Terrace Waterproofing Chemicals and Systems for Every Roof Condition

Terrace leakage: check the state of your terrace first

Damp patches on the top-floor ceiling, water seepage down the walls after rain, peeling paint and standing water on the roof are the usual signs of a leaking terrace. Before choosing a terrace leakage solution, find out why it leaks. Five checks decide the treatment. They need no instruments. If the result is unclear, ask for a site assessment before any material is bought.

Find the right terrace waterproofing method

Match what you found to one route. There is no single best waterproofing for a terrace, only the one that fits its condition. Each route tells you what is done and takes you to its section.

Repair first, rebuild last. Wherever a sound surface remains, Armstrong repairs it: cracks sealed, bad patches rebuilt, then coated. A rebuild from the mother slab is kept for the terrace that is debonded throughout and cannot hold a patch or a slope.

Terrace waterproofing coating finder

Armstrong makes acrylic elastomeric, polyurethane (PU), cementitious, rubberised, polyurea and cool roof waterproof coatings for terraces, and all of them are used in layered build-ups. Every one is a sound choice. They differ in chemistry and finish, so the pick depends on the condition of the terrace, how it is used and what you want from it. Answer three questions for a starting recommendation, then confirm it with an Armstrong expert.

Terrace waterproofing from the RCC mother slab

Full terrace waterproofing from the slab up is the extreme option, used only when the surface is debonded throughout, no sound surface is left to repair, and the roof needs a new slope. If part of the surface is still sound, go back to Repair and coat. Each layer here does one job: the membrane sits on the slab, the screed protects it and carries the slope, the coving and skirting close the edges, and the build-up on top takes the weather.

1. 1
   Remove everything down to the mother slab

   Take off tiles, screed, brickbat coba and old coatings until the RCC slab is exposed. Clean it of dust, laitance and loose material.Why: The membrane belongs on the structural slab, and old screed, cobbles and coatings between them hide leaks.
2. 2
   Inspect and repair the slab

   Mark cracks, honeycombs, construction joints and pipe penetrations. Rebuild damaged concrete with ROOFCRETE AR over a bond coat of ROOFBOND SBR 401. Coat any exposed steel with ALSTRONG ZP 777 first.Why: Cracks, honeycombs and pipe penetrations are repaired first, since the membrane cannot bridge a hole.
3. 3
   Treat cracks and joints

   Open cracks to a 4 to 5 mm V-groove and seal with ROOFEXSEAL PU 212. Cracks take PU 212 only. Expansion joints take ROOFEX-SEAL PS. Joints are detailed, never buried under a rigid screed.Why: Cracks in a terrace move with the heat, so a flexible polyurethane sealant in a groove takes the movement.
4. 4
   Grout pipe sleeves and set the outlets

   Pack around every pipe with a non-shrink grout made with RAPIDSTRONG GROUT ADMIX. Fix rainwater outlets at the true low points of the roof.Why: Every pipe leaves a gap in the slab, and non-shrink grout closes it so water cannot follow the pipe down.
5. 5
   Form the coving

   Build a rounded fillet where the slab meets the parapet, in mortar gauged with ROOFBOND SBR 401 and CONPROOF LW 200. The membrane then turns the corner in a curve.Why: A rounded fillet at the parapet lets the membrane turn the corner as one skin instead of tearing.
6. 6
   Apply the membrane on the mother slab

   Apply ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210 in two coats, over the coving and up the parapet. ROOFCOAT FLEXI 100 is mixed 1 litre to 2 kg of cement with 200 ml of water. Site orders use 200 to 250 ml of water, and up to 500 ml for the primer coat., with 3 to 4 hours between coats. ROOFBOND RFX PLUS 210 is a two-part pack of 5.1 kg liquid and 15 kg powder. Both can be reinforced with fibre mesh as layer 2. The usual practice carries it up to 300 mm above finished floor level.Why: The membrane goes on the mother slab, under the screed, where it is protected, and two coats close the pinholes.
7. 7
   Let the membrane cure

