf says the technique actually ing, however, it’s important to re- er option to consider. The process can be superior to repointing un- alize that the appearance of the consists of applying a thin coat of der certain circumstances. joints will change somewhat as a cement-based grout to the mortar “We’ve had tremendous suc- result. After long exposure to joints and the mortar/brick inter- cess with mask grouting on his- weather, the aggregate in mortar face. T h eB r i c kI n s t i t u t eo fA m e r i- toric buildings where the mortar joints becomes more prominent. add clean water, stirring until the mixture has the consistency of thick batter. Let it set for 10 to 15 minutes, then mix it thor- oughly just before using. Mix on- ly as much material as you can apply within 2 hours. The mate- rial can be retempered as needed within that time, but avoid re- tempering pigmented grout to maintain consistent color. 4. Dampen the mortar joint surfaces, but leave no free water. Then, following the joint lines, Grouting mortar (above), mixed to the apply the grout with a coarse- consistency of thick batter, is brushed fibered brush. Use short, diago- or floated over the wall surface follow- nal strokes to seal the brick/mor- ing the lines of the mortar joints. Brick faces (left) are carefully masked tar interface. Alternatively, you with tape before grouting mortar is ap- can apply the grout with a sponge or textured finish, you’d have a plied. float, using a circular motion. hard time sealing the edges with 5. Carefully strip the masking the tape,” Navis says. Surface grouts contain only very tape before the grout sets. “On the right kind of project, fine aggregate, and it isn’t appar- though, it’s a little faster and less ent in a finished job. The joints Laborious but effective expensive than full repointing— also may appear slightly wider C a lN a v i s of Wi s c o n s i nR e s t o r a- about two-thirds the cost. And a after grouting, if care is taken to tion, Verona, Wis., has performed veterans’ hospital we did back in ensure a good seal at the inter- several mask grouting projects the 1970s is holding up fantasti- face. over the past 20 years. He says cally well.” Lauersdorf says it’s a good idea the process is laborious, but can The hospital project was an to choose a grout color close to be both effective and economical eight-story building, with brick the brick color for best results. under the right circumstances. a c c o u n t i n g f o r a b o u t h a l f t h e Grout manufacturers produce the “Mask grouting works when wall area. Wisconsin Restoration material in a standard gray, but the joints are slightly eroded but crews worked from swing-stage will premix it to specific tints. basically in good shape. You have scaffolds and spent two days on Wisconsin’s guide specification to fill holes and repair deteriorat- each section of wall. The first day allows only premixed colors on ed mortar before applying the was spent masking the brick in state projects, to make sure the grout, so it’s probably not worth- the area covered by one full drop color is consistent. while if much preliminary work o f t h e s c a f f o l d . O n t h e s e c o n d is needed. Also, I’d only recom- day, workers brushed grout on Step by step mend it when you’re working with the joints in the same area, then Mask grouting should be done a hard, smooth brick. With a mat raised the swing-stage again and only when the outside air tem- worked down the wall removing perature is at least 50° F. The the tape. r e c o m m e n d e d p r o c e d u r e i s a s Surface grouting is not a pan- follows: acea for every leaky brick wall, 1. Fill small holes and repair but it can be an effective repair any seriously deteriorated mor- method for some of them. tar joints. Prepare the surfaces for grout application by remov- References ing any dust, dirt, efflorescence, 1. BIA Technical Notes on Brick Construc- paint, or previous water repellent tion 7F “Moisture Resistance of Brick Ma- treatments. sonry,” Brick Institute of America, 11490 2. Cover the brick faces with Commerce Park Dr., Reston, VA 22091. 2. Jerry G. Stockbridge, “Finding the Best strips of masking tape as wide as Way to Repair Mortar Joints,” Masonry the height of the brick. Use a ser- To be effective, grouting mortar must Construction, June 1988, pp.112-115. rated blade held tight against the cover the brick/mortar interface, thus slightly altering the joint’s appearance. wall to cut the strips of tape. Choosing a mortar color close to that PUBLICATION #M940423 3. Place dry grout material in a of the brick can minimize the visual im- Copyright © 1994, The Aberdeen Group clean container and gradually pact. All rights reserved