How to waterproof this base plate and riser

adocholiday

Hi everyone,

Hoping you can help me work around a bit of a mess I made 😂

I'm building a small greenhouse using a kit so all of the timbers are pre-cut to size, however it required me to put in a foundation and my own base plate. I've done that but I over-sized my foundation so the base plate (2x6 treated boards) is short of the edge of the concrete all the way round. Then the riser for the greenhouse (the board on its side in the picture) is also short of the edge of the base plate. At least I planned that to allow myself a bit of grace if I ended up with out of square foundations which I did.

Yes I know I've messed up here quite a bit but it's surely salvageable. The base plate is sitting in the centre of the foundation and the riser is just off centre of the base plate to accommodate the anchors so it's a good solid base. It just looks a bit crap and I have this water proofing situation to resolve. I have a DPC to go under the base plate so it's protected from rising moisture, but no idea what I can do to protect it and the riser from standing water caused by rain. I thought about setting a damp proof membrane on top of the riser that will fall away to the side (added bonus of covering up the crap work!) but if water gets behind that it will have nowhere to go. Would silicone or caulking work? Any suggestions would be very welcome.

https://imgur.com/7W1Ild9

https://imgur.com/YQpYQJz

monseiur

Your foundation seems OK to me but under no circumstances should you use 6'' x 2'' laid flat on concrete as shown in photo as a base plate - it will rot in no time even if treated while the greenhouse resting on it will last for years so replacing it will mean dismantling the greenhouse or it may cause it to come crumbling down in the next storm😢

Instead consider using treated 4'' x 3'' as base plate, fix it to concrete with 12mm anchor bolts - roughly 36'' apart. Place half inch thick plastic shims spaced roughly 24'' apart under timber to create a gap - this is to allow air circulate and ensure that the base plate dries out quickly thus prolonging it's useful life. If you don't have plastic shims to hand slips of some hard wood like teak roughly four inch x half inch or three quarter will do the job - cut them 6'' long so you'll have 1'' sticking out both sides of base plate. Most joinery shops will have suitable bits thrown in their bin - provided they're long enough and the same thickness even if they're different widths it won't matter.

When base plate is fitted cut off the bit of anchor bolts protruding above the nut - you will have to cut a small notch in bottom of greenhouse frame where it will sit on nut.

adocholiday

https://www.boards.ie/discussion/comment/123327741#Comment_123327741

Thanks for the detailed response. Just wondering why a 4x3 would be much better than a 2x6? Wouldn't it rot just the same? I was hoping that by underlaying the 2x6 with DPC and finding some means of waterproofing above it would make the 2x6 perfectly viable by preventing it getting wet. I've no problem going with 4x3's but I'm still going to have the same problem.

Lumen

Recycled plastic base plates?

e.g. https://irishrecycledproducts.ie/product/profiles-and-boards/

monseiur

Having a 6x2 laid on it's edge is a totally different beast to one laid on it's flat due to the natural longitudinal direction of the grain which effects it's load bearing capacity and more importantly in your case how it absorbs moisture/water and how fast it dries out. With a 4'' x 3'' the grain direction will be the same as the 6 x 2 on it's edge. The small disadvantage is that you'll have to be a little more accurate with your measurements as instead of having 6'' wide to work with you'll be down to 4'' 😒

If your base plate is not in direct contact with concrete it will get wet and dry out (also slightly expand and contract) at the same rate as the rest of the greenhouse so should have similar life span. An annual lick of wood preservative, Cuprinol or similar, on both base plate and greenhouse frame would be a bonus. Inside greenhouse keep top soil back at least 4'' from base plate/frame - a few lengths of 9'' x 2'' with a few spacers should do the job.

If you prefer to have a 6'' wide base plate another option is 25mm marine plywood, cut it in 6'' strips and doubled up to give 50mm - you could bolt it directly on to concrete as it's totally waterproof. One sheet would give you 32 feet …………….but it's not cheap.

Lumen

Disagree that untreated marine ply is waterproof. It just has fewer voids and better glue so it's less likely to delaminate. Boat builders use many layers of varnish to achieve full waterproofing.

cheif kaiser

Can you not just paint it all with Bitumen paint?