   Leave the membrane to cure for the time on the data sheet of the product used before the screed goes over it. Keep it clean and free of foot traffic.Why: A membrane covered before it has cured is damaged, and the screed may not bond to it.
8. 8
   Lay the protective screed to slope

   Lay the screed over the specified bond coat, with CONPROOF LW 200 at 200 ml per 50 kg bag of cement, falling to the outlets. Where a large thickness is needed, use graded aggregate in the mix, not a thick cement-rich mortar.Why: The screed protects the membrane from traffic and sun and gives the fall that drains the water.
9. 9
   Cure the screed

   Spray ROOFEXCURE WB at 4 to 6 sq.m per kg so the screed does not dry too fast and craze.Why: A screed that dries too fast in the sun crazes and loses strength.
10. 10
    Build the skirting

    Run a waterproofed mortar skirting along the base of the parapet, over the upturned membrane, for added protection at the edge. The usual practice is 1:3 mortar about 20 mm thick, mixed with CONPROOF 500 at 500 ml per 50 kg bag, up to 300 mm.Why: A mortar skirting over the upturned membrane protects the edge, which is the commonest place for it to be damaged.
11. 11
    Cap the parapet with a coping

    Finish the parapet top with a coping that slopes towards the terrace and projects past the wall face, with a drip groove under the edge.Why: A sloping coping sheds rain away from the wall instead of letting it run down the face.
12. 12
    Finish with the build-up for the condition

    The condition sets the number of layers: two, three, five or, where the damage is heavy and the terrace cannot be rebuilt, seven. One five-layer example for a terrace that must be structurally sound and long lasting: RAINSEAL BMW 250, fibre mesh, RAINSEAL BMW 250, then two coats of RAINSEAL 200, over the screed and the skirting. Leave 3 to 4 hours between coats.Why: The number of layers depends on the condition of the terrace, since a sound roof needs less than a cracked one.

Five-layer terrace coating over a cleaned slab

This is the coating route for a terrace whose slab is sound: the existing surface is cleaned, cracks are sealed, and a primer, fibre mesh and elastomeric coats build a seamless, flexible skin over it. It is quicker and lighter than a screed system and suits a slab that will not be walked on heavily. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Prepare the surface

   Clean the surface of dirt, dust and old coatings. Chip off loose mortar and cement lumps with an electric chipping machine, remove the debris and wire-brush the surface.Why: The primer must grip the slab itself. Old chalky coating or dust acts as a release layer, and the whole system peels off it.
2. 2
   Groove and seal cracks

   Cut each crack to a V-groove or U-groove about 6 mm wide and 6 mm deep, clean it, and fill it with ROOFEXSEAL PU 212, a single-component polyurethane sealant.Why: The sealant stays flexible, so the crack can keep moving without tearing the coat above it.
3. 3
   Primer coat

   Apply one coat of RAINSEAL RWC 902, the grey rubberised elastomeric coating, diluted with about 50% water as a primer.Why: The thin, diluted coat soaks into the pores of the slab and gives the later coats something to bond to.
4. 4
   Fibre mesh and second coat

   Lay 45 GSM fibre mesh over the primer and apply one more coat of RAINSEAL RWC 902 over it, diluted with about 20% water.Why: The mesh reinforces the film across hairline cracks and joints, so a small movement in the slab does not split the coating.
5. 5
   Two coats of the top membrane

   Apply two coats of RAINSEAL 200, the high-solid acrylic elastomeric membrane, diluted with about 20% water.Why: The high-solid film is the actual waterproof layer. The white top coat also reflects the sun and keeps the slab cooler.On site: Let each coat dry before the next goes on, and keep off the surface until the last coat has cured.

