Product
HPMC for construction
The ALC-H series, eight published grades from 400 to 250,000 mPa·s, each with batch data and a TDS.
Application
Cellulose ether and RDP for wall putty
Wall putty is a thin skim coat of binder, filler and cellulose ether that has to bond to the wall, sand smooth and not crack as it dries. The ether decides water retention and workability; the polymer decides water resistance. Starting formulations for interior, water-resistant, flexible and exterior putty are below.
On site
What goes wrong, what to check, and which additive moves
Read the columns left to right before touching the formulation: the substrate and the water account for more failures than the additive does.
| Issue on site | What to check | Additive direction |
|---|---|---|
| The surface powders or dusts when sanded | Binder level, filler grading, whether the wall was primed, and how thick the coat went on | Cellulose ether first, then PVA or RDP. A surface that dusts under the finger is usually under-bound, not over-dry |
| Cracks appear across the wall as it dries | Water ratio, thickness of the pass, whether the substrate was dampened, and the ether level | Cut the water and the thickness before changing the formulation. The ether holds water; it does not stop shrinkage |
| The putty shells off, or blisters soon after application | Dust and loose material on the substrate, suction, damp, and whether the coat was too thick for one pass | Nothing in the formulation fixes a dusty wall. Prime first, then review PVA or RDP level and the pass thickness |
| It cannot be sanded smooth — the paper drags | Ether grade against the filler, tack from RDP or PVA, and whether the dosage crept up over time | Move down one viscosity step before cutting the dosage: a lower-viscosity grade sands more easily at the same water retention |
| It softens or chalks when it gets wet | RDP level, cement content, and whether the water-resistant formulation was actually used | Water resistance comes from the polymer film — 6 kg/t RDP with 150 kg/t cement in our water-resistant line. A hydrophobic additive on its own does not make a putty waterproof |
| Pinholes and a pitted surface after drying | Mixing speed, resting time before use, air trapped in the paste, and the pass thickness | Rest the mix after mixing so the air can escape. No additive replaces that, and a faster mixer only puts more air in |
Work down the middle column before the right one. Changing two things at once is how a formulation trial turns into a rumour.
Mechanism
Where each additive fits
Four components, four jobs. None of them substitutes for another, which is why swapping one for more of another rarely fixes a mix.
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HPMC — keeps the water where the binder is
A dry wall takes water out of a thin coat quickly. The ether holds it long enough for the binder to film rather than being drawn into the substrate, which is the difference between a coat that cures and one that dusts.
-
RDP — the film that survives water
Redispersible powder forms a continuous polymer film through the filler skeleton. It is what keeps the coat from softening when it is soaked, and what gives the flexible formulation its tolerance to movement in the wall.
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PVA — green strength and sandability
In interior grades PVA gives the coat enough early cohesion to be sanded the next day, which is why the interior and the base-coat formulations carry it while the water-resistant one does not.
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Starch ether and hydrophobic powder — workability and water beading
The starch ether thickens the paste so it stays where the trowel leaves it, and the hydrophobic powder makes water bead on the surface. Both are in the flexible formulation, and neither replaces the polymer film underneath.
The part that is not on the label
Adding more binder does not rescue a dusty wall. Most putty complaints are substrate problems — dust, suction, damp or a coat that went on too thick — and a formulation change only hides them until the first heating season.
Starting formulations
Formulations to start from
Taken from the formulation sheet we work from in production, and published here in full — including the levels we would normally keep to ourselves.
Interior and water-resistant putty — kilograms per tonne
The two formulations most orders start from. Binder and filler are the balance of the batch.
| Component | Interior | Water-resistant |
|---|---|---|
| Portland cement | 100 | 150 |
| Ground limestone 325 | 900 | 850 |
| HPMC — ALC-H1000, 100,000 mPa·s | 4.0 | 4.0 |
| PVA | 1.0 | — |
| RDP | — | 6 |
The difference between the two columns is the binder: interior putty relies on PVA for cohesion, water-resistant putty on 6 kg of redispersible powder with more cement behind it.
