# GRP and gel Coat Cracks



## duds

Is is usual on the Motorhome habitation body to find cracks appearing on the roof GRP or gelcoat or around curved edges ? 

Can these be repaired easily and effectively and do they reappear again.? What causes these ? 

Do repairs make the cracks invisible and does the colour match afterwards?

I ahev a nearly new van where these have appeared already.


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## 113016

They are usually stress related, although they can be caused by a thin gap between the gel and the glass fibre matting.
I would not worry too much about smaller ones on curves, however I would not like to see long cracks on the roof.
The smaller ones can be repaired and with the correct colour gel they would be invisible if a good job has been carried out.
If you have quite a few, I would be asking the manufacturer why and most certainly if the vehicle is pretty new.
Again, I am no expert, but I did work within the Marine industry for over 20 years.
One thing, are you sure they are cracks through the gel or is it what we call staring which happened as it came out of the mould and has always been there and you did not notice.


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## Jezport

If you search the forum, a number of people have had this problem and they have posted their experiences.


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## duds

I had a GRP 40 ft boat and no problems ever with cracks.

I wonder if the latest motorhome bodies have poor quality materials used in them.

The crack on my roof is the shape of a spider and actually under one of the roof decals. The van is only a few weeks old.


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## 113016

duds said:


> I had a GRP 40 ft boat and no problems ever with cracks.
> 
> I wonder if the latest motorhome bodies have poor quality materials used in them.
> 
> The crack on my roof is the shape of a spider and actually under one of the roof decals. The van is only a few weeks old.


Hi Duds, 
as your van is only a few weeks old, I would take it back to the dealer and tell them that you want it sorting, either a replacement van or a permanent repair that will not return. (maybe worth taking direct to the builder as I doubt that many dealers are capable of such a repair) 
If they go down the repair route which they probably will, I would insist on something in writing stating that if the same or other cracks appear then a replacement van will be supplied. It is well worth getting in contact with the builder sating the same. 
Get it in writing and keep copies of everything and confirm all your conversations in writing.
Seriously, contact the builder as they are a reputable company and try to keep it friendly but be firm!


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## ramblingon

I think a ladder is a must when taking any MH for the first time get up there and take a good look around before you hand over your cash- place pipe insulation up the undersides of the ladder to protect the body work, loads of vans must have struck overheads with their roof, even new ones!


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## rayrecrok

duds said:


> I had a GRP 40 ft boat and no problems ever with cracks.
> 
> I wonder if the latest motorhome bodies have poor quality materials used in them.
> 
> The crack on my roof is the shape of a spider and actually under one of the roof decals. The van is only a few weeks old.


Hi.

Boats are made to take some extremely hard knocks through hitting things and the action of rough water, the gel coat and build up on motor homes has to be as light as possible for obvious reasons so are built to keep the rain off your head only.. 
Any movement or flexing of the body will cause stress cracks especially if there is some built in furniture or partitions which are rigid parts of the structure and will not move with the outer shell flexing causing stress points.

GRP body's may look all nice stylish and modern but have Achilles Heels with the materials used as they are too flimsy..


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## 113016

duds said:


> I had a GRP 40 ft boat and no problems ever with cracks.
> 
> I wonder if the latest motorhome bodies have poor quality materials used in them.
> 
> The crack on my roof is the shape of a spider and actually under one of the roof decals. The van is only a few weeks old.


Smaller more flexible powerboats were more likely to show such cracks 
Yours sounds like staring which will probably not have penetrated right through and might be just a blemish and nothing to worry about. 
However, it should have been repaired (smoothed out) prior to the decal placing over it. Never seen a roof decal? 
I sugest you see the builder or at least the dealer.


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## Jezport

If the GRP is cracking on a new van I would be wanting a refund, what would it be like after a few years in the sun, rain and ice?


