Waterproofing Admixture for Concrete: Integral Compounds and Plasticizers by Grade

Water seepage in new concrete: check the pour before choosing an admixture

Water gets through concrete along the fine capillaries left behind when excess mixing water dries out. A waterproofing admixture for concrete, also called an integral waterproofing compound, is a liquid added to the mix that narrows and lines those capillaries, so the concrete or plaster resists water through its full depth. A plasticizer works on the same problem from the other side: it gives the workability with less water. This page covers which chemical to mix in concrete for waterproofing, how much waterproofing liquid per cement bag, the plasticizer for each grade, and curing. Six checks decide what your pour needs.

Find the right integral waterproofing compound and plasticizer

Match the pour to one route. Each route takes you to its section.

An admixture makes good concrete better. It does not rescue a wet, badly compacted or uncured mix. Dose, water, compaction and curing decide the result together.

Concrete waterproofing admixture finder

This page covers four Armstrong integral waterproofing compounds and five plasticizers for structural concrete, and each has its place. Answer three questions for a starting combination, then confirm the dose with a site trial and an Armstrong expert.

How much waterproofing liquid per cement bag: integral compounds and their dosage

Every Armstrong integral waterproofing compound is a liquid dosed per 50 kg bag of cement. The dose differs because the formulations differ, and each is effective at its own stated dose. All four suit foundations, slabs, tanks, bathrooms and plaster. Pick by how the concrete is made and what the specification asks for, and an Armstrong expert helps you choose.

1. 1
   Count the cement, then measure the compound

   The dose follows the cement, not the volume of the mix. Count the bags in the batch and measure the liquid for that number.Why: The compound works on the cement, so the dose follows the bags in the batch and not the volume of the concrete.
2. 2
   Add it to the gauging water

   Stir the compound into the mixing water, or add it to the wet mix. Do not pour it onto dry cement. CONPROOF 500 is first mixed into 3 to 5 litres of water.Why: Poured onto dry cement it does not mix evenly. In the water it spreads through the whole batch.
3. 3
   Hold the water down

   Use only enough water for a workable mix. At 200 ml per bag, CONPROOF LW 200 allows the gauging water to be reduced by up to 15%, and the reduction is what raises strength and cuts permeability.Why: Extra water leaves channels that no compound can close. Less water gives denser concrete.
4. 4
   Keep admixtures separate

   Where a plasticizer is used in the same mix, dispense the two separately. Do not premix CONPROOF LW 200 with another admixture.Why: Admixtures can react with each other when premixed. Dispensing them separately avoids that.
5. 5
   Check the cement

   The compounds suit Portland, pozzolana and sulphate-resisting cements. They are not used with High Alumina Cement.Why: The compounds are tested with certain cement types. A different cement can change how they work.
6. 6
   Run a site trial

   Aggregates and sand vary from site to site. A trial mix fixes the dose within the stated range before the main pour.Why: Sand and aggregate differ from site to site, so a trial mix fixes the dose inside the stated range before the main pour.

How to add waterproofing to ready-mix concrete

Ready-mix arrives batched, so the compound cannot go into the gauging water. CONPROOF RMC ADMIX 88 is a free-flow liquid made for this. It is poured into the transit mixer at site, 4.2 to 5 litres for a 6 cubic metre load, and the drum is rotated continuously for 3 to 4 minutes before the concrete is unloaded. CONPROOF No. 1 can also be added to the transit mixer at site and rotated for 3 to 5 minutes.

Waterproof plaster mix: the compound in plaster, mortar and screed

Plaster is thin and exposed, so it gains the most from a compound. CONPROOF 500 at 500 ml per bag is made for plastering and concrete, and CONPROOF No. 1 at 100 ml per bag is listed for external wall plaster and bathroom plaster. In Armstrong's bathroom sequence the protective plaster over the membrane is a 1:3 cement and sand mix with CONPROOF 500, and the cove is a 1:4 mix with CONPROOF LW 200. Cure plaster for at least the first 7 days.

