Sealant is a small but important part in buildings. Improper use always causes plenty of troubles. Knowing how it happens and how to prevent it is more essential and helpful in real work. This paper introduces some use tips and precaution measures to common questions and problems we may get into frequently in construction work.
1. What are the limits of acetic silicone sealant and neutral silicone sealant?
(1) Acetic silicone sealant can’t be applied on the surface of metal, coating glass(include mirror), cement, stone and etc. Or it will result in rustiness, oxidation and corrosion on the surface of substrates, causing stain or adhesive failure.
(2) Neutral silicone sealant can’t be applied on high temperature surface. It is easy to bubble because of its fast speed of releasing methanol gas in curing process. Neutral silicone sealant can’t be applied on copper, lead, zinc and other metals. Or it will result in rustiness, oxidation and corrosion on the surface of substrates, causing stain or adhesive failure.
(3) Neutral silicone sealant can’t be applied in long-time immersion condition, such as on fish tank or aquarium.
2. Why do we must use back up material and prevent triple-sided adhesion?
The main effect of back up material is to avoid triple-sided adhesion. Because triple-sided adhesion will affect the movement capacity of sealant and result in cracking and adhesive failure of sealant.
3. The main reason of chalking, cracking and obvious shrink of silicone sealant:
Inferior materials such as white oil are mixed into silicone sealant in production process, which results in chalking, cracking or obvious shrink.
Precaution: choose high quality silicone sealants from formal manufacturer.
4. The main reason of yellowing or colour changing of silicone sealant：
(1) Incompatible with substrates such as EPDM (Ethylene-Propylene-Diene Monomer), neoprene, asphalt paint, etc.
(2) Acid and alkaline substances such as some cleaner, mortar and other corrosive substances can result in colour changing.
(3) Oxime silicone sealant will discolour easily in acetic conditions.
Precaution: do compatibility test in advance; prevent sealant from contacting with corrosive substances or exposing into corrosive environment.
5. Why will colorful sealant discolour?
Organic or inorganic pigments are added into colorful sealant. Inorganic pigment has fewer color varieties, but it exhibits outstanding resistance to weather and it’s not easy to fade. While organic pigment is just the opposite: more color varieties and easy to discolor.
Precaution: As much as possible to choose inorganic pigments. Try to avoid too bright colors. If organic color is needed, don’t pursue too much similarity.
6. Why does unqualified bonding happen?
(1) No adhesion between sealant and substrate.
(2) Non-standard construction, for example, substrate surface isn’t processed appropriately; curing time or environment doesn’t meet requirements; primer isn’t applied as required; wrong ratio of two component sealant, etc.
Precaution: there is no warranty that any sealant has good adhesion with all substrates. So adhesion and compatibility test is necessary. And apply primer if necessary.
Contaminants on the surface of substrates such as dust and oil should be cleaned as regulation before construction.
One component sealant should be maintained for at least 7 days, and two component should be maintained for at least 3 days. Maintenance time should be extended under low temperature and humidity.
7. What are the main reasons of the swollen phenomenon on silicone sealant?
(1) Unregulated construction. Especially when backing rod is much bigger than the expansion joint size. Backing rod rebounds after sealant scraping, causing sealant deformation.
(2) Panel size and shape. Joints between large size and abnormal-shape ALPs has larger deformation rate.
(3) Low humidity, curing slowly.
(4) Large temperature difference.
8. What are the main causes of bubbling during the curing process?
(1) Air is carried inside while applying sealant. For example, the applying process isn’t coherent and even, or when sealant is finished or trimed repeatedly.
(2) Substrates are not dry as required. Wet foam rod and substrate containing moisture, evaporation of which is causing bubble.
(3) Accessories release gas.
(4) The surface temperature of substrates is too high and sealant cures so fast that released small-molecule gases can’t be eliminated in time.
(5) Sealant reacts with some substrates. For example, alkaline concrete and cement react with sealant and release gas.
9. What are the main causes of the cracking?
(1) Sealant is selected improperly, the movement capacity can’t satisfy designed specification.
(2) The design of expansion joint is improper: expansion joint is too wide to be filled completely and fully.
(3) Installation deviation is too large.
(4) Sealant is extended or compressed excessively before completely cured.
(5) The triple-side adhesion limits sealant’s movement capacity.
(6) The thickness of sealant is too thin, which causes sealant damage or adhesive failure.
10. What’s the cause of the stain of stone?
Stone is porous material. Released substances seep into stone structure easily and result in stain.
Precaution: use stone silicone sealant with special formula; do contamination test before application.
11. What are the main causes of insulating glass sealing failure?
(1) The first butyl sealant is unqualified or not compatible with silicone sealant.
(2) The secondary sealant is filled with mineral oil.
(3) Contact with other sealants filled with mineral oil, such as weatherproofing sealant.
(4) Other factors such as desiccant or processing technology.
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