Tiếng Việt
中文 (中国)
Two factories with the same area and the same coating system, but different quotations — the most common cause lies in something not immediately visible: the condition of the concrete substrate. This article explains the 5 substrate variables that decide price, and what a substrate survey involves, so you understand why a quotation cannot be finalised before the substrate is seen.
This article is about surveying and assessing the substrate before a quotation. It differs from the article on technical moisture-barrier solutions for damp substrates (Epoxy coating on damp floors: moisture-barrier solutions) and from the article on the substrate preparation process (Concrete floor preparation before epoxy coating): here, the only question is how the substrate affects the quotation.
Why does the same area but a different substrate mean a different price?
An epoxy coating only lasts when it bonds firmly to the substrate. A weak, damp, cracked, oil-contaminated substrate, or one still carrying an old coating, forces the contractor to add preparation items before coating — and each item is a cost. A responsible quotation therefore has to reflect the real substrate; it cannot apply one general rate to every substrate. A quotation issued before the substrate has been surveyed is really a quotation based on an assumption about the substrate; when work reveals a different substrate, variations are hard to avoid.
Five substrate variables that decide the quotation
1. Substrate moisture
A damp substrate is the leading cause of blistering and peeling after application (see also Epoxy floor blistering caused by substrate moisture). Moisture can be measured in several ways: the qualitative plastic-sheet test under ASTM D4263, moisture vapour emission rate (MVER) under ASTM F1869, and in-slab relative humidity under ASTM F2170. Commonly cited reference thresholds for standard epoxy are MVER under 3 lb/1,000 sq ft/24h and relative humidity under 75–85% — but these are only general reference thresholds; the technical data sheet (TDS) of the specific product is the deciding basis for each coating system.
2. Strength and surface soundness: dust, powder, weak layers
A low-grade substrate, a friable surface, heavy cement dust or a weak screed layer will not hold a coating, however good the coating is. In such cases the weak layer must be ground away down to sound concrete, sometimes with surface strengthening — items a good substrate does not need.
3. Flatness, undulation and levels
A substrate with hollows, local slopes or level differences between zones needs local levelling before coating. With the self-levelling LevelFlow system, the poorer the substrate flatness, the harder it is to control the amount of levelling material — another reason why a quotation must be tied to an actual survey.
4. Cracks, settlement and expansion joints
Hairline cracks, structural cracks, uneven settlement or failed expansion joints all need separate treatment before coating, and the treatment differs with the cause. Coating over an untreated crack only hides it temporarily; the crack will reflect through the coating surface again.
5. Contamination and old coatings
Oil and grease, chemicals, old paint, adhesives or a peeling old epoxy coating all hinder adhesion. Each type of contamination needs a different cleaning or removal method — degreasing differs from grinding off an old coating — so costs cannot be the same for different substrates.
What does a substrate survey involve?
- Observation and recording: walking the whole floor, photographing cracked, damp, stained and peeling areas, and noting the location of each zone.
- Moisture measurement: using one or a combination of the methods above, measured at many points, especially ground floors, basements and areas that have suffered water ingress.
- Surface soundness check: scraping, tapping, adhesion testing or hardness measurement where equipment is available, to determine whether a weak layer needs to be ground away.
- Defining the scope of treatment: from the results above, the contractor lists the substrate preparation items zone by zone, as the basis for an itemised quotation.
Three substrate scenarios, described without prices
Good substrate: sound, dry, flat, clean concrete — preparation is mainly grinding to create a key, cleaning and vacuuming before priming. Average substrate: some zones need crack repair, local levelling or light moisture treatment — the quotation should state each zone clearly. Poor substrate: high moisture, many cracks, contamination or a widespread weak layer — a full preparation sequence is needed before coating, and a moisture-tolerant coating system may be required if the TDS allows it. Specific prices for each scenario follow the quotation for each project; this article gives no surcharge rate for any substrate type.
A difference to remember: new substrates versus old substrates
A new substrate that has not yet cured or fully dried differs from an old substrate used for many years: the new one carries risks of residual moisture and shrinkage, the old one risks wear, contamination and old coatings. The minimum concrete age before coating depends on the TDS of each product; there is no single figure for all coating systems. Basement and ground floors also differ from upper floors in the risk of rising moisture from below.
Questions to ask the contractor after the survey
- What are the moisture readings for each zone, measured by which method, and how do they compare with the TDS of the proposed coating system?
- Which substrate zones need treatment, by what method, and is that item already in the quotation or charged as a variation?
- If work reveals a worse substrate than the initial survey showed, how are variations recorded and the price agreed before work continues?
Frequently asked questions
Can photos of the substrate sent to the contractor replace an on-site survey?
Photos help the contractor form an initial picture and prepare, but they cannot replace on-site moisture measurement and surface soundness checks. A formal quotation should still be based on a direct survey.
If the substrate looks good to the eye, is moisture measurement still needed?
Yes. Moisture inside concrete cannot be seen with the naked eye, and ground floors and basements need measuring most of all. Skipping this step is a common cause of blistering after application.
Why is a quotation without a survey often cheaper at first but dearer later?
Because that quotation assumes a good substrate and has not yet priced the preparation items. When work reveals a poor substrate, the additional items appear as variations.
Book a substrate survey: send photos and video of the existing substrate via Kadier’s quotation page or contact page, or message Zalo 0899355489 (Hotline/Zalo 0899355489, WeChat wxid_95o54joujyrr12).
Illustration: Sergei Starostin / Pexels (stock photo, not a Kadier project).
