caravan sealant

Motorhome and Caravan Sealant 2022

Motorhome and Caravan Sealant

Motorhome and Caravan Sealant has come on a long way in the last 30 years or so. The advancements in technology allow fewer screws to be used in the construction and the sealant to become an adhesive to bond parts together making the vans stronger.

There are more sealant types than you probably think, if you want to repair your van yourself its worth getting the right one first time. This article should help you pick the correct one for the job and a few tips along the way. 

If you think might have a leak its worth investing in a cheap damp meter just to help confirm your thoughts. It will also help show how big an area is actually affected, sometimes its more than what you think! 

If it’s obvious you have a leak the wallboard inside will no doubt be water stained and the van may smell “damp” as well. Do not ignore these two factors as it can only get worse the longer its left. 

Damp motorhome

As you can see in this picture the actual leak was covered by the toilet itself so it was not obvious it was leaking. A new section of floor would need to be replaced as well. 

Types of Motorhome & Caravan sealant

  • Non-Setting – mastic style sealant in a tube. 
  • Mastic Tape – a medium firm sealing tape that gets put behind a exterior fitting before it gets screwed into position.
  • Butyl Mastic – a buytl rubber mastic tape, usually black.
  • Silicone – A flexible sealant once dry, available in all colours, in a tube. Not for exterior sealing.
  • Polyurethane – a strong flexible sealant and adhesive in one. Used on many modern caravans for construction.
  • MS Polymer – similar to polyurethane but has no solvents in it and a slightly stronger bond. These sealants are mould resistant and are not usually affected by cleaning products. This is the best caravan sealant due to its strength and resistance against the elements.

Check out this video for a brilliant trick when resealing your Caravan or Motorhome. For more tips see further down this page.


This type of sealant has been around for years and as the name suggests it never sets which means it can allow movement and expansion/contraction. This caravan sealant hasn’t been used on new vans for about 15 years or so. It is super easy to work with though and was used mainly on awning rails etc. A sealant gun is required to use.

Mastic Tape

Mastic tape can come in various widths and depths this one pictured here is 32mm wide, the most common size. Its a pliable super sticky tape that can be stretched or doubled up for thicker applications.  Was used to seal everything before tube based sealants became more prominent. Still a good , easy to apply way of sealing items.

Buytl Mastic

Similar to the mastic tape above the buytl tape comes in various size rolls. It remains pliable permanently and is highly resistant to UV. It allows movement in whatever its sealing. Used a lot in mainland Europe caravans and motorhomes. 

buytl caravan sealant
Buytl "rope" sealant ready to go on an Elddis Autoquest Heki rooflight

Silicone Sealant

Silicone Sealant should never be used on the exterior of caravans or motorhomes full stop! It simply fails after a short period as it shrinks due to UV light and just doesn’t adhere, especially with movement as well. In the bathroom yes it works well and can be used on wallboard corner joints too, especially this ivory colour which matches most colour schemes in vans.

Polymer and Polyurethane Sealants

Polymer and polyurethane sealants are the modern way to construct caravans and motorhomes. A Polymer is a chemical compound of connecting molecules and polyurethane is a type of substance made from polymers. The connecting molecules allow for the strength and flex in this sealant.

Sikaflex 522 (Formerly Sikaflex 512) is a modern polymer sealant and adhesive in one. The Sika name is recognised as being a quality product and the 522 formula has been made especially for caravans and motorhomes. Uv resistant, flexible, non-corrosive and bonds pretty much anything to anything. If you are removing rails etc consider sikaflex 522 to use when refitting them as it is far superior to say non-setting. Also available is Sika 521-UV which similar but with higher UV resistance. Available from Amazon.

With similar attributes as Sikaflex 522 Soudal Fix All is UV resistant, flexible and is a sealant adhesive.  This one however is the “turbo” version and is worth a mention if you need to seal something and it be cured in about 20 mins. It’s also available as non-turbo here

Both work really well and are a good alternative to Sikaflex 512 / 522.

Dekalin Dekasyl MS-5 is a MS polymer based sealant made especially for caravan and motorhomes. Its a sealant and adhesive all in one so it is ideal for all sealing purposes and for fitting accessories like bonding solar panels and satellites to roofs. Available from Amazon.

Whats the most common thing to leak?  – This varies from van to van and every manufacturer has its “issues”. Older caravans (15 years or more) I would say awning rails. They were held in place with a lot of screws which means lots of places for water to sneak in. Window rubbers also are prone to leaking, normally from not being particularly well fitted from new. Front window rails too.

On motorhomes it tends to be aluminium framed locker doors, awning rails and skirt rails. Quite often if the skirt rails leak it will rot the floor without you knowing as its under the vinyl until it becomes spongy, by this time it will need wood replacing to rectify.

This damp tester is cheap with excellent reviews on Amazon

Brennenstuhl Moisture Detector MD (Moisture Meter for wood/walls/building material, with LCD Display) anthracite/yellow
  • Moisture Tester to determine the moisture of wood, walls or other...
  • Moisture Sensor with a measuring range of 5 -50% for wood, 1.5 -...
  • Moisture Detector with practical hold function allows measuring...

Last update on 2023-01-29 / Affiliate links / Images from Amazon Product Advertising API

Tips for using Motorhome and caravan sealant

Preparation is the key when resealing something that is leaking.

If its a rail, all of the old sealant needs to be removed. To do this ideally use a plastic scraper especially when removing sealant on the van. One slip with a  metal scraper and you will have another thing to sort out. The idea with a plastic scraper is that its a softer material than the aluminium and is much less likely to cause damage, these would be ideal.

Next, both the rail and the van need to be degreased thoroughly. Panel Wipe is a workshop staple for this or white spirit or similar. This is essential for a good bond and seal.

Apply the sealant or mastic as necessary on the rail and the van ( going over any seams on the van), position the rail on the van, ideally you want excessive sealant to “squidge” out so you know any voids have been filled. Get a couple of screws in it , always use existing holes if its screwed on then the rest will line up.

Then once screwed in position clean off the excess sealant using Panel Wipe or White Spirit using a white lint free cloth (a coloured cloth shows up in the white sealant). Keep turning the cloth every few wipes.

I hope this has given you a insight to the basics of sealant. I advise taking a look at the video on this page if you are thinking of sealing your van as it may save you a lot of time.

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     Please note these are the words and opinion of the author only. Neither the author nor the website can be held responsible for any errors or omissions. You should seek professional assistance if in doubt.