FRP Lining Surface Preparation: Why It Matters
However, failure of FRP linings may not necessarily be attributed to the failure of resin or fibreglass, as there are instances where the surface condition under the lining will be significant.
The preparation of the surface before the application of the FRP lining is crucial for proper adhesion, durability and protection against corrosion in the long run. This is because oil or grease, rust, debris, previous coatings, dirt, water or any other surface condition will affect the lining process.
This is particularly significant in applying FRP lining on mild steel tanks, concrete tanks, pits, trenches, sumps, ducts and other industrial machinery.
What Is FRP Lining Surface Preparation?
The procedure of surface preparation consists of making the substrate ready to receive FRP linings.
This is done using the following factors:
- Base material
- Surface conditions
- Old paint and coating
- Rust and corrosion
- Chemical contamination
- Moisture
- Lining system required
- Project specifications
The surface prepared should be clean and ready for bonding before resin and fibreglass application.
Why Is Surface Preparation Important for FRP Lining?
FRP lining acts as a barrier between the substrate and the environment.
In order for the FRP lining to function efficiently, the bonding of the laminate to the prepared surface is necessary.
Lack of proper preparation could lead to the following:
Poor adhesion
There is a possibility that the liner will not bond properly to the substrate.
Blisters or lifting
Contaminants or moisture may cause defects under the liner.
Peeling or delamination
Areas with poor bonding may peel off because of chemical, moisture, or mechanical damage.
Pre-mature corrosion
Corrosion can still take place under the FRP liner in case the steel is not properly prepared and protected.
Reduced life span
It is possible that the correct selection of the resin system cannot provide an efficient performance with improper surface preparation.
AMPP states that surface preparation is important for the proper application of coatings and linings and that contamination, inappropriate surface profile, moisture, and weak substrates can hinder proper adhesion.
FRP Lining Surface Preparation for Mild Steel
1. Inspect the Surface
Start by checking for:
- Rust
- Deep corrosion
- Loose scale
- Old paint
- Oil and grease
- Dust
- Surface welding defects
- Sharp corners
Defects such as structural defects should first be corrected before lining. Similarly, Plastic Fabricators recommend examination of steel tanks for rust, old paint, deep corrosion and other surface defects before lining.
2. Remove Oil and Grease
Adhesion may be affected by oil, grease and other pollutants.
The right cleaning procedure has to be chosen based on the pollution and recommendations of the lining manufacturer.
3. Remove Rust and Existing Coatings
Loose rust, mill scale, and poorly adhered coatings and other similar weak surfaces need to be prepared by the appropriate surface preparation technique.
Surface preparation could be done by the following techniques:
- Abrasive Blasting
- Power tool Cleaning
- Grinding
- Other Mechanical Preparation Techniques as Approved
AMPP has individual standards for each metal surface preparation process and level of cleanliness.
4. Create the Required Surface Profile
An appropriate surface profile or texture will aid in the bonding of the lining system.
The required surface profile is not an educated guess. It must be determined based on the technical requirements of the resin/lining system and project specifications.
5. Remove Dust
Once the surface is prepared, it should be cleaned to ensure there is no dust or abrasives left behind.
6. Inspect Before Lining
Checking of the surface to be coated is necessary before applying the first coating of resin or laminate. This will ensure that all the necessary criteria have been fulfilled.
FRP Lining Surface Preparation for Concrete
The process for preparing concrete differs from that used for steel.
The surface of concrete can be covered by:
- Dust
- Laitance
- Oil
- Grease
- Weak surface
- Cracks
- Voids
- Moisture
- Existing coating
According to AMPP guidelines, concrete should be inspected for the presence of an existing coating, contaminants, structure, cracks, voids, laitance, and moisture issues prior to coating application.
Based on the condition of the surface, preparation can include any combination of grinding, abrasive blasting, scarification, cleaning, or other mechanical method of preparation.
The aim is to prepare a good surface for the chosen lining system.
Moisture: An Important Factor
It is important not to overlook the moisture level when applying FRP linings.
