Removing motorhome sealant.

[TheMitchells]

Not building related, but i am hoping for advice from the forum on how to remove sealant on motorhome joints.  

 

We have just discovered that our 17 year old motorhome has quite bad damp, within the walls, that really needs sorting.  However, this involves removing all internal units, cutting away the interior walls, removing the damp insulation inside the walls, and then replacing everything!  We have been told it will cost over £10k as it will take 4 weeks.  About 60% of that is labour.  Our motorhome is only worth about £15k yet it is perfect for us and we did not want to replace it for another few years. Internally, there appears to be no mould within the living quarters. it all seems to be within the walls, and so far, we have never smelt or seen mould. Financially, it is just not worth us having the work done.

It is highly likely that water has entered via the external sealant, now 17 years old.  It is all very dry and cracked.  So our thoughts are to just remove and reseal the external joints with Sikaflex 522 ourselves.  And keep it going till we can afford to replace it in a few years or until the damp starts to show in the living area.  

 

Any advice on the best way of removing as much old sealant as i can before I reseal with new?  I've done quite a bit of sealant applications in the past but not sure about how best to remove the old stuff.  Thanks.

[SteamyTea]

25 minutes ago, TheMitchells said:

 

Any advice on the best way of removing as much old sealant as i can before I reseal with new

There will be a solvent that works, but unless you know which adhesive was used, it will be trial and error.

Start with the easy solvents.

White Spirit, Methylated Spirit, Acetone, gasoline and WD40.

Don't convince yourself that with a bit of solvent and a huge amount of elbow grease that it is working. A solvent should make it dead easy to remove.

If none of them work, then it is a case of internet shopping for things like Dichloromethane, my favourite and Xylene (my least favourite), or even Toluene. 

I think it was @Onoff that found a cleaner in Lidl that seemed to remove most things, so maybe trip there on Thursday.

Edited yesterday at 18:59 by SteamyTea

[saveasteading]

 

12 minutes ago, SteamyTea said:

my favourite

You forgot Snibbo.

[TheMitchells]

I'll give these a try.  I do recall WD40 being good for sealant removal.  😊 I guess it may be a case of trial and error and a steady hand with a sharp chisel.

[saveasteading]

I've got some old sealant that I should have thrown away because it was never much good. I will see if solvents are mentioned.

[ProDave]

If you can't see or smell damp or mould, what makes you think the structure has got wet?

 

A well designed caravan / motorhome will be built with all joints lapped the correct way so water does not enter and the sealant is for good measure only.  The one exception to this was an ABI we had in the 90's that when investigating damp (it really was damp and showing) I found to my horror and disbelief the wall to roof joint was lapped the wrong way so it was only the sealant stopping water entering.

 

If there really is water getting in, I am not sure I would be ripping it all apart from the inside, it is the external joints that need investigating and re sealing, mostly roof to walls, and wall external corners.

[Onoff]

56 minutes ago, SteamyTea said:

I think it was @Onoff that found a cleaner in Lidl that seemed to remove most things, so maybe trip there on Thursday.

 

Screwfix No Nonsense remover worked for me.

[MikeSharp01]

I am aware that some manufacturers have had issues with condensation in the walls of their machines it may just be that. Why not look at a dry the panels out solution - drill a pluggable hole, connect a pipe to the hole and a tub of silica gel and see how much moisture you can draw out that way. You can get Silica Gel in volume: https://www.amazon.co.uk/Quart-Replacement-Desiccant-Indicating-Silica/dp/B013L31PQ0 that one is indicating - it changes colour as it gets wet and is likely to be toxic if swallowed - IIRC normal, non indicating, silica gel is harmless though

[ToughButterCup]

Sometimes - with care - a heat gun (hot air, not a flame thrower) will loosen things up a bit

[TheMitchells]

19 hours ago, ProDave said:

If you can't see or smell damp or mould, what makes you think the structure has got wet?

