huangyhg

mortar joints-exterior side of masonry wall
concrete block w/ brick veneer construction:
is it common practice to use concave mortar joints on the exterior side of a concrete block wall? i notice that contracotrs usually don't rake these joint, they just make it flush. is there a structural benefit for using concave joints on the exterior side?
i notice that many joints that are not truly flush...they are recessed a little...not on purpose. i'm not sure if shrinkage has anything to do with it? maybe it's just the workmanship.
if the exterior sde of the wall recieves spray applied insulation/vapour barrier, are these minor recesess a concren?
any experience will be greatly appreciated.
pg
it is not common practice in my area to tool the joints unless the block are the finished surface. block that get covered, say with brick or stucco, typically receive a broom finish or get "floated", meaning a damp sponge is used to rub the joints and fill in holes. this will make the joints flush, or nearly flush.
i can't comment usefully on the barrier, but i wouldn't expect the joint to be a problem unless you are covering holes. even then i don't know it would be a big problem.
concave tooling the joints is the common and optimum way unless the surface treatment dictates something else.
when the joint is tooled to a concave shape, the mortar is compacted and a cement "skin" is created that fills minor voids. the concave shape of the joint permits continuous tooling and blends the joint along the wall. a tooled joint will shed more surface moisture.
raked joints are not conpacted to the same degree and can magnify variations in workmanship and any cosmetic problems with edges and corners. raked joints can cost more and can be used to accent the shadows and patterns of the units and architectural pattern on the faces.
flush joints are used where a surface coating is applied and it desired to keep the coating thickness the same so minimize the effects of the shrinkage/curing of the surface coating. whit some coatings, the joints can "ghost" through the thickness variation. flush joints are cheaper because there is less labor because there is no wait for the mortar to become set enough to tool.
dick
as concretemasonry noted above a concave tooled joint is less permeable and therefore sheds water better. surface water is the killer of masonry construction.
ncma has an excellent book and some technical papers on the practice of tooling joints.
from experience i have seen specifications indicate that a specific radius be applied to the pace of the joints of brick facade and interior faces of cmu.
(don't forget the weeps and wicks!)

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