Primer calculator
Most floor primers are sold as a concentrate in kg or gallon containers and thinned with water on site, and the right dilution depends on the substrate. Pick yours and the calculator gives the concentrate to buy, the water to add and the containers to order, using the dilution table of a manufacturer data sheet.
Calculate the quantityHow much primer do you need?
Enter the floor area, pick the substrate and whether your primer is a concentrate or ready to use. The substrate sets the dilution and a consumption figure from a current manufacturer data sheet for a primer concentrate or for a typical ready-to-use deep primer; replace it with the figure on your bucket.
Default value – replace it with the manufacturer’s figure.
About 5 % stays in the roller, the tray and the bucket.
Optional – shows the material cost for the rounded-up amount.
You need
Enter a floor area to see the quantity.
The result updates as you type – no button to press.
Amount = area × consumption per coat × coats × (1 + allowance). Water = amount × water parts of the dilution.
The figures assume a sound, clean, dust-free substrate. The data sheet of the product you buy has the last word: if its table differs, type its figure into the consumption field. A dispersion primer weighs about 1 kg per liter, so kg and liter containers hold the same amount.
Judging the substrate
- Do the water test on the cleaned floor: sprinkle a few drops. If they soak in and darken the surface within about a minute, the substrate is absorbent; if they stay as beads for several minutes, it is dense or sealed.
- Dense surfaces (compacted cement screed, precast concrete, terrazzo, old tiles) take the strongest mix, 1 part concentrate to 0.5 parts water, at about 0.2 kg of concentrate per m² (0.49 gal per 100 sq ft) according to a current manufacturer data sheet. On old tiles a quartz-filled bonding primer is the alternative; take its rate from its own data sheet.
- Raw concrete takes 1 : 1 at about 0.15 kg per m², porous cement screed 1 : 5 at about 0.03 kg per m². The more absorbent the floor, the thinner the mix: the concentrate figure falls while the mixed primer you roll on stays at roughly 0.2 to 0.3 kg per m².
- Calcium sulfate (anhydrite) screed must be sanded and vacuumed before priming; a typical concentrate is then thinned 1 : 3 at about 0.05 kg of concentrate per m². Check its residual moisture first: at most 0.5 % by the calcium carbide method.
- Let the primer dry to a clear, thin film before the leveling compound or tile adhesive goes on: usually a few hours at 20 °C, longer in a cold or humid room. On old substrates with adhesive residue data sheets ask for drying overnight.
Dilution and consumption by substrate
Concentrate per m² and coat from a manufacturer data sheet for a primer concentrate (29 June 2022); ready-to-use deep primer from a typical product data sheet (100 to 250 ml per m² by absorbency):
| Substrate | Mix (primer : water) and concentrate |
|---|---|
| Smooth, dense: compacted screed, precast concrete, terrazzo, old tiles | 1 : 0.5, ≈ 0.2 kg/m² (0.49 gal per 100 sq ft) |
| Raw concrete slab | 1 : 1, ≈ 0.15 kg/m² (0.37 gal per 100 sq ft) |
| Calcium sulfate screed, sanded | 1 : 3, ≈ 0.05 kg/m² (0.12 gal per 100 sq ft) |
| Porous, very absorbent cement screed | 1 : 5, ≈ 0.03 kg/m² (0.07 gal per 100 sq ft) |
| Chipboard | undiluted, ≈ 0.3 kg/m² (0.74 gal per 100 sq ft) |
| Ready-to-use deep primer | undiluted, 0.1 to 0.25 l/m² (0.25 to 0.6 gal per 100 sq ft) |
What this calculator does — and does not
It does
Work out the concentrate or ready-to-use primer to buy, the water to mix it with and the number of containers, from your area, substrate, product, coats and an allowance for the roller and tray.
It does not
Measure how absorbent or how damp your floor actually is (the water test and a calcium carbide moisture reading on site do that), or plan the flooring on top.
Priming step by step
From the bare floor to a primed surface that is ready for leveling compound or tile adhesive.
Check that the floor is ready
The substrate must be dry, sound and free of dust, oil and release agents. On new screed have the residual moisture measured with the calcium carbide method: cement screed at most 2.0 %, calcium sulfate screed at most 0.5 %. Chisel out loose patches and close cracks.
Sand and vacuum
Sand the binder skin off calcium sulfate screed and any loose surface off cement screed, then vacuum the whole floor with an industrial vacuum cleaner. A broom leaves fine dust behind, and primer on dust does not bond.
Do the water test and choose the mix
Sprinkle water on a few spots. Pick the substrate row from the table: the denser the floor, the less water goes into the mix. Type the figure from your own bucket into the calculator if it differs.
Mix the primer
Pour the concentrate into a clean bucket, add the water from the result line with a measuring jug and stir well. Mix only what you will roll the same day.
Roll it on evenly
Apply a thin, even coat with a roller, a primer broom or a brush, working from the far wall towards the door. Spread out every puddle while it is wet: a pooled film dries glossy and the leveling compound cannot grip it.
Let it dry to a clear film
Wait until the film is clear and no longer tacky, usually a few hours at 20 °C and overnight on old substrates. Keep dust off the primed floor, then pour the leveling compound or comb the tile adhesive within the time its data sheet allows.
