Tile Adhesive Upgrade: From C1 to C2S1 (and What It Costs)

You have a C1 adhesive that works. Now the customer wants porcelain tiles, or 800 mm tiles, or an exterior wall. C1 will not hold. You have to upgrade to C2. This guide shows the path — what to add, what to remove, and what it costs.

Quick Answers

1. Do You Need to Upgrade?

C1 is enough when the tile is small, absorbent, and indoors. Check three things:

Tile size. Over 600 mm on one side → C2.

Water absorption. Below 0.5% (porcelain, vitrified) → C2.

Where it goes. Exterior, wet area, or over a flexible membrane → C2.

If one of these is true, C1 will fail. The tile has nowhere to grip, or the wall moves, and the bond breaks.

2. The Upgrade Path at a Glance

The pattern is simple: every upgrade is buying more polymer.

3. Each Step, What to Add

C0 → C1: Add the polymer

RDP: 5–10 → 12–18 kg/t (RD 7015H or RD 7003M)

Add starch ether 0.3–0.8 kg/t (anti-slip)

That is it. C0 and C1 share the same cement and sand.

C1 → C1T: Add anti-slip

Starch ether: 0.3–0.8 → 0.5–1.0 kg/t

Nothing else changes. T just means the tile does not slide down the wall.

C1 → C2S1: The real jump

RDP: 12–18 → 30–40 kg/t, and switch to a flexible grade (RD 8080F, Tg −8°C)

Add silica fume 15–40 kg/t — fills pores, passes the water immersion test

Remove inert filler (calcium carbonate) — no room for cheap filler

HPMC stays 2–3 kg/t

This is the step most people get wrong. They add RDP but skip the silica fume. Then the adhesive fails the water immersion test at 0.8–0.9 MPa instead of 1.0 MPa.

C2S1 → C2TES1: For large tiles

RDP: 30–40 → 45–55 kg/t

More fine sand (70–140 mesh) for longer open time

More fiber (2–4 kg/t)

4. What Each Step Costs

RDP is the most expensive additive. So the cost of upgrading is mostly the cost of more RDP.

Silica fume adds a little too, but it is cheaper than RDP.

The lesson: upgrading is buying polymer. Cut the RDP and the upgrade fails, no matter what else you add.

5. The Mistakes That Break the Upgrade

1. Adding RDP but skipping silica fume. The bond looks fine at 28 days dry. Then water immersion drops it to 0.8 MPa, and it fails. Silica fume is what gets you through the water test.

2. Trying to replace RDP with HPMC. HPMC gives water retention and workability. It adds nothing to hardened bond. No amount of HPMC replaces polymer.

3. Using the wrong RDP grade. S1 needs transverse deformation ≥2.5 mm. RD 8080F (Tg −8°C) stays elastic. RD 7003M (Tg 3°C) is too stiff and cracks. Match the Tg to the deformation.

4. Cutting cement to save money. C2 strength comes from cement + polymer together. Cut the cement and the whole formula weakens.

5. Upgrading only on paper. The formula changes, but the test does not. Run the four conditioning tests — standard, water, heat, freeze-thaw — before you call it C2.

6. CHARING Products by Step

7. FAQ

When do I have to upgrade from C1 to C2?

When the tile is porcelain (below 0.5% absorption), larger than 600 mm, or going on an exterior wall or wet area. C1 cannot grip a dense porcelain surface.

What is the single biggest cost of upgrading?

RDP. Going from C1 to C2S1 doubles the RDP from 12–18 to 30–40 kg/t, and RDP is the most expensive ingredient.

Can I skip the silica fume?

No. Without it, many C2 formulas fail the water immersion test. Silica fume fills the pores and makes the matrix dense enough to hold 1.0 MPa underwater.

How far can I push RDP down to save money?

In C2, not below 25 kg/t. Below that it will not reach 1.0 MPa. In C1, not below 12 kg/t. Cutting further fails the water and freeze-thaw tests.

Does more RDP always mean better?

Up to a point. RDP raises flexibility and bond, but too much raises cost and lowers compressive strength. Match the dosage to the grade — 30–40 for C2S1, 45–55 for large tiles.

Note: All formulas are based on Northern China temperature and humidity. Adjust HPMC viscosity and dosage to your local climate. Always run lab tests with your own raw materials before production.

For technical inquiries: info@sdcharing.com 

Shandong Charing Industry Co., Ltd. 

www.sdcharing.com