I apologise for the scant information yesterday. We had just moved off, what we thought, was our home and moved into another (friends’) home and that was all I could manage last night.
Please note we are not technical experts. The following information is what we have learned/seen over many years of being around boats (commercial and recreational), reading, teaching maritime and talking to shipping surveyors, master mariners, brokers and many cruisers/sailors etc.
The boat is steel with concrete poured in the engine room as ballast. Under the bathroom, hallway and part of the galley cement has been laid up to the depth of 25 mm (it is also under the holding tank). We could cope with the concrete in the engine room as we had access to it and therefore we could remove it.
Our concerns with concrete (cement and aggregate (or gravel) makes up concrete), it is strong in compression but weak in tension that is why additives such as aggregate (gravel) is used to make concrete and in building/structural work, the additional use of reinforced steel is used.
On boats concrete was primarily used as a cheap form of ballast – however in Europe (for new builds) the use of cement based products in steel boats HAS BEEN BANNED. There is a reason for this.
1. The inside of the hull cannot be maintained against corrosion.
2. The slightest crack allows water ingress. Corrosion occurs with moisture between the steel and the cement.
3. The problem is compounded with cement coverings as whenever the hull is deformed e.g. during haul out or the vessel takes the ground. The deformation of plates creates tension in the cement, which it cannot withstand and it cracks, allowing even more moisture to become trapped between the cement and the hull (more water and oxygen = more corrosion).
Cement is relatively easy to remove compared to concrete, however you have to gain access to it if it is underneath a floor and/or holding tanks and/walls etc. Then it is a major problem.
What should be used is hull plating grease as it protects the steel from corrosion, penetrates any gaps between the ribs and plates and it is flexible.
What also happens with the older boats, the rivets can start to weep, allow more water in, which is tolerable if the moisture can be removed. Condensation is water, causing corrosion.
The problem is you cannot see it and cannot get to it and you do not know what is going on there – it is a silent killer on a hull.
Someone asked if we are talking about ballast or just cement/concrete in the bilge that doesn’t matter. The point is that cement/concrete is on the steel, creating the above problems.
The Technical Expert at a well known insurance company was very helpful in our concerns. We telephoned him to discuss the situation and he said:
- You should avoid concrete in the bilge, we recommend that loose ballast is used.
- Without the grease on the inside of the hull, there is always a problem with rusting between the ribs and hull plating.
- Grease is the best thing to use, it is much better than paint. It should be used on all boats of this type as it seals between the ribs and the plating and it is flexible whereas cement is not and it cracks when the boat is lifted or the boat is on the ground.
- With older hulls there is the problem with rivets popping out (becoming loose).
We are aware that some people use cement/concrete and do not have problems – in our humble opinion, they are lucky.
We welcome other people’s comments/views/knowledge – boats are a personal thing and this is just why cement/concrete doesn’t work for us.
We liked the boat very much – there is other work that needs doing, but that had already been taken into account with our offer.
(Pic – just an example of what corrosion can lead to).