Sealants and putties can contain asbestos if they were applied before 1994. Typical places are the joints between precast concrete panels, the joints between window and door frames and the wall, the putty that holds window glass, and old sealants around penetrations and in wet rooms. The material may be soft and elastic or hard and brittle, and neither tells you anything about asbestos. You get certainty from a laboratory analysis, and the sample should be taken before window renovation, window replacement or resealing joints.
This article covers the sealants and putties found in old buildings, which stages of a window renovation break them, how to take a sample of elastic sealant and brittle putty, and what the result means.
Which sealants are found in old buildings?
Panel joints
In buildings made of precast concrete panels, the joints between the panels are filled with elastic sealant. In the 1960s and 1970s, panel joints were commonly sealed with polysulphide sealants that contained asbestos and PCBs. The joints have been redone during facade renovations, so one building can contain sealants of different ages, and remnants of the old sealant may remain under the new one. Panel buildings are covered in more detail in the article asbestos in apartment buildings.
Joints around windows and doors
The gap between the frame and the wall has been sealed with sealant on the inside and outside, and there is often more sealant at the joints of window sills and trims. These joints always break when a window or door is replaced.
Window putty
In old wooden windows the glass is held in the sash with putty. Over the years the putty hardens, cracks and comes loose in pieces. Traditional window putty was made from chalk and linseed oil, but especially in the 1960s and 1970s many putties and sealants contained asbestos, so old putty cannot be judged asbestos-free by its appearance. Because windows have been restored and reputtied at different times, the windows of one house can have different putties. The putty on inner and outer sashes can also be different products.
Sealants around penetrations and in wet rooms
Sealing compounds at pipe penetrations, firestops, and old corner and connection joints in wet rooms are also sealants. Firestops are covered in the article asbestos in fire protection, and bathroom materials in the article asbestos in the bathroom.
Asbestos and other hazardous substances in old joints
Besides asbestos, old panel and window joints can contain other hazardous substances such as PCBs and lead. An asbestos analysis only tells you about asbestos, so if joints are to be removed on a large scale, the other hazardous substances are investigated separately.
Window renovation: which stages break the putty and sealants?
Intact putty or sealant does not release fibres into the air. In a window renovation, however, they are almost always broken, and different stages concern different materials.
- Removing old putty. The putty is scraped off, or first softened with a heat gun or an infrared heater. Heating makes it easier to remove, but what comes off is the same material, so it is tested before the work.
- Sanding sashes and frames. Repainting also means sanding old paint, whose composition is a separate question. Read the article asbestos in paint.
- Replacing windows. Removing the frame breaks the joint between the frame and the wall, and often the render or mortar around the frame as well. Mortars are covered in the article asbestos in mortar.
- Replacing sills and trims. The sealant underneath and at the joints comes off at the same time.
In a window renovation it is therefore worth taking separate samples of the putty, the frame joint and, if needed, the paint. Then you know which stage has to be done as asbestos work and which does not.
How to take a sample of sealant or putty
Take a sample of each different material: for example one of the putty, one of the outer frame joint and one of the panel joint. If the windows were restored at different times, or different facades have different sealant, take separate samples of them.
- Wear disposable gloves and a respirator of at least class FFP3.
- Choose a spot you can reach safely, for example the corner of a ground-floor window or a panel joint at ground level. Do not climb a ladder just to take a sample.
- Do not heat the material before sampling. Lightly mist the spot with a spray bottle, especially if the putty is dry and crumbly.
- For elastic sealant, cut out a length of about 2–5 centimetres through the full depth of the joint with a sharp knife. If older sealant is visible under the new one, include it too.
- For hard putty, pry off a piece with a putty knife or a narrow chisel, holding an open zip-lock bag underneath so that crumbs fall straight into it. Take only a small piece so the glass stays in place.
- Seal the bag, put it inside a second bag and mark it with the location and material, for example "living room window, outer sash, glazing putty" or "south facade, panel joint".
- Cover the spot with tape and wipe the area with a damp cloth.
Protective equipment is covered in more detail in the article how to protect yourself when taking an asbestos sample, and sending the sample in the article sending an asbestos sample by post.
What does the result of a sealant sample mean?
Onelab analyses the sample with a JEOL SEM-EDS electron microscope in accordance with ISO 22262-1, and the result is sent by email, typically on the day the sample arrives. The result tells you whether asbestos was detected in the sample you sent.
- No asbestos detected: the result applies to the material at the sampling spot and similar material. Windows puttied at different times and joints that have been redone are tested separately.
- Asbestos detected: the material is treated as asbestos-containing. Putty removal, resealing and window replacement are planned as asbestos work insofar as they break that material, and the removal is carried out by a company authorised for asbestos removal work.
If the joints or windows are part of a larger facade or window renovation that requires an on-site asbestos survey, the survey is carried out on site by a qualified surveyor. Onelab is a laboratory, and on-site surveys are handled by our sister brand AsbestiPro.
How much does the analysis of a sealant sample cost?
The analysis costs €39.90 + VAT per sample, and the price is the same for 1–100 samples. Orders of more than 100 samples can be priced separately. Postage is not included. You can order the analysis online and send the sample to the laboratory by post.