Waterproof the slab first, then lay the sloping screed on top

Where the old screed is hollow, cracked or holding water, the screed itself is rebuilt, and the waterproofing goes on the mother slab beneath it. The order matters: the membrane is laid on the structural slab, and the new sloping screed is laid over it, so the membrane stays protected and the slope still drains the water to the outlets. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Strip back to the slab

   Where the old screed is hollow or broken, break it out down to the mother slab, remove the debris and clean the slab with a grinder or wire brush.Why: Waterproofing laid on a hollow screed fails as soon as the screed cracks. The membrane has to sit on the structure.
2. 2
   Groove and seal cracks

   Cut each crack to a V-groove or U-groove about 6 mm wide and 6 mm deep, clean it, and fill it with ROOFEXSEAL PU 212, a single-component polyurethane sealant.Why: Cracks in the slab move; the flexible sealant takes that movement.
3. 3
   Two coats of the cementitious membrane

   Apply two coats of ROOFCOAT FLEXI 100 mixed with cement on the cleaned slab, per the pack instructions.Why: This is the waterproof layer. It is flexible enough to bridge fine cracks and bonds to the slab.
4. 4
   Bond coat

   Apply ROOFBOND SBR 401 mixed with cement as a bond coat over the membrane, and lay the screed while the bond coat is still wet.Why: The bond coat ties the new screed to the membrane. Laying the screed on a wet coat gives a monolithic bond, where a dry coat would let it lift.
5. 5
   Sloping screed

   Lay a 1:2:4 cement-sand-6 mm aggregate screed with CONPROOF 500 at 500 ml per 50 kg of cement, about 40 mm thick on average, falling toward the outlets.Why: The integral compound makes the screed itself dense and water-resisting. The fall stops water ponding, and ponded water is what finds the weak point in the system.
6. 6
   Plaster on the wet screed

   While the screed is still wet, lay a 1:4 cement-sand plaster about 12 mm thick, again mixed with CONPROOF 500 at 500 ml per 50 kg of cement, and finish neatly.Why: Plastering wet-on-wet joins plaster and screed into one layer. A plaster on a dry screed sounds hollow later and cracks away.
7. 7
   Cure at once

   Apply ROOFEXCURE WB immediately after the plaster so that the cement hydrates and the surface does not dry out too fast.Why: A screed that dries too fast in the sun loses its strength and cracks as it shrinks.
8. 8
   Heavy-duty alternative

   For a heavier build-up, use ROOFCRETE AR 576 in the screed and plaster instead, at 2 L per 50 kg of cement, with the screed about 75 mm thick on average and the plaster 12 mm thick.Why: The polymer-modified mortar is stronger and denser, and suits terraces that take traffic or carry planters.

Terrace: polyurethane-bitumen build-up with geo-fabric

Doses, thicknesses and the number of coats change with the surface, the exposure and the site. Use this as the standard sequence and adjust it to the job. This build-up is used on terraces and roof sheets where a black bituminous base is wanted under the top coats.

1. 1
   Prepare the surface

   Clean the surface of dirt, dust and other contamination.
2. 2
   Seal the surface cracks

   Seal any surface cracks with RAINSEAL BXL, the acrylic polymer blended bituminous sealing compound.
3. 3
   Primer coat

   Apply one coat of RAINPROOF PRG 909, the polyurethane blended bituminous coating, diluted with water 1:1 (about 50%) as a primer.
4. 4
   Lay the geo-fabric

   Lay 40 GSM geo-fabric on the wet primer coat, with the strips overlapped.
5. 5
   Coats over the fabric

   Apply two coats of RAINPROOF PRG 909 over the fabric, diluted with about 20% water. Where a white or tinted finish is wanted, finish with two coats of RAINSEAL 200 diluted with 20% water.

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.

Terrace waterproofing: the standard sequence, step by step

This is the standard sequence for this area, in the order it is carried out. Each step prepares the surface for the next, so a step skipped or done out of order shows up later as a leak, a blister or a hollow tile. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Prepare the surface

   Clean the surface of dirt, dust and old coatings. Chip off loose mortar and cement lumps with an electric chipping machine, remove the debris and wire-brush the surface.Why: Every membrane in this sequence is only as good as its grip. It bonds to clean, sound material, not to dust or loose screed.
2. 2
   Groove and seal cracks and joints

