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Tar Coating

Tar-based foundation coatings are widely used to damp-proof exterior foundation walls around the country. Are they effective?

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Tar as a form of damp-proofing has been in use since ancient times thanks to its waterproofing properties. It’s even referenced in the Bible as caulking for Noah’s Ark. Today, tar-based sealants are used for external damp-proofing and waterproofing around the country. 

Homeowners typically think of tar as a material for road construction. What they may not know is that tar is a good damp-proofing material for their homes. It also has many applications as a waterproofing and sealing agent. 

Tar coating

What Is a Tar Coating? 

Tar coating is a heavy, black, and strong-smelling substance that’s used for damp-proofing. A by-product of oil refining, tar is prepared by heating coal in closed iron vessels. The resulting material can be rolled on or sprayed on walls. 

Tar usually contains a huge amount of oily matter with low molecular weight. The material is 100% insoluble in water and can withstand hydrostatic pressure to a certain degree. 

Coal tar is also used in the roofing industry to seal, bond, or repair roofing systems that are deteriorating or leaking. Roofing tar formulas are black. However, some manufacturers have created lighter variants in silver and white colors. Newer formulations are mostly asbestos-free but still contain surface adherents, fillers, and solvents. To be used in the roofing, coal tar must be refined and processed to the required standards. 

How Is Tar Coating Applied? 

When damp-proofing your foundation wall, your building contractor will do the following: 

  • The exterior of the foundation wall will first be cleaned with a broom to remove dust and dirt as these can prevent the tar from adhering to the wall surface. 
  • Holes, cracks, and gaps on your walls will be fixed. By itself, tar won’t seal any crack or hole that’s large. 
  • Tar coating will then be sprayed on the wall’s exterior surface or applied with a roller from one end of the wall to the other end. 
  • The coating will be left to dry for 24 hours. 
  • Once the coat is dry, a latex primer can be applied to the layer of tar. 

Damp-proofing with tar isn’t a typical DIY job. It’s important to note that it’s best done when the home is being built, otherwise, contractors will have to dig up the soil around the foundation to apply the tar coating. Leave it to professionals who have the knowledge and experience to do a thorough job. They will address issues such as joints or cracks in your poured foundation walls and pay attention to areas where pipes penetrate your foundation. These are moisture hotspots and areas that DIY enthusiasts tend to overlook. 

What Affects a Tar Coating? 

A couple of things will determine whether your tar coating will adhere to the walls or not. Here are some of the factors that might come into play during tar application: 

  • How clean the exterior surface of the wall is 
  • Adherence to the manufacturer’s instructions 
  • The chemistry between the masonry wall and water 

Is Tar Coating Effective for Damp-Proofing? 

While concrete foundation walls are strong and durable, they’re also susceptible to water infiltration due to their porous nature. A practical way of dealing with recurring moisture issues is applying tar to the concrete. 

Tar-based coatings will create a tough barrier that stops moisture from the damp soil from seeping into your concrete. Three gallons of tar is enough to cover a 100 sq ft of wall. Once applied to the outer wall, this substance will dry and create a water barrier. Drying times vary from a day to a week, depending on humidity levels and temperature. 

Damp-proofing with tar will remain effective as long as water doesn’t pool around your home’s foundation or the foundation shifts. The truth is tar can’t resist water pressure or hold out against expansive soils like clay. 

Waterproofing the Foundation 

Tar coating alone won’t create or guarantee you a fully waterproof exterior foundation wall. What your foundation needs is an effective interior waterproofing system that addresses different issues. This system should include an interior drainage system to collect any leaking water, a sump pump system to remove this water, and a vapor barrier on the walls to help prevent moisture intrusion. 

Would you like to waterproof your foundation walls? Contact Complete Basement Systems for a free waterproofing inspection. Our experts will assess your foundation walls and your basement and recommend effective waterproofing solutions to keep moisture and underground water at bay. We use proven solutions that are backed by their longtime warranties. 

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