Flexible and exterior putty — kilograms per tonne
Flexible putty for substrates that move, exterior putty for walls that see rain and sun.
| Component | Flexible | Exterior |
|---|---|---|
| Portland cement | 150 | 220 |
| Ground limestone | 650 | 580 |
| Quartz 200 | 150 | — |
| Sand, 80–120 mesh | — | 200 |
| HPMC — ALC-H1000 in flexible, ALC-H1500 in exterior | 4.0 | 4.5 |
| RDP | 4 | 6 |
| Starch ether | 0.5 | — |
| Hydrophobic powder | 2.5 | — |
The flexible column trades cement for quartz to keep the coat from shrinking, and adds starch ether and hydrophobic powder. The exterior column goes the other way: more cement, graded sand, and the higher-viscosity ether to hold water against suction and wind.
Base coat under stone paint — kilograms per tonne
A coarser, more highly bound coat that carries the texture and the weight of a stone-paint finish.
| Component | Base coat |
|---|---|
| Portland cement | 400 |
| Hydrated lime | 40 |
| Sand | 445 |
| Ground limestone 400 | 100 |
| HPMC — ALC-H1000, 100,000 mPa·s | 4.5 |
| RDP | 6 |
| PVA | 1.5 |
| Wood fibre | 2 |
The highest cement content of the five formulations, with lime for workability and wood fibre to hold the coat together while it cures. It is a base coat, not a finish: the stone paint sits on top.
These are starting points, not specifications
These are starting formulations, not specifications. Cement source, sand grading, filler absorption, mixing water and site climate all move the result. Run a trial batch with the materials you actually buy, and adjust the cellulose ether and the polymer level before production.
Grades
Our grades for this application
Putty uses a higher-viscosity ether than tile adhesive, because the coat is thin and the wall takes water out of it fast.
| Grade | Viscosity | Role in this application | Typical dosage |
|---|---|---|---|
| ALC-H1000 | 100,000 mPa·s | Interior, water-resistant, flexible and base-coat formulations | 4.0 kg/t (0.40%); 4.5 kg/t in the base coat |
| ALC-H1500 | 150,000 mPa·s | Exterior: holds water against suction, sun and wind on an exposed wall | 4.5 kg/t (0.45%) |
Grade codes come from the nominal viscosity: ALC-H1000 is the 100,000 mPa·s grade and ALC-H1500 the 150,000 mPa·s one. Batch viscosity is released within −10% / +20% of nominal, measured by the method and under the conditions stated on the COA. Moving up a viscosity step gives more water retention per gram, not a better coat — over-dosed putty drags under the trowel and sands badly.
Diagnosis
Common failures and how to diagnose them
One column for what you see, one for what usually causes it, and one for the single parameter to change first.
| Symptom | Most likely causes | Adjust this first |
|---|---|---|
| Hairline cracks the morning after application | Too much water; the pass went on too thick; hot dry air; strong suction from the substrate | Water and thickness first — on a first coat the formulation is rarely the cause |
| The surface powders under a finger | Under-bound mix; over-sanding; ether level too low for the filler | Binder level, then the ether level, then the sanding grit |
| The paint or the tiling fails later, on a puttied wall | Putty too soft or too water-sensitive under the finish; dust left on the surface; no primer | The putty, not the finish: a water-resistant grade plus a primer is the usual answer |
| A repair patch shows through the paint | Different absorption between the patch and the field; uneven thickness; a different batch | Same batch, same thickness, prime the patch and feather the edge |
| The coat pulls away at a corner bead or a joint | Movement in the substrate; no reinforcement; too much material built up at the bead | Reinforce across the joint and thin the coat at the bead before changing the formulation |
Diagnose in the order the columns are written. A symptom that appears after two weeks is a different fault from one that appears overnight.