Plasticizer for concrete by grade: CONSPLAX and ROOFPLAST dosage per bag

The water-cement ratio decides most of what concrete becomes. Less water gives a denser, stronger, less permeable concrete, but a dry mix cannot be placed or pumped. A plasticizer gives the workability without the water. Armstrong makes a plasticizer or superplasticizer for each band of grades. They differ by fit, and the mix design decides which one is used.

The grade bands are from Armstrong's grade guide. The doses are per 50 kg bag of cement, and a site trial fixes the dose inside the range.

1. 1
   Take the grade from the mix design

   The structural engineer or the ready-mix plant sets the grade and the target slump. The plasticizer follows from that.Why: The grade and slump come from the structural design. The plasticizer follows them and does not change them.
2. 2
   Dose within the stated range and trial it

   Start inside the range in the table and fix the dose by a site trial with your cement, sand and aggregate. Over-dosing a superplasticizer gives very high workability and delays setting.Why: A trial with your own cement and sand finds the dose that gives the slump and strength needed.
3. 3
   Add it to the mix, not to dry cement

   For CONSPLAX 411 R, dissolve 1 litre in 49 litres of clean water and use 1 litre of that batch per bag of cement, which gives the 20 ml dose. Do not exceed 25 ml per bag.Why: The plasticizer must disperse through the wet mix. On dry cement it clumps.
4. 4
   Keep it apart from other admixtures

   ROOFPLAST SP 45 is added on its own and never premixed. ROOFPLAST PC 455 is not used alongside naphthalene based plasticizers.Why: Some plasticizers do not tolerate others in the same mix. They are added on their own.
5. 5
   Use the retardation, or plan for it

   ROOFPLAST SP 45 holds the concrete workable for 4 to 5 hours, which is how cold joints are avoided in a large pour. In a small pour, allow for the later set.Why: A plasticizer that holds the mix workable for hours helps avoid cold joints in a long pour, and the finishing has to be planned for it.
6. 6
   Check the cement type

   ROOFPLAST SP 25 and ROOFPLAST SP 35 are not compatible with High Alumina cement. ROOFPLAST PC 455 is compatible with micro silica, GGBS and fly ash blends.Why: Some plasticizers are not compatible with high alumina cement or with other admixture families.

How to cure concrete without water: place, compact and cure

The admixture is one part of watertight concrete. The rest is site practice: the right amount of water, graded aggregate, full compaction and curing. Proper curing in the first seven days is when the cement gel forms and closes the voids, pores and capillaries. Concrete that dries in the first days stays porous, whatever was in the mix.

1. 1
   Control the water

   Use just enough water for a workable mix. Excess water causes bleeding and segregation and leaves continuous water channels through the concrete.Why: Too much water causes bleeding and leaves water channels through the concrete.
2. 2
   Use well-graded aggregate

   The sand should carry enough fine particles and the aggregate should be well graded, so the mix packs densely.Why: A well-graded mix packs densely, leaving fewer voids for water to travel through.
3. 3
   Compact fully

   Honeycombs and voids are open paths for water. No admixture closes them.Why: Honeycombs and voids are open paths for water, and no admixture closes them.
4. 4
   Treat construction joints

   Where a pour stops and restarts, ROOFEX is applied at the construction joint as a slurry or dry powder at 1.5 kg per sq.m, and ROOFEX COP is dry-packed at the same rate before the next pour. Where new concrete is cast against old, ROOFBOND EP is brushed on and the concrete is placed while it is still tacky.Why: A joint is a plane where the old and new concrete never fully bond, so it is sealed on its own.
5. 5
   Cure from the first day

   Water-cure for at least seven days, or spray a curing compound. IS 456:2000 asks for at least 7 days of moist curing with ordinary Portland cement and at least 10 days with blended cements or mineral admixtures.Why: The cement forms its gel and closes the pores in the first seven days. Concrete that dries out in that time stays porous whatever is in the mix.
6. 6
   Spray the curing compound at the right time

   ROOFEXCURE WB is sprayed as soon as the slab is free of visible surface water, typically 1 to 2 hours after placing. On shuttered concrete and precast elements it goes on as soon as the formwork is removed. Hold the nozzle about 450 mm from the surface and pass back and forth for an even white film.Why: Sprayed too early it washes into the surface, and too late the concrete has already begun to dry. Timing keeps the film continuous.