In particular, it concerns:
- Concrete tanks
- Pits
- Trenches
- Sumps
- Subsurface structures
- Cleaned or moist surfaces recently
An excessive moisture level can affect adhesion and lead to premature degradation of the linings.
What moisture level is appropriate will depend on the resin used and the type of linings.
What Happens If Surface Preparation Is Poor?
The first mistake many people make is thinking that a thick FRP layer can cover up any defects on the surface.
They cannot.
In case there is any contamination, debris, or defect on the substrate surface, the lining will just cover them for a while.
Some of the problems associated with such mistakes include:
| Surface Problem | Possible Result |
|---|---|
| Oil or grease | Poor adhesion |
| Loose rust | Delamination |
| Dust | Weak bonding |
| Old loose coating | Peeling |
| Excess moisture | Blistering or adhesion problems |
| Cracks/structural defects | Continued substrate movement or damage |
| Poor surface profile | Reduced bond |
| Sharp edges/irregularities | Laminate defects |
The protective coating system will not be able to make up for the inadequate substrate preparation.
FRP Lining Preparation Checklist
Before application, check:
✓ Inspected substrate conditions
✓ Removed rust and any loose material
✓ Removed oil and grease from substrate surface
✓ Removed any defective existing coating
✓ Repaired all cracks and substrate defects
✓ Obtained correct substrate surface profile
✓ Removed dust and any loose materials
✓ Checked moisture conditions
✓ Treated corners, joints and penetrations
✓ Inspected prepared surface before applying lining
The above checklist can be included in an industrial procedure.
Why Corners, Joints and Pipe Entries Need Extra Attention
Preparation of large surface areas is easier as compared to detailed preparation.
The following are areas that require careful consideration:
- Tank corners
- Welds
- Flanges
- Pipe penetrations
- Drains
- Expansion joints
- Crazing
- Penetrations
Such areas are hard to prepare because of their complexity and may pose weak spots in case of hasty preparation.
Joint, corner, drainage, pipe entry/penetration sites are especially emphasized by Plastic Fabricators when carrying out FRP lining procedures.
Surface Preparation Is Different for Every Project
No single process of preparation applies to all FRP lining jobs.
For instance, preparation of:
Chemical Tank – MS
Is different from:
Concrete Wastewater Trench
Which is different from:
Existing FRP Equipment
These variables among others such as the substrate, chemicals, temperature, condition and resin should dictate the process of preparation.
According to Plastic Fabricators, “its FRP lining specifications incorporate the substrate, chemicals, concentration, temperature, mechanical exposure, moisture, reinforcement and resin.”
What Should You Tell an FRP Lining Contractor?
A proper request should include:
- Substrate material
- Dimensions of the tank/pit/trench
- Chemical or process fluid
- Chemical concentration
- Temperature
- Surface condition at present
- Coating, if any
- Desired lining thickness, if available
- Pictures
- Drawings
- Site conditions
For instance:
FRP lining for MS chemical storage tank for 98% sulphuric acid at 60°C. Tank capacity: 5 KL. Desired lining thickness: 3 mm.
Complete information helps the manufacturer analyze the substrate and choose the appropriate lining system rather than just assuming. Plastic Fabricators provides an identical request form for project-based FRP lining needs.
Final Takeaway
FRP lining is only as good as the substrate that lies beneath it.
Surface preparation aids in removal of contamination, rectification of substrate issues and creation of the necessary substrate condition for proper adhesion and performance of the lining system.
Prior to installing FRP lining, it is important to conduct inspection of substrate, cleaning from contamination and weak substrate, attain necessary substrate condition, test moisture if necessary and focus on corners, joints, drains and penetrations.
Industrial surface preparation process must be based on the substrate, chemical exposure, temperature and lining system and cannot be generalized for all projects.
Do you require FRP lining for MS tank, concrete tank, trench, pit or industrial surface? Provide us with substrate details, chemical exposure, temperature and photos of your site to receive our recommendations.