In areas prone to seismic movement, a lot of property owners are giving some thought to replacing the roofing pointing.  Constant shifting and "knocks" can loosen the mortar and lead to a leaking roof.

There are two options when replacing your roof pointing.  Traditional cement based pointing and flexible water based polymer pointing. 

Traditional cement based mortar is attractive and has stood the test of time over many centuries.  Provided it is laid by skilled tradesmen, it will add to the appearance of your roof and give years of maintenance free protection.  Correct mixing and application is essential and should be carried out by an experienced roofing contractor.  Mortar can be dyed to match the surrounding roofing tiles and is a lot cheaper than flexible pointing pastes. 

Problems with cracking are usually a result of incorrect application at the build stage. If the cement mix is not applied properly it will cause cracking. The ratio of sand and cement is very important. It is essential to get the correct mix of cement and aggregates. If insufficient cement is included in the mix it will become too weak and deteriorate faster. A good ratio for roofing cement is three parts sand to one part cement. The mix should be turned sufficiently to ensure an even distribution of cement.

It is also important to retard the cure time of the roofing mix. It is very important to slow down hydration of the mix. If the cement is allowed to dry out too quickly it will cause problems. This is especially important in warmer climates. If the roofing mix is allowed to dry too quickly it will result in a poor bond. The cement will not attach properly to the tiles.

  The cure time can be slowed by keeping the pointing mixture damp. Old carpet soaked in water is laid on top of the ridge tiles. This traps in moisture and stops the sun prematurely drying out the mortar. This will prevent cracks and extend the life of the roof pointing.  

Acrylic roof pointing paste comes in a variety of colours to match the roof. Acrylic roofing mortar comes in a variety of colours.  It offers a secure bond at the pointing stage and remains flexible.  Again, providing it is applied properly it will give a neat and attractive appearance to your roof.  The added benefit of flexibility gives a better fixing in areas with ground movement.

Ridge tiles are bedded in the normal way using traditional portland cement. The roof pointing is then applied 3 to 5mm thick. Flexible acrylic roof paste is more difficult to apply than cement mortar. If done incorrectly the surface has a tendency to drag leaving a rough finish. With practice it is possible to achieve a smoother concrete like finish.

If you always keep your trowel wet it will stop the acrylic dragging. Do not add water to the pointing paste. The water will ruin the mix. You need to apply flexible pointing in a clean movement. Apply it smoothly and don't overwork the surface. The pointing needs at least three hours to form a suitable surface. If it rains even lightly the pointing will have to be re-done. The water enters the pointing and it collapses.

I still prefer the look of traditional pointing over acrylic pastes. Further, traditional mortar is time tested and durable. However in areas of high seismic movement the new breed of roofing mortars are well worth considering.