   Open every crack and joint to a V-groove about 6 mm wide and deep, clean it out, and fill it with ROOFEXSEAL PU 212, the single-component polyurethane sealant.Why: A hairline crack moves with temperature. A rigid coating over it cracks along the same line, but a flexible sealant in the groove moves with it.
3. 3
   Stop the leaks

   Where water comes through, grout it through drilled holes as in the section above: 12 to 14 mm holes, rubber nozzles fixed with cement and RAPIDSTRONG QS 113, cement slurry made with RAPIDSTRONG GROUT ADMIX (250 g per 50 kg of cement), RAPIDSTRONG GROUT PB 66 or ROOFEX GP pumped at about 140 psi until refusal, then seal the holes with ROOFCRETE AR and cement.Why: The membrane goes on a dry, stable surface. Water pushing from behind lifts any coating laid over it.
4. 4
   Two coats of the cementitious membrane

   Apply two coats of ROOFBOND RFX PLUS 210 as a slurry, about 1.5 kg per sq.m in total, over the slab and up the vertical surfaces to 300 mm above finished floor level. Put the second coat on once the first has set enough to take it.Why: Two coats close the pinholes a single coat leaves, and the 300 mm upturn means water on the floor cannot run behind the membrane at the wall.
5. 5
   Pond to test

   Pond water on the floor for 7 days and check the ceiling below for any damp patch before anything is laid over the membrane. Some specifications call for a ponding test without fixing a period, so the test period is set by the job.Why: This is the only moment a leak can be fixed easily. Once the screed and tiles are on, finding and repairing the same leak means breaking all of it out.
6. 6
   Protect open terraces with a sloped screed

   On an open terrace, lay an M20 screed falling toward the outlets, about 75 mm thick on average, with an integral waterproofing compound in the mix. Cut 3 mm by 3 mm grooves at 600 mm spacing in both directions.Why: The screed protects the membrane from sun, foot traffic and tools and gives the slope that drains the water. The grooves let the screed move with the heat without cracking across.
7. 7
   Form the cove at the wall junction

   Chip off loose material and clean the junction. Apply ROOFBOND SBR 401 mixed with cement as a bond coat, then form a cove at the 90 degree junction up to 6 inches (150 mm) in 1:4 cement-sand mortar mixed with CONPROOF LW 200 at 200 ml per 50 kg of cement, finished neatly.Why: A sharp 90 degree corner is where coatings tear and crack first. A cove lets the membrane run round the corner as one continuous skin.
8. 8
   Seal around every pipe

   Seal the periphery of each pipe with polymer concrete made with ROOFCRETE AR 576. Fix a socket around the pipe, grout the socket with the same polymer concrete, and prove it with a ponding test.Why: A pipe passing through a slab leaves a gap that ordinary mortar shrinks away from. This is one of the commonest places for a leak to come back.

Terrace leakage repair: fix cracks and patches, then coat

The terrace leakage repair route for most homes and buildings. Roof cracks are sealed, sound areas stay, damaged areas are cut out and patched, and the coating goes on last.

1. 1
   Clean and mark

   Remove dust, moss, oil and any loose or blistered coating. Mark every crack, joint, pipe and low spot.Why: Coatings bond to a clean surface, and marking every crack and low spot means none is missed.
2. 2
   Repair cracks and joints

   Cracks anywhere across the terrace are opened to a V-groove and sealed with ROOFEXSEAL PU 212 only, which accepts ±25% movement. Expansion joints take ROOFEX-SEAL PS, 6 to 25 mm wide in one application.Why: A crack across a terrace opens and closes with the heat, so it needs a flexible sealant to keep it sealed.
3. 3
   Cut out and patch the damaged areas

   Break out hollow, loose or crumbling patches down to sound material. Rebuild them, and build up any low spots, with ROOFCRETE AR 576 over a bond coat of ROOFBOND SBR 401, so the surface is sound and water runs to the outlet.Why: A hollow or crumbling patch cannot hold a coating, so it is rebuilt with repair mortar to the level of the rest.
4. 4
   Make good the coving and skirting