Acceptance
How to test and accept the mix
What to measure, the method that makes the number comparable, and the shortcut that makes a failing batch look like a passing one.
| What to test | How it is measured | The usual false pass |
|---|---|---|
| Bond strength to the substrate | EN 1015-12 pull-off, on the substrate the job actually uses | Tested on a smooth steel or plastic mould, which reads far higher than a real wall |
| Water absorption of the water-resistant grade | EN 1015-18 capillary absorption on a cured specimen | A splash test, or a specimen cured longer than the standard allows |
| Flexibility and crack bridging | Draw-down on a flexible substrate, bent after full cure | Judged by hand while the coat is still green, which passes almost anything |
| Sandability | A draw-down sanded after 24 hours with a stated grit | Sanded immediately, before the film has set, then reported as easy to sand |
| Workability and open time | Trowel a coat and time how long it stays workable in the conditions of use | Tested in the shade in the morning and then used on a sunlit wall in the afternoon |
| Incoming HPMC viscosity | The COA value against the nominal, within −10% / +20% | One COA reused across deliveries — match the batch number on the COA to the bags |
Ask for the batch number on the COA and match it to the bags before the material reaches the mixer — that one check catches most of the rest.
Where it is used
Wall putty in the field
Interior walls and ceilings — skim coat over cement or gypsum plaster
Water-resistant putty in kitchens, bathrooms and wet rooms
Exterior walls — exterior and flexible formulations
Base coat under stone paint and textured finishes
Patch repairs and levelling before painting
Service
What you get with the order
Free sample
A 200 g sample from stock, so the first trial batch runs on your filler, not ours.
Batch data
A COA with every batch: viscosity released within −10% / +20% of nominal, with the method behind it.
Lead time
5–15 days from order confirmation, from 1 metric ton per grade, shipping to 30+ export markets.
Enquiries are answered within 12 working hours. Samples ship from stock; the trial batch stays your decision.
FAQ
Wall putty: questions buyers ask
How much HPMC does a wall putty need?
4.0–4.5 kg per tonne — 0.40–0.45% — covers the interior, water-resistant, flexible and exterior formulations we start from. Interior, water-resistant and flexible putty sit at 4.0 kg, the base coat and the exterior putty at 4.5 kg because the wall takes water out of the coat faster. Below that the coat dusts and drags; well above it the paste turns sticky and sands badly. Confirm it on your own limestone before a production run.
Should I use 100,000 or 150,000 mPa·s for putty?
Start at 100,000 mPa·s, which is ALC-H1000, and move to 150,000 — ALC-H1500 — only when the wall is exposed. Four of the five formulations use the 100,000 grade: interior, water-resistant, flexible and the base coat under stone paint. The exterior formulation steps up because sun, wind and suction all pull water out of the coat at once. A higher-viscosity ether gives more water retention per gram, so the dosage does not simply scale up.
Why does my putty crack as it dries?
Cracks are usually shrinkage, and shrinkage comes from water and from coat thickness long before it comes from the ether. Cut the water, keep the pass thin, and dampen a very absorbent wall before the first coat. The cellulose ether holds the mixing water long enough for the binder to film, but it cannot stop a coat that was mixed wet from shrinking as that water leaves. If cracks persist at the same thickness, move to the flexible formulation.
What actually makes a putty water-resistant?
A continuous polymer film, which in our formulation means 6 kg per tonne of RDP with 150 kg of cement behind it. The film closes the pores water would otherwise travel through, so the coat does not soften or chalk when it is soaked. A hydrophobic powder makes water bead on the surface, which looks convincing in a demo but does not replace the film — that is why the water-resistant column carries RDP and the interior column does not.
Can the same formulation be used inside and outside?
No, and the difference is not cosmetic. Interior putty is built on 100 kg cement and 900 kg limestone with PVA for cohesion; the exterior formulation carries 220 kg cement, graded sand and the 150,000 mPa·s ether to survive rain, sun and suction. Using the interior mix outside usually looks fine for one season and then fails. The flexible formulation is a separate case again: it is for substrates that move, and it works indoors or out.
How do I test a putty before accepting a delivery?
Ask for the batch COA, then test bond strength to EN 1015-12 on the substrate the job uses, capillary water absorption to EN 1015-18 for a water-resistant grade, and a draw-down for sandability. The common false pass is testing adhesion on a smooth mould instead of a real wall, which flatters every formulation. Match the batch number on the COA to the bags on the pallet before the material goes into the mixer.
Send us your wall putty formulation
Tell us the substrate, the class you have to reach and the materials you buy locally. The reply includes the TDS, a grade recommendation and a free 200 g sample.