How to apply roughcast with a manual coating sprayer?
How to Apply Roughcast with a Manual Coating Sprayer
Preparation is the key to success. Without it, you could end up with all your future efforts wasted and back to square one minus a lot of money.
Wall Preperation
The first thing that needs to be done before you apply roughcast is to ensure that the wall is clean and not in need of any repairs. If this isn’t done properly then the finish of the roughcast not be as you desired.
Step 1 - Clean and Repair Wall
Make sure the wall area to be covered is free from dust, moss, loose brickwork or mortar. Any damaged areas must be repaired.
Make sure the wall area to be covered is free from dust, moss, loose brickwork or mortar. Any damaged areas must be repaired.
Step 2 - Dampen Wall
Brush the wall with water so that it is damp but not saturated, ready for the first mix. This will prevent the wall absorbing the water in the mix and drying too quickly.
When an applied mix dries out too quickly, it doesn’t bond to the wall adequately. When this happens, the applied mix can crack, become loose and fall away from the wall.
Brush the wall down with water so that it’s damp but not saturated, ready for the first mix. This helps the render to stick to the all and prevents it from drying out too fast.
When an applied mix dries out too quickly, it doesn’t bond to the wall adequately. When this happens, the applied mix can crack, become loose and fall away from the wall.
Choosing Your Equipment for Applying Roughcast
Step 1 - Choosing Your Cement
First, decide on the type of cement you want to use. The base coat or first coat can be made with general-purpose cement but you may want to use white cement for the finishing coat as this can give a more attractive finish in contrast to the stones and pebbles.
White cement is similar to grey cement in all aspects except for its high degree of whiteness.
As it’s a longer process to produce the white cement, it is more expensive than ordinary grey cement so be aware of this when making your decision.
First, decide on the type of cement you want to use. The base coat or first coat can be made with general-purpose cement but you may want to use white cement for the finishing coat as this can give a more attractive finish in contrast to the stones and pebbles.
White cement is similar to grey cement in all aspects except for its high degree of whiteness.
As it’s a longer process to produce the white cement, it is more expensive than ordinary grey cement so be aware of this when making your decision.
Step 2 - Choose Your Stone or Gravel
Choose the type of stone or gravel (aggregate) you want to put into your cement mix.
Measure the area to be covered (multiply the height of the wall by the width) and allow one 25kg bag to cover approximately 2-3 square metres of wall coverage (depending on the mix used). Make sure you have enough aggregate to complete the area to be covered before you start.
The average aggregate used for roughcasting is between 4mm (5/32″) and 8mm (5/16″) in size.
Unlike pebble-dashing where the pebbles need to be supplied in bags for reasons explained under What is pebbledash? the aggregate for roughcasting can be bought in bulk form rather than bags. It is a lot cheaper to do it this way too.
As with pebble dashing, however, the aggregate must be stored on a solid, hard, dry surface away from contaminants such as soil, fallen leaves etc.
Mixing the aggregate to obtain a consistent colour mix is not an issue as the aggregate will be covered in the cement mix. Just simply add it to the concrete mix with a shovel.
Choose the type of stone or gravel (aggregate) you want to put into your cement mix.
Measure the area to be covered (multiply the height of the wall by the width) and allow one 25kg bag to cover approximately 2-3 square metres of wall coverage (depending on the mix used). Make sure you have enough aggregate to complete the area to be covered before you start.
The average aggregate used for roughcasting is between 4mm (5/32″) and 8mm (5/16″) in size.
Unlike pebble-dashing where the pebbles need to be supplied in bags for reasons explained under What is pebbledash? the aggregate for roughcasting can be bought in bulk form rather than bags. It is a lot cheaper to do it this way too.
As with pebble dashing, however, the aggregate must be stored on a solid, hard, dry surface away from contaminants such as soil, fallen leaves etc.
Mixing the aggregate to obtain a consistent colour mix is not an issue as the aggregate will be covered in the cement mix. Just simply add it to the concrete mix with a shovel.
Step 3 - Choose Your Sand
Make sure you choose the correct sand for the job in hand!
Building sand is not ideal as it allows moisture to pass through more readily once the mix is set on the wall.