   Where the corner is a sharp angle, form a coving. Where the skirting is cracked, hollow or missing, rebuild it. At the roof-to-wall junction there are two ways to reinforce the corner. Either lay RAINSEAL FLEX TAPE under the coating, or build the reinforcement from the coating itself: one coat over the coving and up the wall, geo-fabric bedded into it while it is wet, then a second coat over the fabric.Why: A sharp corner or cracked skirting is where a coating fails first, so it is made good first. The geo-fabric between two coats ties the corner into one reinforced skin, the same layered method used on the flat roof.
5. 5
   Apply the build-up for your route

   A sound terrace takes two layers. A cracked or patched one takes three, with fibre mesh as layer 2. One in bad condition takes five. Carry every coat over the coving and the skirting, and apply successive coats at right angles. RAINSEAL 200, RAINSEAL RWC 902 and RAINSEAL BMW 250 can each be thinned with up to 20% water. Leave 3 to 4 hours between coats, for every coat of every coating. For higher abrasion resistance, sprinkle sand over the last coat while it is still wet, then apply the final coats on top of it.Why: The build-up is chosen for the condition of the roof, since a sound roof needs fewer layers than a cracked one.
6. 6
   Cure, then pond test

   RAINSEAL 200 needs 3 days of air curing before foot traffic, and RAINSEAL RWC 902 needs 3 days at 30°C before water testing. Then flood the roof for 24 to 48 hours and check the ceiling below.Why: A flood test shows any leak while it is easy to fix, before the finishes hide it.

Tiled terrace leakage: waterproofing without removing tiles

Most tiled terraces leak through the joints and the edges, not through the tiles, so terrace leakage can often be treated without removing tiles or breaking the floor. What is done depends on whether the tiles are still bonded to the bed below.

Check the tiles first

Then choose one of five options

Five-layer systems: consumption and dilution, layer by layer

The RAINCARE PRC and RAINPROOF PUF five-layer systems build the same sequence: a primer, fibre mesh, a grey coat, a white fibre-reinforced coat and a reflective top coat. These are the dilutions and consumptions by layer, so the quantity can be worked out before the job. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Layer 1: primer

   For the RAINCARE PRC 5 Layer System, dilute the black PU-bitumen primer 1:1 with water and apply about 200 ml per sq.m. For the RAINPROOF PUF 5 Layer System, dilute with about 50% water and expect about 5 sq.m per litre.Why: The primer seals the dust and pores of the slab and gives the next coats something to bond to.
2. 2
   Layer 2: mesh

   Lay 40 or 45 GSM fibre mesh, 1 m wide, with 50 mm overlap on the primed surface.Why: The mesh holds the film together across cracks, and the overlap stops a seam opening.
3. 3
   Layer 3: grey coat

   Apply the grey acrylic coat. For PRC, dilute with about 50% water and apply about 400 ml per sq.m. On the PUF system, dilute with about 20% water and expect about 4 sq.m per litre.Why: This coat saturates the mesh and builds the thickness of the waterproof film.
4. 4
   Layer 4: white fibre-reinforced coat

   Apply the white fibre-reinforced coat, adding up to 200 ml of water, at about 350 ml per sq.m.Why: A second reinforced film adds thickness and toughness against foot traffic and weather.
5. 5
   Layer 5: reflective top coat

   Finish with the super-white solar reflective coat, diluted about 20%, at about 300 ml per sq.m. See the RAINCARE PRC 5 Layer System and RAINPROOF PUF 5 Layer System pages for the full system.Why: The white coat reflects heat, so the slab runs cooler and expands and contracts less.

Terrace waterproofing layers: two, three, five or seven coats

How many coats of terrace waterproofing are needed? The condition of the terrace decides the number of layers. The coating in each layer is a separate choice, made by roof and finish. The diagrams show the layers as they sit on the roof, numbered in the order they are applied. Fibre mesh is always layer 2.

