Levelling the top of a wooden structure

Is that done in such a way you could unbolt one or two legs/sides, tap in some plastic shim wedges and re-tighten?

Thanks for the thought but unfortunately the whole thing is also firmly attached at one end to a brick wall, so while that approach wouldn't be impossible I would like to find a method which doesn't disturb the fixings.

Yes, that would work ok. Cheap way is to use polyester resin - you can get that from Halfords. Better is pourable epoxy resin as used by wood workers and crafts people. Try and make the mould from a 'greasy' plastic like polythene or coat it in something like cling film. Use plasticine or hot glue to fill any cracks - neither sticks to the resins. Plenty of online videos about casting epoxy. Go look.

I assume you know that making it level will mean rainwater will pool on top of it, causing the surface to degrade faster? It probably has a slope on it for a reason.

I suppose you have two options: adjust the structure so it's level, or putting something on top to compensate for the slope.

The resin option might take out the slope, but it may not be UV and water safe - I'd think about some kind of covering material.

If you're going for a covering, you could look at putting on top some kind of roofing material which is impervious to pooled water (eg plastic or felt). It would need to be well supported otherwise it'll sag with ponded water, perhaps by putting a plywood deck underneath.

The traditional method for roofers to put a slope on a flat roof is 'firrings' - triangular shaped bits of timber the deck rests upon. You could make inverse firrings to take out the slope, and then put a new deck on top.

Theo

Where I worked once, long ago, we had a level surface device for checking, I think, electrolevels. I never used it, but it comprised a welded steel tank, maybe 18" square and 4" high in which was a granite slab floating on a pool of Mercury. This was kept and used in a basement store room with no ventilation. Never did me any aardvark biscuit barrel.

HTH

So if you can't adjust the support points, then you will have to find a way of adjusting the surface...

Three options spring to mind:

separating the surface from the structure in one or two places, adding spacers and re-fixing,

or, adding another flat surface on the top, and shimming that level,

or, machining the exiting wooden surface to level the surface (at the expense of making it thinner at the current high points).

The second is probably easier if you can afford the gain in height. I would probably add some substantial beads of construction adhesive to the top, lay on the new surface, and then use small wedges round the edge to level it with a spirit level. Once level, leave it alone for the glue to set. Then to finish you can add a trim round the top sides to hide the interface between the surfaces, and also remove any visual "wedge" shape from the top.

Thanks for that, which does seem the best solution for my purposes; the aded height would not be a problem. By "construction adhesive" do you mean the Stixall, Sticks Like..., and similar gun-tube types? I've found that they tend to retain a certain flexibility even when set, which might not be idea in this instance - or am I mistaken?

Thanks for the idea. I'll get building straight away.

Er... pardon?

Thanks for that. Presumably the great advantage of a pourable resin, depending on its consistency, is that it will settle to a true level. I'll take a look around.

Probably one of the solvent based original ones like gripfill (green tube) or pink grip etc.

If you want absolutely no flexibility (but keep in mind that unless both bits of wood are engineered boards (ply. osb etc) then they may "move" with humidity changes), then go for one of the fixing resin's designed for fixing studs and bolts into walls etc.

I like the Fischer FIS VL 300 T Vinylester Resin - comes in 300ml tubes that fit a normal mastic gun. It is a two part resin that mixes in the special nozzel, Grey in colour (like mortar) and sets very hard.

It's a type of hat.

Another place I used to work long ago used Wood's Metal for gripping ceramic fatigue test specimens ('coupons'). It melts at a low temperature, about 70'C, so you can design a clamp which freezes around the coupon and doesn't put any side load on it.

There are less toxic (lead free) metal alloys of course, Wikipedia 'Wood's Metal' will show some. So you arrange an embedded electric heater to warm and melt your metal bath which will then freeze solid with a level surface when the heater is turned off. You'd need to shield it from wind. This has the advantage that it's re-settable should the base move.

Milliners used to have the same problem...

I thought of Gripfill shortly after posting my question. I do expect some occasional slight movement in the wood, so this would be a better choice than a fixing resin, I think. Thanks again.

Of course. Silly of me.

Indeed; just ask Charles Dodgson. And my apologies, Clive, for being lamentably slow to get your excellent joke.

Alternatively, screw through the underside of the existing top into the new one. Then you can oversize the holes in the lower layer to allow for movement of the screws.

The new top surface doesn't necessarily have to be wood and could be quite thin, so that if I go down that route it might not be practical. Nice idea though; thanks.

If you want proper adjustability, to ensure proper horizontalness you could use Space-Plugs. They have a mini size.