How to reliably seal the gap between the chimney and the roof

When the chimney pipe exits through the roof, a gap remains that must be sealed. Since the chimney heats up, ordinary cement-sand mortar is not suitable for this purpose, as it will crack. The problem can be solved on a budget by making a special asbestos-cement mortar, characterized by high temperature resistance.

Materials:

• cement;
  
• sheet asbestos (can be used);
  
• water.

Gap filling process

To seal the gap, you need to prepare a heat-resistant compound. To do this, you need to tear sheet asbestos into small pieces. Its thickness and condition do not matter.

This can be either new or previously used sheet. The pieces are about the size of a thumbnail, maybe a little larger. The flaps are prepared until their volume is equal to half the volume of the required solution.

Then cement is added to the asbestos in a 1:1 ratio.

The components must be mixed dry.

After mixing, add a little water to them. You need to make a thick mixture with the consistency of sealant.

The resulting composition is left for 5-10 minutes, then mixed again and applied to the area.Due to the reinforcement with asbestos fibers, it does not fall into the gap. The composition is first applied around the pipe. The more you use it, the less likely it is that a crack will develop in the frozen mortar in the future. But you don't need to use too much.


If the gap between the pipe and the slate is sealed using an overlay plate, then a slope should also be formed for the water to flow down so that precipitation does not accumulate in the waves in front of the chimney. Before applying the mortar, you need to clean off the dirt and lichen from the slate so that the cement can adhere to it properly. The composition is applied on top with a wet hand or a paint brush dipped in water to make the surface smooth without open pores. If necessary, the remaining solution can be used to quickly repair cracks in slate.

After a day, in dry, warm weather, the solution will set almost to the hardness of the stone. After 28 days, the cement will gain full strength, but the chimney can be used even earlier. It is enough for the asbestos concrete to dry, after which you can safely use the chimney for its intended purpose. If you rush, a crack may appear in the wet mortar near the pipe, and then everything will have to be redone.

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