Mastic, silicone, sealants and foams.

[Nickfromwales]

Let’s discuss the different products and their correct placement / applications.

 

Following on from this post:

 

 

[Nickfromwales]

Popular products for myself, are:

 

Illbruck FM330 expanding foam. Airtight, closed cell, and goes off very hard compared to off the shelf foams from the BM’s etc.

 

CT1 vs silicone, from a robot in cyberspace:

 

The key difference is that CT1 is not a silicone; it's a proprietary TRIBRID® sealant and adhesive with a unique polymer formula, while silicone is a class of materials known for their flexibility, water resistance, and sealing properties. CT1 offers advantages over traditional silicones, such as superior strength and color retention, and the unique ability to be applied in wet conditions without shrinking or cracking, unlike many silicones. CT1 functions as an all-in-one product for sealing, bonding, and caulking, whereas silicone is primarily a sealant, with its strength and properties varying significantly depending on the specific formulation.  

 

CT1

• Technology: Uses TRIBRID® Technology, a unique polymer that makes it stronger and more durable than traditional hybrid products. 
   
• Application: Can be applied in wet conditions, even underwater. 
   
• Features:
  • No shrinkage or cracking. 
     
  • Excellent color retention (white stays white, clear stays clear). 
     
  • Solvent-free and food-safe. 
     
  • Bonds to many materials, including metals, glass, wood, and concrete. 
     
  • Can be painted after curing with water-based paints. 
     
• Function: Functions as an all-in-one sealant, adhesive, and caulk. 
   

Silicone

• Composition: 

  A material (polymer) known for its elasticity and water resistance. 

   
• Application: 

  Some silicones are not suitable for use in wet conditions or on wet surfaces during application. 

   
• Features: 

   

  • Can have a long shelf life. 
     
  • Good for creating waterproof seals. 
     
  • Prone to shrinking, cracking, or degrading in certain environments, depending on the type. 
     
  • Can lose its color over time. 
     
• Function: 

  Primarily used as a sealant in applications like bathroom and shower enclosures. 

[SimonD]

For my triple glazed windows I used the Soudal SWS thermal and airtight system. It doesn't use a silicon but a hybrid polymer sealant. From soudal's website https://www.soudal.co.uk/pro/applications/airtight-sealing:

 

Soudaseal 215LM

Add to quick access

Product description

Hybrid polymer facade sealant

Premium quality, low modulus Hybrid Polymer sealant. Extended open time versus silicones to allow longer tooling of product. Primerless adhesion on nearly all common construction materials such as plastics, masonry, metals and wood - even when surfaces are damp. Can be used on sensitive metals such as lead. Non-staining when applied on natural stone substrates. High performance mechanical properties. UV resistant. Free of isocyanates, solvents, halogens and acids. Paintable with all water-based paints. Airtight when used as part of Soudal Window System - SWS®.

 

The foam is:

 

Soudafoam Gun Win. & Door SWS

Add to quick access

Product description

Elastic PU gunfoam

Airtight premium quality polyurethane expanding foam filler for use around windows & doors. Superior thermal and acoustic insulation properties. Totally airtight after curing. The product is highly flexible once cured, based on FLEXIFOAM® technology, which gives improved durability. Single component Gun Grade foam. Rapid curing. Primerless adhesion on most construction materials.

 

And then finished to the interior with:

 

Acryrub SWS

Add to quick access

Product description

Acrylic sealant

High quality elastic silanised sealant and gap filler based on acrylic polymers. Conform DIN EN ISO 11600 F12,5E. Used for airtight sealing of interior joints and window connections with movement of up to 12,5%. Part of the Soudal Window System.

 

I used the acryrub on a lot of interior timber frame joints, e.g. between wide sole plate and glulam ring beam and then between ring beam and the stud wall.

 

On other windows I used a different brand of expanding tapes like Compriband.

