7 Step Guide to Waterproofing Your Home

Before waterproofing a building, one thing to make sure is that the damp issue actually needs it. Not all damp problems require waterproofing.

Leaks from plumbing, damaged gutters or poorly maintained roofs are common causes of damp and should be fixed first. Waterproofing is only effective once these basic issues are ruled out or repaired.

Read on below to find out all you need to about how this is done.

Waterproofing – Common Defects and Solutions

Before applying any waterproofing, it’s essential to identify the real cause of any damp issues. Start by using our Damp Diagnosis Guide and check for hidden issues in our Finding Leaks Project.

Once diagnosed you can target the problem effectively with a lasting solution. Below, we’ll cover the most common building defects that require urgent waterproofing, starting at the roof and working down to the foundations.

1. Chimney Stack Damp

Damp around the chimney stack is often caused by water seeping through the masonry. Signs include stains in the loft or on ceilings below.

Common Causes to Check:

• No ventilated chimney cap
• Cracked or missing pointing
• Spalled or crumbling bricks
• Bird nests blocking airflow or gutters

Waterproofing Options and Procedures

In order to resolve any chimney stack damp issues, read through the following suggestions:

1. Render the chimney stack: Clean the surface thoroughly, apply a suitable primer, then render using sand and cement mixed with a waterproofing additive. This seals out moisture and resists contamination from old soot, salts, and resins.
2. Use a specialist water repellent: Choose a product designed for high salt levels. Standard solvent-based silicone sprays aren’t strong enough for chimney stacks.
3. Apply a waterproof coating: Cement-based tanking slurry or bitumen products can work short-term, but may not bond well over time without proper surface prep.

Suggested Products

Once you have settled on a repair method, you will need to use the correct products, here are a selection of some of teh best we know of:

• SBR (Styrene Butadiene Rubber): Mix with sand and cement to improve adhesion and waterproofing in renders. Ideal for bonding to concrete or applying thinner screeds.
• Enviroseal Plus Ultraproof / Everbuild Waterseal: A high-performance silicone cream that repels water. Water-based and long-lasting, it protects brick, stone, render, plaster and concrete surfaces.
• Technoseal / Black Jack DPM: A tough bitumen-based coating available in black or white. Forms a flexible rubber membrane, suitable for interior and exterior use. Easy brush-on application.

Need help tackling damp problems around chimney breasts? Our dedicated guide covers practical solutions step by step.

2. External Wall Damp – Penetrating Damp Above the Damp Proof Course

Next on the list to check on is external wall damp. In essence this is damp that penetrates through external walls that are above the damp proof course.

Check for Common Faults as follows:

• Damaged or poorly laid brickwork
• Cracked or missing pointing
• Windows without proper cill ‘drips’ to direct water away
• Blocked cavities preventing water drainage
• Missing cavity trays or weep vents
• Gaps where pipes or cables enter the wall
• Worn or missing sealant around windows and doors

Waterproofing Options and Procedures

To protect your external walls from penetrating damp, consider these effective waterproofing methods:

1. Render the walls: Clean thoroughly, apply a primer, then render with a sand and cement mix that includes a waterproofing additive. This helps seal porous or salt-contaminated masonry.
2. Water repellent treatment: Use a high-quality, salt-resistant repellent. Avoid standard solvent-based silicones, they may not be effective on older walls.
3. Waterproof coatings: Apply a cement-based tanking slurry or bitumen-based coating to create a durable moisture barrier.
4. Slate hanging: Common in conservation areas, this traditional method uses hanging slates to shield walls while maintaining heritage appearance.
5. Air gap membrane: Fix a plastic dimpled membrane to the wall with plugs, then render over it. This creates a ventilated barrier to keep walls dry.
6. Masonry paint: Choose a breathable, algae-resistant masonry paint for ongoing surface protection and a clean finish.

Suggested Products

For a long-lasting and effective waterproofing repair, using the right materials is essential. Here are our top recommendations:

• SBR (Styrene Butadiene Rubber): Add to sand and cement render for improved bonding to concrete or old render. It also boosts waterproofing performance.
• Enviroseal Plus / Everbuild Waterseal: A high-performance, silicone-based water repellent. Offers up to 15 years of protection for brick, stone, plaster, and render.
• Technoseal / Black Jack DPM: A brush-on bitumen coating available in black or white. Cures to form a tough, flexible rubber membrane for waterproofing walls and floors.
• Mesh Damp Proof Membrane: Dimpled plastic sheeting for internal or external use. Plaster or render can be applied directly onto the mesh surface for a dry finish.

