I put in a bunch of bullnose brick in a landscape application and some of them have hairline cracks usually between the mortar in the joint and the brick itself. I'm not really worried about it - I have no freeze here but I'd like to know why it may have happened so I can avoid it in the future. It was my first time working with this type of brick and it was a little tricky because there is so much side buttering involved.
I used a 2.5-1 Portland - sand mix with a small amount of fireclay. I used this relatively rich mix because I wanted the mortar to stick to the brick when buttering. It may be my lack of experience but I know that a N-type mix would fall off very easily especially since the nose part of bullnose joint has no support from underneath.
Tooling the joints on these is a little tricky. I had to sort of scrape some mortar out because you start off with a flush joint and also I think I found out it's better to use a wider tool than normal or else the concave part of the joint is much narrower than the total joint width. Also, you can't tool too hard near the nose or you'll just push out the mortar.
I either covered the bricks with plastic or kept them wet for a few days to avoid cracks.
Also, inevitably you get a lot of mortar on the surface of these bricks. I cleaned them with a dmap sponge and in the beginning I may not have realized that getting excessive water on the joint will probably weaken it. I assume it's better to use a damp sponge.
If I had to guess I'd say the reason some cracks showed up is from too much adjustment of the brick after placement, excessive water from cleaning and possibly some shrinkage due to the rich mix.
Any tips are appreciated.
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