Exterior Waterproofing near you

The Park Service's list of usual causes is worth reading slowly because it is also a repair list: leaking roofs, clogged or deteriorated gutters and downspouts, missing mortar, and cracks and open joints around door and window openings. Its conclusion follows directly, and it is the sentence that should govern most waterproofing decisions on a masonry house: if historic masonry buildings are kept watertight and in good repair, water-repellent coatings should not be necessary.

Rising damp and condensation are separate problems with separate cures. The guidance notes that a water-repellent coating will not solve rising damp and in fact may be likely to exacerbate it, because it slows evaporation and can force the moisture higher in the wall. Condensation behaves similarly: once water vapor gets inside a wall and condenses at a cold spot, it becomes liquid water, and liquid water cannot escape through a coating even though vapor can.

Salts are the reason a wet wall gets worse rather than staying the same. Excessive moisture carries soluble salts from the masonry units or the mortar through the wall, and while salts that appear on the surface as efflorescence are usually relatively harmless, salts that crystallize beneath the surface create pressure that can spall the face off. The Park Service warns that coatings can be especially damaging when applied to masonry that contains salts, because they limit the flow of moisture through it.

The two terms are used interchangeably in sales conversations and they describe completely different materials. As the Park Service puts it, water-repellent coatings, often referred to incorrectly as sealers but which do not or should not seal, are intended to keep liquid water from penetrating the surface but to allow water vapor to enter and leave, or pass through, the surface of the masonry. Waterproof coatings, by contrast, seal the surface from liquid water and from water vapor, are usually opaque or pigmented, and include bituminous coatings and some elastomeric paints.

For above-grade masonry the guidance on waterproof coatings is close to absolute: in most instances they should not be applied to historic masonry, the possible exception being below-grade exterior foundation walls as a last resort, and generally waterproof coatings including elastomeric paints should almost never be applied above grade. The failure mode is specific. Water that enters the wall from the ground or the inside cannot escape, freezes in cold weather and causes spalling, and eventually leaves by the path of least resistance, damaging interior finishes or popping the coating off the face of the masonry with pieces of the masonry attached.

Even the breathable kind has conditions. A water-repellent coating should never be applied to a damp wall, because the moisture stops it adhering and penetrating, and if it does adhere it holds the moisture in. Where a coating is genuinely justified, the guidance is to apply it only in selected areas rather than over an entire building, to treat extreme exposures such as parapets or elevations subject to driving rain rather than everything, and to remember that coatings are not permanent and must be reapplied periodically, which is hard to schedule when the product is invisible.

Real diagnosis starts outside and above the stain, because water runs down and sideways along framing before it appears. Gutters, downspouts and their extensions get checked first, since a downspout discharging against a wall reproduces a rainstorm on one spot several times a day. Then the openings, then the junctions, then the penetrations.

Roof-to-wall intersections are the classic culprit on multi-level houses. Building America's guidance for existing homes explains that step flashing is bent at a right angle with half against the wall and half interwoven with the roof shingles, and that kick-out flashing at the lower end directs water runoff away from the adjoining wall and usually into a gutter. Where a leak is traced there, the retrofit means removing siding to expose enough wall to install new flashing properly and integrate it with both the roof underlayment and the wall water-resistive barrier in shingle fashion. Sealant across the top of old flashing does not do this and never has.

Openings and penetrations follow the same logic. Building America's flashing guidance calls for rigid, flexible or fluid-applied pan flashing at window and door sills, side flashing that extends over the pan flashing, top flashing that extends over the side flashing, and all of it integrated with the drainage plane layer, whether that is housewrap, taped sheathing or a liquid-applied coating. At pipes, ducts and wiring the same guidance calls for metal flashing that directs water down and out, with sealant used as part of the detail rather than as the detail.

Ask what is being fixed, not what is being applied. A defensible scope names the entry points the contractor believes are responsible, describes the repair at each one, and states what will be done if water still appears afterwards. A scope that says only a number of square feet and a product name is an application, not a repair, and it will be very hard to argue with later.

Be skeptical of the small test patch as proof. The Park Service notes that testing a water-repellent coating by applying it in one small area may not be helpful in determining its suitability, because water can enter and leave through the surrounding untreated areas and there is no way to tell whether the coated area is breathable. A small trial does tell you whether the product changes the appearance of the masonry, which is a different and still useful question.

Finally, ask about reversibility and appearance. Coatings can be very difficult, if not impossible, to remove from masonry if they fail or become discolored, and some darken or discolor certain masonry or leave a glossy or shiny appearance. On a house you intend to keep, those are not small details. Get the product named in writing, get the extent of the application drawn on an elevation, and get the reapplication interval stated rather than implied.

Two waterproofing quotes are often not comparable because one is a diagnosis and the other is a coating. The variables that genuinely move the price are how much of the wall has to be opened to reach the flashing, the height and access on the affected elevation, whether cladding or masonry has to be removed and reinstated, how many openings and penetrations are involved, whether repointing is part of the work, and whether the building is old enough that lead-safe practices apply to any painted surfaces disturbed.

LokalMatch connects you to people and stops there. Describe the leak once, saying where and when it shows up inside, which elevation it is on and what the wall is made of, and waterproofing contractors, masons and siding crews covering your area contact you directly; the pros pay for the requests they receive and the service is free for homeowners. LokalMatch does not inspect walls, does not perform waterproofing, does not set prices and does not vet, rank or recommend any contractor, so ask each one how they intend to find the leak before you compare what they intend to charge for it.