3. External Wall Damp – Penetrating Below Damp Proof Course

It’s normal for walls below the damp proof course (DPC) to hold some moisture from natural ground damp. However, if you see visible wet patches or staining, this could signal a problem like a leak, high ground levels, or damaged DPC, and it should be investigated promptly.

Eliminate Building Faults

To fix external wall damp below the damp proof course, check for these common causes:

• High ground levels near walls – such as raised soil, paths or roads
• Items against the wall – like soil heaps, debris, timber posts or garden walls
• Poor drainage – blocked drains, soakaways or sloping driveways that direct water towards the house

Waterproofing Options and Procedures

To fix damp issues below the damp proof course (DPC), consider these proven methods:

1. Render the wall – Apply a primer, then sand and cement mixed with waterproofer. This seals the surface and blocks moisture. Clean surfaces thoroughly first to remove salts and contaminants.
2. Use a waterproof coating – Apply a cement-based tanking slurry or a bitumen-based product for a strong, water-resistant barrier.
3. Install an air gap membrane – Fix a dimpled plastic sheet with special plugs, extending it down to meet a French drain at foundation level for extra drainage.
4. Apply masonry paint – Use a high-quality, algae-resistant masonry emulsion to add a breathable, water-repellent finish.

Suggested Products

For your chosen repair method to be effective, using the correct products is a must and here is what we suggest:

• SBR Bonding Agent – Mix with sand and cement render to boost adhesion to existing concrete or render. Also improves waterproofing and durability.
• Technoseal / Everbuild Waterseal – A brush-on bitumen-based coating (black or white) that dries to form a tough, waterproof rubber membrane.
• Geotextile Membrane – A dimpled plastic sheet with an integrated filter layer. Ideal for use below the damp proof course alongside Technoseal and a French drain system.

4. Damp Internal Plaster – Above the Damp Proof Course

Damp plaster can seriously damage your interior décor and is often a sign of a deeper issue. Fixing it properly means identifying the root cause and using the right repair method.

Common Causes to Check:

• Leaking chimneys – see Section 1 above
• Penetrating damp – see Section 2 above
• Bridged damp proof course – see Section 3 above
• Hidden leaks – from old mains or heating pipes buried in floors or walls
• Neighbour’s raised floor level – often on shared (party) walls where concrete floors are installed above your DPC

Waterproofing Options and Procedures

To fix damp internal plaster issues above the damp proof course, follow these proven methods:

1. Re-render with Sand and Cement – Mix in a salt inhibitor or waterproofer. Apply a skim of Multifinish plaster on top. Be sure to fully remove all old plaster. Avoid using bonding or browning plaster, especially as dabs or around beadwork.
2. Avoid Surface Coatings – Do not use tanking slurry, bitumen products, or PVA/Unibond above the DPC. These can trap moisture and cause it to spread elsewhere.
3. Install Air Gap Membrane – Fix dimpled plastic membrane with plugs. Finish with Bonding Plaster for a clean, breathable surface.

Suggested Products

For a lasting fix to damp internal plaster, use the right products from the start:

• SBR Waterproofing Additive – Mix with the water in your sand and cement render. It blocks moisture and salts from rising through plaster, helping preserve paint and finishes.
• Mesh or Damp Proof Membrane – Dimpled plastic sheeting ideal for direct plastering with Carlite Bonding or for dot-and-dab plasterboard. It creates a barrier between damp walls and interior surfaces.

5. Damp Internal Plaster – Below the Damp Proof Course

Damp plaster below the DPC (Damp Proof Course) often signals moisture rising from ground level or poor construction. Here’s how to identify teh cause and then fix it and prevent any future occurrances:

Fix Common Building Issues

• Plaster touching the floor – draws moisture up from unsealed walls or floor joints.
• High external ground levels – can bridge the DPC and let water seep through.
• Blocked wall cavities – prevent proper drainage and trap moisture inside.

