In our old houses, I have used lots of different silicones and acrylic caulks and PU foams to draft-proof gaps, such as around window frames and skirting boards. Some are sold as non-shrinking, but even so, after a few years they all seem to shrink a little and the crack reopens.

Has anyone found a good gap-sealing goop that stays sealed for many years?

Ideally it would be paintable and allow a little movement.

How about expanding sealing tape, generically called compriband but now actually improved such as https://www.ecologicalbuildingsystems.com/product/contega-fiden-exo, no doubt less premium-price brands too, and Compriband is still sold, probably improved. I'd love advice on best value brand.

Posted By: revorI have had very mixed performance from expanding foam tapes in my experience they do not perform well in very exposed situations. Driving drain does saturate them and they can work like a sponge and track water downwards like a pipe water and will find any weak spots in your construction and let in. Very good at draughtproofing. I still use it but would not entertain it in exposed situations without a proper sealant behind it.

Yes, it's a first line of defense that needs either a sealant behind or some kind of well-detailed flashing / tray to direct the water out. Get that right and the plus is that, when used to seal against timber, the permeability of the foam should enable dampness to evaporate, rather than it being trapped behind an imperfect impermeable sealant where it may contribute to decay. Which is why I've specified it for some exposed timber windows on a project next year.

I use Sika Flex marine, expensive but good. Used on the house build 12 years ago and on various metal roofs around the place.
Michael

I've never had a problem with expanding foam tapes, they are ideal for uneven gap filling, you just need to select the right one. The impregnated ones made for exterior application are fine, IMO. You can always belt and brace the job with a mastic bead over the top to give an even appearance.

If you do need sealant that does not crack then +1 for Sikaflex used in caravans/motorhomes. It deals with lots of flex and differential expansion of materials with temperature changes. I think you can paint it also - need to check.

I have also been using CT1 as a heavy duty sealant. Again expensive but is stronger and better than normal silicon sealants. CT1 you can paint like caulking so if caulking is cracking it could be a good alternative inside. You cannot paint normal silicon.

For inside sealing around the house I used low expanding Soudal genius - squashing the straw to get nozzle into gaps. Mine is a 50s house with cavity. It bonds everything together and helps to seal things up. This helps the final seal not having to hold the movement of the wood / plastic etc on its own.

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