External wall issues

Early brick walls

Brick walls are remarkably robust, and even if the early quality of bricks does not match modern standards, the solid walls and rubble-filled walls of the 1400 to 1600 period are worthy of admiration for performance. All bricks were hand-made, and because they have different compositions they can deteriorate at different rates.

The lime mortar that was used to lay bricks makes the wall capable of containing slight movement without cracking, and the capacity to move needs to be allowed for in any refurbishment or reinforcing scheme. The key to brickwork repair is to understand that matching them is very difficult, and sympathetic mortar repairs are critical. Hard cement mortar pointing will only cause further decay to the brickwork, and should never be used. Harsh or aggressive washing is also harmful, as it removes the fire layer and makes the bricks more susceptible to frost attack and penetrating moisture ingress.

Modern masonry waterproofing sealants should not be used on this type of wall, however tempting the remedy may appear, as it can just as easily trap moisture within the wall, and is a short-term remedy requiring constant reapplications. To prevent road spray soaking the wall, low-level slate plinths can be added to the foot of walls. As long as the plinth does not rise too high this remedy seems to work very well, but can sometimes need adjustment to correct the height.

Brick was commonly used as an outer layer for facades, and occasionally these additional leafs can splay from the original structure if the tie-back mechanism fails or is inadequate. This type of bowing or apparent leaning usually requires a full rebuild and careful opening-up works, and consultation needs to be undertaken to establish the most likely fault, before money is committed.

In the 1520s, the walls of high-quality houses often were colour washed, and the pointing would be picked out. Colour washes did not last very long, but could be reintroduced as an ideal way of providing a sympathetic protective top coat for struggling brickwork. Always seek expert advice on colour choice and mixes, as fundamental historical mistakes are easily made.

Take care when specifying lime mortars for repair works, as common working practices can result in conflicts of opinion. An example of this is the commonly understood 1:3 lime to sand ratio for mortar, which traditionally was prepared using not slaked lime (calcium hydroxide) but unslaked quicklime (calcium oxide). This increases in volume when slaked, making the resultant mix more lime rich than the original stated ratio. Under analysis, most historic lime mortars fall within a range of 1:1.5 to 1:2. Modern lime, which is much more accurately produced, would be better mixed at 1:1.5 to 1:2 to replicate the older mixes.

All brick walls of this era are vulnerable to decay by the introduction of hard cement mortars. These should not be placed over softer lime mortars, as they cause the bricks to erode faster.

Brick in the 1800s

The Brick Tax emerged in 1784 to help pay for the expensive American War of Independence. The tax had an effect on the size of bricks (tending to make larger sizes more economical), and a popular dimension before the 1800s had been the 10 x 5 x 3 inches. Not to be outdone, the government altered the tax in 1803 to include these sizes, and so the 9 x 4.5 x 3 size was developed. Brick-making did not die out completely as a result of the tax, and there was stiff competition between the manufacturers. By the 1850s, mass production techniques were well developed and in 1870 the now familiar smooth and regular 'Fletton' was widely available. Throughout the period, brick-making was still a relatively regional affair, and local defects were contained to their regions. Between 1810 and 1850 there was a distinct difference in the size of bricks between the north and south. The 'northern gauge', epitomised by the Accrington brick, was commonly perceived to dominate the regions north of the Bristol Channel to the Wash.

Mortars

Lime mortars were traditionally used. However, the introduction of cement mortars in 1824 means that not all 'Victorian' properties can be assumed to have lime mortar. Many historians point to cement mortar only being popular after the war years. However the build-speed benefits are thought to have spread the use of cement mortar and Portland cement/lime mixes very quickly. It is a common mistake when pointing to get the mortar mix wrong, which can cause the brick faces to spall. Cement mixes should not be used on lime mortar beds. Cement mortars are hard, whereas lime mortars can be easily scratched with a metal implement. Coloured aggregates were used in mortars, and the advent of hydraulic limes improved build speeds in the industrial and civil engineering sectors.

Brick spalling and poor maintenance

Generally bricks from this period have stood the test of time but, nevertheless, can begin to spall after generations of freeze-thaw action. However, the most likely causes of defects are poor repairs, lack of maintenance and in particular, poor workmanship on the chasing in of flues and cabled media services.

Spalled bricks need to be attended to in good time. They can often be carefully removed and then turned to hide the decay. Some favour tile-stitching (the insertion of tile slips into walls), which may be an appropriate repair for cracks in historic brickwork.

Avoid the use of coloured mortar or thin brick slips to build up decayed brick faces. The use of cement mortars vastly accelerates the decay of the bricks.

Gutter overspill causes large amounts of water to cascade down walls, and can cause significant damage. Properties from this era can suffer from the addition of poorly thought-through guttering systems, and it can be a prudent measure to rearrange runs and make sure they are actually connected to drains and properly constructed soakaways.

Clearly not many cable or satellite dish installers or gas fitters go on conservation courses. There is a growing trend to drill from the inside with core drill bits and hammer action drills, which blows the face off the brickwork. The universal application of a variety of mastics tends to be the modern solution to the provision of a good fit for such installations.

Removal of older technologies, such as TV aerials and overhead telephone cables, tends to result in snapped screw heads or large holes left in the wall. The extent of accumulated damage to a property can be so great that even simple alteration or upgrade projects can require a significant amount of direct supervision.

Damp penetration through walls

This can occur for a number of reasons. Walls of this era have no particular feature that makes them more prone to water penetration than other solid walls. However, an added complication can be that brick outer skins can impede the evaporation rate required by a timber-framed wall, if it is having to disperse higher moisture levels from within the house. The balance between moisture generation and ventilation would need to be explored in some detail in these cases.

Defects in solid brick walls with renders

Do not underestimate the significance of hairline cracks in renders. They can deposit relatively large amounts of water into solid walls. If this cannot escape, moisture levels rise and various symptoms can evolve. This classically happens when cement renders are added, in the belief that a seal on the wall will prevent water ingress. Timber-framed and earth-constructed buildings in particular can suffer major structural damage if moisture builds up behind a cement render. Careful removal of cement renders can be difficult, and sometimes partial removal is all that is possible in the medium to short term. If this is the case, it is better to remove this from the base of the walls and where good air circulation and sunshine prevail.

While a non-hydraulic render may be appropriate in certain circumstances, in many cases a mix with a faster and harder set may be desirable. Lime renders require considerable skill and understanding to apply, and significantly more attention between coats. The selection of contractors needs careful consideration and a degree of advanced planning.

Water penetration through brick infill panels

Brick noggins within timber-framed panels are either exposed or limewashed, and are sometimes more than just infill as they can have a structural effect on the walls. Where they meet the bottom rail of the framed panel, rainwater can rest and find routes in. As with most solid structures, these infill panels can be overwhelmed by intense and prolonged weather, or be saturated by other sources such as leaking gutters. Evaporation is still the principal means of preventing water entering the house, and there is much to be said for not tampering with the wall at all, if major water saturation has been eliminated or reduced.

Pointing in lime mortar is critical to these panels, as there is differential thermal movement between the brick and timber that needs facilitating. A bevel on the joint between the timber and brick helps divert water away from this weak spot. Coating the bricks with modern cement renders is not appropriate, and great care is required if removing such coats, as the bricks' protective faces can become damaged. Paint systems used on these multi-material walls should be chosen carefully.