Waterproofing Options and Procedures

To fix damp plaster below the damp proof course (DPC), we suggest the following methods:

1. Waterproof Coating – Apply a cement-based tanking slurry, followed by a sand and cement render, then a plaster skim.
2. Air Gap Membrane – Fix dimpled membrane sheets to the wall with plastic plugs, then plaster over with Carlite Bonding.
3. Seal Floor-to-Wall Joints – Cut a 25mm x 25mm channel at the joint and fill it with waterproof mortar to block moisture.

Suggested Products

As well as using the correct fixing method, it’s essential that the right products are also used. Here is a selection of what we suggest:

• Tanking Slurry – A cement-based powder mixed with water to create a thick, paint-like coating. Brush it onto walls to form a waterproof barrier before rendering.
• Mesh Membrane / Damp Proof Membrane – Dimpled plastic sheets for internal walls. Ideal for plastering with Carlite Bonding or attaching plasterboard using dot and dab.
• Fillet Seal – A flexible, cement-based mortar for sealing floor-to-wall joints and filling cracks. Supplied as a powder and mixed with water to form a stiff, waterproof seal.

6. Damp Solid Floor

If you notice damp patches on concrete, brick, slab, or tiled floors, act quickly to avoid further damage. Even if the surface looks solid, hidden issues can cause long-term problems.

Check for Common Faults

• Undetected water leaks – from old mains pipes or buried heating systems
• High ground levels outside – water can seep into the floor
• No damp proof membrane – common in older properties

Waterproofing Options

To fix damp in solid floors, try one of these proven waterproofing methods:

1. Tanking Slurry – A cement-based waterproof coating. Not a vapour barrier but effective under a sand and cement screed.
2. Epoxy Vapour Barrier – A two-part epoxy paint that blocks moisture. Ideal beneath timber floors and screeds.
3. Air Gap Membrane – Lay dimple-side down. Cover with tongue and groove chipboard, MDF, or a sand and cement screed.
4. Joint Sealing – Cut floor-to-wall junctions to 25mm x 25mm and fill with waterproof mortar. Always combine with one of the above methods.

Suggested Products

To use in conjunction with your chosen fixing method, here follows a selection of products:

• Tanking Slurry – Cement-based mix applied directly to floors before rendering with sand and cement.
• Air Gap Membrane – Dimpled plastic sheeting laid over the floor. Can be topped with screed or timber flooring.
• Fillet Seal – Flexible cement mortar for sealing floor-to-wall joints and cracks in solid floors.

7. Damp Basement or Cellar

Basements and cellars often suffer from damp floors and walls, even if the structure appears sound. If you notice water seeping through brick, stone, or concrete, it’s time to investigate and fix the root cause.

Eliminate Building Faults

• Undetected leaks from old water mains or buried heating pipes
• High water table levels, underground springs, or wells
• Connected basements or cellars with existing water ingress

Waterproofing Options

After identifying the cause of damp in your basement or cellar, choose the best waterproofing method from the options below:

1. Cement Tanking – Apply a cement-based coating to walls and floors. This creates a water-resistant layer (not vapour-proof) and can be screeded over with sand and cement.
2. Air Gap Membrane –
   
   Floors:Walls:Important:
3. Joint Sealing – Cut out floor-to-wall junctions to at least 25mm x 25mm and fill with waterproof mortar. Always combine with membrane or tanking to stop moisture at the floor edge.
4. Sump and Pump System – For basements with active water ingress, install a sump and pump to actively drain water and protect internal finishes and contents.

Suggested Products

To effectively treat damp in basements or cellars, we recommend the following specialist products:

• Tanking Slurry – A cement-based waterproof coating. Brush onto walls or floors, then render with sand and cement or screed over.
• Air Gap Membrane – Dimpled plastic sheets. Lay on floors beneath screed or wood flooring. For walls, choose mesh-backed or plain membranes—suitable for plastering, plasterboarding, or lining with insulation boards.
• Fillet Seal – A flexible, waterproof mortar used to seal floor-to-wall joints and cracks in solid floors. Essential for preparing damp-prone areas.
• Sump and Pump with Perimeter Drainage – Vital in areas at risk of flooding. Installed beneath the membrane system to actively remove water and keep the space dry.

Diagnosing water or damp issues can be tricky, what looks like one problem is often caused by something else. Our step-by-step waterproofing guide above is designed to help you identify the real source and choose the right fix.

While this checklist covers the most common causes and solutions, don’t hesitate to consult a qualified professional if you’re unsure. Getting expert advice early can save time, money, and future damage.