Blown Bricks

[greenep]

I have a 1930's house which is predominantly rendered with a 12 (ish) course exposed brick level at the bottom.

My problem is that a number of these bricks have 'blown'. I suspect the pointing has deteriorated over the years, never replaced and damp has gotten into the bricks, frozen and blown the facia. Anyway, my question. Can I just knock out the old bricks and stick in replacements?

Any comments greatly appreciated?

 

[oilman]

I suspect the pointing has deteriorated over the years,.......

This is the function of pointing, though perhaps not quite so quickly. Walls consist of blocks and mortar. You have a choice, the pointing can be sacrificed or the blocks can be sacrificed. Which is easier to fix? Don't make the mistake of putting in cement based pointing. Your house was probably built using lime, and the bricks can get rid of their moisture through the mortar. Use cement in your pointing and say good-bye to the bricks.

You can cut away the bricks to about 1" deep and insert slips or do the whole brick if you're enthusiastic.

 

[legs-akimbo]

I have noticed oilman that you are very enthusiastic about lime and the using of ... but the advise you are giving is usually incorrect i am sorry to say.
A 1930's property would have been constructed using portland cement which has actually been widely used since the mid nineteenth century.
Certainly lime mortars are more permeable and allow the passage of air and moisture through the brick or stone if used as a render coat,or pointing on materials that traditionally would need to accomodate movement, for example stone, brick and cob (dried earth), which were widely used to build cottages and barns.
Modern materials are complimented by the use of portland cement mixes which work well when the construction relies on its rigidity for strength and to resist movement.
On the other side of the spectrum where the materials are relatively soft the use of lime mortars allow for the passage of moisture from the core of the wall to the surface whereby it naturally evaporates, damp is kept under control by the depth of the wall whereby moisture is readily absorbed and also released. In short a hard inflexable portland mortar should allways be used where the wall is of equal hardness and on softer traditional materials the reverse is true and lime mortars are essential so as not to trap the moisture and further compound the damp problems.
Greenep my advice would be to chop out the perished bricks using a good s.d.s. drill with hammer action, drilling holes through the bricks also helps for easier removal, replace with like for like and weather struck point in 4:1 red sand/ cement.... happy chopping!!

 

[oilman]

Portland cement may have been available since mid-nineteenth century, but it is certainly the case that lime was still being used well after the first world war. Portland cement's attribute is that it allows builders to get walls up faster than with lime mortar. Cement is still causing difficulties with modern bricks with all the salts having to come out through the bricks and not through the mortar as the mortar is too impervious. Apart from a few places where the ground is stable, trying to make a structure rigid is difficult. Witness the cracks which form below most windows, and not just around the mortar joints as with lime, but bricks torn apart.

 

[legs-akimbo]

I agree that salt crystallisation can occur using portland cement as it is theese salts that cause the stone to decay, where water evaporates the salts are left behind in ever increasing concentrations . theese crystals fill the pores of the walls causing them to disintegrate. But I reiterate this only occurs when primarily the structure is of a soft material in nature,whereas lime mortars absorb moisture and evaporation occurs through the joints rather than the stone itself.
Quite apart from the impracticall considerations of lime putty which takes weeks if not months to fully cure it really is a material that needs to be specified only where the original was of the same, though hydraulic limes, which are readily available which are stronger and denser, may be a ready alternative as they still attain a high degree of flexibility and permeability and still offer the physical properties of traditional lime mortars. Any construction that in no way used lime mortars will absolutely not need the substitution thereof from porland cement mortars. Building movement will allways occur and in the vast majority of cases if it happens at all is of no great consequence, modern building practises now accomodate for movement within the structures so is not really a relevant issue in construction today .

 

[oilman]

Quite apart from the impracticall considerations of lime putty which takes weeks if not months to fully cure......

Overcome by pozzolanic additives, giving a broadly similar characteristic to hydraulic limes.