Spongy floor prognosis

The floor is made as sandwich construction,between the ply inner and outer is a filling of styrafoam (The stuff that is used to protect goods in transit but in sheet form)The outer "skin" top and bottom is plywood which is bonded to the foam sheet.When that bonding fails the inner floor moves as people walk on it.that movement destroys the foam sheet.When this is allowed to continue one will end up with sunken sections of floor which cannot be rectified.So the repair should be carried out as soon as possible! (obviously all in my own opinion!)

My 8 year old Swift caravan developed a soggy floor around the central kitchen area.  The standard remedy of inserting wooden dowels and epoxy resin would have involved removing part of the vinyl flooring which covers the whole floor.  Upon inspecting the floor from underneath while my wife stood on the affected area the deflection was of the same magnitude below.  A temporary support to the underside of the floor reduced the sag.  This gave me the idea that additional support to the floor might cure the problem and it has.  Using a timber frame supported off the Alco chassis screwed to the underside of the floor the problem has been solved.

The long term solution is to rebond the plywood skin/ skins to the foam core.

Drill holes from below, through the bottom skin and the core but not into the floor skin. Insert the spout of an expanding polyurethane foam can into the holes and introduce a small amount of foam into the top, then the bottom void. Don’t use much because the foam expands a lot, potentially distorting the floor. The foam will expand then set hard, with good adhesive strength holding the surfaces permanently.

Your repair will restore the floor to a ‘good as new’ state. Permanently.

I have seen the result of the unskilled using expanding foam to repair a floor!!!!!Use the proper thixathropic bonding kit!!!

Dave, ‘thixotrophic, is a property which is stiff when static and more fluid under pressure. Yoghurt is an example, or household paint which flows under the pressure of a brush. Whatever you are advising, thixotrophic isn’t it.

Yes,it flows until such time as the hardener works and then sets!So that is why it is used to repair delaminated sandwich construction floors!It flows into the delaminated area and then sets!!!Ideally of course you need to support the underside and put weights on the top side until the adhesive is cured.I speak as a person who has repaired quite a few floors in the 20 years I worked for a caravan dealership!!!!

 I take it that you have not read or understood the labels or advice given by the manufacturers.

I have just ordered a 2 part floor repair kit and will be doing the repair as described by dave.  

I had to do it on our previous van in 2 areas when it was about 6 -7 years old, current van is 15 years old and has one small area to fix.

The method which I described is one which we used successfully and was also in use at our caravan dealer when we called in on another matter. In both cases, drilling from below was done in order to preserve the vinyl floor covering or a carpet which extends under bunks. Like non drip paint, thixotropic products may be chosen for their convenience, but that’s an option not essential. If there’s no vinyl floor covering to protect, there’s no need to drill from below, working uncomfortably. Maybe I’m wrong in assuming that most caravans have vinyl  coverings and removable carpets today. Ours certainly has.

Whilst I know of the various kits and/or adhesives available, the original question was what would happen to the floor if it wasn’t repaired. This is just out of curiosity as I do intend to rectify it. Because of some mobility issues, crawling under the caravan would be difficult so it will be done from above a job that I am certainly capable of doing. Is the vinyl covering stuck down all over or is it just at the sides of the caravan?