A curing compound is a film on the surface. Do not spray it on standing water or in rain. Crystalline coatings are cured by fog or mist spray and are not covered with a membrane curing compound.

Is an integral waterproofing compound enough? Where concrete still needs more

An integral compound waterproofs the body of the concrete. It does nothing for a joint, a pipe sleeve, a crack or a honeycomb, and those are where most leaks start. So the compound supports a surface membrane in exposed and wet locations and does not replace it.

Seeping concrete: grout through drilled holes before any lining goes on

When water leaks, seeps or sweats through porous, honeycombed or cracked concrete, it has to be stopped inside the concrete first. This is the standard negative-side method for tanks, pools, basements, lift pits and retaining walls. A lining laid over concrete that is still seeping is pushed off by the water behind it: it blisters, lifts and fails. Grouting through drilled holes fills the internal voids and capillaries along the path of the water, so the surface is dry and sound before the coating or membrane goes on. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Drill the injection points

   Drill 12 to 14 mm holes with an electric drill into the leaking or honeycombed zone, to the depth the member needs (14 to 16 mm on thick retaining walls).Why: The holes intercept the pathways the water is travelling along, so the grout reaches the voids instead of just sitting on the surface.
2. 2
   Fix the nozzles

   Fix a rubber injection nozzle in each hole with a quick-setting putty of cement mixed with the set accelerator RAPIDSTRONG QS 113. For active flow, the single-component plugging compound RAPIDSTRONG PLUG can be used to fix the nozzle instead.Why: The nozzle must be locked into the hole before pumping starts. If it is not, the pressure blows it out and the grout runs back out of the hole.On site: The datasheet gives RAPIDSTRONG QS 113 at 500 ml to 2 L per 50 kg of cement and asks for a site trial, so trial the dose on the job before fixing every nozzle.
3. 3
   Seeping or sweating concrete: cement slurry

   Mix a cement slurry with a non-shrink grout additive and pump it into each nozzle with a grout pump at about 140 psi, until that point refuses to take any more. Any of three additives can be used: RAPIDSTRONG GROUT ADMIX at 250 g per 50 kg of cement, RAPIDSTRONG GROUT PB 66 (a polymer grout additive, dosed as on its datasheet) or ROOFEX GP (a crystalline grout compound, dosed at 250 g per 50 kg of cement).Why: The slurry fills the internal voids and capillaries. The additive keeps it from shrinking away from the concrete as it sets, which an ordinary cement slurry does, and the crystalline option also seals the capillaries.On site: Work from the lowest nozzle upward on a wall, so the slurry pushes the water and air out ahead of it.
4. 4
   Running or gushing water: polyurethane resin

   Where water is flowing or gushing, cement slurry would simply wash away before it sets. First stop the surface flow with RAPIDSTRONG PLUG in a V-groove, then inject RAPIDSTRONG GROUT PU, the single-component polyurethane grout, with air-compressed injection equipment at about 500 g per grout point.Why: The polyurethane reacts with the water itself, expanding and stiffening to block the flow, so it works where cement cannot.On site: A hard-working point can take 0.3 to 0.75 kg. Polyurethane grouting alone only stops the flow; it is not a guaranteed waterproofing system, so follow it with the lining or coating the structure needs.
5. 5
   Remove the nozzles and seal

   Once grouting is complete, remove the nozzles and patch every hole flush with a putty of ROOFCRETE AR and cement.Why: This leaves a smooth, sound, watertight surface ready for the final lining.
6. 6
   Check before lining

   Look at the face again after the grout has set. Any point still wet gets another nozzle beside it before the coating, membrane or plaster goes on.Why: A single wet patch left behind becomes the first blister under the new lining.

