Expert advice

Sooner or later a silicone sealant joint in the bathroom or in the kitchen has to be repaired — because the joint has been damaged, for example, or because mold has started to grow in the old bead. But before new silicone sealant is applied, the joint has to be cleaned of the old sealant, of mold and of other contamination.

Why the old sealant has to be removed

Applying new sealant over old silicone makes no sense: the new sealant simply will not bond to the old one and the joint will not be tight. A joint with sealant residue left in it cannot be repaired, so the old sealant has to be removed completely.

Caulking guns fall into two categories: consumer guns — guns for the DIY market, as it is now usually put — and professional guns. Consumer guns are noticeably cheaper, and buyers who do not see what a professional tool gives them choose on price alone. A professional caulking gun, meanwhile, has a great many advantages. Let us go through them on the example of the professional half-barrel gun KUDO^® KUSGUN12.

Hybrid adhesive sealant: what is it?

Hybrid sealants, known mostly as MS polymers or SMP (Silyl Modified Polymer), were first introduced by the Japanese company Kaneka about 40 years ago. They are a hybrid polymer of polyurethane and silicone. The material obtained by crossing polyurethane with silicone has the strengths of both and is free of their weaknesses.

Where hybrid polymer materials are used

The range of applications of hybrid polymer materials follows from their all-round properties and is therefore extremely wide: they are used as adhesives and sealants in construction, in the home, and in the aircraft, automotive and shipbuilding industries.

The most common mistake in working with PU foam sealant is not moistening the joint enough.

Foam cures under the action of moisture. What happens when there is not enough of it is what we set out to show in the experiment below.

We filled two cups with the same PU foam sealant. In one of them the foam was moistened, in the other it was not. All the other conditions were identical, yet in one cup the foam cured and in the other it did not. This is why the joint must always be misted with water before it is filled with foam, and then misted once more after filling. And the joint must not be covered with vapor barrier tape until the foam has fully cured.

The KUDO^® range includes metallic spray paints with two types of pigment: leafing and non-leafing. They differ both in appearance and in other properties.

A sealant for a bathroom has to meet several specific requirements. First, it must resist mold growth. Second, it must be water-resistant. Third, it must be elastic, because the joints that need sealing in a bathroom are often subject to movement. On top of that, a bathroom sealant needs good adhesion to a range of materials.

To find a suitable sealant, look at the sealant selection chart. It shows that two types meet all of these requirements: hybrid and silicone sealants.

Hybrid sealants are a versatile, balanced solution: they combine the best of polyurethane, silicone, acrylic and rubber sealants and adhesives. Their main advantages are that they can be applied to a damp surface, have high strength and good adhesion, do not yellow, give off no odor and, most important, resist mold and mildew well. The flip side of that strong adhesion and high strength is that a hybrid sealant is harder to remove if it ever has to come off.

Silicone sealants are either acetoxy cure or neutral cure, depending on the curing system. Acetoxy sealants give off a sharp smell of acetic acid while they are being applied; neutral cure sealants are practically odorless. Acetoxy sealants are used on stainless steel, glass, ceramics and wood, but they are not compatible with alkaline materials (cement, lime, gypsum), marble or granite, and they corrode metals. Neutral cure sealants can be used without such restrictions.

We are often asked whether detergents and household cleaners can be used to remove dirt from sealant in the kitchen and the bathroom.

In rooms with high humidity we recommend general purpose silicone or sanitary sealants. Sanitary sealants differ from general purpose ones in their higher fungicide content, which makes them more resistant to mold and mildew.

Both general purpose and sanitary silicone sealants resist most cleaning and washing products. Common store-bought drain cleaners, for instance, cannot damage a KUDO^® sealant. If you intend to use industrial chemicals, however, we recommend testing their effect on the sealant first.

The chart and the simple selection table below make it easy to choose a sealant for the type of work you are planning.

What are the advantages of a foam adhesive over the traditional anchor fixing of thermal insulation boards?
The obvious answer is that installation gets much simpler: no rotary hammer, no drilling into the wall. But that is only one advantage out of many. To see what else you gain by using a foam adhesive instead of anchors, let us first look at what goes on inside a wall when a facade is insulated with these materials.

The range of foam guns on sale is huge. Prices differ by a factor of tens: the cheapest cost a few hundred rubles, the most expensive a few thousand. Let us look at the parameters and properties worth paying attention to when choosing a gun.