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## camoyboy

The other thing that can cause a spider type of gel crack is if a fixing has been used on the inside that is too long. It could be that it has just touched the underside of the outer panel and caused the crack, and this would look like a star or spider. Normally you would be able to feel a slightly raised pimple in the centre.
This is just another possiblity and the more likely cause on a new vehicle. Changing the fixing will relieve the stress but a repair to the outside is still required.
Colin


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## eurajohn

The make up of a boat and the modern GRP based motorhome is totally different, for a boat or older GRP (or maybe short / small production) motorhomes, it will almost be totally manual i.e. the gel coat will be brushed onto the inside of the mould and the matting and resin will be hand laid and rolled / stippled (to remove air from the lay up), the mat will be laid to whatever thickness is required for the finished item. The starring mentioned will be most likely caused when the finished lay up was removed from the mould as it is not un-common to hit the outside of the mould with rubber mallets to aid the release, if the hit is overzealous starring will happen to the finished article as well as the mould, if in the mould, this will show in subsequent items taken from the mould although only as a mirror image of the damage to the mould. the modern motorhome panel will not be a manual operation as such the gel will be sprayed onto the mould as will be the resin and mat, this allows a considerably finer control of thickness to be achieved, very important with the modern motorhome as thickness also means weight and extra cost, unfortunately a thin panel is also not very self supporting so the panel will be made up to be a laminate, interior wallboard then foam insulation with the GRP outer skin providing the weatherproof cosmetic outer; the result is an extremely strong light construction, however it is more vulnerable to damage etc. than a thick manual lay up.
When looking to repair, I would suggest it would be well nigh impossible to carry out an invisible repair to gel coat cracks, most will be repaired and then finished cosmetically by paint which will be very good when first carried out but as time passes the different rates of degradation of the painted area and adjoining panels will be very evident, how many vans a few years old do you see that have different shades around the various panels, not necessarily because they have had repairs just that the various parts i.e. habitation door will have been produced by a different factory than the rest of the panels


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## duds

all those replies are very helpful but I still wonder if the spider shaped crack appeared after the vehicle left the factory to the dealer. I have discovered that the construction of the habitation GRP is done by subcontractors, plastics fabricators, and not the manufacturer, It may be that a problem has arisen with the material or quality of finish as I had similar issues on my last van only a few months old and those included blisters and holes as well as cracks to the roof. In this case the mark is under a decal running up the front of the roof past the rooflight opening and change of colour on repair will not be evident in future but i wonder about more cracks appearing as I use the van more and the shakes start to flex the bodywork. The warranty only last 2 years.


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## eurajohn

Hi duds, the blisters and holes you mention would most likely to have been air trapped between the gel and resin/mat layup, not un-common with hand lay up but quite unusual in a semi auto process, not normally a problem other than cosmetic. Cracks are normally caused when there is flexing of the panel and some parts of it are held tightly whilst other areas can move. Starring is almost always a sign of impact of some sort or indeed as suggested previously by an overlength screw pushing against the inside of the panel


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## rosalan

Hi 
I realise it is some time since you posted this thread but I have only just come across it. 
A spider type of crack is usually caused by a blow or some form of impact. I know because I nudged my van with my car. The nature of the material means that over time, minute particles of dirt will enter and make it more obvious the cracks may also continue to grow. The cure is fairly drastic and not too cheap. Each individual crack will need routing out and filling with the correct material before respraying or the unit will need replacing and respraying. 
I hope all has gone well. 
Alan


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## duds

I have a spider crack on the front of the roof above the cab where impact could not have caused such. The crack is under a decal and will have to be repaired at the factory under warranty. The vehicle is only a few weeks old and I am told is cosmetic. Probably caused by a screw too long used on inside under fitting. A warning to all to check the state of roof GRP regularily.


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## Jean-Luc

My MH had a (too) close shave with a toll booth, TG I was not driving at the time. Below is part of the result which was repaired to perfection by a boat yard using a gel coat repair kit supplied by Rapido, colour perfect and no need for paint.


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