Sharp sand (sand with grit in it) is recommended as it repels moisture better than building sand and helps to ‘knit’ the mix together better allowing for a stronger mix which is ideal for rendering work such as roughcast.
As with the aggregate, the sharp sand can be supplied in bags or in bulk. Remember, buying in bulk is a far cheaper option if you have the area to accommodate this.
Make sure you choose the correct sand for the job in hand!
Building sand is not ideal as it allows moisture to pass through more readily once the mix is set on the wall.
Sharp sand (sand with grit in it) is recommended as it repels moisture better than building sand and helps to ‘knit’ the mix together better allowing for a stronger mix which is ideal for rendering work such as roughcast.
As with the aggregate, the sharp sand can be supplied in bags or in bulk. Remember, buying in bulk is a far cheaper option if you have the area to accommodate this.
Mixing Roughcast
Step 1 - Enlist the Help of a Co-Worker
If possible, always have two people carrying out the work. One can be mixing while the other one does the spraying.
If possible, always have two people carrying out the work. One can be mixing while the other one does the spraying.
Step 2 - Add Clean Water
Always use clean water when mixing. The mix properties can be affected otherwise and any screed work could potentially fail.
Always use clean water when mixing. The mix properties can be affected otherwise and any screed work could potentially fail.
Step 3 - Add Waterproofer
Waterproofer should be added into the mix before applying to the wall. This will help prevent rainwater penetrating the cement mix and getting to the brickwork.
Always read the usage instructions on the container to ensure the correct amount is used with each mix.
Waterproofer should be added into the mix before applying to the wall. This will help prevent rainwater penetrating the cement mix and getting to the brickwork.
Always read the usage instructions on the container to ensure the correct amount is used with each mix.
Step 4 - Add Plasticiser
Always use a cement or mortar plasticiser when mixing.
This will give a smoother effect to the cement mix and give you a bit more time to work with the mix before it starts to dry.
Always use a cement or mortar plasticiser when mixing.
This will give a smoother effect to the cement mix and give you a bit more time to work with the mix before it starts to dry.
Applying the Base Coat
Step 1 - Re-Dampen Wall if Required
You may need to dampen the wall again before applying your base coat, to ensure the mixture sticks to the wall properly and does not dry out too quickly.
You may need to dampen the wall again before applying your base coat, to ensure the mixture sticks to the wall properly and does not dry out too quickly.
Step 2 - Mix Base Coat
A standard mix for the base coat would be 2 parts cement and 1 part lime to 4 parts sand, mixed with clean water.
If more than one coat is required before applying the roughcast, it is common practice to apply each consecutive coat with a weaker mix (approximately a third more sand in the mix) to the previous one.
This ensures that the base coat and each consecutive coat is a stronger compound than the finish coat, allowing for a stronger bond with less risk of the finish coat pulling off the layers underneath.
For example: First coat 2:1:4 (cement:lime:sand); Second coat 2:1:6 (cement:lime:sand) and so on.
A standard mix for the base coat would be 2 parts cement and 1 part lime to 4 parts sand, mixed with clean water.
If more than one coat is required before applying the roughcast, it is common practice to apply each consecutive coat with a weaker mix (approximately a third more sand in the mix) to the previous one.
This ensures that the base coat and each consecutive coat is a stronger compound than the finish coat, allowing for a stronger bond with less risk of the finish coat pulling off the layers underneath.
For example: First coat 2:1:4 (cement:lime:sand); Second coat 2:1:6 (cement:lime:sand) and so on.
Step 3 - Apply Base Coat and Scratch
Once applied to the wall, you should scratch lines into the mixture using a plasterer’s scratcher, also known as a ‘scarifier’. This will allow proper adhesion between the coats.
You can scratch any pattern you wish, but try and ensure the surface is as even and smooth as possible, so that your next layer is level.
If applying more than one layer before the finish layer, each previous layer must be scratched to ensure they stick together properly. This should also be done for patchwork (repairing a small area of the wall already roughcast).
The base coat should be completely dry before applying the second coat. (Commonly, the finish coat which is the roughcast mix, is the third coat when roughcasting).