 

If there really is water getting in, I am not sure I would be ripping it all apart from the inside, it is the external joints that need investigating and re sealing, mostly roof to walls, and wall external corners.

Its definitely damp.  We had seen a little bobbling in the 'wallpaper' of the lounge area, and had noticed it was spreading a bit.  But then, after seeing a very nice new MH at a dealership, the salesman offered to take a look at ours to give us a part exchnage price.  we agreed, just to give ourselves an idea of the value of our van, as we are not planning to change it anytime soon.  We were horrified when he pointed out several areas of softness/sponginess in the walls and said it was damp within the structure.  When we got home, we borrowed a damp meter and confirmed his findings.  But when the experts at our local repair shop took a good look, it was actually worse than we thought.  And to get to the damp within the walls, they do have to remove all the units. We assume they would need to remove the actual internal wall and replace with new insulation and wall. Such a shame 😩. 

Sandwich bonding is the current construction technique used by most caravan
manufacturers and coachbuilt motorhome converters in an effort to reduce weight and
cost. This doubles as insulation, the ‘filling’ being either expanded polystyrene (white) or
Styrofoam (blue) insulation. The amount of insulation varies, with 22-25mm thickness on
average, usually more in the ‘winterised’ vehicles and in the floor area.

The  exterior joints of most of the wall panels are sealed with sealant and its clear most of it has degraded, dried out and cracked, letting in rain.  I had said for a while that we ought to renew the sealant but hubby didnt think it needed doing.  He's regreting that now, though it obviously had damp already in the walls when we bought it.  We've had it 6years and its been great.  

I feel quite sad for the 'old lady'. 

[TheMitchells]

we are thinking of having alook at an area under the bench seat to see what is actually happening in the wall and if its something we can sort out ourselves.  But I can certainly start removing and resealing areas before that - it will just have to wait till its a little cooler! 

[TheMitchells]

19 hours ago, MikeSharp01 said:

I am aware that some manufacturers have had issues with condensation in the walls of their machines it may just be that. Why not look at a dry the panels out solution - drill a pluggable hole, connect a pipe to the hole and a tub of silica gel and see how much moisture you can draw out that way. You can get Silica Gel in volume: https://www.amazon.co.uk/Quart-Replacement-Desiccant-Indicating-Silica/dp/B013L31PQ0 that one is indicating - it changes colour as it gets wet and is likely to be toxic if swallowed - IIRC normal, non indicating, silica gel is harmless though

Thanks, its certainly worth a look.  Some areas are showing 30% dampness which is pretty bad.  They normally say up to 15% is a level for concern.  We'll be taking an area out undr a seat to give ourselves a better idea what is actually happening. 

[ProDave]

Let us know what you find when you open up a trial area.

 

I still have mixed feelings on this, if the damp is not causing a real problem, I would carry on and live with it.  If you take what you have been told literally it is scrap now with a repair cost quoted to you of what it is worth.  A bit like in the boating world, scrapping a boat with osmosis.

 

While it is warm, get a portable dehumidifier in there to dry it out.

 

Can you post some pictures of the outside, roof to wall joints and wall corner joints.

 

[saveasteading]

If you can stop the liquid water coming in at metal laps, wndow joints etc then you are winning. 

The next stage is the dampness inside drying out. With windows open snd the summer temperatures it might be slow but will happen.

That's unless any water is between 2 impermeable layers.  Only then might some holes or stripping back be worthwhile.

But it's mostly plasterboard or hardboard isn't it?

[ProDave]

Usually hardboard on the inside of a caravan, or something similar perhaps thin ply etc.

 

My thought is still leaning to a very slight leak or condensation within the structure that has led to a gradual build up.  That's why I would be trying a dehumidifier and I mean a proper mains powered one not a tray or magic crystals.  This weather is perfect for it, heat to drive the moisture out and the dehumidifier to remove it.

 

Repeat you damp readings after a week of that running.