Basecoat and Mesh – YouTube Series Episode 5

To run alongside our new YouTube series, we have a dedicated series of blogs detailing the processes described in the series. We will cover every single step of the installation process, from an unprepared substrate, all the way to the aftercare stage. This includes customer and system aftercare. The series is broken up into the following steps:

1. Starter Track
2. Priming
3. Insulation, adhesive, and fixings
4. Beading and verge trims
5. Basecoat and mesh
6. Topcoat (priming and rendering)
7. Tips and aftercare
8. Our other services

Episode 5 shifts focus onto the reinforcing basecoat and mesh layer. A basecoat reinforcement layer is an essential component of any EWI system. It works hand in hand with the other layers in the system to protect your external walls. It’s long been reported that a basecoat layer provides a long-lasting and crack-free finish for your property. Not only is a basecoat important for structural integrity, but it also improves the overall appearance of the finished facade.

Before we start looking at the process, it’s worth mentioning that by this point, all your insulation should be level & secured to the wall, all your beading and verge trims should be fitted and installed and finally, all your tools and mixing buckets should be clean and ready to use.

Choosing a basecoat

EWI PRO sell a range of dual-purpose basecoat adhesives, each tailor-made to best suit different EWI projects.

For those of you working on a render-only project, we would suggest using EWI-225 Premium Basecoat, perhaps our strongest and most versatile basecoat. If you are looking for a more affordable alternative, you could also consider our new 222p Performance Basecoat.

For those of you insulating with EPS, we always suggest using the EWI-220 EPS basecoat, which is specially enhanced to bond with the EPS material.

For those of you insulating with Kingspan® or Rockwool®, we would again recommend using EWI-225 Premium Basecoat, which is ideal for this type of heavier insulation. 225 would also be advised when using a Render carrier board, or working on an ICF construction.

Check the weather forecast

This step may seem like common sense, but the success of your basecoat will depend on the conditions in which it was applied. All basecoat work must be protected from rain, snow, strong winds and direct sunlight. Never apply any basecoat in temperatures below 5℃ or over 30℃.

Mix the basecoat

All our basecoats require paddle mixing with clean, cold water before they are ready to use. Each basecoat requires a different amount of water so do give a quick check of the instructions on the packaging. These numbers are provided purely as a guide but you may prefer to change the water amount slightly depending on your application technique. Mix the basecoat with water until you have achieved an even consistency. Leave the bucket for 5-10 minutes after mixing, and then give it that all-important second mix.

Apply the basecoat and mesh

Fibreglass mesh is another component in all our EWI systems which works to prevent the facade from cracking. Depending on your project, you may opt to use our standard strength mesh roll or if you require additional impact resistance you may instead choose to use high-strength panzer mesh. The EWI Store sells our fibreglass mesh in both 1 and 50m2 rolls.

Basecoat & Mesh are applied together but there are 3 techniques to choose from when it comes to putting it on the wall.

The one-pass method applies 4-6mm of basecoat using a steel notched trowel. The fibreglass mesh is then embedded within the basecoat in vertical strips using your
trowel’s flat edge.

The two-pass method initially applies only half the basecoat, around 3-4mm, then the mesh is placed on top in vertical strips and embedded again using the flat edge of a notched trowel. Another coat of basecoat is then applied onto the mesh at a thickness of 2-3mm and It’s crucial you do this while the first coat is still wet.

While both methods are reliable and effective, we always recommend our customers use a spray machine where possible. Spray Machines are a no-brainer given the time they save and the convenience they offer. Our basecoats work with most market spray machines such as Euromair or Kaleta. Some are powerful enough to spray up to 40 bags of EWI-225 in under 1hr. This
rate of coverage is impossible to match by hand-applying.

Regardless of your chosen method, each Fibreglass Mesh strip should overlap its neighbouring strip by approximately 100-150 mm. (47-Typical-Mesh-overlapping-detail-1)

Bear in mind that high-stress corner areas, such as those on window and door frames always require a second layer of mesh. Often called Stress patches, these are laid on at 45 degrees and are usually 300-500mm wide. Like the vertical strips of Mesh, the stress patches also need embedding into the basecoat. (46-Typical-Stress-Patch-detailing-1)

Achieve a clean, smooth finish

Whilst it might be tempting to settle for a slightly uneven basecoat, it’s going to become a real problem when applying your silicone render, especially if you’re using a smaller grain size like 1mm.
Once you’ve embedded the mesh and whilst the basecoat is still workable, make the facade as smooth as possible. There is no official technique for this. Most installers achieve this using a trowel or speed skim, but it’s not uncommon to rub up the basecoat layer with a sponge float as well. Once complete, your basecoat layer should be no thicker than 6mm.

Wait for the basecoat to dry

Your final step is to wait for the basecoat to dry. As you’ll expect, the basecoat drying time depends entirely on the weather conditions. Typically, this can be anywhere from 24-72 hours, and in some cases even longer. Once it’s dry, you are ready to move on to applying the decorative silicone render.