Monday, April 28, 2014

Quality Control - Fired Brick Masonry

Working on early childhood development centers in Rwanda has had me inspecting a lot of masonry construction. There was very little quality assurance put in place when the projects began, so for the most part it has been regular inspections, identifying mistakes, demolishing parts of walls, and re-building correctly. Going forward, a robust total quality management plan will be introduced form the beginning, complete with minimum qualifications, written instructions and signage, assigned people responsible for quality, checklists (pre-construction, during construction, and post), mock-ups, etc. Here are some of the most common errors.
 
 
This wall shows what is supposed to be a Flemish bond, but the header bricks (the single brick running perpendicular to the wall) are cut. The masons do this because the dimensions are bad / inconsistent. If they put the headers in so they are flush with the outside of the building, then there are large divots on the inside where the brick isn't long enough. Ideally, the bricks would be long enough to be flush on the inside and outside (as long as two brick widths plus mortar). We've asked them to pre-select the longest bricks and use them for headers and then to center the headers so there is a small divot on either side. Once Identified as a problem, I prepared signage to have on sites as a teaching tool / prompt, but more needed to happen at the beginning of construction.
 


Another common mistake is bad grout. We're getting very inconsistent mixes (bricks can often be easily removed from walls after the grout is dry). One reason is nobody uses lime, so it is just a small amount of cement and some very dirty sand (often not river sand and they haven't been washing). Regardless of the mix, instead of 1 cm mortar joints, we're seeing as much as 5 cm. This is partly because of un-skilled / un-trained masons, but also because of bricks with different dimensions than assumed by the architects. The architects have shown every single brick in their drawings and when foremen see a certain number of rows of brick under the window sill with specific dimensions given, they are increasing the amount of mortar per row to get the bricks to the level shown on the plans. Going forward, we need to clarify that the mortar joint dimensions are critical (1 cm) and that heights and number of brick courses shown on the drawings for some items, like window heights, have some flexibility.



 
Finally, the rebar in masonry buttresses and columns is new for most masons and we've seen lots of problems. Ideally, the two rebar are spaced 10 cm apart, centered over the buttress or column, and the bricks are woven between the rebar. We're getting rebar poorly set in the foundation, so getting bricks between them / incorporating them into buttresses is difficult. Often, the masons will push the two rebar together and treat them as one because it is easier to lay brick around, though much less structurally secure. Even when it is pointed out that rebar are in the wrong position within a column foundation, we have seen the masons bend the rebar at the bottom to get them where they should be so the entire column becomes wobbly as there is slack in the rebar (and the grout isn't very sticky). 





2 comments:

  1. For masonry construction suitable design and perfect construction is really needed a lot. nypavingandmasonry can also inform you about this

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  2. Thanks Abir. We're probably a bit out of your service area in Rwanda, but it was good to see some examples of quality work in your photo gallery. Best regards.

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