Which primer for which floor
| Substrate | Primer | Mix (primer : water) | Concentrate per m² | Before you prime |
|---|---|---|---|---|
| Compacted cement screed, precast concrete | Dispersion primer concentrate | 1 : 0.5 | ≈ 0.2 kg | Vacuum; residual moisture at most 2.0 % |
| Raw concrete slab | Dispersion primer concentrate | 1 : 1 | ≈ 0.15 kg | Remove laitance and release agents |
| Porous cement screed | Dispersion primer concentrate | 1 : 5 | ≈ 0.03 kg | Second coat if the first one vanishes |
| Calcium sulfate screed | Dispersion primer concentrate approved for it | 1 : 3 | ≈ 0.05 kg | Sand and vacuum; residual moisture at most 0.5 % |
| Old tiles, terrazzo | Dispersion primer, or a quartz-filled bonding primer | 1 : 0.5, or undiluted | ≈ 0.2 kg, or per data sheet | Degrease; replace hollow-sounding tiles |
| Chipboard | Dispersion primer concentrate | undiluted | ≈ 0.3 kg | Screw down every loose board |
| Mastic asphalt, paint, plastic, epoxy or bitumen residue | Special bonding primer named on the data sheet | ready to use | per data sheet | An ordinary dispersion primer does not hold here |
Tools and materials
| Item | Quantity |
|---|---|
| Primer concentrate or ready-to-use primer | from the calculator |
| Industrial vacuum cleaner | 1, before priming |
| Floor sander or grinder (calcium sulfate screed) | rent for a day |
| Clean bucket and stirring stick, or a drill with a slow paddle | 1 per room |
| Measuring jug for the water | 1 |
| Roller with extension pole, or a primer broom | 1, plus a brush for edges and corners |
| Roller tray | 1 |
| Calcium carbide moisture reading (new screed) | from the screed installer or a floor layer, at least one per room |
| Gloves and safety glasses | 1 set |
Common mistakes
Priming a dusty floor
How to spot it: The dried primer rubs off as gray powder; the leveling compound sounds hollow later
Fix: Vacuum with an industrial vacuum cleaner, not a broom, and prime again
Leaving puddles
How to spot it: Glossy patches or a skin that peels off
Fix: Spread puddles out with the roller or broom while wet; scrape off dried skins
Too much water on a dense floor
How to spot it: Water drops bead up, yet the primer was mixed 1 : 3 or thinner
Fix: Use 1 : 0.5 on dense surfaces as the data sheet says
Undiluted primer on porous screed
How to spot it: A shiny film sits on top instead of soaking in; air bubbles rise in the leveling compound
Fix: Thin it as the table says so it penetrates, and roll a second coat if needed
Covering a tacky film
How to spot it: A fingerprint stays in the primer
Fix: Wait until the film is clear and dry; overnight on old substrates
Ordinary primer on old tiles or paint
How to spot it: Water beads up; the film peels off with adhesive tape
Fix: Degrease, then use the 1 : 0.5 mix or a quartz-filled bonding primer
Priming calcium sulfate screed without sanding
How to spot it: A shiny, soft binder skin on the surface
Fix: Sand, vacuum, then prime 1 : 3
When to call a professional
Priming is a job a careful amateur can do. Call a floor layer or the screed installer when the substrate itself is in doubt:
- The calcium carbide reading is above the limit, or the screed is younger than the drying time on its data sheet
- Underfloor heating that has not been heated up and recorded
- Cracks, hollow-sounding areas or a surface that crumbles under a scratch with a nail
- Old adhesive residue of unknown type, mastic asphalt or bitumen
- A damp or fast-track screed where an epoxy primer as a moisture barrier is being considered
Frequently asked questions about primer
How much primer do I need per m²?
It depends on the dilution. With a typical primer concentrate you buy about 0.2 kg per m² for a dense floor (mixed 1 : 0.5), 0.15 kg for raw concrete (1 : 1), 0.05 kg for sanded calcium sulfate screed (1 : 3) and 0.03 kg for porous cement screed (1 : 5). A ready-to-use deep primer takes 0.1 to 0.25 l per m². Worked example: 20 m² (215 sq ft) of dense screed needs 4 kg of concentrate, 4.2 kg with the 5 % allowance, so one 5 kg container (about 1.1 gal, two 1 gal containers), mixed with 2.1 l (0.55 gal) of water.
Why does an absorbent floor need less concentrate?
Because it is primed with a thinner mix. On porous screed the primer has to soak deep into the pores instead of forming a film on top, so the data sheets add more water: 1 : 5 instead of 1 : 0.5. You roll on roughly the same amount of mixed primer, about 0.18 to 0.3 kg per m², but far less of it is concentrate.
How do I know which substrate I have?
Do the water test: drops that soak in within a minute mean absorbent, drops that bead up mean dense or sealed. Calcium sulfate screed is usually a flowing screed: very flat, light gray to beige, often with a thin binder skin that has to be sanded off; the builder or the screed installer can tell you. Old tiles, paint and sealed floors are dense: clean and degrease them and use the 1 : 0.5 mix or a quartz-filled bonding primer.
How many containers is that, and how does it round?
The calculator divides the amount by your container size and always rounds up, because you cannot buy part of a container. Concentrates are commonly sold in 1, 5, 10 and 20 kg containers; in the United States primers are sold by the gallon. A dispersion primer weighs about 1 kg per liter, so a kg figure and a liter figure are practically the same amount.
When do I need two coats?
When the first coat soaks in completely and leaves no film, which is typical on very porous cement screed and on sanded calcium sulfate screed under a cement-based leveling compound, and whenever the data sheet of the leveling compound asks for it. Let the first coat dry, then roll the second at the same dilution; the Coats field doubles the amount.
Planning the floor on top
Once the primer has dried, the free Autolay planner works out the tiles, planks or laminate for it — the material list and waste — from a photo of your floor plan, an IFC building model or a 3D scan.
Start planning