 

I also used a lot of Soudal Soudatight LQ for junctions and window reveals where necessary:

 

Air- and vapour tight membrane

Soudatight LQ is a high-quality fibre reinforced polymer membrane which forms an air and vapour tight elastic membrane after drying. The product can be quickly and easily applied with a brush in the desired layer thickness on almost any mineral substrate. Fills cracks up to 5 mm due to fibre-reinforcement. Once dried a second coat (or more) can be applied if required, after which it can be painted or plastered over. The black variation changes colour after drying, from blue to black. The white version does not have this colour indication.

 

I've also used quite a bit of tapes for windows from Passivehaus Systems:

 

https://passivehousesystems.co.uk/product-category/window-tape/

 

And also their tapes for airtightness at osb junctions for house airtightness barrier.

 

https://passivehousesystems.co.uk/shop/?filter_tax_product_cat=80&filter_location=internal&query_type_location=or

 

Internally when I need somethng for bathrooms/kitchens etc. I use CT1 as @Nickfromwales has so many times recommended.

[Oz07]

Can ct1 be used for glazing units or does it effect the black rubber round the edge? I know silicon is a no no but its hard to find something paintable that is good for this in timber windows

[Nickfromwales]

2 hours ago, Oz07 said:

Can ct1 be used for glazing units or does it effect the black rubber round the edge? I know silicon is a no no but its hard to find something paintable that is good for this in timber windows

I've installed loads of mirrors with it, with zero issue. Can't see why not, and it's less aggressive so doesn't react with things the way silicone seems to.

 

Plus, CT1 can be painted whereas silicone cannot.

[Adrock]

I've used a fair bit of OB1, which as far as I'm aware is a copy of CT1.

 

Anyone ever used CT1 power grab and bond? 

 

@Nickfromwales where do you get the illbruck foam? I could do with a bit of that. 

[Nick Laslett]

Another product to consider is Sikaflex EBT+ as an alternative to decorators caulking. It can be painted and doesn’t shrink. Also UV stable and suitable for exterior use. 
 

Obviously, decorators caulk is much cheaper. 

 

I also used a lot of Siniat Foil Roll Intumescent Acoustic Sealant for my stud walls. Just following the ‘White Book’ instructions. There maybe cheaper alternatives, not sure if this is a category where there is a big difference in quality. 
 

Illbruck SP525 for sealing larger exterior gaps, and ‘painting’ over expanding foam to protect it from UV light. 

 

 

Edited Monday at 20:39 by Nick Laslett

[Onoff]

1 hour ago, Adrock said:

Anyone ever used CT1 power grab and bond? 

 

Yes. I used it to stick ceramic tiles to marine ply. 

 

 

 

[Adrock]

Good stuff?

[Onoff]

10 hours ago, Adrock said:

Good stuff?

 

Kevin Cashin at C-Tec, the makers of CT1 suggested it. The tiles have been on I'm guessing 6+ years now and are going nowhere. 

 

 

The bath sides slope in slightly too. The end and side panels are removable for access to the pump and plumbing. There's discreet fixings covered with silicone. I didn't grout just used Forever White so everything can flex and be cut out easily. 

 

 

[jack]

Great thread @Nickfromwales

 

I've pinned it for visibility.

[Super_Paulie]

13 hours ago, Nick Laslett said:

Sikaflex EBT+

my go-to, plus it smells sensational.

[Mr Punter]

14 hours ago, Nick Laslett said:

Sikaflex EBT+ as an alternative to decorators caulking

 

I don't think it is a good alternative.  Caulk is a cheap acrylic filler that is easy to apply and smooth before painting, especially when moistened.  You can wipe it off with a damp cloth.  It cannot be left exposed as it will look poor.  It cannot be used in wet areas or outside.  I hate caulk around electrical switches and sockets.  Just awful.

 

EBT+ is a polyurethane based adhesive /  gap filler that can be used outside.  It is more difficult to finish.  It is very sticky and difficult to remove.

