While trawling the forums I have seen plenty about epoxy, GRP resin, and cyano for modelling and to date I have seen little about expanding PU glues which is a little surprising as I have used this for many years, particularly as I get it from site for free which is a bonus.

Expanding polyurethane glues have sone considerable advantages for marine modelling as they come in many differing types and their one common denominator is they are all moisture activated and can be used on wet or moist timber, and their expanding properties mean they often give a greater bond strength than the rapid epoxies many people use. This expanding property means they fill any tiny gaps as they expand to harden and this 100% contact area means it also prevents the ingress of moisture and fuels into joints which are less then perfect, so how do they work.

Expanding PU glues come in a range of curing times from 5 minutes to overnight and if you apply them to dry joints it means you have a reasonable working time to adjust or move joints around before you activate them, so how do we activate them? Basically you add water, this starts the expansion and curing process and many people do this by using a small plant sprayer and give the joint a quick blast to begin the curing process.

Expanding means it has gap filling properties and for through the hull fittings such as propellor shafts it is an ideal adhesive as it bonds and fills any remaining gaps which could leak and as it is a PU glue it han be readily trimmed or shaped using standard modelling tools. If more gap filling is required you can let your first layer expand slightly and add an additional layer or two as the expanding process of the first layer will begin the activation of additional layers, and the fact it uses water or airborne moisture to activate it means it is a good waterside adhesive to keep in the spares box.

Martin, do you find any issues with mould with aliphatic glue?

Charles, I think you are going to extremes here as generally industrial PU does not need a respirator, goggles, gloves and a full body suit to use and in general goggles and gloves are usually a contractual requirement on most sites today along with the obligatory Hi Viz vest which many people appear to see as a fashion accessory.

You can read the COSHH sheets if you go to the manufacturers website and download it or you can usually request a written version by post from most manufacturers, we get them as a matter of course for our H&S files for each project as they are a requirement.

Martin, yes I have and while this seems to be less of a problem, or no problem on a sealed joint that it once was it seems to be a problem on exposed joints generally. uncovered and is not generally identifiable to the naked eye and we only determined it as mould when we had laboratory testing done. Mould does weaken a joint by some margin and can let go when put under load.