capillary action

[cyclop]

This forum seems to have a plethora of knowledgable folk in many disciplines so here goes.My pop top eriba caravan has a leak.Cracked high level rear light fixed.Awning rail resealed professionally.Have removed rear and side lockers and destapled the roof lining revealing foam insulation some of which was soaking,removed and dried.After much searching,I,ve isolated a possible cause.A low spot in the fibreglass roof allows a shallow pool of water abutting the upstand part of the roof to form .An aluminium moulding covers this and acts as a securing point for the pop top canvas.This moulding is just a pushfit.Now,my question is,could water now get inside the van via capillary action,especially on a windy ,wet day.I believe it could and does.Any thoughts or experience of this?

[thirdcrank]

My answer based on O-level physics from six decades ago is yes, it could be capillary action, for which all you need is a narrow enough "tube" for it to be drawn through. IIRC, the tube needs to be too narrow for the liquid to form a meniscus on its surface and by "trying" to do so it is drawn through the tube. Other forces such as wind should not really affect it, but the wind could be causing the initial supply of water. AFAIK, the only ways to prevent it, are to seal the tube completely, or widen it so the capillary action doesn't work, although the latter would allow water in in other ways eg driven in by the weather.

[merseymouth]

Hi There, Something in my noggin thinks "Osmosis" may be relevant? I could of course be well wide of the mark TTFN MM

[thirdcrank]

My O-level biology tells me it's not osmosis which is the movement of a liquid through a permeable membrane whereby the weaker solution loses liquid to the stronger, tending to balance them.

[NATURAL ANKLING]

Hi,
I have an eriba roof
The upstanding on the main roof is tall enough (without going for a look in the rain) not to let water in IIRC.
The pop up roof which holds the rubber seal between pop up and main roof on mine was a really bad fit on mine, but before that it never leaked.
You just remove the rubber completely and lower the pop up roof carefully on to main roof.
Then trace around the pop up roof with a felt pen lying on its side (fat pen maybe) raise the roof and cut off any badly protruding bits then recheck.

On my van the rubber sealant was not enough behind all the trims to seal water out, I resealed all the all the trims!
The windows are prone to leaking where they seal on van wall, crinkled aluminium panel, needs plenty (only use eriba mastic!) mastic here.

They are not that well finished I.M.O.

The aluminium panels can corrode badly if there are gaps behind the trims...............seven years and there will be holes

Some picture would help with confirming what part you are talking about.
Fire away any questions, I have owned mine for over twenty years and do all the work including replacing panels and reinforcing the metal tube frame for rear rack etc.

Motorhome but same panel construction.

[Vorpal]

A low spot in the fibreglass roof allows a shallow pool of water abutting the upstand part of the roof to form .An aluminium moulding covers this and acts as a securing point for the pop top canvas.This moulding is just a pushfit.Now,my question is,could water now get inside the van via capillary action,especially on a windy ,wet day.I believe it could and does.Any thoughts or experience of this?

It seems likely. Driving in the rain can force water into all sort of nooks and crannies you'd never otherwise know were there.

As above, picture might help. But if the moulding is just push fit, can you seal it around with silicon? It would mean getting some silicon sealant remover to get it off, if you need to take the moulding off, but maybe that's better than the water ingress?

[Paulatic]

Very topical, I’ve just had an awning rail off cleaned and resealed using a30mm x4mm mastic tape. ( reminds me of blutac ). Also used Sikaflex EBT from Screwfix which is similar to the caravan sealant Sika 512.
In another caravan I’m working on water ingress from two tiny holes, I believe inflicted from the strimmer throwing up grit. I’ve repaired those with an expoy resin.
Don’t use bathroom Silicon and I don’t believe you’ll need Eriba special stuff. You need something which remains flexible. I use white spirit in a spray bottle to remove old sealant then clean off with meths before the new.
I’ve had two pop tops which we loved but in both the weak point was at the folding part.
I’ve never used Captain Tolleys but people say it works for small cracks.

[cyclop]

Ok ,some pictures I hope.Taken from inside,looking toward the back rt. hand side of the pop top opening.Water is creeping over the upstand and making its way under the headlining,onto the subframe member and wetting the foam insulation.The ally profile can be seen.Thinking I should put sealant in the well of the profile.

[Paulatic]

To get this right
The deep side of that aluminium fits over the raised lip of the roof. I’d think it unlikelywater could get around that but what’s to stop it being refitted with a rubber or sealant?
Is it more likely there is cracking in the fibre glass around the base of the lip allowing the pool to seep through. If so that could be a case for Captain Tolley.

[cyclop]

Yes,exactly.Pretty sure it,s not leaking through the fibreglass so currently drying everything and will attempt to seal.

[NATURAL ANKLING]

Hi,
The Eriba stuff is a mastic, your apply it using my gun.
Paulatic, Have you use the eriba stuff ever,Only asked because I am curious to find something which is similar but cheaper and easier to get hold of. It's a type of butl rubber Similar to seem sealant on cars, But the stuff you normally buy does not set very quickly, Too runny.
The eriba mastic is very fluid when you apply forms of skin within a day also.
But it never hardens so parts can be dismantled easily later, a little heat helps here also.
Don't use silicon rubber ever!
Impossible to dismantle aluminium parts without distorting and if you have to take them apart.
When I replaced my awning trim I had a mastic strip to but this does not extruded right To the edges so you need to fill this gap as well.
Leaving any gaps under the trim holds water and thus collect dirt and grit not to mention allows corrosion to.
eriba uses self tapping steel screws, After tapping a new hole with a screw I replace with stainless screws, Makes sense.

On the 0P'sproblem, I agree water Unlikely to go up that upstanding, considering also that the roof will be down so there is no forced water.
I think you might be right the crack in fibreglass is more likely.
Needs completely drying and cleaning and a good inspection looking for cracks

(Text by speech)

[NATURAL ANKLING]

Hi,
Does the water drip off the aluminium up standing inside van?
If it does your original diagnostics is correct.
If it does not, the wadding is damp then suspect What we have suggested.

[cyclop]

Water dripping off aluminium so,yes,still suspect capillary action via a sodden canvas in that corner.There is also rucking and a join in the headlining at that point,thus creating more tiny pathways for potential ingress .

[NATURAL ANKLING]

Hi,
whilst it is all sodden, It's going to be difficult to tell where the water is coming from.
You are going to have to dry it all out first. The dripping at the moment may well be from the Saturated wadding.
It's possible that your original diagnosis is correct, but I've never had this problem in 30 year Old van, also never done any work in that area.
When it's all dry you need to do thorough inspection of the fibreglass roof.
I will still bet it's more likely a crack in the fibreglass Than capillary action.
That's a crack in the upstanding fibreglass lip?
With the roof down I get a pool of water well for small Puddle.
But you can only tell when you lift the roof on the water comes down outside.
But this is more from behind the Roof seal of the pop-up parts.
The water can settle next to the upstanding as the roof is not Perfectly curved.

[Graham]

Don't forget to consider condensation as a source of wetting, mould & rot.

Water vapour can get anywhere / everywhere, leading to interstitial condensation.

I get the impression that it is a non-trivial problem in caravans, motorhomes & the like. . . especially around cold spots.