What each layer does

Why two, three, five or seven

Which coating goes in which layer

The number of layers and the coating are two separate choices. Any base coat can be used in a two, three, five or seven-layer build-up, and so can any topcoat. Leave 3 to 4 hours between coats. RAINSEAL 200, RAINSEAL FRC 623, RAINSEAL CFR 613, RAINSEAL RWC 902, RAINSEAL CLEAR 202 and the RAINSEAL BMW 250 base coat can each be thinned with up to 20% water.

The coating families, and where each fits

All of these are used as layers in a build-up. None is a lesser product. The table shows what each family is chosen for.

Other conditions

Armstrong 5, 6 and 7 layer terrace waterproofing systems

Besides the build-ups an applicator assembles on site, Armstrong offers eight named systems in which every layer is specified: primer, base coats, reinforcing mesh as layer 2 and topcoat. Engineers specify them by name. Each links to its own page with the full layer list.

Which one for which terrace

See all Armstrong waterproofing systems with layer diagrams

Other surfaces on a roof: gutters, wooden decks and steel pillars

A roof has more than slab. Rain-water gutters, wooden decks and pergolas, and iron pillars all leak or rot at their own weak points, and each takes the same family of coatings. Doses, thicknesses and coats are the standard figures; the site and the exposure decide where they move.

1. 1
   Rain-water gutters

   Clean the gutter, prime with RAINSEAL RWC 902 diluted 50%, lay 45 GSM fibre mesh with a coat of RAINSEAL RWC 902 diluted 20%, then finish with coats of RAINSEAL RWC 902.Why: A gutter holds water for hours, so it needs a continuous, reinforced film with no seams.
2. 2
   Wooden decks and terraces

   Clean the surface and apply two coats of RAINSEAL RWC 902, the grey rubberised elastomeric coating, diluted about 20%.Why: The flexible coat moves with the timber as it swells and shrinks with the weather.
3. 3
   Steel pillars

   Apply ALSTRONG ZP 777 first, then a coat of RAINSEAL RWC 902 diluted about 20%.Why: The zinc-rich primer protects the steel from rust, and the flexible coat above it keeps rain off the primer.

Parapet, coving and skirting: where roof leakage starts

Roof leakage starts at the parapet wall junction, drain outlets and pipe openings far more often than in the open field. These seven details apply on every route.

What the coping does

Terrace waterproofing chemicals and products by stage of work

How much waterproofing material for a 1,000 sq.ft terrace

Approximate quantities from each product's stated coverage, for 1,000 sq.ft (93 sq.m). Rough surfaces use more. Upturns, coving and skirting are extra. An Armstrong expert confirms the final quantity after seeing the site.

Standards and tests for roof waterproofing

• IS 3067 is the Indian code of practice for damp-proofing and waterproofing of buildings, including the fillet and upturn at the parapet.
• ROOFCOAT FLEXI 100 is tested to ASTM D412, ASTM C836 and ASTM D4541.
• RAINSEAL 200 is tested to ASTM C836, ASTM E903, ASTM E-96 and ASTM D4541.
• RAINSEAL RWC 902 is tested to ASTM D-412, ASTM D-471 and ASTM C-836.
• CONPROOF LW 200 conforms to IS 2645:2003.
• Acceptance test: a pond test of 24 to 48 hours on the finished roof, after the work is complete and cured.

Terrace waterproofing material calculator

Enter the size of your terrace and choose a build-up to see how much waterproofing material it needs. The calculator gives quantities only. Use the button at the end to talk to an Armstrong expert about your quantity.

Seven mistakes that bring terrace leakage back

1. Coating over dust, loose particles or damp. The coating bonds to the loose layer and peels with it.
2. Coating over a hollow screed. The coating fails with the layer under it.
3. Using a coating to fix the slope. Waterproofing is never a substitute for drainage.
4. No coving. The coating splits at the sharp corner.
5. No skirting, no coping, or a coating that stops at the floor. Water gets behind the edge.
6. Too few layers for the condition. A two-coat finish on a cracked, moving roof has no reinforcement to carry the movement.
7. No final check. After the work is complete and cured, the roof is flooded for 24 to 48 hours and the ceiling below is checked, so a missed spot shows at once.

Terrace waterproofing questions and answers