Once applied to the wall, you should scratch lines into the mixture using a plasterer’s scratcher, also known as a ‘scarifier’. This will allow proper adhesion between the coats.
You can scratch any pattern you wish, but try and ensure the surface is as even and smooth as possible, so that your next layer is level.
If applying more than one layer before the finish layer, each previous layer must be scratched to ensure they stick together properly. This should also be done for patchwork (repairing a small area of the wall already roughcast).
The base coat should be completely dry before applying the second coat. (Commonly, the finish coat which is the roughcast mix, is the third coat when roughcasting).
Applying the Second or Final Coat
The second coat or ‘finishing coat’ of roughcast is usually the same thickness as the base coat, although the mix ratio is slightly weaker than that of the base coat (approximately a third more sand added to the mix). This ensures that the finish coat doesn’t pull away the base coat.
Step 1 - Mix Final Coat
A standard mix for the roughcast would be 1 part cement to 2-3 part sand mixed with clean water. The stone or aggregate as it is known is then put into the mix.
This is usually a 4-5 part aggregate to add to the above mix. Measuring the amounts is known as gauging.
It is really important to gauge each product going into the mix. As a guide:
6 – 8mm (1/4 – 13/16″) aggregate: cement, sand, aggregate (1:2:4 to 5 mix ratio respectively)
Less than 6mm (1/4″) aggregate a 1:2:6 mix may be preferable
A standard mix for the roughcast would be 1 part cement to 2-3 part sand mixed with clean water. The stone or aggregate as it is known is then put into the mix.
This is usually a 4-5 part aggregate to add to the above mix. Measuring the amounts is known as gauging.
It is really important to gauge each product going into the mix. As a guide:
6 – 8mm (1/4 – 13/16″) aggregate: cement, sand, aggregate (1:2:4 to 5 mix ratio respectively)
Less than 6mm (1/4″) aggregate a 1:2:6 mix may be preferable
Step 2 - Fill Sprayer with Mix
Fill the manual coating sprayer with the roughcast mix and rotate the handle while moving the sprayer up and down and left to right until the area to be done is covered in a smooth even layer or matches the current finish it is mating up to.
Fill the manual coating sprayer with the roughcast mix and rotate the handle while moving the sprayer up and down and left to right until the area to be done is covered in a smooth even layer or matches the current finish it is mating up to.
Step 3 - Practice on Rough Area
It is not easy to apply roughcast, so if you’re a beginner, take some time to practise on a piece of scrap board before attempting to spray your wall.
Being able to spray the concrete mix evenly against a wall requires a keen eye so as to produce an even coating with no missed spots or patchiness.
If a large area is needed to be done, don’t continually move along the wall…apply coverage into smaller squares, being careful to overlap and merge each area before drying out occurs.
Uncovered areas, no matter how small, will reduce the amount of protection against the weather and will look unsightly. Apply the roughcast mix generously to avoid this.
It is not easy to apply roughcast, so if you’re a beginner, take some time to practise on a piece of scrap board before attempting to spray your wall.
Being able to spray the concrete mix evenly against a wall requires a keen eye so as to produce an even coating with no missed spots or patchiness.
If a large area is needed to be done, don’t continually move along the wall…apply coverage into smaller squares, being careful to overlap and merge each area before drying out occurs.
Uncovered areas, no matter how small, will reduce the amount of protection against the weather and will look unsightly. Apply the roughcast mix generously to avoid this.
Step 4 - Dampen Roughcast
Don’t allow the finish coat to dry out too quickly or it may shrink too fast and crack. Spray the area with water and allow it to dry gradually over two or more days. This is important, more so on hotter days.
Buildings do move, so small cracks can appear years later and require repair.
Don’t allow the finish coat to dry out too quickly or it may shrink too fast and crack. Spray the area with water and allow it to dry gradually over two or more days. This is important, more so on hotter days.
Buildings do move, so small cracks can appear years later and require repair.
Step 5 - Clean Up
Ensure all tools used to carry out the task have been cleaned down and correctly stored away.
Ensure all tools used to carry out the task have been cleaned down and correctly stored away.