Concrete already cast without an admixture, or seeping

An admixture cannot be added to hardened concrete. The repair works from the surface, starting with the smallest fix that reaches the problem. In every case loose, old and flaking material is removed first.

Best waterproofing admixture for concrete: compare the Armstrong range

These are the Armstrong products on this page that go into the mix or onto fresh concrete. None is a lesser product. The table shows what each is made for.

Liquid or powder waterproofing compound?

Armstrong's integral waterproofing compounds are liquids. A liquid disperses at once and evenly through the mix, so the whole depth of the concrete gets the same protection. Armstrong's crystalline product, ROOFEX, is a powder with a different job: it is brushed on as a slurry, or shaken dry onto fresh concrete at 1.6 kg per sq.m before final trowelling, and grows crystals in the pores of the surface zone.

IS 2645 and IS 9103: two standards for two jobs

IS 2645:2003 is the Indian Standard for integral waterproofing compounds for cement mortar and concrete. Its main test is water permeability: a treated sample must let through no more than half the water an untreated one does. That 50% is the limit, and products pass it by different margins. IS 9103:1999 covers concrete admixtures such as plasticizers and superplasticizers. A product made for one standard is not assumed to meet the other, which is why a plasticizer is not a substitute for an integral waterproofing compound. The article integral waterproofing admixtures explained goes deeper.

Concrete waterproofing chemicals and admixtures by stage of the pour

How much waterproofing admixture for 100 bags of cement

Quantities for 100 bags of 50 kg, worked out from each product's stated dose. A 1,000 sq.ft roof slab 125 mm thick is about 11.6 cubic metres of concrete, and the number of bags in it depends on your mix design. An Armstrong expert confirms the final quantity after seeing the site.

Standards and stated test figures for waterproof concrete

• IS 2645:2003, integral waterproofing compounds for cement mortar and concrete: CONPROOF LW 200 and CONPROOF 500 comply, and CONPROOF No. 1 is listed as BIS certified to IS 2645.
• CONPROOF LW 200: water permeability below 15%, against the 50% maximum allowed in IS 2645. Corrosion resistance to JIS Z 1535 (modified). Chloride below 0.1%, free from sulphates.
• IS 9103:1999, concrete admixtures: CONSPLAX 411 R, ROOFPLAST SP 25, SP 35, SP 45 and PC 455 comply.
• ROOFPLAST SP 45 also complies with BS 5075 Part 3 and ASTM C-494 Type G. ROOFPLAST PC 455 also complies with BS 5075 Part 1 and ASTM C 494.
• ROOFEXCURE WB and ROOFEXCURE WX comply with ASTM C-309, the specification for liquid membrane-forming curing compounds. ROOFEXCURE WB is Type 1D, Class B, and is also listed to IS 15865:2018.
• All figures are from Armstrong test data. Site results vary with cement, aggregate, water and workmanship, so a site trial fixes the dose.

Waterproofing admixture calculator: by cement bags or concrete volume

Enter the area of the pour, which is also the area sprayed with curing compound. Then enter either its thickness or the number of cement bags. Quantities only.

Seven mistakes that make waterproof concrete leak

1. Dosing by eye. The dose is per 50 kg bag of cement, measured every batch.
2. Pouring the compound onto dry cement. It goes into the gauging water or the wet mix.
3. Adding water at site to make the mix flow. A plasticizer gives workability. Water gives capillaries.
4. Premixing two admixtures. The compound and the plasticizer are dispensed separately.
5. Poor compaction. No admixture closes a honeycomb.
6. Cutting curing short. The first seven days decide how dense the concrete becomes.
7. Skipping the membrane. On terraces, in bathrooms and in tanks the compound supports the membrane and does not replace it.

Waterproof concrete questions and answers