huangyhg

corrosion in masonry
we have recently moved into a 100years old house, constructed in class 1 engineering bricks. there is a small area which is stained with white deposits causing the bricks to flake.
any ideas what this is caused by or any suitable references
ianrawson...you should probably check a bit closer.
the white stain is likely efflorescence, a calcium deposit that is a result of moisture moving into and out of mortar. it is not likely that the bricks have a significant amount of calcium in them that would create this type of staining.
the flaking is likely a result of wet-dry cyclic deterioration of the brick. this is relatively common in older brick. you are likely seeing this in isolated or inconsistent locations, a result of variability in the manufacturing of the brick.
having both of these issues occurring indicates that the brick and mortar that are not sealed with a waterproofing material. you should check the mortar and brick for integrity, repair the damage, then seal the brick and mortar with a penetrating waterproofing material such as a siloxane compound (i.e, prime-a-pell 200 or similar).
to check the integrity of the brick and mortar, use a "scratch" test. you can do this by taking a screwdriver or knife and dragging its point along the surface of both the brick and the mortar. using moderate to strong pressure, you should not be able to gouge the brick, just make a scratch in it. for the mortar, if gouging occurs with light pressure or if the mortar sand comes out with your fingernail scratching on the surface, the mortar is "dead". it will require replacement to a significant depth by tuckpointing. if moderate pressure required, the mortar can be sealed but will likely require some repointing (tuckpointing) to a depth of about a quarter of an inch or slightly more. if significant pressure is required to gouge the mortar or if only a scratch results, the mortar is good.
i agree with ron, but i would not seal the brick until you know that the efflorescence has stopped. even with the soluble salts in the bricks or mortar, efflorescence will not occur, or will be very minor, if water is not migrating in the wall. i would first clean the efflorescence through scrubbing. if it it too stubborn to be cleaned this way, wet the wall, clean with a solution of 1 part muriatic acid to 12 parts water, and rinse the wall thoroughly when done.
next perform the tests ron recommends and replace damaged/soft/spalled bricks and remove all deteriorated mortar to the depth of sound mortar below, but to a minimum depth of 1/4". proper tuckpointing procedures really help it last in the long run and increase its weathertightness; don't do it halfway.
i would then leave the brick for at least a year before sealing it with the siloxane. it needs to dry out thoroughly, and you need to confirm that the efflorescnce mechanism (water migration bringing the salts to the wall surface) has been broken. then i would apply the siloxane.
the wait, to me, is key. if water is still getting in, the siloxane will prevent the salts from migrating to the surface. they can then build-up, exert pressure, and cause the bricks to spall.
thanks ron for the great tips on checking the soundness of bricks and mortar. i would agree with mattman. the problem with brick sealing is that it not only stops moisture coming in but also stops it getting out. many buildings, particularly old ones were designed to take a bit of moisture and then dry out. sealing is like putting a plastic raincoat on. any moisture from the inside can't breathe out and any leak in the plastic overcoat allows moisture in but it is much harder for it to get out.
carl bauer
thanks for the advice gentlemen.
my initial thoughts are that the migration of water will not have stopped, since there has probably been no alteration in the groundwater or drainage characteristics of the surrounding subsoil area in recent years.
it is going to be difficult to attempt any sort of drainage in this area because an underground cellar/basement exists down to eight feet below the finished ground level.
am i therefore right to presume that the best course of action, if water migration is still evident after a year, is continual maintenance of the affected area by replacing bricks as they become damaged and re-pointing.
ianrawson:
in reading this thread, i assumed at the start that all the discussion was about above grade masonry. your last post makes me think you are worried about a below grade problem. regardless of the situation, the problem will continue unless you solve the question of how the water is getting into the wall in the first place. i would offer the following:
1. if the masonry is above grade, check roof coping joints, roof flashings and parapet walls for open joints where water can get in. caulking, repointing or new flashing should stop the water infiltration.
2. on the wall face check lintel areas, window sills, and wall areas for cracks and repair in the same manner as #1.
3. for below grade walls, check for areas around the foundation where surface water can pond. regrade the lawn or paving to drain water away from the building and extend downspout runners etc.
4. if the problem is groundwater, solutions get expensive very fast: draintile, sump basins, waterproofing etc.
once the water source is found and corrected, then the sealers mentioned by others can have a positive effect. there are specialty contractors that do this sort of work but, be sure you talk to two or three, get prices and references.
best of luck.

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