Coastal Painting

The technical team at Promain recently received a ‘phone call from a Contractor who was looking for a suitable Sika primer to use under black Bitumen. He was not sure if Sika Bonding Primer was the correct product. We thought you might be interested to know our response and recommendations. Below is a bit of info about what happened.

Initial Contact

Initially, we discussed the Contractor’s requirements. We discovered that black Bitumen was to go onto an outside wall surface. The customer told us that it was detailed on the specification he had received from his client. This caused us some concern. Black bitumen did not seem to be the right product for the substrate in question.

Promain always strive to supply the right product (at the best price). Alarm bells had started to tinkle. We asked if we could know a bit more of the facts. Listening to the details, we found out more about the problem that the client was experiencing.

The Project

The property, an Edwardian building, was suffering from water ingress to the side wall. The house is as far south as you can go – right on the coast. In fact, the wall had been receiving a real battering. With a south westerly driving wind and rain, water was being forced through the recently painted render. This water was migrating into the building and causing damp and mould to the rooms inside. The client had specified the use of black Bitumen as a coating to solve this issue.

It was essential to find out the level of dampness on the outside of the wall. Too much and any action taken, no matter what it was, at this point would be rendered futile. No applied product would stick. This would mean a waste of the client’s money. I asked the contractor if he could carry out a moisture reading on the wall. But as he didn’t have a suitable device, this wasn’t possible.

Luckily, one of my colleagues was close to the location the very next day. He took the opportunity to carry out a quick survey for us. He reported back that the wall was wet, but not saturated.

We had to be honest and express our concerns about utilising Bitumen to waterproof the side wall.

Bitumen Paint
Bitumen Paint

The Problems With Bitumen

I felt that Bitumen, although an excellent product, was not really suitable for this application due to the nature of the location. The main concerns being:

  • The surface was not below groundBitumen is an ideal product for creating a waterproof barrier to foundations, on areas such as cast concrete which has been backfilled with soil, making it stable and unlikely to crack or move.
  • It would be subject to ultra violet (UV) light – this would soon break down the Bitumen.
  • Looking to the future – Bitumen becomes brittle with age.

The location of the problem was three floors up, subject to wind, rain and sun damage and was an old building which would be prone to a little movement. Its construction was of a soft brick, similar to old London stocks, with a lime mortar. The render was originally a lime based render with horse hair added to help strengthen it and reduce the likelihood of cracking.

We were horrified to discover that a previous repair to this had been with a sand and cement mix!! A tragic use of the wrong product.

I strongly believed that a rigid product like Bitumen was not the correct product. Furthermore, Bitumen will also suffer during the summer as it tends to become ‘live’ again, when it gets hot, and Bitumen running down a wall would look a right mess! Not to mention that this will soon allow the water to penetrate into the building again.

Then it would be back to square one and the Contractor would soon get a bad name for carrying out shoddy work, not really his fault though, he would just doing as he was told.

The Specification

The specification I proposed, on behalf of Promain, was as follows:

  1. Clean the wall with a jet wash to remove any dirt and salt: This is essential as the building is on the promenade road, where there will be airborne pollution from cars and lorries. My biggest concern though, was salt from the sea spray which is extremely corrosive and will attack any paint coating that is put on top.
  2. Destroy any residual Mould or Fungi Spores: Clean with CentreCoat GS37 Fungicidal Wash to kill any moss or other organic growth, simply dilute with water and apply with a backpack sprayer.
  3. Have an overnight breather: Once the wall is dry and free from contamination it is best left over night.
  4. Finish with the correct products: A coat of Rust-Oleum Pegafix Universal Primer could be applied (by brush or roller) to provide outstanding adhesion for the topcoat of a waterproofing paint.
  5. Follow with two coats of Rust-Oleum Murfill Waterproofing Paint

Rust-Oleum Murfill Waterproofing

This paint is an exceptionally outstanding coating. It has been formulated to provide many years of protection against some of the harshest weather conditions.

Murfill Waterproofing Paint is in fact specified by Trinity House the body which maintains Lighthouses around the coasts of Britain, proof, if still needed, that this coating really will keep the water out.

Rust-Oleum Murfill Waterproofing Paint is not only a wonderful easy-to-apply water based masonry paint for waterproofing masonry, but it is also extremely flexible – making it ideal for buildings that suffer from movement.

Murfill Waterproofing is not suitable for all buildings – although it was exactly right, in this case, as many older buildings like this property “need to breathe”.

Having been constructed from traditional materials, such as timber and/or lath and plaster, without cavity walls, these buildings rely on the air pressure within the building. This confined pressure is fractionally greater than the external air pressure. This forces any moisture out of the walls, keeping them dry.

If a non-permeable coating is applied to the exterior of the wall it will act like a polythene sheet. It will therefore keep the moisture in.

I have seen older buildings that have been coated with a waterproof render or a non-permeable paint by builders and decorators.

The thought will be that they are protecting the building from becoming saturated but the resulting consequence is that the oak sole plates crumble and the walls start to collapse; becoming dangerous under the weight of the upper levels and roof.

Murfill Waterproofing Paint benefits from being vapour permeable, so it will not stop the passage of water; letting the building breathe and dry out during dry weather.


So, rather than taking a risk and causing dangerous and costly damage to your building, please take a little advice from somebody who has more experience! We are passionate about paint! The Promain Technical Team are at your service, just ask the question.


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