[Nickfromwales]

10 hours ago, Mr Punter said:

 

I don't think it is a good alternative.  Caulk is a cheap acrylic filler that is easy to apply and smooth before painting, especially when moistened.  You can wipe it off with a damp cloth.  It cannot be left exposed as it will look poor.  It cannot be used in wet areas or outside.  I hate caulk around electrical switches and sockets.  Just awful.

 

EBT+ is a polyurethane based adhesive /  gap filler that can be used outside.  It is more difficult to finish.  It is very sticky and difficult to remove.

But you’ve failed to comment on how good it smells? 

[Nickfromwales]

On 29/09/2025 at 20:41, Adrock said:

I've used a fair bit of OB1, which as far as I'm aware is a copy of CT1.

 

Anyone ever used CT1 power grab and bond? 

 

@Nickfromwales where do you get the illbruck foam? I could do with a bit of that. 

https://www.dortechdirect.co.uk/catalog/product/view/id/3337.html?gad_source=1&gad_campaignid=17178602520&gbraid=0AAAAADt-Kn3UBXyOZR0vEG_JM_vZTmbQs&gclid=CjwKCAjw_-3GBhAYEiwAjh9fUK0DFMamvrz5o04Rdcyabesg7HS5_9qpOjUeEjy5SmbMj_yq1AzzWRoCY1wQAvD_BwE

[sgt_woulds]

CT1 really is 'The problem solver'

 

I've used it for repairing and 'stretching' concrete roof tiles on my south-facing roof (10 years on and no issues)

 

I've used it for sealing various external areas that need to be 100% waterproof for the life of the building, but a little bit of flex for expansion and contraction of differing materials.

Internal or external makes no difference to performance as far as I can tell.

 

We once made the mistake of using CT1 to seal a cable entry through a wall for a PV system.  When the owner decided to extend their house, we came back to move the system.  It took 5 hefty men in a tug-o-war on the cables to pull the plug of mastic out of the wall!

 

I've hung a hook (with a wide base) from a ceiling beam that has held a 20kg bike in the air for 2 years now.

 

We completed an emergency repair to a chimney flaunching in driving rain and a howling gale.  Inspected it two days later when the rain had finally stopped, and it was rock solid.  The homeowner decided not to have the pot re-bedded.  To my knowledge, it has never been properly repaired, but I'd be 100% confident that the CT1 will still be perfect.

 

We found that the clear CT1 flows better and has a slightly longer curing time, which is useful if you need to smooth it.  It is also better for repairs that need to remain invisible. 

 

It's a bugger if you get it on bare skin, though!  One trick for smoothing with fingers - lots of spit.  It's disgusting, but human spit allows your skin to slide over the top of CT1 without sticking - if you try to do the same with water, you will just gunk your fingers.  (Spit doesn't work as well on the coloured varieties for some reason - these just seem to be more sticky in  general)

 

I always keep a tube of CT1 in my toolbox, just in case.

 

 

I've tried the Wickes BT1 alternative, but the grip doesn't seem as strong, it doesn't stick as well on damp surfaces, and the clear version goes yellow in the sun.  It is about £1.80 cheaper than CT1 per tube, and is fine for indoor use, but I wouldn't hang a bike off it or make a long-term roof repair...

 

 

[Onoff]

31 minutes ago, sgt_woulds said:

I've tried the Wickes BT1 alternative

 

It's not a Wickes product.

 

BT1 is made by C-Tec who make CT1 but it's specifically meant for bathrooms etc as it has anti bacterial / anti microbial properties. 

[sgt_woulds]

Ah, and there's me believing what the man in the store said.  Explains a lot 🙂

 

I won't be using it to re-enact the 'Solvite' adverts anyway!  With CT1, you could probably have hung an elephant under the helicopter...

[Onoff]

I've used The Dogs B******s and Sticks Like Sh!t to stick tiles to moisture resistant plasterboard. 

 

CT1 is no good for fixing leaking heating oil or hydraulic tanks.